CBSE Class 10

Chapter 9 Heredity and Evolution Class 10 Science Important Questions with Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Heredity and Evolution Class 10 Important Questions and Answers Science Chapter 9

Very Short Answer Questions

Question 1.
Who proposed the theory of inheritance of acquired characters ?
Answer:
Jean Baptiste Lamarck (1809).

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
Give an example of a vestigial organ present in human body.
Answer:
Vermiform appendix.

Question 3.
Who proposed the theory of natural selection ?
Answer:
Charles Darwin (1859) proposed the theory of natural selection.

Question 4.
In terms of evolution, what is the significance of homology between a human hand and a wing of a bird ?
(CBSE Foreign 2004)
Answer:
Homology indicates that there is common ancestry between a human hand and a wing of a bird. They have the same fundamental structure but are different in external morphology and functions.

Question 5.
Name the scientist who established the laws of inheritance.
Answer:
Gregor Johann Mendel.

Question 6.
Define inheritance.
Answer:
The transmission of characters from parents to offspring is known as inheritance.

Question 7.
What is the function of genes in an organism ?
Answer:
Genes are the carrier of the genetic information for body functions and passage from one generation to another.

Question 8.
What is gene ? (CBSE Delhi 2006 C, 2007, CCE 2014)
Answer:
Gene is a unit of inheritance which consists of a linear segment of chromosome or DNA that takes part in expressing a particular character.

Question 9.
What is speciation ?
Answer:
Speciation: It is the formation of newer species from the pre-existing ones due to accumulation of variations through various processes like isolation, stoppage of gene flow, genetic drift, and natural selection that lead to inability to interbreed.

Question 10.
List any two factors that could lead to speciation.
Answer:
It is the formation of newer species from the pre-existing ones due to accumulation of variations through various processes like isolation, stoppage of gene flow, genetic drift, and natural selection that lead to inability to interbreed.

Question 11.
What are homologous organs ?
Answer:
Homologous Organs: They are organs which have similar origin, similar development and similar internal structure but have different forms and functions.
Examples: Fore-limbs of Horse, human hand, flipper of whale, wing of bird or bat.

Question 12.
Give the respective scientific terms for studying

1. The mechanism by which variations are created and inherited
2. The development of new type of organisms from the existing ones.

Answer:

1. Genetics,
2. Speciation.

Question 13.
Write the contribution of Charles Darwin in the field of ‘evolution’.
Answer:
In 1859, he proposed the “Theory of Natural Selection”.

Question 14.
No two individuals are absolutely alike in a population. Why ?
Answer:
Due to appearance of variations caused by reshuffling of genes, mutations and acquired traits.

Question 15.
Where are genes located ?
Answer:
Genes are located over the chromosomes/DNA as linear segments.

Question 16.
What is heredity ?
Answer:
Heredity: It is the transmission of genetic traits from one generation to the next with the help of genes.

Question 17.
The first trophic level in a food chain is always a green plant. Why ?
Answer:
A food chain as well as an ecosystem is sustained by food energy which is build up only by green plants.

Question 18.
In F₁ generation what does F₁ stand for ? (CCE 2015)
Answer:
First filial generation (generation of hybrids).

Question 19.
A bacterial cell is different from cells of other organisms. Name the feature which makes it different from others. (CCE 2015)
Answer:
Prokaryotic nature while eukaryotic nature (having organized nucleus) is found in other organisms.

Question 20.
In case of round yellow and green wrinkled, which is dominant trait set ? (CCE 2015)
Answer:
Round yellow.

Short Answer Questions (2 Marks Each)

Question 1.
What are fossils ? How do they tell us about process of evolution ? (CBSE AI. 2008, 2008 C)
Answer:
Fossils: They are remains or impressions of past organisms that lie hurried in the rocks and other structures belonging to various ages.
Fossils Indicate Evolution

1. Different types of organisms appeared in different ages. Many of them have later on disappeared. Some gave rise to other organisms while a few are persisting even now.
2. Early forms were simple. Most of the later forms became more and more complex.
3. Fossils of different ages indicates the path of evolution,
   
4. Some fossils have characteristics intermediate between two groups, e.g., Archaeopteryx between reptiles and birds. They indicate the path of evolution.
5. Phylogeny of some organisms has been worked out with the help of fossils e.g., Horse.

Question 2.
Describe briefly four ways in which individuals with a particular trait may increase in population.
(CBSE Foreign 2008)
Answer:
The individuals with a particular trait will increase in number if the trait provides :

1. More Food: The trait helps in obtaining more food that leads to increased growth and reproduction.
2. Useful Variations: The trait helps the individuals to adapt to environment and achieve greater success in struggle for existence.
3. Genetic Drift: It causes genetic fixation of a trait which, therefore, occurs, in whole of the progeny.
4. Differential Reproduction: The trait gives extra benefit to the individuals in survival and reproduction.

Question 3.
“Variations that confer an advantage to an individual organism only will survive in a population.” Justify.
(CBSE Delhi 2008 C, CCE 2011)
Answer:
Useful variations give advantage to individuals in obtaining more food, adaptation to environmental changes and higher success in the struggle for existence. They give benefit in survival and reproduction. Differential reproduction increases the useful variations in the populations. Other individuals with harmful variations will be eliminated. For example, some bacteria have ability to tolerate high temperature. In warm environment non-tolerant bacteria will be killed. Others with tolerance to high temperature will survive and multiply.

Question 4.
“The sex of the children are determined by what they inherit from their father and not the mother.” Justify. (CBSE Delhi 2008 C, CCE 2011)
Answer:
Ovum produced by would-be-mother is always of one type (22 + X). Sperms produced by would-be father are of two types, gynosperms (22 + X) and androsperms (22 + Y). If gynosperm (22 + X) fertilizes the ovum (22 + X), the sex of the child will be female (44 + XX). If androsperms (22 + Y) fuses with the ovum (22 + X), the child born will be boy (44 + XY). Therefore, only father is responsible for the sex of the children.

Question 5.
Give one example of each of the characters that are inherited and the ones that are acquired in humans.
Mention the difference between the inherited and the acquired characters. (CBSE 2010)
Answer:
Inherited Trait: Fused and Free ear lobes.
Acquired Trait: Muscular body of a wrestler.
Difference: Acquired trait develops during the life time of an individual which affects somatic parts and dies with the death of the individual. Inherited trait is obtained from the parents, influences genes or germ cells and is passed on to the next generation.

Question 6.
(a) Write foil form of DNA.
(b) Why are variations essential for the species ? (CCE 2011)
Answer:
(a) DNA. Deoxyribose nucleic acid.
(b) Many of the variations have no immediate benefit to the species. They function as preadaptations which can be beneficial under certain environmental conditions like heat tolerance variation if the temperature of the area rises.

Question 7.
How do sexual and asexual reproduction lead to spéciation ? Give one point for each. (CCE 2011)
Answer:

1. Sexual reproduction produces a lot of variations due to reshuffling of chromosomes and crossing over.
   Variations help in natural selection and spéciation.
2. Asexual reproduction also develops variations occasionally due to errors in DNA replication. These variations help in natural selection and speciation.

Question 8.
List four tools used to study evolutionary relationships. (CCE 2011)
Answer:

1. Study of fundamental and correlated characters.
2. Study of homologous organs.
3. Study of fossil ancestors.
4. Molecular phylogeny.

Question 9.
State the importance of chromosomal difference between sperms and eggs of humans. (CCE 2013)
Answer:
Human eggs are of one type with a chromosomal complement of 22 + X. Human sperms are of two types with chromosomal complements of 22 + X and 22 + Y. Sex of the child will be determined by which sperm type fuses with the egg. Sex of the child will be male if 22 + Y sperm fuses with the egg (22 + Y, 22 + X). It will be female if 22 + X sperm fuses with the ovum (22 + X, 22 + X).

Question 10.
Insects, octopus, planaria and vertebrates possess eyes. Can we group these animals together on the basis of eyes that they possess ? Justify your answer giving reason. (CCE 2014)
Answer:
No. Eyes of the above four types of animals are structurally quite different. They are analogous structures.

Question 11.
In an area A, the leaf material available to beetles was very less. What are the two consequences seen in these beetles ? (CCE 2014)
Answer:

1. Average weight of adult beetles decreases,
2. There is decrease in the number of beetles.

Question 12.
Explain how do organisms create an exact copy of themselves. (CCE 2014)
Answer:
Organisms create an exact copy of themselves in the form of offspring by passing their genetic traits to them. This is done through propagules in asexual reproduction and gametes in sexual reproduction.

Short Answer Questions (3 Marks Each)

Question 1.
Explain how the sex of the child is determined genetically at the time of conception in human beings.
(CBSE A.I. 2009, CCE 2011, 2012)
Answer:
In human beings sex is determined by a pair of chromosomes called sex chromosomes. Sex complement of a female is XX while that of a male is XY. The complement is formed at the time of fertilization of the ovum by the sperm, i.e. conception. The ovum is always of one type, 22 + X. Sperms are of two types, gynosperms (22 + X) and androsperms (22 + Y). Fusion of an androsperm (22 + Y) with an egg (22 + X) produces a zygote (44 + XY) that will develop into male baby. Fertilization of an ovum (22 + X) with a gynosperm (22 + X) will form a zygote (44 + XX) that grows into a female baby. Sex of the child cannot be changed afterwards by any method. It is determined at the time of conception.

Question 2.
Distinguish between acquired and inherited traits, giving one example of each. Why are the traits acquired during life time of an individual not inherited ? (CBSE A.I. 2009 C, 2014, 2017, Delhi 2016, 2017)
Answer:
Differences between Acquired and Inherited Traits

(b) Non-inheritance of Acquired Traits: Traits acquired during life time of an individual influence only the non-reproductive organs. There is no influence on the DNA of germ cells. Only the germ cells transfer traits from parents to offspring. Non-reproductive organs have no such role. Traits acquired by them die with the death of the individual.

Question 3.
Name the organism Mendel used for his experiments. Explain about F₁ and F₂ progeny obtained by Mendel when he bred tall and short varieties of the organism he experimented with.
(CBSE A.I. 2010, CCE 2012)
Answer:
Organism: Garden or Edible Pea (Pisurn sativum).

Question 4.
Name two homologous structures in vertebrates. Why are they so called ? How do such organs help in understanding an evolutionary relationship ? (CBSE A.I. 2010)
Answer:
Fore limbs of Horse and Man are homologous structures which have similar origin, similar development and similar internal structure but have different external forms and functions. Homologous structures indicate that similar structures can be modified to perform different functions or undergo evolution.

Question 5.
With the help of a suitable example, explain natural selection. (CBSE Foreign 2010)
Answer:
Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. Peppered Moth of England has two forms, light grey and dark grey. Prior to industrial revolution, tree trunks in the forests around
Manchester were light greyish green due to presence of lichens. Most of the Peppered Moth found in the area were light coloured with dark spots which could not be spotted easily by predator birds. During 1845 to 1890, air pollution killed the lichen flora. The deposition of soot changed the colour of the tree trunks to blackish one. Peppered Moth of the area also exhibited switch over to melanic or blackish form.
It provided better survival value against dark background. The light grey form largely disappeared as it could be easily spotted by predator birds and devoured.

Question 6.
Genotype of a plant bearing purple flowers is PP and one with white flowers is pp. When these are crossed :
(a) What colour of the flowers would you find in F₁ progeny ?
(b) Give the percentage of white flowers if F₁ plants are self pollinated.
(c) In what ratio would you find PP and Pp in F₂ progeny ? Draw flow chart in support of your answer.
(CCE 2011)
Answer:
(a) Purple
(b) 25%
(c) 1:2

Question 7.
(a) What are fossils ?
(b) Are the wings of a butterfly and wings of a bat analogous organs or homologous organs ? Justify your answer. (CCE 2011)
Answer:
(a) Fossils: Fossils are remains, traces and impressions of the past organisms that are found in rocks and other structures of different ages.
(b) Analogous: Though performing a similar function, the wings of the two are fundamentally different in their origin and structure. Wings of a butterfly are integumentary = outgrowths while they are modified fore-limbs in bat.

Question 8.
(a) In a monohybrid cross of tall Pea plants denoted by TT and short pea plants denoted by tt, Preeti obtained only tall plants (denoted by Tt) in F₁ generation. However, in F₂ generation she obtained both tall and short plants. Using the above information, explain the law of dominance.
(b) What is genetic drift ? (CCE 2011)
Answer:
(a) Appearance of trait of shortness in F₂ generation shows that the trait was present in F₁ generation but was not expressed while the trait of tallness expressed itself. The trait which expresses itself in the presence of its contrasting form is called dominant. The other trait which is unable to express its effect in the presence of its contrasting trait is known as recessive.
(b) Genetic Drift: It is random change in gene frequency in small isolated population owing to factors other than natural selection that results in fixation of certain alleles and elimination of some others.

Question 9.
(a) State any two factors that could lead to the rise of a new species.
(b) How do analogous organs provide evidence in favour of evolution ? (CCE 2011)
Answer:
(a) Natural selection/geographical isolation, mutations/genetic drift leading to reproductive isolation.
(b) Analogous organs, though quite different in basic structure and development have been modified or undergone evolution to form similar functional structures, e.g., wings of butterfly (outgrowths of integument) and bird (modification of fore limbs).

Question 10.
(a) Why traits such as intelligence and knowledge connot be passed on to next generation ?
(b) How can we say that birds are closely related to reptiles and have evolved from them ?. (CCE 2011, 2014)
Answer:
(a) Traits like intelligence and knowledge are acquired characters. They do not modify the DNA of germ cells. Therefore, they are not passed on to progeny.
(b) Cleidoic eggs and scales are found in both reptiles and birds, indicating their close relationship. Birds have evolved from reptiles as they have developed completely four-chambered heart (instead of incompletely four-chambered heart of reptiles), a toothless beak, fore-arms modified into wings and covering of feathers (as found in dromaesaurs).

Question 11.

1. “Organs or features may be adapted to perform new function during evolution.” Justify this statement by giving an example.
2. “Older, body designs are not inefficient”. Give a suitable example in support of this view. (CCE 2011)

Answer:

1. Many organs and features have been formed through modification of existing structures. Limbs have been evolved from lobed fins of lung fishes. Wings have evolved from fore limbs in birds and bats. Feathers which became part of wings and body covering in birds had already been developed in dromaesaurs.
2. Bacteria continue to live comfortably and competitively in most of the habitats though their body design is very old and very simple as compared to more modern and elaborate body design of aquatic insects or fish. Therefore, older body designs are not inferior or inefficient.

Question 12.
Why are some Pea plants tall and others short in nature ? Explain with reference to role of genes in controlling characteristics. (CCE 2011)
Answer:
Genes control characters through the synthesis of specific proteins. The proteins take part in formation of body structures, enzymes, hormones and other biochemicals. In case of height in Pea, the protein takes part in producing hormone for growth in height. If the protein is working efficiently, more hormone would be produced and Pea plant becomes tall. However, if the protein is less efficient, small quantity of hormone would be formed and the Pea plant will remain short.

Question 13.
Distinguish between analogous organs and homologous organs. Identify the analogous and homologous organs amongst the following : Wings of an insect, wings of a bat, fore-limbs of frog, fore-limbs of human.
(CCE 2011, 2012)
Answer:
Difference:

Identification:

1. Analogous Organs: Wings of an insect and a bat.
2. Homologous Organs: Fore-limbs of Frog and Human.

Question 14.
Study the given data and answer the questions that follow :

Answer:

1. The data indicates that in F₁ generation only dominant traits (round seed, yellow seed) are observed while the recessive ones remain unexpressed.
2. The genes of the two characters (shape of seed and colour of seed) assort independently, show recombination and give an F₂ ratio of 9 (both dominant) : 3 (one dominant) : 3 (second dominant) : 1 (both recessive).

Question 15.
(a) Place the following in correct sequence : Natural selection, migration, new species and gene flow.
(b) Why are wings of Bat and wings of bird called analogous organs ?
(c) Evolution of Cauliflower, Broccoli, Cabbage, Red Cabbage are all from Wild Cabbage. Is this an example of natural selection or artificial selection ? Justify. (CCE 2011)
Answer:
(a) Migration — Gene flow — Natural selection —New species.
(b) Wings of Bat contain long fingers and a covering of patagia or skin folds. Wings of Bird contain reduced fingers and a covering of feathers.
(c) Artificial selection, as the various forms have been created’ by farmers by selectively picking up mutations found in cultivated plants.

Question 16.
(a) Explain giving examples how artificial selection has helped in the formation of newer varieties of Cauliflower/ vegetables.
(b) List the steps involved in the formation of new species.
(c) How different races of human beings belong to the same species. (CCE 2011, 2012)
Answer:
(a) During long history of cultivation of wild cabbage, newer varieties have been formed due to picking up of selected variations by the farmers. It is called artificial selection, e.g., Cabbage (closer leaves), Kale (large leaves), Kohlrabi (swollen stem), Brussel’s Sprout (large axillary buds), Broccoli (immature green flowers), cauliflower (cluster of strile flowers), Red cabbage (cabbage with red leaves).
(b) Steps in Formation of New Species. Separation of a subpopulation (spatial or geographical isolation), Stoppage of gene flow, genetic drift, accumulation of variations, natural selection, reproductive isolation.
(c) Different races of human beings belong to the same species because they can interbreed among themselves and produce fertile offspring.

Question 17.
(a) Explain the terms analogous and homologous organs with examples.
(b) How does homologous organs explain the process of evolution. (CCE 2011)
Answer:
(a) Analogous Organs: They are organs which have similar appearance and function but are quite different in their origin, development and anatomy.
Examples: Wings of Butterfly (integumentary outgrowths) and bird (modified fore-limbs).
Homologous Organs: They are organs which have similar origin, similar development and similar internal structure but have different forms and functions.
Examples: Fore-limbs of Horse, human hand, flipper of whale, wing of bird or bat.
(b) Homologous organs show how structures with similar internal structure and similar origin have been modified or evolved to become different externally for performing different functions like flying in birds, swimming in whale and grasping in humans by fore-limbs.

Question 18.
Explain how Mendel’s experiment shows that traits are inherited independently.
(CCE 2011, CBSE AI. 2016)
Answer:
Mendel performed crosses, e.g., round yellow seeded and wrinkled green seeded pea plants. Fj plants were round yellow seeded (both dominant traits). On self breeding, F2 plants were found to be of four types — round yellow (9), round green (3), wrinkled yellow (3) and wrinkled green (1). Out of these, two types are recombinations (round green, wrinkled yellow) which can develop only if the traits of the two characters assorted independently.

Question 19.
Briefly explain the role of natural selection and genetic drift in spéciation by citing an example.
(CCE 2011, CBSE Foreign 2016)
Answer:
Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. In a beetle population of mostly red colour, a few green beetles appear due to variation. While red beetles are eaten by crows, the green beetles are spared. The number of green beetles will gradually rise while that of red beetles will decline and ultimately disappear. Here, natural selection is being exerted by crows resulting in a new type of beetle population.
Genetic drift is random change in gene frequency in a small isolated population, fixing some alleles and eliminating others. Suppose in the red beetle population some blue beetles appear due to mutation. An elephant tramples the bush and kills all the red beetles. The surviving small population of beetles will be of blue colour though it has no selective advantage.

Question 20.
(a) What is spéciation ? Mention the factors due to which this can happen. (CCE 2012)
(b) Explain whether the traits like eye colour and height are genetically inherited or not.
(c) Do power to lift weight and reading French also belong to same category ? Justify your answer.
(CCE 2 011)
Answer:
(a) Speciation. It is the formation of newer species from the pre-existing ones due to accumulation of variations through various processes like isolation, stoppage of gene flow, genetic drift, and natural selection that lead to inability to interbreed.
(b) Yes. Traits like eye colour and height are genetically inherited. Like other inherited traits they are passed from one generation on to the next and so on.
(c) No. Power to lift weight or read French are acquired characters. They are not passed from one generation to the next.

Question 21.
(a) Write two factors which could lead to rise of new species.
(b)

1. What is the scientific term of the organs shown here ?
2. How do these organs provide evidence in support of evolution ? (CCE 2011)

Answer:
(a) Spatial or geographical isolation, accumulation of variations and natural selection.
(b)

1. Homologous organs,
2. They are fore limbs which have the same basic plan and anatomy but have undergone evolution and become modified to perform different functions.

Question 22.
One plant with dominant tall height bearing purple flowers crossed with another plant with recessive dwarf and white flowers.
(a) What do the plants of F₁ generation look like ?
(b) What type of cross is it ?
(c) What is the phenotypic ratio in F₂ generation and name the type of plants obtained according to phenotypic ratio. (CCE 2011)
Answer:
(a) All tall and purple flowered
(b) Dihybrid cross,
(c) Nine tall and purple flowered : Three tall and white flowered :Three dwarf and purple flowered : One dwarf and white flowered.

Question 23.
(a) Why a mouse whose tail has been removed by surgery does not produce tailless mice ?
From the set of figures, make a pair of homologous and analogous organs each and give one reason in case of both to justify your answer. (CCE 2011, 2012)

Answer:
Taillessness of mouse is an acquired character. It is not based in genes of germ cells. Therefore, it is not passed on to the next generation.

1. Homologous Organs — Fore limb of humans and wing of bird/bat. They have the same body plan being made of humerus, radioulna and hand.
2. Analogous Organs — Wing of Bat and wing of bird. In bird the fingers are reduced and the wing is covered by feathers.

Question 24.
In Bat the fingers are elongated and the wing is covered by patagium or fold of skin.
(a) “Recent fossils are found closer to the earth’s surface.” Comment on the statement.
(b) List two factors which could lead to the rise of new species. (CCE 2011)
Answer:
(a) Fossils occur in sedimentary rocks which have been formed through sedimentation of mud and silt at the
bottom of sea and deep lake. Naturally older fossils will lie embedded deep down while the recent fossils would be found in the upper layers near the surface.
(b) Genetic drift, accumulation of variations and natural selection.

Question 25.
(a) Name the sex chromosomes present in human male and human female.
(b) With the help of a flow chart determine genetically in human beings the sex Female Male of the offspring if the sperm carrying X-chromosome fertilizes the egg.(CCE 2011)

Answer:
(a) Human Male —XY.
Human Female – XX.
(b) Female offspring.

Question 26.
Guinea pig having black colour when crossed with guinea pig having same colour produced 100 offspring, out of which 75 were black and 25 were white. Now find out
(a) What is the possible genotype of the guinea pig ?
(b) Which trait is dominant and which is recessive ?
(c) What is this cross called as and what is the ratio of F₂ progeny obtained from this cross ? (CCE 2011)
Answer:
(a) Genotypes —Bb, Bb.
(b) Black colour (B) is dominant while white colour (b) is recessive.
(c) Monohybrid cross: Phenotypic ratio – 3 : 1.

Question 27.
(a) Name an animal which can change sex. What does it indicate ?
(b) Explain the importance of fossils in evolutionary relationship. (CCE 2011)
Answer:
(a) Ophyotrocha — male in young state and female later on. Change is sex indicates that it is not determined genetically.
(b) Significance in Evolution

1. Flora and Fauna:. Fossils depict the flora and fauna of different ages. The fossils of early ages were of very simple plants and animals. The fossils of more and more complex plants and animals belong to subsequent times.
2. Descent with Modification: Study of fossils shows that plants and animals of one age seem to be descendants of plants and animals of previous age.
3. Missing Links: Study of fossils has shown that how birds have developed from reptiles or how seed plants have evolved from ferns.
4. Fossils have revealed the evolutionary stages of some organisms,

Question 28.
Give appropriate terms for the following : (a) The trait which can express itself in next generation.
(b) The trait an organism has due to inheritance.
(c) Origin of a new species from pre-existing one. (CCE 2011)
Answer:
(a) Dominant trait.
(b) Inherited trait.
(c) Speciation.

Question 29.
Answer the following questions :
(a) What enables bacteria to survive better in a heat wave ?
(b) How is the stability of DNA of the species ensured ?
Which type of organisms will have more variations, sexually or asexually reproducing organisms ? Justify your answer. (CCE 2011)
Answer:
A pre-adaptation to tolerate higher temperature will enable bacteria to survive better in a heat wave. DNA is stable because of its double stranded nature, semi-conservative replication during reproduction and transcription for cellular activités.
Sexually reproducing organisms show more variations due to reshuffling of chromosomes and crossing over alongwith errors of DNA replication. Very few variations occur in asexually reproducing organisms which are caused by only occasional errors in DNA replication.
Mendel selected Pea Plant for his experiments. List two reasons.

Question 30.
State the meaning of recessive and dominant genes. (CCE 2011)
Answer:
Appearance of dwarf plants in F₂ generation indicates that F₁ plants contained the traits of both tallness and dwarfness. However, only the trait of tallness expressed itself. The trait which expresses itself in the hybrid is called dominant while the other which is unable to express itself in the presence of dominant trait is called recessive trait.

1. Recessive Gene: It is an allele of a gene which is unable to express its effect in the presence of its contrasting allele (e.g., t)
2. Dominant Gene: It is an allele of a gene which can express its effect whether present in homozygous or heterozygous state (e.g., T in TT or Tt).

Question 31.
What are fossils ? How are they formed ? Write their one significance. (CCE 2011)
Answer:
(a) Definition: Fossils are remains, traces and impressions of the past organisms that are found in rocks and other structures of different ages.
(b) Formation: Fossil formation or fossilisation occurs in bogs, lava and in sediments at the bottom of deep waters where there is little oxygen and rate of decay is slow or absent. Dead bodies settle down at the bottom which get covered by sand and silt. Under acidic conditions some silica can penetrate cells of dead organism and form perfect fossil. In other cases, softer parts decay ultimately and hard parts persist as fossils. Impressions, moulds and casts develop if all parts decay after some time. The sedimented mud and
sand harden to form sedimentary rock which may come to the surface due to upheavals in earth. This exposes the fossils.
(c) Significance in Evolution

1. Flora and Fauna: Fossils depict the flora and fauna of different ages. The fossils of early ages were of very simple plants and animals. The fossils of more and more complex plants and animals belong to subsequent times.
2. Descent with Modification: Study of fossils shows that plants and animals of one age seem to be descendants of plants and animals of previous age.
3. Missing Links: Study of fossils has shown that how birds have developed from reptiles or how seed plants have evolved from ferns.
4. Fossils have revealed the evolutionary stages of some organisms, e.g., Horse.

Question 32.
(a) Define heredity.
(b) Which of the following traits cannot be passed to the progeny ? Justify. (CCE 2011)

1. Rudimentary eyes of Planaria.
2. Absence of tail in a mouse (after surgical removal).
3. Low weight of starving beetle.

(c) Name the vegetables that have been obtained from wild cabbage by artificial selection when farmers opted for

1. Arrested flower development of wild cabbage
2. Swollen parts of wild cabbage. (CCE 2011)

Answer:
(a) Heredity: It is the transmission of genetic traits from one generation to the next with the help of genes.
(b)

1. Rudimentary Eyes of Planaria. Transmitted to next generation as it is a genetic trait.
2. Absence of Tail in Mouse. It is an acquired character and is not passed to progeny due to absence of connection to genes of germ cells,
3. Low weight of Starving Beetle. Acquired character which cannot pass to the next generation.

(c)

1. Arrested Flower Development. Cauliflower
2. Swollen Parts. Kohlrabi.

Question 33.
(a) Name the scientist who gave the idea of evolution of species by natural selection
(b) What conclusion did Mendel draw from his experiments about traits ?
(c) Arrange the following according to evolution : Cockroach, Mango Tree, Gorilla, Fish. (CCE 2011)
Answer:
(a) Charles Darwin (1859)
(b) Unit characters, Paired factors, Dominance, Principle or law of segregation (purity of gametes). Principle or law of independent assortment.
(c)

1. — Mango Tree —
2. Cockroach —> Fish —> Gorilla.

Question 34.
State how evolutionary relationships can be traced by the study of homologous organs. (CCE 2011)
Answer:
Homologous organs have similar internal body plan and anatomy. Fore limbs of all tetrapods have pentadactyl structure being made of humerus, radioulna, carpals, metacarpals and phalanges. However, they perform different functions in different tetrapods like absorbing shock of jumping in Frog, creeping in lizard, flying in birds or grasping in humans. These organs clearly indicate a common ancestry from which different modifications occurred that suited them in their habitats.

Question 35.
Fill in the blanks.

Answer:
(a) — await round
(b) —Tr.
(c) — tR
(d) — TtRr.
(e) — tall round.

Question 36.
(a) Giving reasons, state whether the following are homologous or analogous organs :

1. Wing of a bat and wing of a bird.
2. Fore limbs of human and bird.

(b) Define variation. (CCE 2012)
Answer:
(a)

1. Wing of Bat and Wing of Bird. They are analogous. Wing of bat has long digits and a fold of skin called patagium. Wing of bird has reduced digits and is covered by feathers.
2. Fore Limb of Human and Bird. They are homologous as they have a similar origin and similar internal structure or body plan (humerus, radio-ulna, hand).

(b) Variation: It is the difference in morphology, physiology and other traits that occurs amongst individuals of the same parentage, breed, race and species.

Question 37.
In a cross between plants with purple flowers and plants with white flowers, the offspring of F₁ generation had all white flowers. When F₁ generation individuals were self-bred, the F₁ generation gave rise to 100 individuals, 75 of which had white flowers. Make a cross and answer the following :
(a) What are the genotypes of F₂ individuals ?
(b) What is the ratio of white to purple flowered plants in F₂ generation ?
Answer:

(a) Genotype of F₂ Progeny: 1WW : 2Ww : 1 ww
(b) Ratio: 3 white : 1 purple.

Question 38.
(a) Explain geographical isolation.
(b) State with reasons whether the following are homologous or analogous organs :

1. Wings of butterfly and wings of a bat.
2. Fore limbs of frog and human. (CCE 2012)

Answer:
(a) Geographical Isolation: Prevention of mating between breeding groups due to geographical or physical barriers (e.g., Valley, Mountain, Water body) is called geographical isolation. The isolated populations develop different variations and changes in physiology and behaviour to form new species.
(b)

1. Wings of butterfly are integumentary outgrowths while wings of bat are modified fore limbs. The two are analogous structures.
2. Fore limbs of frog and human are homologous structures as both have the same body plan and internal structure which in frog are modified to absorb shock during fall on ground while in human they take part in grasping.

Question 39.
Look at the picture and write its name after identifying it. Also give its significance (two points)
(CCE 2012)

Answer:
(a) Fossil dinosaur skull (Rajasaurus).
(b) Significance:

1. The fossil indicates that different types of organisms lived in different periods on earth.
2. The study of fossils indicates that organisms of one age are descendents of organisms of previous age.

Question 40.
A husband has 46 chromosomes. His wife has 46 chromosomes. Then why do not their offspring has 46 pairs of chromosomes which is obtained by the fusion of male and female gametes ? Support your answer with a neat illustration. (CCE 2012)
Answer:
Gametes do not possess the same number of chromosomes as are present in individuals. Meiosis occurs prior to formation of gametes. This reduces the number of chromosomes to one half in gametes. In humans, the gametes carry only 23 chromosomes (one half of 46). Fusion of two gametes restores the number of 46 chromosomes in the zygote. Therefore, the human offspring does not have 46 pairs of chromosomes.

Question 41.
(a) What is meant by evolution of species ?
(b) List and describe any two evidences for evolution. (CCE 2012)
Answer:
(a) Evolution of Species. It is accumulation of inherited variations in a section of existing species that ultimately leads to the formation of a new species.
(b)

1. Galapagos islands have 14 different species of finches which have evolved from a small population of birds migrating from mainland into these islands.
2. Similarly Porto Scento Rabbits have developed into new species.

Question 42.
“It is a matter of chance whether a couple will give birth to a boy or a girl.” Justify the statement and support your answer with a neat illustration. (CCE 2012, 2014)
Answer:
Mother produces only one type of eggs, 22 + X. Father produces two types of sperms, gynosperms 23 + X and androsperms 22 + Y. The two are produced in equal proportion. It is a matter of chance that an androsperm (22 + Y) or gynosperm (22 + X) first reaches the egg (22 + X) and fuses with it to form a male or female offspring.

Question 43.
(a) “Our teeth and an elephant’s tusks are homologous organs”. Justify this statement.
(b) What do the analogous organs indicate ? (CCE 2012)
Answer:
(a) Elephants tusks are modified incisor teeth which are used for digging, fighting and tearing bark from trees. For this they come out of mouth. Human teeth remain inside the mouth. Human incisors are used for biting. Since, the two types of teeth have the similar origin and composition they are homologous in nature which perform different functions.
(b) Analogous organs are structurally different organs which have been modified to appear similar and perform similar function, e.g., wings of insects and wings of birds.

Question 44.
“Red beetles live in bush with green beetles. Eventually, the number of green beetles increases as compared to red beetles.”
(a) Give reason for this increased number of green beetles.
(b) State two advantages of variations. (CCE 2012)
Answer:
(a) Red beetles arc quite conspicuous in green bushes. They are picked up by crows for feeding. Green beetles are not easily distinguishable from green leaves of bushes. Therefore, they are not devoured by crows. Population of green beetles will, therefore, increase while that of red beetles will decrease.
(b) Advantages of Variations,

1. Variations function as preadaptations to help the organisms to survive in adverse conditions.
2. They help individuals in struggle for existence and natural selection.

Question 45.
(a) Define inherited traits.
(b) “Inherited traits are capable of directing evolution”. Justify the statement and support your answer by giving two reasons. > (CCE 2012)
Answer:
(a) Inherited Traits: They are genetically controlled traits which are passed from parents to offspring,
generation after generation.
(b) Evolution: Since, genetic material or genes have a tendency to mutate and form alleles, a number of inherited or genetically controlled variations occur in the traits. The variations which are useful in a given environment are helpful to the individuals to survive and reproduce resulting in natural selection. For example, feather covered fore limbs helped some early dinosaurs to glide and then fly. The forelimbs also got modified to suit this flight. This resulted in evolution of wings as are found in birds.

Question 46.
Name two homologous structures in vertebrates. Why are they so called ? How these organs help in understanding an evolutionary relationship ? (CCE 2012)
Answer:
Paddle of whale and wing of a bird are two homologous organs which have similar basic plan and internal structure. They are externally quite dissimilar and perform different functions, swimming in whale and flying in bird. Their similar internal structure points to their common ancestry. Modification or evolution occurred in them to produce present forms.

Question 47.
(a) Define fossil.
(b) Identify this fossil of invertebrate from this diagram and write its name.
(c) What evidence does it provide in favour of evolution ? (CCE 2012)
Answer:
(a) Fossil: It is remains, trace or impression of a past organism that occurs in the rocks of older ages.
(b) Ammonite, a cephalopod mollusc that occurred on earth some 200 million years ago and underwent mass extinction
Why do traits of thin and low body weight not inherited to the next generation. Answer in detail along with dinosaurs.
(c) Evidence for Evolution: Different types of organisms appeared on earth, flourished and then disappeard leaving their modified descendants and relatives to repeat the process.
It is evolution or descent with change.

Question 48.
Study the given diagram and answer the following question : (CCE 2012)


Answer:
Due to lesser availability of nourishment, beetles of second generation remain small and thin. However, it is not an inherited trait but an acquired character. The acquired character is not transferred to the progeny. The progeny (third generation) developed into normal weight and size individuals when food became plenty.

Question 49.
A round seeded plant (RR) is crossed with a wrinkled seeded plant (rr). Find out the phenotype and genotype of F₁ and F₂ generations. (CCE 2012)
Answer:

Phenotypic Ratio : 3 round seeded : 1 wrinkled seeded.
Genotypic Ratio : 1 pure round seeded (RR) : 2 hybrid round seeded (Rr). 1 wrinkled seeded (rr).

Question 50.
Define the following with one example of each
(a) Genetic drift
(b) Natural selection
(c) Reproductive isola-tion. (CCE 2012)
Answer:
(a) Genetic Drift: It is random change in gene frequency in small isolated population, fixing some alleles and eliminating others. Suppose in a population of red coloured beetles, some blue coloured beetles appear due to mutation. If all the red coloured beetles are eliminated due to trampling by an elephant, the surving beetles will be all of blue colour, though blue colour has no selective advantage.
(b) Natural Selection: It is survival and preferential reproduction by those individuals which show better adaptation to existing environment. In a population of red and green beedes, crows eat more of red beedes. Green beedes are spared due to their colour which is of adaptive advantage against the background of green foliage.
(c) Reproductive Isolation: It is absence of interbreeding between members of different species. Reproductive
isolation maintains the sanctity of a species. It is also basic to the formation of new species from an isolated population. The latter accumulates variations that prevent mating between it and the parent population.

Question 51.
Mendel studied the inheritance pattern of traits in a Pea plant. According to this study, he obtained 9 : 3 : 3 : 1 ratio of certain traits in progeny of F₂ generation. Based on it answer these questions :

1. What trait did he study ? How do they represent themselves. .
2. What was the trait of F₁ progeny ?
3. Which rule does this inheritance pattern suggest ? (CCE 2012)

Answer:
(a) Tall and round seeded plant (TTRR) was crossed with dwarf and wrinkled seeded plant (ttrr).
(b) Plants of F₁ generation were all tall and round seeded (TtRr).
Progeny of F₁ that is F₂ generation, contained tall and round seeded, tall wrinkled seeded, dwarf round seeded and dwarf wrinkled seeded plants in the ratio of 9 : 3 : 3 : 1. Appearance of dwarf round seeded and tall wrinkled seeded plants shows recombination of traits of the two characters. The phenomenon is called principle of independent assortment.

Question 52.
A cross was carried out between a pure bred tall Pea plant and a pure bred dwarf Pea plant and F₁ progeny was obtained. Later the F₁ progeny was selfed to obtain F₂ progeny. Answer the following questions :
(a) What is the phenotype of the F₁ progeny and why ?
(b) Give the phenotypic ratio of the F₂ progeny.
(c) Why is the F₂ progeny different from F₁ progeny ? (CCE 2013)
Answer:
(a) Tall, as the trait for tallness is dominant over the trait for dwarfness,
(b) 3 tall : 1 dwarf,
(c) Sagregation of alleles for the two traits and their random fusion during the formation of F₂ progeny (TxT, Txt, Txt, txt).

Question 53.
Tabulate two distinguishing features between acquired traits and inherited traits with one example of each.
(CCE 2013)
Answer:

Question 54.
“Sex of a new born is a matter of chance and none of the parents may be considered responsible for it”. Justify this statement with the help of flow chart showing determination of sex of a new born. (CCE 2013)
Answer:
Sex of the child is determined by the gametes that fuse to form zygote which later grows into offspring. Human females (44 + XX) produce only one type of ova (22 + X). Human males (44 + XY) form two types of sperms, androsperms (22 + Y) and gynosperms (22 + X). Both are formed in equal number. It is a chance factor whether an androsperm or a gynosperm fuses with egg to form 44 + XY or 44 + XX child. A child that obtains an X-chromosome from father will be girl and the one who inherits a Y-chromosome will be boy.

Question 55.
Marriage between cousins is a taboo in most of the countries of the world except in some Asian countries
(a) Why should the marriage between close cousins be prevented ?
(b) Which measures will you take to prevent such practices ? (CCE 2013)
Answer:
(a) Marriage between close cousins is similar to inbreeding. The recessive traits (of genetic defects) present in such families will become homozygous and cause the incurable diseases.
(b) Measures :

1. Marking the families where cousin marriages are common,
2. Selecting their school going children and holding seminar or discussion about ill effects of marriage in close relatives in which such children are made to participate.
3. Cousin marriages often occur where early marriages are practised. The families should be advised to allow dieir children’to get higher education. Such educated persons will themselves come to know about the defects in marriages among close cousins.

Question 56.
How can you say that in Mendel’s monohybrid cross, the F₂ dominants are not all the same ? (CCE 2013)
Answer:
allowing them to self breed. One third of the dominants will breed true and produce offspring with only dominant trait. Two third of the dominants will behave as hybrids (like F₁ individuals) producing both dominant and recessive individuals in the ratio of 3:1.

Question 57.
A cross was made between pure breeding pea plants one with round and green seeds and the other with wrinkled and yellow seeds.
(a) Write the genotype of F₁ progeny. Give reason for your answer.
(b) Write the different types of F₂ progeny obtained alongwith their ratios when F₁ progeny was selfed.
(CCE 2014)

Answer:
(a) The phenotype is due to nonexpression of recessive alleles in the presence of their dominant alleles.
(b) F₂: 9 round yellow, 3 round green , 3 wrinkled yellow, 1 wrinkled green.

Question 58.
(a) Mendel, in one of his experiments with pea plants, crossed a variety having round seeds with one having wrinkled seeds. Write his observations giving reasons of F₁ and F₂ progeny.
(b) List any two contrasting characters other than roundness of pea seeds that Mendel used in his experiments with pea plants. (CCE 2014)
Answer:
(a)
Phenotypic Ratio: 3 round seeded : 1 wrinkled seeded.
Genotypic Ratio: 1 pure round seeded (RR) : 2 hybrid round seeded (Rr). 1 wrinkled seeded (rr).
The reason for all rounded seeds in F₁ generation and 75 % rounded seeds in F₂ generation is the inability of recessive trait of wrinkled seeds to express itself in the presence of dominant trait of round seesds.
(b) TT and tt (height), YY and yy (seed colour).

Question 59.
“A trait may be inherited but may not be expressed.” Justify this statement with the help of a suitable example. (CCE 2014, CBSE A.I. 2016, 2017)
Answer:
A cross between parents with pure dominant (say TT) and pure recessive (say tt) traits produces hybrids or F₁ individuals with dominant trait only but on self fertilization the F₂ generation comes to have both individuals with dominant and recessive traits in the ratio of 3:1. Obviously F₁ individuals have received the recessive trait but the same is unable to express itself in the presence of dominant trait.

Question 60.
(a) Which type of organs are shown in the figure.
(b) Which type of origin and structure do these organs have ?
(CCE 2014)

Answer:
(a) Wings of Dragon fly and wing of bird.
(b) Wings of Dragon fly are extensions of integument while wing of bird is modified fore limb. The two are analogous structures.

Question 61.
An organ like wing in birds is an advantage to the organism. Did it appear in different stages or was formed due to a single sudden change. (CCE 2014)
Answer:
Organs like wings appeared in different intermediate stages and not through sudden change. Wings were preceded by feathers in small extinct dinosaurs called dromaesaurs. They were also present on the fore limbs. The feathered fore limbs helped the small animals in longer jumps. It was followed by gliding and then flying.
There are two interbreeding groups of a population in a particular area.

Question 62.
In situation A, population groups reach each other, in B they cannot.
(a) In which situation new species will not be formed and why ?
(b) Which kind of fossils retain the minute details ? (CCE 2014)
Answer:
(a) In situation A, due to free flow of genes between population groups.
(b) Petrifications where silica and other minerals penetrate the dead bodies and replace their contents molecule by molecule.

Question 63.
Explain with an example for each, how the following provides evidences in favour of evolution in organisms :
(a) Homologous organs
(b) Analogous organs
(c) Fossils. (CCE 2015, CBSE Delhi 2017)
Answer:
(a) Homologous organs: Homologous organs have similar internal body plan and anatomy. Fore limbs of all tetrapods have pentadactyl structure being made of humerus, radioulna, carpals, metacarpals and phalanges. However, they perform different functions in different tetrapods like absorbing shock of jumping in Frog, creeping in lizard, flying in birds or grasping in humans. These organs clearly indicate a common ancestry from which different modifications occurred that suited them in their habitats.
(b) Analogous organs: Analogous organs, though quite different in basic structure and development have been modified or undergone evolution to form similar functional structures, e.g., wings of butterfly (outgrowths of integument) and bird (modification of fore limbs).
(c) Fossils: They are remains or impressions of past organisms that lie hurried in the rocks and other structures belonging to various ages.

Question 64.
Explain :
(a) Speciation
(b) Natural selection (CCE 2015)
Answer:
(a) Speciation: It is the formation of newer species from the pre-existing ones due to accumulation of variations through various processes like isolation, stoppage of gene flow, genetic drift, and natural selection that lead to inability to interbreed.
(b) Natural Selection: Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. In a beetle population of mostly red colour, a few green beetles appear due to variation. While red beetles are eaten by crows, the green beetles are spared. The number of green beetles will gradually rise while that of red beetles will decline and ultimately disappear. Here, natural selection is being exerted by crows resulting in a new type of beetle population.
In an experiment, Mendel obtained 1014 plants out of which 787 were having round seeds and 227 had wrinkled seeds in F₂ generation.

Question 65.
(a) What is the approximate ratio obtained in F₂ generation ?
(b) Under which law do you find this ratio ?
(c) Why is this law so called ? (CCE 2015)
Answer:
(a) 3:1
(b) Law of segregation or principle of purity of gametes.
(c) Law of segregation is known so because the two factors or alleles of a character separate and pass to different gametes at the time of gametogenesis. As a result a gamete contains only one factor of a character. Homologous organs are different from analogous organs.

Question 66.
(a) Mention the two characteristics that decides about analogy and homology between two organs.
(b) On what basis is the classification of organisms into prokaryotes and eukaryotes done ? (CCE 2015)
Answer:
(a)

1. Origin of the organ and its basic plan of structure.
2. Analogous organs have similar functions and appearance. Homologous organs have different functions and appearance. The same are caused by evolution.

(b) Presence (eukaryotes) and absence (prokaryotes) of nuclear organisation.

Question 67.
Who was Gregor John Mendel ? What was his contribution to heredity ? (CCE 2015)
Answer:
Gregor Johann Mendel (1822 – 1884) is known as father of genetics as he discovered the mechanism of transmission of characters from one generation to the next. Mendel was born in Silician, a village in Heinzendorf (now part of Czech Republic) on July 22, 1822 to a farmer’s family. He was a brilliant student. After graduation, Mendel joined monastery at Brunn (then in Austria, now Brno in Czechoslovakia) in 1843 at the age of 21. He became priest in 1847. In 1851, Mendel went to University of Viena for study of Science and Mathematics. He returned to Brunn as substitute teacher (because he failed to clear his examination for teaching certificate). Mendel served as teacher for 14 years. Later he was made abbot of the monastery.
Humans have cultivated the wild cabbage for thousands of years. Then by artificially selecting the traits a variety of plants have been obtained. Write the characteristics feature of each of the following :

Question 68.
(a) Kohlrabi, Cauliflower, Broccoli, Cabbage.
(b) Since how long cabbage has been cultivated for ? (CCE 2015)
Answer:
(a)

1. Kohlrabi: Swollen stem.
2. Cauliflower: Sterile condensed inflorescence.
3. Broccoli: Green immature flowers in bunches.
4. Cabbage: Terminal enlarged bud.

(b) Cabbage has been in cultivation for over 2000 years.

Question 69.
Explain the formation of sub-population in neighbourhood by taking the example of beetle. (CCE 2015)
Answer:
Beetles have a tendency to remain restricted to a few nearby bushes on which they live, feed and reproduce. In a large population of beetles spread over a mountain range, a number of separate segments of population will occur depending upon the spread of groves of bushes. As there is little gene flow among separated segments of population, they develop and accumulate their own variations and form sub-populations. A sub-population can further evolve into reproductively isolated population if natural barrier develops between it and other sub-populations, e.g., a glacier, water body, mountain cut.

Question 70.
(a) Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish a common evolutionary origin ? Justify your answer.
(b) “Birds have evolved from reptiles”. State evidence to prove the statement. (CCE 2015)
Answer:
Answer:
(a) Eyes of the above four types of animals are structurally quite different. They are analogous structures.
(b) Cleidoic eggs and scales are found in both reptiles and birds, indicating their close relationship. Birds have evolved from reptiles as they have developed completely four-chambered heart (instead of incompletely four-chambered heart of reptiles), a toothless beak, fore-arms modified into wings and covering of feathers (as found in dromaesaurs).

Question 71.
At what stage is sex determined in human beings ?
Answer:
At the time of conception.
In human beings sex is determined by a pair of chromosomes called sex chromosomes. Sex complement of a female is XX while that of a male is XY. The complement is formed at the time of fertilization of the ovum by the sperm, i.e. conception. The ovum is always of one type, 22 + X. Sperms are of two types, gynosperms (22 + X) and androsperms (22 + Y). Fusion of an androsperm (22 + Y) with an egg (22 + X) produces a zygote (44 + XY) that will develop into male baby. Fertilization of an ovum (22 + X) with a gynosperm (22 + X) will form a zygote (44 + XX) that grows into a female baby. Sex of the child cannot be changed afterwards by any method. It is determined at the time of conception.

Question 72.
What will happen if both the characters present in F₁ generation pass together in F₂ generation ? (CCE 2015)
Answer:
They will remain linked together. There will be no recombination. The F₂ phenotypic ratio will be 3 : 1 as in monohybrid cross.

Question 73.
A child questioned his teacher that why do organisms resemble their parents more as compared to grand parents. In which way will teacher explain to the child ? (CCE 2015)
Answer:
A child receives two chromosomes of each type, one from each parent (50 : 50). These chromosomes have been inherited from only one of the two paternal grand parents and one of the two maternal grand parents. Hence, resemblance with grand parents will be lesser than resemblance with immediate parents.

Question 74.
A boy of 15 years has attached ear lobes and weight of 65 kg. Which of these is an acquired character and which is inherited ? Give reason for your choice.
Answer:
Attached Ear Lobes. Inherited character. Body Weight. Acquired character. There is no effect of environment on attached ear lobe while acquired character of weight can vary. Inherited trait is obtained from parents and is passed on to next generation. Acquired trait develops during life time of the individual. It is neither inherited nor passed on to next generation.

Question 75.
Rohit will be out of station for a week. He gave his aquarium to Raju, a friend in the neighbourhood for that
(a) Why did Rohit do that ?
(b) What does Rohit expect from Raju ?
(c) What will happen to the aquarium if left for a week unattended ?
(d) Why was Rohit keen on leaving the aquarium with his friend ? ( CCE 2015)
Answer:
(a) So, that the aquarium is looked after.
(b) To feed the fishes, change water and keep the instrument for aeration working.
(c) The fish will die.
(d) Rohit had full faith in his freind’s sincerity.

Question 76.
(a) “Males are heterogametes”, Why ?
(b) Differentiate between inherited and acquired characters by giving two points. (CCE 2015)
Answer:
(a) Human males produce two types of sperms (22+X and 22+Y). Therefore, they are called heterogametic.
(b)

Question 77.
In one of his experiments with Pea plants, Mendel observed that when a pure tall Pea plant is crossed with a pure dwarf Pea plant, in F, or first generation only tall plants appear,
(a) What happens to the trait of the dwarf plants in this case ?
(b) When the F₁ generation plants were self fertilized, he observed that in the plants of second generation (F₂) both tall and dwarf plants were present. Why it happened ? Explain briefly.
(CBSE Delhi 2016)
Answer:
A number of different types of variations develop in a population. All of them do not have survival value. However, some of them are pre-adaptations which can be beneficial under certain environmental conditions. For example, in a heat wave most of the bacteria will die but a few having pre-adaptation or variation to tolerate heat wave will survive and multiply. Actually selection of variants by different environmental factors constitutes the basis for evolution.

Question 78.
In a monohybrid cross between tall Pea plants (TT) and short Pea plants (tt), a scientist observed only tall Pea plants (Tt) in the F₁ generation. However, on selfing the F₁ generation Pea plants he obtained both tall and short plants in F₂ generation. On the basis of above observations with other angiosperms also, can the scientist arrive at a law ? If yes, explain the law. If not, give justification for your answer. (CBSE Delhi 2016)
Answer:
Yes, The scientist would arrive at the law of dominance. The law states that when both the alleles of a character are present together in an individual, only one expresses its trait. It is called dominant trait. The other trait which remains suppressed though its allele is present is called recessive. This happens in F₁ generation. However, due to segregation and chance’coming together of the two alleles, both the dominant and recessive traits appear in F₂ generation.

Question 79.
List two differences in tabular form between dominant and recessive traits. What percentage/proportion of the plants in F₂ generation/progeny were round in Mendel’s cross between round and wrinkled seeded Pea plants ? (CBSE Foreign 2016)
Answer:
Differences:

The trait of rounded seed is dominant over wrinkled seed. In F₂ generation the rounded seed appears in 75% of the population as the phenotypic ratio is 3 : 1 duration.

Question 80.
List three factors that provide evidence in favour of evolution in organisms and state the role of each in brief. (CBSE Foreign 2016, 2017)
Answer:

1. Homologous organs: They are organs with similar internal structure and similar origin which have bacome modified or evolved to perform different fractions, e.g., fore limbs used for flying in birds, swimming in whale and grasping in humans.
2. Analogous Organs: They are organs which have different internal structure and different origin but have evolved to perform similar function, e.g, wings in birds and moth.
3. Fossils: They are remains or impressions of past organisms. Fossils indicate that different organisms lived in different periods and that organisms of one age have evolved from organisms of previous age.

Question 81.
Explain Mendel’s experiment with peas on inheritance of characters considering only one visible contrasting character. (CBSE Foreign 2016)
Answer:
Mendel crossed Garden Pea plants having contrasting visible traits, e.g., tall and dwarf, violet and white flowered.
In F₁ generation there were no halfway characteristics. A cross between pure tall and pure dwarf plants yielded only tall plants in F₁ generation. There were no medium height plants. When F₁ plants were self bred, the F₂ plants were not all tall plants. Instead, both tall and dwarf plants appeared in ratio of 3 : 1. It means that the trait for dwarfness was present in F₁ generation but was not expressed while the trait for tallness expressed itself.

The trait of tallness which expresses itself in the presence of its contrasting form is called dominant. The other trait of dwarfness which is unable to express its effect in the presence of its contrasting trait is known as recessive.

Question 82.
“Evolution and classification of organisms are interlinked”. Give reasons to justify this statement.
(CBSE A.I. 2017)
Answer:

1. Classification divides organisms into groups and subgroups on the basis of their similarities and dissimilarities. In a large group, all the organisms possess some similar basic or ancestral characters. In its subgroups, each subgroup has some common derived characters. They are different from other subgroups. The derived characters have developed only through evolution.
2. Classification helps in tracing the evolutionary relationships amongst organisms by studying the basic and derived traits.
3. The more characters two species have in common, more closely are they related, e.g., leopard and tiger.

Long Answer Questions (5 Marks each)

Question 1.

1. What is genetics ?
2. Give the common name of the plant on which Mendel performed his experiments.
3. What for did Mendel use the term factors and what are these factors called now ?
4. What are genes ? Where are the genes located ? (CBSE Delhi 2006)

Answer:

1. Genetics: It is the branch of biology that deals with the study of heredity and variations.
2. Garden or Edible Pea.
3. Factors: They are particulate inheritable entities which control the expression of traits of a character, e.g, T for tallness, t for dwarfness. The factors are now called genes.
4. Genes: They are units of inheritance that take part in expression of particular characters. Genes are located over the chromosomes as linear segments.

Question 2.
(i) What are chromosomes ? Where are they seated ? (CBSE Foreign 2008)
(ii) What is a sex chromosome ?
(iii) Explain the mechanism of sex determination in human beings.
Answer:
(i) In case of asexually reproducing organisms, there is no gametogenesis and fertilization. Chance separation and chance pairing of genes and their chromosomes are absent. Therefore, asexually developed individual carries the same genes and their chromosomes as are present in its parent.
(ii) Allosomes (Gk. alios— other, soma—boay) or sex chromosomes are those chromosomes which determine the sex of the individual in unisexual organisms. Human beings have 23 pairs of chromosomes.
(iii) Establishment of male and female individuals through differential development of their sex organs is called sex determination. In some organisms sex is determined by environmental conditions. In others including human beings, it is determined genetically.
Environmental Determination of Sex.

1. Crepidula (marine mollusc) and Bonellia (marine worm) develop into females if growing alone. In the company of a female, they develop into males.
2. In turtle, Chrysema picta an incubation temperature above 33°C produces females while a temperature below 28°C produces only males.
3. In lizard, Agama agama, high incubation temperature produces male offspring.
4. Annelid Ophryotrocha is male in young state and female later on. Snails are also known to change sex.

Question 3.
(a) What is geographical isolation ?
(b) Illustrate formation of a species with the help of an example where individuals are very different from each other and are capable of reproduction among themselves. (CCE 2011)
Answer:
(a) Geographical Isolation. Prevention of mating between breeding groups due to geographical or physical barriers (e.g., Valley, Mountain, Water body) is called geographical isolation. The isolated populations develop different variations and changes in physiology and behaviour to form new species.
(b) Over 160 breeds of dogs have come up due to selective breeding and artificial selection. Similarly, there are about 800 breeds of cattle. They differ in size, height, features, behaviour, colour and other traits. However, all dogs belong to one species of Canis familiaris while all cattle belong to one species of Bos indiens. Despite their structural and behaviour differences all the breeds belonging to the same species can interbreed and produce fertile offspring. However, if interbreeding is prevented by spatial isolation these different breeds can develop reproductive isolation and form new species, e.g., Porto Santo rabbits, Galapogos finches.

Question 4.
Name any five vegetables generated from a common ancestor through artificial selection rather than natural selection. Also mention the features for which each vegetable is selected. (CCE 2011)
Answer:
Artificial Selection in Wild Cabbage. The plant has been under cultivation for more than 2000 years as food plant. Artificial selection carried out at different times have given rise to following vegetables.

1. Closer leaves provided more value to the food plant. Artificial selection of variants in this direction has given rise to a large terminal bud being used as vegetable. It is cabbage.
2. Selection of larger leaves for enhancing food value of the plant has produced the leafy vegetable of kale.
3. Swollen stem parts could increase food value. It resulted in selection of swollen stem in Kohlrabi.
4. Brussel’s Sprout. The large axillary buds are used as a vegetable.
5. The plant with immature green flowers has been selected as a vegetable.
6. Here selection has been for a cluster of sterile flowers.

Question 5.
a) Define evolution.
(b) Mention any four ways by which individuals with -a particular trait may increase in a population. (CCE 2013)
Answer:
(a) Evolution: It is the formation of newer types of organisms from the pre-existing ones through modification, i. e., descent with change or modification.
(b) Fossils Indicate Evolution

1. Different types of organisms appeared in different ages. Many of them have later on disappeared. Some gave rise to other organisms while a few are persisting even now.
2. Early forms were simple. Most of the later forms became more and more complex.
3. Fossils of different ages indicates the path of evolution,
4. Some fossils have characteristics intermediate between two groups, e.g., Archaeopteryx between reptiles and birds. They indicate the path of evolution.
5. Phylogeny of some organisms has been worked out with the help of fossils e.g., Horse.

Question 6.
(i) What is meant by traits of an individual ?
(ii) Explain inherited trait and acquired trait.
(iii) Define spéciation. List the factors which could lead to rise of new species. (CCE 2013)
Answer:
(i) Traits: They are distinguishable expressions of well defined morphological or physiological features of an individual, e.g., tall and dwarf in height.
(ii) Inherited Trait: It is genetically controlled trait which is passed from parents to the offspring, generation after generation, .e.g, fused or free ear lobe.
Acquired Trait: It is variation which an individual develops during its life time due to effect of environmental factors, use and disuse of organs and conscious efforts, e.g., education, music.
(iii) Speciation: It is the formation of newer species from the pre-existing ones through modifications and reproductive isolation.
Factors:

1. Absence of gene flow amongst sub-populations due to the presence of physical barriers, long distance, differences in habitats, environmental and climatic conditions.
2. Accumulation of different variations in the different sub-populations of the species.
3. Natural selection of particular traits in a particular environment.
4. Genetic Drift. Separation of a small population, changes in its allele frequency, new mutations and adaptations to new habitat.
5. Reproductive Isolation. Accumulation of different variations and genetic drift result in absence of interbreeding in the previous subpopulations of a species. This results in the formation of new species. e.g., Finches of Galapogos islands.

Question 7.
(a) Distinguish between acquired traits and inherited traits.
(b) What is speciation ? What are the factors responsible for it ? (CCE 2013)
Answer:
(a)

(b) Speciation: It is the formation of newer species from the pre-existing ones through modifications and reproductive isolation.
Factors:

1. Absence of gene flow amongst sub-populations due to the presence of physical barriers, long distance, differences in habitats, environmental and climatic conditions.
2. Accumulation of different variations in the different sub-populations of the species.
3. Natural selection of particular traits in a particular environment.
4. Genetic Drift. Separation of a small population, changes in its allele frequency, new mutations and adaptations to new habitat.
5. Reproductive Isolation. Accumulation of different variations and genetic drift result in absence of interbreeding in the previous subpopulations of a species. This results in the formation of new species. e.g., Finches of Galapogos islands.

Question 8.
What are fossils ? How are they formed ? Explain how fossils support evolution. (CCE 2013)
Answer:
Fossils: They are remains or impressions of past organisms that lie hurried in the rocks and other structures belonging to various ages.
Formation: Fossil formation or fossilisation occurs in bogs, lava and in sediments at the bottom of deep waters where there is little oxygen and rate of decay is slow or absent. Dead bodies settle down at the bottom which get covered by sand and silt. Under acidic conditions some silica can penetrate cells of dead organism and form perfect fossil. In other cases, softer parts decay ultimately and hard parts persist as fossils. Impressions, moulds and casts develop if all parts decay after some time. The sedimented mud and
sand harden to form sedimentary rock which may come to the surface due to upheavals in earth. This exposes the fossils.
Fossils indicate Evolution:

1. Different types of organisms appeared in different ages. Many of them have later on disappeared. Some gave rise to other organisms while a few are persisting even now.
2. Early forms were simple. Most of the later forms became more and more complex.
3. Fossils of different ages indicates the path of evolution,
4. Some fossils have characteristics intermediate between two groups, e.g., Archaeopteryx between reptiles and birds. They indicate the path of evolution.
5. Phylogeny of some organisms has been worked out with the help of fossils e.g., Horse.

Question 9.
Define the following :

1. Gene
2. Genetic drift
3. Recessive trait
4. Evolution
5. Genetics. (CCE 2014)

Answer:

1. Gene: They are units of inheritance that take part in expression of particular characters. Genes are located over the chromosomes as linear segments.
2. Genetic Drift: It is random change in gene frequency in small isolated population owing to factors other than natural selection that results in fixation of certain alleles and elimination of some others.
3. Recessive Trait: It is a trait which is unable to express its effect in the presence of its contrasting trait.
4. Evolution: It is the formation of newer types of organisms from the pre-existing ones through modification, i. e., descent with change or modification.
5. Genetics: It is the branch of biology that deals with the study of heredity and variations.

Question 10.
In organisms, some changes pertain to body cells and are not inherited whereas some changes pertain to germ * cells and are inherited.
(a) Name the two types of variations respectively.
(b) Explain the two ways by which individuals with a particular trait may increase in a population.
(CCE 2014)
Answer:
(a) Body Cells: Somatic variations. They die with the death of the individual.
Germ Cells: Germinal variations. They are passed on to the next generation and are, therefore, inherited.
(b)

Question 11.
How do Mendel’s experiments show that the
(a) Traits may be dominant or recessive,
(b) Traits are inherited independently.
(CCE 2015, CBSE Delhi 2017)
Answer:
(a) Dominant and recessive traits can be proved by monohybrid cross. A cross between pure tall Pea plant with a pure dwarf Pea plant yields only tall plants in F₁ generation. Self pollination in F₁ plants results in appearance of both tall and dwarf plants in the ratio of 3 : 1. Absence of dwarf plants in F₁ generation and their reappearance in F₂ generation in 25% population shows that the trait for dwarfness is recessive. It does not express its effect in the presence of allele for tallness. The factor for tallness is dominant over the factor for dwarfness.
(b) That traits are inherited independently can be proved by a dihybrid cross like RRYY and rryy. In F₁ generation all the plants were having round seeds with yellow colour. On self pollination, the F₂ generation has 4 types of plants—round yellow (9), round green (3), wrinkled yellow (3) and wrinkled green (1). While round yellow and wrinkled green are parental types, the other two (round green and wrinkled yellow) are recombinants. Recombinants can appear only if the traits are inherited independently.

Question 12.
What are fossils ? How are they formed ? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of process of evolution. (CCE 2015, CBSE Foreign 2016, 2017)
Answer:
Fossils: They are remains or impressions of past organisms that lie hurried in the rocks and other structures belonging to various ages.
Formation: Fossil formation or fossilisation occurs in bogs, lava and in sediments at the bottom of deep waters where there is little oxygen and rate of decay is slow or absent. Dead bodies settle down at the bottom which get covered by sand and silt. Under acidic conditions some silica can penetrate cells of dead organism and form perfect fossil. In other cases, softer parts decay ultimately and hard parts persist as fossils. Impressions, moulds and casts develop if all parts decay after some time. The sedimented mud and
sand harden to form sedimentary rock which may come to the surface due to upheavals in earth. This exposes the fossils.
Age of Fossils: Age of Fossil Organisms,

1. Relative Dating. Fossils closer to the surface are more recent than the ones present midway which in turn are more recent than the ones present in deeper layers of rocks.
2. Radioactive or Absolute Dating. Fossil or piece of fossil containing rock is analysed for radioactive decay
   (uranium —> lead, radioactive Potassium —> argon, ^l4C content) to calculae the age.

Role of Fossils in Study of Evolution:

1. Different types of organisms appeared in different ages. Many of them have later on disappeared. Some gave rise to other organisms while a few are persisting even now.
2. Early forms were simple. Most of the later forms became more and more complex.
3. Fossils of different ages indicates the path of evolution,
4. Some fossils have characteristics intermediate between two groups, e.g., Archaeopteryx between reptiles and birds. They indicate the path of evolution.
5. Phylogeny of some organisms has been worked out with the help of fossils e.g., Horse.

Question 13.
Give differences :
(a) Heredity and variations
(b) Dominant and recessive traits,
(c) Natural and artificial selection. (CCE 2015)
Answer:
(a) Differences Between Heredity and Variations

(b) Differences Between Dominant and Recessive Factors

(c) Differences Between Natural Selection and Artificial Selection

Question 14.
(a) Why do we say that homozygous plants produce pure progeny ?
(b) Define heterozygous.
(c) Explain how the process of speciation takes place. (CCE 2015)
Answer:
(a) Homozygous Plants: They possess identical alleles of a character (e.g., IT ). All their gametes come to have the same type of allele (e.g., T) so that fusion of two such gametes produce the genetic make up (TT) similar to the parent. This will continue for generations so that such plants are called pure lines.
(b) Heterozygous: It is an individual having both the contrasting alleles of a character (e.g., Tt). Heterozygous individuals is called hybrid.
(c) Speciation: It is formation of newer species from pre-existing ones due to reproductive isolation of segments of their population. Scpeciation is of two types, sympatric and allopatric.
Sympatric speciation occurs in the same area due to mutations in a section of population that result in its reproductive isolation from the rest of population.
Allopatric speciation: It occurs in sub-population occurring in different and mutually exclusive areas of distribution due to physical barriers (e.g., valley, mountain, water body), ends of a long range and genetic drift. They accumulate different variations and become transformed into different species.

Question 15.
Given here is a schematic diagram showing Mendel’s experiment on pea plants with yellow round and green wrinkled seeds. Answer the following questions :
(a) Complete the diagram by filling numbers 1-6.
(b) Write the phenotypes of F₁ progeny,
(c) Name the phenotypes produced in F₂ progeny upon self pollination of F₁ progeny. (CCE 2015)

Answer:
(a)

1. 1- YR,
2. 2-YR,
3. 3-yr,
4. 4-YyRr,
5. 5-YyRr,
6. 6-YyRr.

(b) Yellow round seeded.
(c) Yellow round seeded 3 : Green wrinkled seeded 1.

Question 16.
(a) How many pairs of chromosomes are present in human beings ? Out of these how many are sex chromosomes ? How many types of sex chromosomes are found in human beings ?
(b) “The sex of a new born child is a matter of chance and none of the parents may be considered responsible for it.” Draw a flow chart showing determination of sex of new born to justify this statement. (CCE 2015)
Answer:
(a) 23 pairs. Out of them one pair are sex chromosomes or allosomes. In females, both the sex chromosomes are similar and are called XX. In males, the two sex chromosomes are different, X and Y.
(b) Sex of the child is determined by the gametes that fuse to form zygote which later grows into offspring. Human females (44 + XX) produce only one type of ova (22 + X). Human males (44 + XY) form two types of sperms, androsperms (22 + Y) and gynosperms (22 + X). Both are formed in equal number. It is a chance factor whether an androsperm or a gynosperm fuses with egg to form 44 + XY or 44 + XX child. A child that obtains an X-chromosome from father will be girl and the one who inherits a Y-chromosome will be boy.

Question 17.
(a) Observe the ears of students of your class. Which variations do you observe related to ear ? What do you conclude ?
(b) Why did Mendel choose Pea plant for his expeirments ? Give 3 reasons. (CCE 2015)
Answer:
(a) Ear lobes: Attached and Free Ear Lobes
Observe the lower part of pinna or ear lobe of your class mates. Find out that there are two types of ear lobes, free (hanging separately) and attached (non-hanging). Out of 50 students, the students with attached ear lobes are fewer, say 8. The remaining students (42 here) have free ear lobes. Calculate the percentage of free ear lobes and attached ear lobes.


Now find out the ear lobes of the parents of your class mates. Attached ear lobes often occur in cases where one of the two parents of children having attached ear lobes. Free lobes always oscur in those cases where one or both the parents have free lobes. This is possible only when the trait of ear lobe is represented in an individual by two factors or alleles, E and e. Persons with free ear lobes have EE and Ee. Persons with attached ear lobes have ee. The two alleles separate at the time of gametogenesis, so that a sperm or egg has only one allele £ or e but not both. The two alleles come together during fertilization.

(b) Mendel’s Experimental Material:
Mendel chose Garden Pea or Edible Pea (Pisum sativum) as his experimental material because of

1. Easy availability of detectable contrasting traits of several characters,
2. Flower structure normally allows self fertilization but cross fertilization can also be carried out easily.
3. Annual nature of the plant,
4. Formation of a large number of seeds by each plant,
5. Requirement of little care except at the time of cross breeding.

Mendel selected seven visible characters, each with two contrasting traits (Figure 4.5). They were given symbols, dominant with capital alphabet symbol (e.gtallness T) while the recessive were given small alphabet symbol (e.g., dwarfness t). All the plants were pure breeding. They formed the parent (P) generation.

Question 18.
(a) “Evolution has occurred in stages”. Justify the statement.
(b) Differentiate between eye and eyespots. Which animal possesses eye spots ? (CCE 2015)
Answer:
(a) Evolution does not proceed continuously in one direction. A number of stages occur with each stage giving rise to one or more branches. Both humans and chimpanzee are closely related but neither of them has given rise to the other. Rather they have evolved from a common ancestor which neither gave rise to modern day chimpanzee nor modern human in one step. Instead, descendants of this ancestor gave rise to various forms. One of them gave rise to chimpanzee. Another gave rise to humans. A third one formed great apes.
(b) Eye is an organ of the body that forms images of the surroundings. Eye spot is a light sensitive area of the body surface where images are not formed but sensitivity about the surrounding is perceived, e.g., Planaria.

Question 19.
Give reason for the following :
(a) Traits acquired during lifetime of an individual are not inherited.
(b) All humans belong to a single species.
(c) Variations keep on accumulating during reproduction and do not disappear in next generation.
(CCE 2015)
Answer:
(a) Acquired variations influence only the somatic cells. They die with the death of the individual.
(b) Delimitation of a species is based on the presence of a common gene pool, free inbreeding and reproductive isolation. Differences in size, colour and looks are based on preponderance of specific alleles and their interactions with the environment. All human beings, despite presence of different races, belong to same species (Homo sapiens) because they share the same gene pool, can marry amongst themselves and produce fertile offspring.
(c) They are inherited variations. Most of them are produced during reproduction due to reshuffling of chromosomes, recombinations, and some due to mutations. Inherited variations are passed on to next generation.

Question 20.
What is meant by spéciation ? List four factors that could lead to spéciation. Which of these cannot be a major factor in the spéciation of self-pollinating plant species. Give reason to justify your answer.
(CBSE Delhi 2016)
Answer:
Speciation: It is the formation of newer species from the pre-existing ones through modifications and reproductive isolation.
Factors:

1. Absence of gene flow amongst sub-populations due to the presence of physical barriers, long distance, differences in habitats, environmental and climatic conditions.
2. Accumulation of different variations in the different sub-populations of the species.
3. Natural selection of particular traits in a particular environment.
4. Genetic Drift. Separation of a small population, changes in its allele frequency, new mutations and adaptations to new habitat.
5. Reproductive Isolation. Accumulation of different variations and genetic drift result in absence of interbreeding in the previous subpopulations of a species. This results in the formation of new species. e.g., Finches of Galapogos islands.

Self Pollinating Plants: Geographical isolation has little role in spéciation of self pollinating plant species because there is already no gene flow among members of the species. Pea or Wheat which is self pollinated (due to pollination in bud condition) is not affected by any type of isolation. However, self pollinated plants can accumulate variations due to mutations and other factors and form new species.

Question 21.
(a) Why did Mendel choose Garden Pea for his experiments ? Write two reasons,
(b) List two contrasting visible characters of Garden Pea, Mendel used for his experiments
(c) Explain in brief how Mendel interpreted his results to show that the traits may be dominant or recessive. (CBSE Foreign 2016)
Answer:
(a) Garden Pea As Experimental Material:

1. Availability of true breeding varieties,
2. Both self and cross pollination are possible.
3. Small size, short life cycle, easy to grow and maintain.

(b) Contrasting Traits:

1. Height: Tall and dwarf,
2. Seed Shape: Round and wrinkled
3. Seed Colour.
4. Yellow and green.

(c) Interpretation by Mendel: Mendel crossed Garden Pea plants having contrasting visible traits, e.g., tall and dwarf, violet and white flowered.
In F₁ generation there were no halfway characteristics. A cross between pure tall and pure dwarf plants yielded only tall plants in F₁ generation. There were no medium height plants. When F₁ plants were self bred, the F₂ plants were not all tall plants. Instead, both tall and dwarf plants appeared in ratio of 3 : 1. It means that the trait for dwarfness was present in F₁ generation but was not expressed while the trait for tallness expressed itself.

The trait of tallness which expresses itself in the presence of its contrasting form is called dominant. The other trait of dwarfness which is unable to express its effect in the presence of its contrasting trait is known as recessive.

Question 22.
Define evolution. How does it occur ? Describe how fossils provide us evidence in support of evolution.
(CBSE A.I. 2016)
Answer:
Evolution: It is the formation of newer types of organisms from the pre-existing ones through modifications or accumulation of variations.
Mechanism:

1. Absence of gene flow amongst sub-populations due to the presence of physical barriers, long distance, differences in habitats, environmental and climatic conditions.
2. Accumulation of different variations in the different sub-populations of the species.
3. Natural selection of particular traits in a particular environment.
4. Genetic Drift. Separation of a small population, changes in its allele frequency, new mutations and adaptations to new habitat.
5. Reproductive Isolation. Accumulation of different variations and genetic drift result in absence of interbreeding in the previous subpopulations of a species. This results in the formation of new species. e.g., Finches of Galapogos islands.

Fossils As Evidence of Evolution:
Fossils: They are remains or impressions of past organisms that lie hurried in the rocks and other structures belonging to various ages.
Fossils Indicate Evolution

1. Different types of organisms appeared in different ages. Many of them have later on disappeared. Some gave rise to other organisms while a few are persisting even now.
2. Early forms were simple. Most of the later forms became more and more complex.
3. Fossils of different ages indicates the path of evolution,
4. Some fossils have characteristics intermediate between two groups, e.g., Archaeopteryx between reptiles and birds. They indicate the path of evolution.
5. Phylogeny of some organisms has been worked out with the help of fossils e.g., Horse.

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 9 Heredity and Evolution are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 13 Magnetic Effects of Electric Current Class 10 Science Important Questions with Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Magnetic Effects of Electric Current Class 10 Important Questions and Answers Science Chapter 13

Very Short Answer Questions

Based on magnet and magnetic field

Question 1.
Identify the poles of a magnet in the figure.

Answer:

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
What is the direction of magnetic field lines outside a bar magnet ?  (CBSE 2010, 2011)
Answer:
From North pole to South pole.

Question 3.
What does crowding of magnetic field lines indicate ? (CBSE 2010, 2011)
                                             Or
What does the degree of closeness of magnetic field lines near the poles signify ? (CBSE 2012)
Answer:
Crowding of magnetic field lines indicates that magnetic field in that region is strong.

Question 4.
At what place of the magnet are the magnetic field lines denser ? [CBSE (All India) 2007]
Answer:
Near the poles of the magnet.

Question 5.
What is meant by magnetic field ? [CBSE (Delhi) 2007, 2009, 2014]
Answer:
The space around a magnet or current carrying conductor within which its influence can be felt by a magnetic substance like iron is called magnetic field.

Question 6.
How is the direction of magnetic field at a point determined ? [CBSE (Delhi) 2007]
Answer:
Direction of magnetic field is determined by a compass needle. The direction of magnetic field is towards the north pole of the compass needle at a point.

Question 7.
What is SI unit of magnetic field ?
Answer:
tesla (T).

Question 8.
What is the direction of magnetic field lines inside a bar magnet ?
Answer:
From South pole to the North pole.

Question 9.
Define a magnetic field line ? (CBSE (All India) 2006, 2010, 2015)
                                        Or
What are magnetic field lines ? (CBSE 2011, 2013)
Answer:
It is a curve around a magnet or a current carrying straight conductor such that the tangent at any point on the curve gives the direction of magnetic field at that point.

Question 10.
Give two uses of a magnetic compass. (CBSE 2013)
Answer:

1. It is used to determine the direction of north and south of earth.
2. It is used to draw the magnetic field lines around a bar magnet.

Based on magnetic field due to current through a straight conductor

Question 11.
How is the strength of the magnetic field around a wire related to the strength of the electric current flowing in the wire ? (CBSE 2004)
Answer:
The strength of magnetic field B increases with the increase in the electric current I and vice-versa. That is, Bocl.

Question 12.
How can it be shown that magnetic field exists around a wire through which direct current is passing ?
[C.B.S.E; (Delhi) 2004]
Answer:
By placing a magnetic compass near the wire. If magnetic compass needle shows the deflection magnetic field exists around the wire.

Question 13.
What is the nature of magnetic field lines around a current carrying wire ?
Answer:
Concentric circles centred at the wire.

Question 14.
State the rule used to determine the direction of magnetic field produced around a straight conductor carrying current. [CBSE (Delhi) 2009; CBSE (All India) 2009, 2011, 2012, 2015]
Answer:
This rule is used to find the direction of the magnetic field produced by the current carrying conductor around it.
Statement : If a current carrying conductor is imagined to be held in the right hand such that the thumb points in the direction of the current, then the curled fingers of the hand indicate the direction of magnetic field (Figure 14).

If current in a conductor flows in the upward direction, then the direction of magnetic field around the conductor is in anticlockwise direction. On the other hand, if current in a conductor flows in the downward direction, then the direction of the magnetic field around the conductor is in clockwise direction.

Question 15.
State the rule to determine the direction of a force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular. (CBSE 2013, 2014, 2015)
Answer:
Fleming’s left hand rule
Statement : Stretch the left hand such that the thumb, first finger and the central finger are mutually perpendicular to each other. If the First finger points in the direction of the magnetic Field and the Central finger points in the direction of Current, then the thumb will point in the direction of Motion (or Force) as shown in figure 24.

Thus, in Fleming’s left hand rule, first finger shows the direction of the magnetic field. The central finger shows the direction of electric current flowing in the conductor. Thumb shows the direction of force on the conductor or the direction of motion of the conductor

Question 16.
A compass needle shows deflection when brought near a current carrying conductor. Why ? (CBSE 2015)
Answer:
A compass needle is a small magnet. When it is brought near a current carrying’ conductor, it experiences a magnetic force due to the magnetic field around the current carrying conductor. Hence, it gets deflected due to this magnetic force.

Question 17.
Draw a sketch of the pattern of field lines due to a current flowing through a straight conductor.
[CBSE (Delhi) 2009, 2011]
Answer:

Based on magnetic field due to current passing through a circular wire or loop

Question 18.
Draw the magnetic field lines through and around a single loop of wire carrying electric current.
(CBSE 2015)
Answer:

Question 19.
Draw the pattern of magnetic field lines of the field produced by a current carrying circular loop.
(C.B.S.E 2010, 2011, 2012)
Answer:

Based on magnetic field due to current in a solenoid

Question 20.
What is a solenoid ? (CBSE (Delhi) 2009, 2010, 2011, 2012, 2013, 2015)
Answer:
A solenoid is a long, helically wound coil of insulated copper wire.

Question 21.
Write one application of magnetic field of current carrying solenoid. (CBSE Sample Paper)
Answer:
Magnetic field of current carrying solenoid is used to make soft iron as an electromagnet.

Question 22.
Draw the pattern of field lines of magnetic field through and around a current carrying soleniod.
(CBSE (Delhi) 2009, 2011, 2012, 2013, 2015)
Answer:

Question 23.
What does the direction of thumb indicate in the right hand thumb rule ?
Answer:
Direction of the flow of current.

Question 24.
How is an electromagnet made ?
Answer:
An electromagnet is made by placing a soft iron bar in a current carrying solenoid.

Based on force on a current carrying conductor placed in a magnetic field

Question 25.
Write an expression for the force acting on a conductor of length l carrying current (I) and placed perpendicular to the magnetic field (B).
Answer:
F = BIl

Question 26.
State the rule to determine the direction of a force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular. (CBSE 2013, 2014, 2015)
Answer:
Fleming’s left hand rule
Statement : Stretch the left hand such that the thumb, first finger and the central finger are mutually perpendicular to each other. If the First finger points in the direction of the magnetic Field and the Central finger points in the direction of Current, then the thumb will point in the direction of Motion (or Force) as shown in figure 24.

Thus, in Fleming’s left hand rule, first finger shows the direction of the magnetic field. The central finger shows the direction of electric current flowing in the conductor. Thumb shows the direction of force on the conductor or the direction of motion of the conductor.

Based on electric motor

Question 27.
What is electric motor ? (CBSE 2012)
Answer:
A device which converts electrical energy into mechanical energy.

Question 28.
What is the principle of electric motor ? (CBSE 2012)
Answer:
A current carrying conductor placed perpendicular to the magnetic field experiences a force.

Based on Electromagnetic Induction.

Question 29.
Define electromagnetic induction. (CBSE 2011, 2012, 2015)
Answer:
The phenomenon of producing induced current in a closed coil due to the changing magnetic field is called electromagnetic induction.

Question 30.
State the rule of determine the direction of current induced in a coil due to its rotation in a magnetic field.
(CBSE 2015)
Answer:
Fleming stated a rule to determine the direction of induced current in a conductor. This rule is known as Fleming’s Right hand rule.
Fleming’s Right hand Rule: “Stretch the right hand such that the first finger, the central finger and the thumb are mutually perpendicular to each other. If the First finger points along the direction of the field (magnetic field) and the Thumb points along the direction of Motion of the conductor, then the direction of induced. Current is given by the direction of the Central finger (Figure 30).

Thus, in right hand rule, first finger shows the direction of the magnetic field. The central finger shows the direction of induced current in the conductor. The thumb shows the direction of motion of the conductor in the magnetic field.
Note : Fleming’s Right hand rule is also known as Dynamo Rule.

Question 31.
How is induced current in a secondary coil related to current in a primary coil ? [CBSE (All India) 2009)]
Answer:
When current in a primary coil changes, induced current in the secondary coil is set up.

Question 32.
Name any one method to induce current in a coil. (CBSE 2015)
Answer:
Electromagnetic induction.

Based on Direct current and Alternating current

Question 33.
What is frequency of AC in India ? (CBSE 2010, 2011, 2013)
                                       Or
State the frequency of power supply generated in India. (CBSE 2012)
Answer:
50 Hz

Question 34.
What is the frequency of direct current (D.C) ? (CBSE 2013)
Answer:
Zero.

Question 35.
What is the meaning of the term “frequency” of an alternating current ? What is its value in India ?
(CBSE Sample Paper, CBSE 2014, 2015)
Answer:
Frequency of an alternating current means how many cycles it makes in one second. In India, frequency of AC is 50Hz or cycle/second.

Question 36.
Why is an alternating current considered to be advantageous over direct current for long range transmission of electric energy 1 (CBSE Sample Paper, 2012, 2014)
                                                       Or
State one advantage of A.C. over D.C. (CBSE 2011, 2014, 2015)
Answer:
AC can be transmitted to long distant places without much loss of electric energy with the help of a transformer.

Question 37.
How is the type of current that we receive in domestic circuit different from the one that runs a clock ?
(CBSE 2015)
Answer:
The current received in domestic circuit is alternating current and the one that runs a clock is direct current. Alternating current varies in magnitude and changes its direction periodically. However, magnitude of direct current may or may not change with passage of time but its direction remains the same.

Based on electric generator

Question 38.
What is electric generator ?
Answer:
A device used to convert mechanical energy into electrical energy.

Based on Domestic Electric Circuits

Question 39.
Out of three wires live, neutral and earth, which one goes through ON/OFF switch ? (CBSE 2013, 15)
Answer:
Live wire.

Question 40.
In a domestic electric circuit, mention the potential difference between live wire and neutral wire and frequency of A.C. (CBSE 2013)
Answer:
220 V and 50 Hz.

Question 41.
Mention the colour convention for live, neutral and earth wires. (CBSE 2015)
Answer:
Live wire is covered with an insulation of red or brown colour. Neutral wire is covered with an insulation of black colour and earth wire is covered with an insulation of green or yellow colour.

Question 42.
What do you understand by the current rating of an electric fuse ? (CBSE 2012)
Answer:
The maximum amount of current that can be passed through the fuse wire without melting it.

Question 43.
Name the material generally used to make electric fuse. (CBSE 2006, 2012, 2013, 2014, 2015)
Answer:
Copper or alloy of lead and tin.

Question 44.
An alternating current has frequency of 50 Hz. How many times does it change its direction in one secotid ? [CBSE (Delhi) 2004 (S), 2012, 2013]
                                                                               Or
How many times does AC used in India change direction in one second ? (CBSE Sample Paper)
Answer:
Since frequency is 50 Hz, so a.c. completes 50 cycles in 1 second. Therefore, it reverses its direction 100 times in one second.

Question 45.
List two characteristics of the material to be used in fuse wire. (CBSE 2014, 2015)
Answer:

1. Melting point of the material used to make fuse wire should be low.
2. Resistance should be low.

Question 46.
State the function of a ‘fuse’ in a circuit. How is it connected in the domestic circuit ? (CBSE 2013, 2014)
Answer:
Fuse is a safety device which prevents the damage of an electric, appliance connected in a circuit. It is connected in series in the domestic circuit.

Question 47.
Name the electric device that converts mechanical energy into electric energy.(CBSE Sample Paper 2017-18)
Answer:
Electric generator.

Question 48.
What is the function of earth wire in electrical instruments ? (CBSE Sample Paper 2017-18)
Answer:
Earth wire in electrical instruments save us from electric shocks.

Question 49.
Explain what is short circuiting of an electric supply. (CBSE Sample Paper 2017-18)
Answer:
When live wire and neutral wire of an electric circuit comes in direct contact accidently, then short circuiting takes place.

Question 50.
What is the usual current rating of the fuse wire in the line to feed
(a) lights and fans ?
(b) Appliances of 2 kW or more power ? (CBSE Sample Paper 2017-18)
Answer:
(a) 5 A
(b) 15 A.

Short Answer Questions (2 & 3 Marks)

Based on magnet and magnetic field

Question 1.
In the figure below, identify the poles marked P and Q as North Pole or South pole. Give reason for your answer. (CBSE 2010)

Answer:
Both P and Q are North poles. Magnetic field lines emerge from North pole.

Based on magnetic field due to current through a straight conductor

Question 2.
State the factors on which the strength of magnetic field at a point due to a current carrying conductor depends. State the rule which gives the direction of magnetic field. (CBSE 2010, 2013)
Answer:
The strength of magnetic field at a point due to current carrying conductor depends on

1. strength of electric current flowing in the conductor.
2. the distance of the point from the conductor.
   Right hand thumb rule: If a current carrying conductor is imagined to be held in the right hand such that the thumb points in the direction of the current, then the curled fingers of the hand indicate the direction of magnetic field (Figure 14).
   

Question 3.
Describe an activity to show that magnetic field is generated around straight current carrying wire.
[CBSE (All India) 2008, 2010, 2011, 2013, 2015]
                                                                                 Or
With the help of a labelled circuit diagram describe an activity to illustrate the pattery of the magnetic field lines around a straight current carrying long conducting wire. (CBSE Sample Paper 2017-2018)
Answer:
Describe an activity to plot the magnetic field around a straight conductor carrying current.

1. Take the thick piece of wire consisting of ten turns of insulated copper wire and a card board.
2. Pass this thick wire through a hole in the card board placed horizontally as shown in  Fig 13.a
   
3. Now pass electric current (about 4 A) through the wire by pressing the key and sprinkle some iron filings on the card board around the wire.
4. Tap the card board gently.

Observation : We find that the iron filings are arranged in concentric circles around the wire as shown in figure 13(a). If magnetic compass is placed near the current carrying wire and at different positions, we get concentric circles around the wire as shown in figure 13(b). These concentric circles around the wire carrying current represent the magnetic field around the wire.

Question 4.
A horizontal power line carries current in east to west direction.What is the direction of the magnetic field due to the current in the power line at a point above and at a point below the power line ?
(CBSE 2013, 2015)
Answer:
According to right-hand thumb rule :

1. the direction of magnetic field at a point above the power line is from south to north,
2. the direction of magnetic field at a point below the power line is from north to south.
   

Question 5.
A magnetic compass is placed near a current carrying wire. What will you observe

1. When current in the wire is increased,
2. When the magnetic compass is displaced away from the wire ?
                                                                        

                                                               Or
A magnetic compass shows a deflection near a current carrying wire. How will the deflection of the compass get affected if current in the wire is increased ? Support your answer with reason.
(CBSE Sample Paper 2012, 2013)
Answer:

1. We observe that the deflection of the needle of the magnetic compass increases. This is because the magnetic field strength due to a current carrying wire increases, when current in the wire is increased.
2. We observe that the deflection of the needle of the magnetic compass decreases. This is because the magnetic field strength due to a current carrying wire decreases with the increase of the distance from the wire.

Question 6.
Draw a diagram to show how a magnetic needle deflects when it is placed above or below a straight conductor carrying current de¬pending on the direction of the current in the conductor.
(CBSE 2010)

Answer:
Direction of deflection of magnetic needle due to the current pass¬ing through a conductor can be found using Ampere’s swimming rule as shown in figure A.

Question 7.
A student performs an experiment to study the magnetic effect of current around a current carrying conductor with the help of a magnetic compass. He reports that :

1. The degree of deflection of the magnetic compass increases when the compass is moved away from the conductor.
2. The degree of deflection of the magnetic compass increases when the current through the conductor is increased

Which of the above observations of the student appears to be wrong and why ? (CBSE 2010, 2011)
Answer:
Observation

1. is incorrect. Degree of deflection of magnetic compass depends on the strength of the magnetic field produced by the current carrying conductor. Magnetic field increases with the increase in the current through the conductor and hence degree of deflection of the magnetic compass increases.
2. Magnetic field decreases with the increase in the distance from the conductor and hence degree of deflection of the magnetic compass decreases when the compass is moved away from the conductor.

Question 8.
With the help of a diagram describe an activity to show that an electric current can affect a magnet.
(CBSE 2014)
Answer:
When a straight conductor carries electric current (dc), a magnetic field is set up around the conductor. This magnetic field causes the deflection in the needle of the magnetic compass.
Describe an activity to plot the magnetic field around a straight conductor carrying current.

1. Take the thick piece of wire consisting of ten turns of insulated copper wire and a card board.
2. Pass this thick wire through a hole in the card board placed horizontally as shown in  Fig 13.a.
   
3. Now pass electric current (about 4 A) through the wire by pressing the key and sprinkle some iron filings on the card board around the wire.
4. Tap the card board gently.

Observation : We find that the iron filings are arranged in concentric circles around the wire as shown in figure 13(a). If magnetic compass is placed near the current carrying wire and at different positions, we get concentric circles around the wire as shown in figure 13(b). These concentric circles around the wire carrying current represent the magnetic field around the wire.

Based on force on a current carrying conductor placed in a magnetic field

Question 9.
Why does a current carrying conductor kept in a magnetic field experience force ? What is the direction of force acting on the conductor ? (CBSE 2010, 2011, 2015)
Answer:
A current carrying conductor contains moving negatively charged particles (i.e., electrons). Each electron experiences a force (= Bev). The total force experienced by electrons is equal to the force experienced by the conductor. This force acts perpendicular to both the magnetic field and the direction of current in the conductor. The direction of the force acting on the conductor is determined by Fleming’s left hand rule.
A proton enters a magnetic field at right angles to it as shown in figure.

Question 10.
What is the direction of the force acting on the proton ?

Answer:
According to Fleming’s left hand rule, the force acting on a current
carrying conductor placed at right angles to a magnetic field is perpendicular to the directions of current {i.e. flow of positive charges) and the magnetic field.
The arrow showing the direction of proton represents the direction of current in a conductor, therefore, the force acting on the conductor is perpendicular to the plane of the paper and in upward direction.

Question 11.
State the rule to determine the direction of force experienced by a current carrying conductor in a magnetic field. How will this force get affected on :

1. Doubling the magnitude of current ?
2. Reversing the direction of current flow ? (CBSE 2010)

Answer:
Fleming’s left hand rule:
Statement : Stretch the left hand such that the thumb, first finger and the central finger are mutually perpendicular to each other. If the First finger points in the direction of the magnetic Field and the Central finger points in the direction of Current, then the thumb will point in the direction of Motion (or Force) as shown in figure 24.

Thus, in Fleming’s left hand rule, first finger shows the direction of the magnetic field. The central finger shows the direction of electric current flowing in the conductor. Thumb shows the direction of force on the conductor or the direction of motion of the conductor
Force, F = B I l.

1. When magnitude of current is doubled, the magnitude of the force is also doubled.
2. The direction of the force is reversed, when the direction of the current flow is reversed.

Question 12.
A student while studying the force experienced by a current carrying conductor in a magnetic field records the following observations :

1. The force experienced by the conductor increases as the current is increased.
2. The force experienced by the conductor decreases as the strength of the magnetic field is increased.

Which of the two observations is correct and why ? (CBSE 2010, 2011)
Answer:
Force experienced by a current carrying conductor in a magnetic field is given by F = B I l, where B is magnetic field, I is current and l is the length of the conductor.
Observation

1. is correct because F increases with increase in I. However, observation
2. is incorrect because F increases with increase in B.

Question 13.
Describe with the help of a labelled diagram an activity to demonstrate the force acting on a current carrying conductor due to magnetic field. (CBSE 2014, 2015)
Answer:
Describe an activity to show that a current carrying conductor placed perpendicular to the magnetic field experiences a force.

1. Fix a horse shoe magnet on the top of the table.
2. Place a long and thin strip of aluminium on two wooden supports such that it passes between the North and South poles of the magnet.
3. Connect a battery across the ends of the aluminium strip through a key (K) as shown in Figure 23(a).
   
4. Now close the key so that current (I) flows through the strip. [Figure 23 (b)].

Observation: When current flows through the aluminium strip, it moves upward. If the direction of current is reversed, the aluminium strip moves downward.
Conclusion: A current carrying conductor (aluminium strip) placed in a magnetic field experiences a force in a direction perpendicular to the direction of the magnetic field. Due to this force, the current carrying conductor is displaced from its rest position.

Question 14.
An α-particle enters a uniform magnetic field at right angles to it as shown in figure. Stating the relevant principle, explain in which direction will this α.-particle move ? (CBSE 2014)

Answer:
According to Fleming’s left hand rule, the force acting on a current carrying conductor placed perpendicular to a magnetic field is perpendicular to the direction of current (i. e., flow of positive charges) and the magnetic field. Here, direction of α-particle (i.e., positive charge) is the direction of current. Hence, according to Fleming’s left hand rule, the direction of force acting on α-particle is perpendicular to both the direction of motion of α-particle and the direction of magnetic field. Hence, α-particle will move perpendicular to the plane of the paper and in downward direction.

Question 15.
State whether an alpha particle will experience any force in a magnetic field if (alpha particles are positively charged particles)

1. it is placed in the field at rest.
2. it moves in the magnetic field parallel to field lines.
3. it moves in the magnetic field perpendicular to field lines.

Justify your answer in each case. (CBSE 2015)
Answer:
Force acting a particle having charge q moving with velocity u in a magnetic field B is given by
F = qv B sin θ …………..(i)
where θ is the angle between velocity V and magnetic field B.

1. When alpha particle is at rest i.e. V = 0, then
   F = 0 (No force)
2. When alpha particle moves parallel to the magnetic field, θ = 0°, then
   F = qvB sin 0° = 0 (No force)
3. When alpha particle moves perpendicular to magnetic field, θ = 90°, then
   F = qvB sin 90° = qvB (maximum force) on magnetic field due to current passing through a circular wire or loop

Question 16.
How does the strength of the magnetic field at the centre of a circular coil of a wire depends on
(a) radius of the coil
(b) number of turns of the wire of the coil ? (CBSE 2010, 2011, 2012, 2015)
Answer:
The strength of magnetic field at the centre of the circular coil is
(a) inversely proportional to the radius of the coil and
(b) directly proportional to the number of turns of the wire of coil.

Question 17.
The magnetic field produced by a current carrying circular coil having n turns is equal to n times the magnetic field produced by a current carrying circular coil having a single turn. Explain, why ? (NCERT Question Bank)
Answer:
As the direction of the current flowing in each turn of the coil is same, so the direction of the magnetic field produced by each turn is also the same. The magnetic field produced by each turn will therefore get added up to give the magnetic field produced by a coil of n turns. Hence, magnetic field produced by a coil of n turns = n times the magnetic field produced by a coil having a single turn.

Question 18.
Current is flowing clockwise in a circular coil lying in the plane of a table. Using Right Hand Thumb rule, state the direction of the magnetic field inside and outside the coil.

                                                                                               Or
Consider a circular loop of wire lying in the plane of a table. Let the current pass through the loop clockwise. Apply the right hand rule to find the direction of the magnetic field inside and outside the loop. [CBSE (Delhi) 2009]
Answer:
Magnetic field inside the coil is perpendicular to the plane of the table and in the downward
direction. However, outside the coil, the magnetic field is perpendicular to the plane of the table and in the upward direction.

Question 19.
How will the magnetic field be produced in a current carrying circular coil change if we

1. increase the value of current
2. increase the distance from the coil
3. increase the number of turns of the coil. (CBSE 2010, 2011)

Answer:
Magnetic field will

1. increase with the increase in the value of current
2. decrease with the increase in the distance from the coil and
3. increase with the increase in the number of turns of the coil.

Question 20.
Describe an activity to show that magnetic field is produced by an electric current flowing through a circular coil of a wire. [CBSE (Foreign) 2008, 2010]
Answer:
Describe an activity to plot the magnetic field around a current carrying circular coil of a wire.

1. Take a thick copper wire in the form of a circular loop. Pass this circular wire through a cardboard supported over a table in the horizontal position (Figure 17).
   
2. Now connect the ends of this wire with a battery through a key (K), rheostat and ammeter (A).
3. Allow the current to flow through the circular wire by closing the key K.
4. Now plot magnetic field lines around the wire with the help of a magnetic compass needle.

Observations: Magnetic field lines as shown by dotted circles are observed. This shows that a magnetic field is produced by an electric current flowing through a circular coil of a wire. The size of these circles increases as we move away from the wire. At the centre of the circular wire, the field lines become straight and perpendicular to the plane of the coil.

Based on magnetic field due to current in a solenoid

Question 21.
On what factors does the magnetic field produced by a current carrying solenoid depend?
(CBSE 2011, 2012, 2013)
Answer:

1. the strength of the current flowing through the solenoid.
2. the number of turns of the wire of the solenoid.
3. the nature of the material inside the solenoid.

Based on Electromagnetic Induction

Question 22.
Name the scientist who discovered that a moving magnet can be used to generate electric current. With which name is this phenomenon known ? (CBSE 2011, 2015)
Answer:
Michael Faraday. Electromagnetic Induction.

Question 23.
What is an electromagnet ? Mention any two uses of an electromagnet. (CBSE 2013)
Answer:
A soft iron placed inside a current carrying solenoid acts as an electromagnet. Electromagnet is used in electric bells, telephone receivers, microphones, to lift iron pieces etc.

Question 24.
Give three differences between an electromagnet and a permanent magnet. (CBSE 2015)
Answer:

Question 25.
What are permanent magnet and electromagnet ? Give two uses of each.
Answer:
Permanent magnet has fixed north and south pole. The strength of the magnetic field of a permanent magnet cannot be changed.
When a soft iron rod is placed inside a current carrying solenoid, it becomes an electromagnet. The strength of the magnetic field of an electromagnet can be increased or decreased by increasing or decreasing the current flowing in the solenoid. The polarity of electromagnet can be changed by changing the direction of current through the solenoid.
Uses of permanent magnet : Permanent magnets are used in loudspeakers and simple electric motors.
Uses of electromagnet : Electromagnets are used in electric bells, electric horns, television etc.

Question 26.
Explain the meaning of the word “electromagnetic” and “induction” in the term electromagnetic induction.
(CBSE Sample Paper, CBSE 2014)
Answer:
“Electromagnetic” means production of induced current in a closed coil due to the change in magnetic field. “Induction” means the induced current is produced without the actual contact of the closed coil and the moving magnet.

Question 27.
A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its south pole towards one face of the coil is
(a) moved quickly towards it ?
(b) moved quickly away from it ?
(c) placed near its one face ?
(d) name the phenomena involved. (CBSE 2010)
Answer:
(a) There is deflection in the needle of the galvanometer.
(b) There is deflection in the needle of the galvanometer but in opposite direction.
(c) There is no deflection in the needle of the galvanometer.
(d) Electromagnetic induction.

Question 28.
A coil made of insulated copper wire is connected to a galvanometer. What will happen to the deflection of the galvanometer if this coil is moved towards a stationary bar magnet and then moved away from it ? Give reason for your answer and name the phenomenon involved. (CBSE 2010, 2011)
Answer:
When coil is moved towards a stationary bar magnet, magnetic field linked with coil increases. Hence, induced current is produced in the coil. Due to this current, needle of galvanometer deflects. When coil is moved away from the coil, magnetic field linked with the coil decreases, Hence, induced current is again produced in the coil but in opposite direction. Thus, needle of galvanometer deflects but in opposite direction.
Phenomenon : Electromagnetic induction.

Based on Direct current and Alternating current

Question 29.
Current-time graphs from two different sources are shown in the following diagrams.

Now answer the following questions.

1. Name the type of current shown by graph A and graph B.
2. Name any one source of the current shown by graph A and graph B.
3. What is the frequency of current in case B ?
4. Write two difference between the current shown by graphs A and B. (CBSE 2010)

Or
Write one difference between A.C. and DC. (CBSE 2012, 2013, 2015)
Answer:

1. Graph A represents direct current (DC). Graph B represents alternating current (AC).
2. A dry cell is the source of current shown by graph’A. An AC generator is the source of current shown by the graph B.
3. From graph B, time period, T = 0.02 s. Therefore, frequency of current,
   

4. Direct current	Alternating current
   1. The magnitude of direct current is constant and flows in one direction only. 2. Direct current cannot be used for large scale supply of electricity for household purpose. 3. The frequency of direct current is zero.	1.      The magnitude of AC changes with time and direction of alternating current reverses periodically. 2.      Alternating current is used to run electrical appliances like electric bulb, electric heater, electric iron, refrigerator etc. 3.       Frequency of alternating current in India is 50 Hz.

Question 30.
What is the basic difference between AC generator and DC generator ?
Answer:

1. In AC generator, slip-ring type commutator is used and in DC generator split-ring type commutator is used.
2. AC generator converts mechanical energy into electrical energy in the form of alternating current. DC generator converts mechanical energy into electrical energy in the form of direct current.

Based on Domestic Electric circuit

Question 31.
List two safety measures commonly used in electric circuits. Explain the main function of each.
(CBSE 2015)
Answer:
Alternating current flowing through a wife is dangerous if the wire is touched bare footed. Moreover, when current flowing through the wire exceeds a certain limit, it can burn the electric circuit. So, we have to take safety measures while using electricity.
These safety measures are given below :

1. 1. 1. Electric Fuse. An electric fuse is a safety device used to save the electrical appliances like electric bulbs, electric, tubes, T.V. etc. from burning when large current flows in the circuit. Electric fuse is a wire made of copper or aluminium or tin-lead alloy. The melting point of the material of which the electric fuse wire is made should be low. Electric fuse is connected in series with an electric device like bulb, T.V., refrigerator etc.
         Suppose a fuse is not connected in the path of a live wire of the circuit, in such case, the circuit may be over heated if the current in the circuit exceeds the safe limit. There is a chance of short circuiting of the circuit which causes the fire. So to avoid short circuiting of the circuit, a fuse must be put in the path of the circuit.
         Fuse wares are usually rated as 5 A or 15 A. A circuit in which bulb or a tube is to be connected, the fuse is rated as 5 A. It means, this circuit can 4 draw maximum 5 A current. If current in this circuit becomes greater than 5 A, the fuse wire melts and the circuit is switched off automatically. Hence the circuit can be saved from burning.
         Similarly, a circuit in which a heating appliance like an electric heater or a geyser is to be connected, the fuse rated as 15 A is used. Commonly used, electric fuses are shown in Figure 36.
         

1. The insulation on the wire should be of high strength so that it may not melt easily when wires are heated due to large current flowing through them.
2. Wires carrying electricity should not be touched bare footed. The live wire is at higher potential and the earth is at zero potential. If we touch the live wire bare footed, a large current will pass through our body. So we will receive a severe shock. This shock affects our nervous system and may cause even death. Therefore, while using electricity, we must wear gloves made of insulated material and shoes of rubber sole so that current may not flow through our body.
3. Electric appliances like heater, toaster, refrigerator etc. are frequently touched by us with bare hands. If per chance, the insulation on live wire melts, then the live wire may touch the metallic case of the appliance. In that case, current passes though the metal casing of the appliance. If we touch this casing with bare hands, we will receive a severe shock. To avoid such an accident, metal casings of all electric appliances must be earthed. One end of copper wire is connected with metal casing of the electric appliance. The other end of the copper wire is connected to the copper plate which is buried deep inside the earth. This system of connecting the metal casing of an electric appliance with a copper plate buried deep inside the earth is known as earthing. Earthing is represented by a symbol shown in figure 37.
   

Question 32.
An electric fuse of rating 3 A is connected in a circuit in which an electric iron of power 1 kW is connected which operates at 220V. What would happen ? Explain. (CBSE 2012)
Answer:

This current is greater than the rating of the fuse (i.e. 3A). Hence, the fuse will melt and the circuit breaks. Therefore, electric iron will not work.

Long Answer Questions

Question 1.
Explain, the construction and working of an electric motor using a well labelled diagram.
Answer:
Electric motor converts electrical energy into mechanical energy.
Principle: Electric Motor is based on the fact that a current carrying conductor placed perpendicular to the magnetic field experiences a force.

1. Armature coil: It consists of a single loop of an insulated copper wife in the form of a rectangle. Rectangle ABCD shown in figure 25 is an armature coil.
   
2. Strong field magnet: Armature coil is placed between two pole pieces (N and S poles) of a strong magnet. This magnet provides a strong magnetic field.
3. Split-ring type Commutator. It consists of two halves (R₁ and R₂) of a metallic ring. The two ends of the armature coil are connected to these two halves of the ring. Commutator reverses the direction of current in the armature coil.
4. Two carbon brushes B₁ and B₂ press against the commutator. These brushes act as the contacts between the commutator and the terminals of the battery.
5. A battery is connected across the carbon brushes. This battery supplies the current to the armature coil.

Question 2.
Describe the construction and working of A.C. generator with the help of a labelled diagram. How can you convert AC generator to DC generator ?
Answer:

An electric device used to convert mechanical energy (kinetic energy) into electrical energy (electricity) is called an electric generator.
Principle: Electric generator works on the principle of electromagnetic induction. When the coil of electric generator rotates in a magnetic field, induced current flows in the circuit connected with the coil.
types of electric generator

1. AC generator
2. DC generator

AC generator: AC generator converts mechanical energy into electrical energy in the form of alternating current or AC.
DC generator: DC generator converts mechanical energy into electrical energy in the form of direct current or DC.                                                AC Generator Construction : The main components of AC generator are (Figure 33) :

1. Armature : Armature coil (ABCD) consists of large number of turns of insulated copper wire wound over a soft iron core.
2. Strong field magnet : A strong permanent magnet or an electromagnet whose poles (N and S) are cylindrical in shape is a field magnet. The armature coil rotates between the pole pieces of the field magnet. The uniform magnetic field provided by the field magnet is perpendicular to the axis of rotation of the coil.
3. Slip Rings : The two ends of the armature coil are connected to two brass slip rings R₁ and R₂. These rings rotate along with the armature coil. Rings R₁ and R₂ are at different heights.
4. Brushes : Two carbon brushes (B₁ and B₂), are pressed against the slip rings. The brushes are fixed while slip rings rotate along with the” armature. These brushes are connected to the external circuit across which the output is obtained.

Working : When the armature coil ABCD rotates in the magnetic field provided by the strong field magnet, it cuts the magnetic field lines. Thus, the changing magnetic field produces induced current in the coil. The direction  of the induced current in the coil is determined by the Fleming’s right hand rule.
The current flows out through the brush B₁ in one direction in the first half of the revolution and through the brush B₂ in the next half revolution in the reverse direction. This process is repeated. Therefore, induced current produced is of alternating nature. Such a current is called alternating current.
DC generator or Dynamo Construction:

1. Armature coil. It consists of large number of turns of insulated copper wire wound on iron core in the form of a rectangle coil. Rectangle coil ABCD shown in figure 34 is an armature coil.
   
2. Strong field magnet. Armature coil is placed between two pole pieces (N and S poles) of a strong magnet. This magnet provides a strong magnetic field.
3. Split-ring Type Commutator. It consists of two halves (R₁ and R₂) of a metallic ring. The two ends of the armature coil are connected to these two halves of the ring.
4. Two carbon brushes B₁ and B₂ press against the commutator.
5. The output is shown by the glowing bulb connected across the carbon brushes.

Working of d.c. generator: When the coil of d.c. generator rotates in the magnetic field, induced potential difference is produced in the coil. This induced potential difference gives rise to the flow of current through the bulb and hence the bulb glows.
In d.c. generator, the flow of current in the circuit is in the same direction as long as the coil rotates in the magnetic field. This is because one brush is always in contact with the arm of the armature moving up and the other brush is in contact with the arm of the armature moving downward in the magnetic field.
Note: AC generator can be converted into DC generator by replacing slip rings used in AC generator by a split ring type commutator.

Question 3.
What is an electromagnet ? What decides its polarity ? How it differs from a permanent magnet ? List the three factors and explain how strength of an electromagnet depends on these. (CBSE 2013)
Answer:
When a soft iron bar is placed inside a solenoid carrying current, it becomes a magnet as long as current flows through the solenoid. Such a magnet is known as electromagnet.
In fact, the magnetic field inside the solenoid magnetises the soft iron bar placed in it, which acts as an electromagnet. (Figure 22).

Strength of an electromagnet can be increased by

1. increasing the current through solenoid and
2. increasing the number of turns of the solenoid. The polarity of electromagnet is decided by the direction of current flowing in the solenoid.

Uses of electromagnets

1. They are used to lift heavy iron pieces. They are fitted on cranes heavy objects of scrap iron.
2. They are used in many devices like electric bell, electric horn, telephone receiver, electric relay, microphones, radio set, television, loudspeakers etc.

Question 4.
Describe an activity to show how a moving magnet may be used to generate an electric current. State the rule to find the direction of electric current generated in a coil in this manner.
(CBSE 2015)
Answer:
When a bar magnet moves towards or away from the closed coil, galvanometer shows a deflection. The deflection in the galvanometer indicates that current is flowing through the coil. This electric current is called induced electric current.
It was Michael Faraday, who performed a simple experiment to show that an electric current can be produced in a closed circuit without the use of an electro-chemical cell or battery but by moving a bar magnet towards or away from the closed circuit.
Explanation :

1. When a magnet is moved towards the coil, more and more magnetic field lines pass through the coil as shown in figure 28(b).
   
   Thus, magnetic field around the coil increases. The increase in magnetic field induces potential difference (or voltage) across the ends of the coil. As the coil connected to the galvanometer forms a closed circuit, so induced potential difference makes the current to flow through the circuit. The presence of this current in the circuit is shown by the deflection of the galvanometer.
2. When a magnet is moved away from the coil, the magnetic field around the coil decreases. The decrease in magnetic field induces potential difference across the ends of the coil. This induced potential difference (or voltage) produces current in the circuit. The presence of the current in the circuit is shown by the deflection of the galvanometer. The current in the circuit is known as induced current.
3. When the magnet is stationary, the magnetic field around the coil is constant. Therefore, no potential difference is set up across the coil. Hence, no current flows through the circuit.

Direction of Induced Current in a Conductor (Fleming’s Right Hand Rule):
Fleming stated a rule to determine the direction of induced current in a conductor. This rule is known as Fleming’s Right hand rule.
Fleming’s Right hand Rule: “Stretch the right hand such that the first finger, the central finger and the thumb are mutually perpendicular to each other. If the First finger points along the direction of the field (magnetic field) and the Thumb points along the direction of Motion of the conductor, then the direction of induced. Current is given by the direction of the Central finger (Figure 30).

Thus, in right hand rule, first finger shows the direction of the magnetic field. The central finger shows the direction of induced current in the conductor. The thumb shows the direction of motion of the conductor in the magnetic field.
Note : Fleming’s Right hand rule is also known as Dynamo Rule.

 Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 13 Magnetic Effects of Electric Current are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 7 Control and Coordination Class 10 Science Important Questions with Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Control and Coordination Class 10 Important Questions and Answers Science Chapter 7

Very Short Answer Questions

Question 1.
Write the function of hormone thyroxine in our bodies. (CBSE Delhi 2004)
Answer:
It controls basal metabolic rate and regulates metabolism of carbohydrates, fats and proteins.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
Name the part of hind brain which takes part in regulation of respiration. (CBSE Delhi 2004)
Answer:
Medulla oblongata.

Question 3.
Which hormonze helps in lowering the level of blood glucose in human beings ? (CBSE Delhi 2004)
Answer:
Insulin.

Question 4.
We suddenly withdraw our hand when a pin pricks. Name the type of response involved in this action.
(CBSE Delhi 2004)
Answer:
Reflex action.

Question 5.
Which hormone is responsible for the development of moustache and beard in man ? (CBSE Foreign 2004)
Answer:
Testosterone.

Question 6.
Which type of glands in human body secrete hormones ? State any one location for them.
(CBSE Foreign 2004)
Answer:
Endocrine or ductless glands, e.g, thyroid in neck region around trachea.

Question 7.
Name the structural and functional units of human nervous system. (CBSE A.I. 2004 C)
Answer:
Neuron.

Question 8.
What is neuron ? (CBSE Delhi 2007)
Answer:
Neuron or nerve cell is a structural and functional unit of nervous system that is specialised to receive, conduct and transmit impulses.

Question 9.
What are phytohormones ? (CBSE A.I. 2007, CCE 2011, 2012)
Answer:
Phytohormones are chemical substances other than nutrients produced naturally in plants which regulate growth, development, differentiation and a number of physiological processes, e.g., auxin, gibberellins, abscisic acid, cytokinins.

Question 10.
Name the largest cell present in human body. (CBSE Delhi 2008)
Answer:
Neuron (length 90-100 cm).

Question 11.
What is the function of the hormone secreted by the endocrine gland pituitary ? (CBSE Foreign 2008)
Answer:
It generally controls the secretory activity of another endocrine gland, e.g., TSH (thyroid stimulating hormone) on thyroid for release of thyroxine.

Question 12.
Why is the use of iodised salt advisable ? (CBSE Delhi 2008, CCE 2014, 2015)
Answer:
Iodine is an essential component of diet as it is required for synthesis of hormone thyroxine needed for proper metabolism of protein, fat and carbohydrates. Deficiency causes goitre, cretinism and myxoedema.

Question 13.
Name two tissues that provide control and coordination in multicellular animals. (CBSE Delhi 2009)
Answer:

1. Nervous tissue
2. Endocrine tissue.

Question 14.
Define reflex action. (CBSE Delhi 2009, CCE 2012, 2015)
Answer:
It is an automatic, spontaneous nerve mediated response to a stimulus without consulting the will of the individual.

Question 15.
Define chemotropism. (CBSE A.I. 2009, 2010, CCE 2011, 2012, 2013)
Answer:
Chemotropism. It is directional growth movement of curvature that occurs in response to a chemical stimulus. Ex. movement of pollen tube in style.

Question 16.
A young green plant receives sunlight from one direction only. What will happen to its shoots and roots ?
(CBSE Delhi 2009 C)
Answer:
(a) Shoots bend towards the source of light—positive phototropism.
(b) Roots bend away from the source of light—negative phototropism.

Question 17.
Name the plant hormones which help or promote

1. Cell division
2. Growth of stem
3. Inhibits growth. (CBSE Delhi 2009 C, CCE 2012, 2013)

Answer:

1. Cell division. Cytokinins.
2. Growth of stem. Gibberellins.
3. Inhibits growth. Abscisic acid.

Question 18.
Name the gland which secretes growth hormone.
Answer:
Pituitary gland.

Question 19.
How is the spinal cord protected in human body ?
Answer:
Overlying meninges and vertebral column.

Question 20.
A potted plant is made to lie horizontally on the ground. Which part of the plant will show

1. Positive geotropism
2. Negative geotropism ? (CBSE Delhi 2010)

Answer:

1. Positive Geotropism: Root
2. Negative Geotropism: Stem.

Question 21.
Name the hormone that helps in regulating level of sugar in our blood. Name the gland that secretes it.
(CBSE AI 2010)
Answer:
Hormone: Insulin.
Gland: Pancreas.

Question 22.
Mention the function of hind brain in humans.
Answer:

1. Posture and equilibrium
2. Reflexes, blood pressure, heart beat, breathing.

Question 23.
Name any two types of tropisms.
Answer:
Phototropism, geotropism.

Question 24.
Mention the function of adrenaline hormone.
Answer:
To prepare the body for meeting an emergency.

Question 25.
State the main function of abscisic acid in plants.
Answer:
Inhibition of growth and induction of dormancy for overcoming stress conditions.

Question 26.
Which hormone is injected to a diabetic patient and why ? (CCE 2010)
Answer:
Insulin is injected to a diabetic patient in order to meet deficiency of the hormone that is essential for uptake of glucose by cells.

Question 27.
Name the hormone secreted by an endocrine gland during emergency. Name the gland.
Answer:
Hormone: Adrenaline.
Gland: Medulla of adrenals.

Question 28.
What do we call the movement of shoot towards light ?
Answer:
Positive phototropism.

Question 29.
Name the plant hormone responsible for elongation of cells.
Answer:
Auxin.

Question 30.
Which part of the brain controls posture and balance of the body ?
Answer:
Cerebellum.

Question 31.
Name the part of the neuron through which the information travels as an electric impulse.
Answer:
Axon or nerve fibre.

Question 32.
Name the part of the neuron where information is acquired.
Answer:
Dendrite.

Question 33.
What is synapse ?
Answer:
Synapse is a narrow fluid-filled gap which functions as communicating junction between axon end of one neuron and dendrite tip of next neuron.
All information of our environment is detected by specialised tip of some nerve cells.

Question 34.
Mention the name given to such tips and also mention where they are located. (CCE 2012, 2013)
Answer:
Receptors. Receptors are located in sense organs—skin, inner ears, eyes, nose, tongue.

Question 35.
While watering a rose plant, a thorn pricked Ritas hand. How would she respond to this situation ? Provide the term for such a response. (CCE 2012)
Answer:
Rita will immediately withdraw her hand from the rose plant even before feeling the pain. The phenomenon is called reflex action.

Question 36.
What is meant by tropic movements ? (CCE 2012)
Answer:
Tropic movements are directional paratonie curvature movements of growth which generally occur in cylin¬drical organs with direction of movement being determined by the direction of stimulus.

Question 37.
A boy runs on seeing a stray dog. His breathing becomes very fast and blood pressure also increases. Name the hormone found to be high in his blood and the gland which produces it. (CCE 2012, 2013)
Answer:
Hormone. Adrenaline. Gland. Adrenal medulla.

Question 38.
How shoot and root of a plant respond to light ? (CCE 2012)
Answer:
Shoot: It is positively phototropic to unilateral light.
Root: It is either neutral or negatively phototropic to unilateral light.

Question 39.
State the main function of abscisic acid in plants.
Answer:
Abscisic acid is a growth inhibitor that induces dormancy in buds and seeds.

Question 40.
How do the shoot and root of a plant respond to the pull of earths gravity ? (CCE 2012)
Answer:
Main shoot is negatively geotropic while main root is positively geotropic. Their branches are generally plagiogeotropic.

Question 41.
Name two components of central nervous system in humans. (CCE 2012)
Answer:
Brain and spinal cord.

Question 42.
Mention the part of the body where gustatory and olfactory receptors are located. (CCE 2012)
Answer:
Gustatory Receptors. Mostly tongue.
Olfactory Receptors. Olfactory epithelium in upper part of nasal chambers or nose.

Question 43.
Name the sensory receptors found in the nose and on the tongue. (CCE 2012)
Answer:
Gustatory Receptors. Mostly tongue.
Olfactory Receptors. Olfactory epithelium in upper part of nasal chambers or nose.

Question 44.
Which body organ is surrounded by meninges. (CCE 2013)
Answer:
Brain and spinal cord (central nervous system).

Question 45.
In multicellular organisms how the various activities are controlled and coordinated ? (CCE 2013)
Answer:
By nervous and hormonal systems collectively called neuroendocrine system.

Question 46.
Define phototropism. (CCE 2013)
Answer:
It is directional movement of curvature which occurs in plants in response to unilateral exposure to light.

Question 47.
Which system facilitates communication between central nervous system and other parts of the body ?
(CCE 2013, 2014)
Answer:
Peripheral nervous system (PNS).

Question 48.
In case of a spinal cord injury, identify the signals that will be disrupted. (CCE 2014)
Answer:
Neuromuscular signals from areas served by spinal cord, viz., limb movement, sensations of touch and pain, spinal reflexes.

Question 49.
Name the tissue in animals which provides control and co-ordination to them. (CCE 2015)
Answer:
Nervous tissue.

Question 40.
Differentiate between the movement of leaves of the sensitive plant and the movement of a shoot towards light. (CCE 2015)
Answer:
Movement of leaves of sensitive plant is hapnonastic turgor movement while movement of shoot towards light is phototrophic growth movement.

Question 51.
Name one plant hormone which inhibits growth. Write its one function. (CCE 2015)
Answer:
Abscisic acid. It includes dormancy in buds and seeds.

Question 52.
State the role of the brain in reflex action. (CCE 2015)
Answer:
It functions as a relay centre for transferring impulse from sensory to motor neurons in several reflex actions called cerebral reflexes, e.g, closure of eyes exposed to flash of light, salivation at the sight or smell of food. In spinal reflexes it acts as information collecting and evaluation centre without any direct involvement in reflex action.

Question 53.
Mention the part of brain which controls the involuntary action like blood pressure, salvination, etc.
(CCE 2015)
Answer:
Medulla oblongata.

Question 54.
Name the part of the neuron

1. Where information is acquired
2. Through which information travels. (CCE 2016)

Answer:

1. Dendrites
2. Axon.

Question 55.
Name the hormone in humans which regulates carbohydrate, protein and fat metabolism in the body. Mention the site where it is synthesised. (CCE 2016)
Answer:
Hormone—Thyroxine. Site—Thyroid.

Question 56.
(a) State the function of the following plant hormones :

1. Abscisic acid
2. Cytokinin.

(b) Define chemotropism. (CCE 2016)
Answer:
(a)

1. Function of Abscisic Acid. Inhibits growth and induces dormancy.
2. Function of Cytokinin. Cell division, Differentiation and countering apical dominance.

(b) Chemotropism: It is directional growth movement of curvature that occurs in response to a chemical stimulus. Ex. movement of pollen tube in style.

Short Answer Questions (2 Marks Each)

Question 1.
Name two hormones secreted by pancreas. Write one function of each hormone named.
(CBSE Delhi 2007)
Answer:
Insulin (secreted by (3-cells of islet of Langerhans)
Recognition of glucose by cells for absorption and conversion of glucose into glycogen in liver and muscles.
Glucagon (secreted by a-cells of islet of Langerhans)
Formation of glucose from glycogen and other sources and its release into blood.

Question 2.
Name the hormone responsible for regulation of

1. Metabolism of carbohydrates, fats and proteins
2. Balance of calcium and phosphate
3. Blood pressure
4. Water and electrolyte balance.
   (CBSE Delhi 2008)

Answer:

1. Thyroxine
2. Parathormone (also calcitonin)
3. Adrenaline
4. ADH or vasopressin and aldosterone (a mineralocorticoid).

Question 3.
What is reflex action ? Explain the mechanism of reflex action with a suitable example.
(CBSE Foreign 2008, CCE 2012, 2015)
Answer:
Reflex Action: It is an automatic nerve mediated response to a stimulus without consulting the will of the individual, e.g., withdrawal of hand on being pricked or coming in contact with hot surface.
Mechanism: The stimulus for reflex action is picked up by a receptor located in the organ on which stimulus is acting. One or more sensory neurons carry the impulse from receptor to the central nervous system (e.g., spinal cord). CNS functions as modulator. It transfers the sensory nerve impulse to one or more motor neurons. The motor neurons carry the impulse to effectors which provide a proper response to the stimulus.

Stimulus ———>Receptor ———>Sensory neurons ——–>CNS ——–>Motor neurons ——-> Effectors
———>Response.

Question 4.
Name the three major regions of human brain. Which part of brain maintains posture and equilibrium of the body ? (CBSE Foreign 2008)
Answer:
Major Regions of Brain

1. Fore Brain: Olfactory lobes (2), Cerebrum (2 cerebral hemispheres) and diencephalon.
2. Mid Brain: Cerebral peduncles (crura cerebri) and four quadrigemina.
3. Hind Brain: Cerebellum, pons and medulla oblongata.

Question 5.
Maintenance of Posture and Equilibrium. Cerebellum.
(a) Distinguish between voluntary and involuntary actions of our body.
(b) Choose involuntary actions, amongst the following :
Reading, Beating of heart, Salivation in the mouth on viewing tasty food, Talking.(CBSE Foreign 2008)
Answer:
(a) Differences between Voluntary and Involuntary Actions

(b) Beating of heart, salivation in the mouth on viewing of tasty food.

Question 6.
Explain the cause of shoots of the plant bending towards light ? (CBSE Delhi 2008, CCE 2010, 2011)
Answer:
Stems are positively phototropic and bend towards the direction of light. The movement is due to occurrence of more auxin on the darker side and lesser auxin on the illuminated side. As a result, there is more growth on the darker side which causes the stem to bend towards light.

Question 7.
What are nastic and curvature movements ? Give one example of each. (CBSE Delhi 2009)
Answer:
(a) Nastic Movements: They are non-directional curvatures movements of turgor or growth where the movements are determined by the structure of the responding organ irrespective of the direction of stimulus which is generally diffuse. Ex. Drooping and folding of leaves in Sensitive Plant in response to shock (seismonasty).
(b) Curvature Movements: They are changes in orientation of some plant parts in relation to others caused by intrinsic or external stimuli. Ex. Sleep movement or nyctinasty of legume leaves, bending of stems towards light (or positive phototropism of stems).

Question 8.
Draw a diagram of a nerve cell and label on it following :
(a) Nucleus
(b) Dendrites (CBSE Delhi 2009 C, CCE 2010)
Answer:

Question 9.
What are plant hormones ? Write two functions of auxin. (CBSE A. I. 2009 C)
Answer:
Definition: Phytohormones are chemical substances other than nutrients produced naturally in plants which regulate growth, development, differentiation and a number of physiological processes, e.g., auxin, gibberellins, abscisic acid, cytokinins.
Function of Auxin:

1. Cell Enlargement. They bring about growth of cells. In shoots auxin is effective above a concentration of 10 ppm while in roots the required concentration is 0-0001 ppm.
2. Several plant movements are mediated by differential distribution of auxin, e.g., geotropism, phototropism.

Question 10.
Name the two main regions of our central nervous system. Which one of them plays a major role in sending command to muscles to act without involving thinking process ? Name the phenomenon involved.
(CBSE A.I. 2010)
Answer:

1. Brain and spinal cord,
2. Spinal cord plays a major role in mediating muscle action without involving thinking process,
3. The phenomenon is called reflex action.

Question 11.
Name the hormone secreted by human testes. State its functions. (CBSE A.I. 2010)
Answer:
Hormone: Testosterone.
Functions:

1. Development of male sex characteristics and secondary sex organs during puberty,
2. Maintenance of male sex characteristics and male sex organs thereafter.

Question 12.
Name and explain the function of the hormone secreted by the pituitaiy gland in humans. (CBSE A.I. 2010)
Answer:
Pituitary gland secretes several hormones,

1. Somatotrophic or growth hormone stimulates growth by increased anabolic activity, enlargement of long bones, muscles and visceral organs, synthesis of more proteins and retention of calcium.
2. FSH (follicle stimulating hormone) stimulates sperm formation in testes and development of ovarian follicles in ovaries.

Question 13.
Explain how the human body responds to secretion of adrenaline into blood. (CCE 2010)
Answer:
Adrenaline reduces blood supply to skin and digestive system but increases the same to skeletal or voluntary muscles. There is increase in breathing rate and heart beat. The body becomes ready to deal with an emergency. Further, endocrine system controls and coordinates many processes of the body where nervous system has no role, e.g., cell permeability, cell division, cell growth, cell differentiation, development of sex organs, secondary sex characters and several other activities. Any discrepancy can lead to a disorder, e.g, dwarfism and gigantism, hypothyroidism (simple goitre, cretinism, myxedema), hyperthyroidism (exophthalmia).

Question 14.
Name the gland and hormone secreted by the gland which are associated with the following problems :
(i) A girl has grown extremely tall
(ii) A woman has swollen neck. (CCE 2014, 2015)
Answer:
(i) Pituitary, excessive secretion of growth hormone causing gigantism.
(ii) Thyroid, reduced secretion of thyroxine causing hypothyroidism or goitre.

Question 15.
A doctor advised a patient to go on a diet without sugar and take insulin injections also. Name the disease he is suffering from. Why has he been given the two advices ? (CCE 2014)
Answer:
Disease. Diabetes mellitus. The disease is due to insufficiency of insulin secretion which results in nonabsorption of glucose by cells and its nonconversion into glycogen in liver and muscles. Excess sugar present in blood is partly passed out alongwith urine. Sugar free diet will reduce quantity of sugar in the blood. Injections of insulin will help the cells to pick up glucose for their metabolism and allow liver and muscles to convert it into glycogen.

Question 16.
Name the following :

1. A gland present in females but not in males,
2. A gland that secretes hormones as well as digestive juice or enzyme,
3. A gland associated with brain,
4. A gland that is associated with kidneys. (CCE 2015)

Answer:

1. Ovary/Mammry glands
2. Pancreas
3. Pituitary
4. Adrenal.

Question 17.
Trace the sequence of events through a reflex arc with occur when a bright light is focussed on your eyes.
(CCE 2015)
Answer:
Cerebral reflex: It functions as a relay centre for transferring impulse from sensory to motor neurons in several reflex actions called cerebral reflexes,
Reflex Arc: Reflex action requires a stimulus, a receptor organ, sensory neurons, a part of central nervous system, motor neurons and effector organ. The pathway taken by a stimulus to travel from receptor organ to effector organ is known as reflex arc. Its components are as follows (Fig. 2.4).

Stimulus——>Receptor organ ——> Sensory neurons ——> CNS——> Motor neurons ——> Effector organ——>Response.

Receptor Organ: It is a tissue or organ which receives the stimulus for initiating nerve impulse, e.g., skin, eye, ear.

Question 18.
State the source of secretion and function of the following hormones :

1. Thyroxine
2. Insulin
3. Growth hormone. (CCE 2015)

Answer:
Source :

1. Thyroxine — Thyroid,
2. Insulin — Pancreas,
3. Growth hormone — Pituitary.

Function :

1. Thyroxine: Regulates metabolism of carbohydrates, fats and proteins, release of energy and body activity.
2. Insulin: Regulates blood glucose by its absorption in liver, muscles (for formation of glycogen) and individual cells (for metabolic activity).
3. Growth Hormone (GH) or Somatotrophic Hormone: Regulates growth and development of the body through anabolic activity for growth of bones, muscles and visceral organs.

Question 19.
Write the function of the following :

1. Sensory Neuron
2. Cranium
3. Vertebral column
4. Motor Neuron. (CCE 2015)

Answer:

1. Sensory Neuron. Picking up sensation from the receptor and passing it to CNS.
2. Cranium. Protection of brain.
3. Vertebral Column. Protection spinal cord.
4. Motor Neuron. Taking message from CNS to muscle, gland or organ to perform its function.

Question 20.
Draw a neat and labelled diagram of neuro-muscular juction. (CCE 2015)
Answer:

Question 21.
Identify the parts of a neuron

1. Where information is acquired,
2. Through which information travels
3. Where the impulse must be converted into a chemical signal. (CCE 2015)

Answer:

1. Dendrites
2. Axon
3. Synapse, neuromuscular junction.

Question 22.
What is reflex arc ? Why have reflex arcs evolved in animals ? (CCE 2016)
Answer:
Reflex arc is the pathway taken by a stimulus to travel from the receptor organ to the effector organ through CNS without consulting the will of the individual. It produces a quick, immediate and involuntary response where delay can be harmful. Reflex arcs evolved in animals as a survival mechanism before the development of intelligence.

Question 23.
Name the hormone which is released when we are in a scary situation. Write two effects of the hormone on our body that enable the body to deal with the situation. (CCE 2016)
Answer:
Adrenaline (from adrenal medulla): Adrenaline/emergency hormone/triple Fhormone

1. Reduces blood supply to peripheral blood vessels and gastrointestinal tract,
2. More blood flows to skeletal and heart muscles.
3. Increases breathing and gives more oxygen to muscles,
4. Increases heart rate,
5. Mobilises more glucose to muscles for higher activity.

Question 24.
How does our body maintain sugar level ? (CCE 2016)
Answer:
Sugar level is maintained with the help of two hormones secreted by pancreas.
Insulin (secreted by (3-cells of islet of Langerhans)
Recognition of glucose by cells for absorption and conversion of glucose into glycogen in liver and muscles.
Glucagon (secreted by a-cells of islet of Langerhans)
Formation of glucose from glycogen and other sources and its release into blood.

Question 25.
State the sequence of events through a reflex arc which occur when bright light is focussed on your eyes.
(CCE 2016)
Answer:
The sensation of bright light is picked up by receptors present over the eyes. The sensation travels to superior quadrigemina through sensory neurons. The impulse is here transferred to motor neurons that reach the pupil and eye lids to close the eyes.

Short Answer Questions (3 Marks Each)

Question 1.
Define hormones. Name the hormone secreted by thyroid. Write its functions. Why is the use of iodised salt advised to us ? (CBSE Delhi 2008, CCE 2011)
Answer:
Definition: Nervous stimulation is for only short duration while certain activities require prolonged stimulation. Therefore, multicellular animals have also a second system of communication called endocrine system. Endocrine system operates through chemicals called hormones.
Hormone of Thyroid. Thyroxine.
Functions of Thyroxine: It controls

1. Basal metabolic rate or BMR.
2. Metabolism of carbohydrates, fats and proteins.
3. Physical activity
4. Body temperature
5. Heart beat
6. Development
7. Nervous activity.

Iodised Salt: Iodine is essential for formation of thyroxine. In its deficiency, thyroid undergoes overgrowth causing goitre. Common salt is iodised to prevent occurrence of goitre.

Question 2.
Which animal or plant hormone is associated with the following :

1. Increased sugar level in blood.
2. Changes at puberty in boys
3. Inhibits growth of plants.
4. Rapid development of fruits
5. Dwarfism
6. Goitre. (CBSE Delhi 2008 C)

Answer:

1. Increased sugar level in blood. (Deficiency of) Insulin,
2. Changes at puberty in boys. Testosterone.
3. Inhibits growth of plants. Abscisic acid,
4. Rapid development of fruits. Auxin.
5. Dwarfism. Deficiency of somatotrophic or growth hormone
6. Goitre. Deficiency of Thyroxine.

Question 3.
What is phototropism ? How does it occur in plants ? Describe an activity to demonstrate phototropism.
(CBSE A.I. 2009, 2010, CCE 2012, 2014, 2015)
Answer:
Definition of Phototropism. It is directional growth movement of curvature which occurs in plants in response to stimulus of unilateral light.
How does it occur ? Phototropism is caused by increased auxin on shaded side and decreased auxin on illuminated side. Increased auxin causes increased’growth in shoot (which bends towards light, positive phototropism) and reduced growth in roots (when bends away from light, negative phototropism). Demonstration of Phototropism.

Question 4.
What is hydrotropism ? Describe an experiment to demonstrate hydrotropism. (CBSE A.I. 2009)
Answer:
Definition of Hydrotropism: Hydrotropism is directional movement of curvature which occurs in response to unilateral stimulus of water.
Experiment:
Apparatus: Trough with perforated base, saw dust, water, seeds of Pea/Gram, wooden support.
Procedure: Take a trough with perforated base. Fill it with saw dust. Moisten the same. Sow several seeds of Pea or Gram. Place the trough in slanting position by means of a wooden block. Keep the saw dust moist by sprinkling water at intervals. Observe after 2-3 days.
Observation: As the radicles come out of the seeds, they are seen to move towards the perforations. They come out of the pores and hang downwardly for some time under the influence of gravity. However, after some growth they bend back and enter the perforations to reach moist saw dust in complete disregard of gravity (Fig. 2.11).

Inference: Bending of radicles back into moist saw dust is hydrotropic movement. It occurs despite being against the force of gravity.

Question 5.
How does feed back mechanism regulate hormone secretion ?
Answer:
Feed back system is a regulatory mechanism in which presence of certain level of substance promotes or inhibits its further formation. Common control is through negative feed back. Here regulation is through opposite action. Positive feed is rare as during uterine contraction at child birth. Regulation of thyroxine production by its concentration in blood is an example of negative hormonal feed back system. Concentration of thyroxine in blood is detected by hypothalamus. If it is low, hypothalamus produces TSH-RH. The latter stimulates pituitary gland to produce TSH or thyroid stimulating hormone. TSH passes into circulatory z system and reaches thyroid. Thyroid begins to secrete more thyroxine.

Question 6.
(a) If the cerebellum is not functioning properly, what are the activities of our body affected ?
(b) How do muscle cells move ? (CCE 2010)
Answer:
(a) Posture and equilibrium (balance) of the body.
(b) It is the place of apposition of motor end plate of a neuron with the surface of the muscle. Motor end plate consists of a number of knobbed branches. A knob or bouton is plugged into shallow depression present on surface of muscle fibre called sole plate. A narrow space or synaptic cleft occurs between the two.
On excitation the knob of motor end plate passes out acetylcholine which reaches the Ach receptors on the surface of muscle. The excitation spreads over the whole muscle fibre. The latter contracts.

Question 7.
If you keep the potted plant horizontally for 2-3 days, what type of movements would be shown by the shoot and root after 2-3 days. Why ? (CCE 2010)
Answer:
The plant shows geotropic response. The terminal part of the shoot bends upwardly. It is negative geotropic response. The terminal part of the root bends downwardly. It is positive geotropic response. The response is due to more auxin on the lower side which causes more growth on the lower side of the stem and no growth on the lower side of the root.

Question 8.
(a) What is endocrine gland ?
(b) Name any two endocrine glands present in a human body and write hormones secreted by them.
(CCE 2011)
Answer:
(a) Endocrine gland is an isolated gland which does not have a duct for draining out its scretion but instead pours the same into circulatory system for reaching the target sites.
(b)

1. Thyroid-Hormone thyroxine
2. Islets of Langerhans in Pancreas-Hormones insulin and glucagon.

Question 9.
Which part of nervous system controls reflex arcs ? With the help of a diagram trace the sequence of events which occur when we touch a hot object. Mention the part of the neuron that acquires information and the form in which information travels. (CCE 2010, 2011, 2015)
Answer:
Control of reflex arcs is carried out by CNS, chiefly spinal cord.
Sequence of Events. The hot object functions as a stimulus. The stimulus is received by receptors present in the skin. Sensory neurons carry the information as electrical impulse from the receptors to the CNS. CNS possesses relay neurons that transfer the information as electrical impulse to motor neurons. The motor neurons conduct the impulse to effector organs which in this case are muscles that pull away the arm before the information reaches brain.

Question 10.
Name the hormone synthesised at the shoot tips. How does it help the plant to respond to light ?
(CCE 2011)
Answer:
Hormone Synthesised at shoot tip. Auxin.
The shoot responds to unilateral light by bending towards it. This is caused by migration and synthesis of more auxin on the shaded side as compared to the illuminated side. Higher concentration of auxin on the shaded side causes more growth as compared to illuminated side. This bends the shoot towards the light.

Question 11.
(a) Which hormone is responsible for the changes noticed in males at puberty ?
(b) Deficiency of which hormone leads to dwarfism
(c) Name the hormone which is injected to a diabetic patient. (CCE 2011)
Answer:
(a) Testosterone
(b) Growth hormone/somatotrophic hormone
(c) Insulin.

Question 12.
(a) What is the structural and functional unit of nervous system ? Name its any two components.
(b) Which structure in a neuron helps to conduct a nerve impulse

1. towards the cell body
2. away from cell body. (CCE 2011)

Answer:
(a) Neuron. Components. Dendrites, cell body and axon.
(b)

1. Dendrites
2. Axon.

Question 13.
Ram has met with an accident. After that he has lost the capacity to

1. walk in straight line
2. smell anything
3. Does not feel full after eating. Which part of the brain is damaged in each case ? (CCE 2011)

Answer:

1. Hind brain-Cerebellum
2. Fore brain-cerebrum (temporal lobes).
3. Fore brain—hypothalamus.

Question 14.
How does our body respond when adrenaline is secreted into the blood ? (CCE 2011, 2012, 2013, 2014)
Answer:
Adrenaline/emergency hormone/triple F hormone

1. Reduces blood supply to peripheral blood vessels and gastrointestinal tract,
2. More blood flows to skeletal and heart muscles.
3. Increases breathing and gives more oxygen to muscles,
4. Increases heart rate,
5. Mobilises more glucose to muscles for higher activity.

Question 15.
(a) What is tropism ?
(b) How is brain protected in our body ?
(c) Name the part of brain responsible for precision of voluntary actions and maintaining body posture and
balance of the body. (CCE 2011, 2012)
Answer:
(a) Tropism. It is the phenomenon of directional paratonie growth movement of curvature in which the direction of movement is determined by the direction of stimulus, e.g., phototropism, geotropism, hydrotropism.
(b) Protection of Brain,

1. Bony box or skull on the outside,
2. Meninges over the brain.
3. Presence of cerebrospinal fluid both outside and inside the brain to absorb shocks.

(c) Cerebellum.

Question 16.
State the sequence of changes that takes place in a human body when it prepares itself to protect from a scary or dangerous situation. (CCE 2011, 2012)
Answer:
Both sympathetic nervous system and hormone adrenaline of adrenal medulla work together in preparing the body for protection from a scary or dangerous situation.

1. Heart beats faster so as to provide more blood and its contained oxygen and glucose to muscles,
2. Blood supply to peripheral vessels and digestive tract is reduced. More blood becomes available to skeletal muscles.
3. Breathing rate increases due to dilation of bronchioles, increased activity of diaphragm and rib-muscles.

Question 17.
(a) Which plant hormone is present in greater concentration in the areas of rapid cell division ?
(b) Give one example of a plant growth promoter and plant growth inhibitor. (CCE 2011)
Answer:
(a) Cytokinin.
(b)

1. Plant Growth Promoter—Auxin/Gibberellin.
2. Plant Growth Inhibitor—Abscisic acid (ABA).

Question 18.
(a) Which organ secretes a hormone when blood sugar rises in our body ?
(b) Name the hormone and name one enzyme released by this organ. (CCE 2011)
Answer:
(a) Pancreas
(b)

1. Insulin
2. Trypsin/pancreatic amylase/lipase.

Question 19.
(a) Which part of the brain controls involuntary actions ?
(b) Write the function of any two regions of it. (CCE 2011)
Answer:
(a) Involuntary actions are mostly controlled by hind brain.
(b)

1. Medulla Oblongata: It regulates rate of breathing, rate of heart beat, blood pressure and reflexes like swallowing, vomiting, coughing, sneezing, salivation and peristalsis.
2. Cerebellum: Maintaining equilibrium or posture in various activities of the body and coordinating muscular activity of the body.

Question 20.
(a) Name the hormones secreted by thyroid, pancreas and adrenal glands. Write one function of each of these hormones. (CCE 2011)
Answer:

Question 21.
(a) If the cerebellum is not functioning properly, state the activities of our body that are affected,
(b) How do muscle cells move ? (CCE 2011)
Answer:
(a) Maintenance of posture or balance of body and coordination of body activities will be impaired.
(b) Excitation of neuron is transferred to muscle at the neuromuscular junction by the release of acetylcholine from the knobs of its motor end plate. Acetylcholine is picked up by Ach receptors present on the surface of muscle fibre. This induces the mucles fibre to contract.

Question 22.
Why does the shoot of the plant bend towards light when it is kept inside a card-board box with a small hole ?
(CCE 2011)
Answer:
Light coming from the hole in card-board falls on one side of shoot. Auxin diffuses from the illuminated side to shaded side. Higher concentration of auxin brings about more growth on the shaded side. As a result, the shoot bends towards the side of the hole.

Question 23.
(a) What is geotropism ?
(b) Describe an experiment to demonstrate positive and negative geotropism. (CCE 2011)
Answer:
(a) Geotropism : It is directional growth movement of curvature which occurs in response to force of gravity. Main root shows positive geotropism while main stem shows negative geotropism.
(b) Experiment. Place a well watered potted plant on its side (horizontally) in sunlight. Keep watering the plant on alternate days. Observe after 3-4 days. The terminal part of the shoot bends upwardly. It shows negative geotropic response. The terminal part of the root bends downwardly. It shows positive geotropic response.

Question 24.
(a) Define tropic movement.
(b) Why do multicellular organisms need another means of communication between cells besides nervous
coordination ? (CCE 2011, 2012)
Answer:
(a) Tropic Movement: It is directional paratonie growth movement of curvature in which direction of movement is determined by the direction of the stimulus. They mostly occur in cylindrical organs. Growth response occurs due to differences in the distribution of auxin.
(b) Need For Another System of Communication. Nervous system cannot meet all the requirments of a multicellular organism because

1. Nerve impulse cannot reach every cell of the body,
2. Nervous stimulation is for only short duration while certain activities require prolonged stimulation.

Therefore, multicellular animals have also a second system of communication called endocrine system. Endocrine system operates through chemicals called hormones. Hormonal secretion passes to all parts of the body but the hormone triggers activity in cells that have recceptors for them. The information can pass persistently. Further, endocrine system controls some processes where nervous system cannot have any role, e.g., cell growth, cell differentiation, development.

Question 25.
Draw a diagram of human brain and label cerebrum, cerebellum, medulla and fore brian on it.
(CCE 2012)
Answer:

Question 26.
List in tabular form three differences between nervous control and chemical control. (CCE 2012)
Answer:

Question 27.
Draw a diagram of reflex arc and label on it sensory neuron, motor neuron, relay neuron and receptors.
(CCE 2012)
Answer:

Question 28.
List in tabular form three differences in the movement of leaves of a touch-me-not plant when touched and movement of a tendril towards a support. (CCE 2012)
Answer:

Question 29.
A gland secretes a particular hormone. The deficiency’of this hormone in the body causes a particular disease in which the blood sugar level rises,

1. Name the gland and the hormone secreted by it.
2. Mention the role played by this hormone.
3. Name the disease caused due to deficiency of this hormone. (CCE 2012)

Answer:

1. Pancreas, insulin,
2. Insulin makes the body cells receptive to glucose which is then absorbed by them from the blood. In liver and muscles, it also helps in conversion of absorbed glucose into glycogen.
3. Diabetes mellitus.

Question 30.
Mention the role of each of the following :

1. Cerebellum
2. Fore brain
3. Medulla. (CCE 2012)

Answer:

1. Cerebellum: Maintaining equilibrium or posture in various activities of the body and coordinating muscular activity of the body.
2. Seat of intelligence and control of movements,
3. Medulla Oblongata: It regulates rate of breathing, rate of heart beat, blood pressure and reflexes like swallowing, vomiting, coughing, sneezing, salivation and peristalsis.

Question 31.
(a) Draw the structure of a neuron and label the nucleus and cell body,
(b) Name the part of neuron

1. Where information is acquired
2. Through which information travels as an electric impulse. (CCE 2012)

Answer:
(a)

(b)

1. Information Acquired. Dendrites,
2. Information Travels as Electric Impulse. Axon.

Question 32.
How the timing and amount of hormone released is regulated ? Explain with the help of an example.
(CCE 2012, 2015)
Answer:
The timing and amount of hormone released depends upon feed back system. The requirement of hormone is monitored by a regulatory organ which may be gland itself (e.g., pancreas) or hypothalamus. For example, after meals the glucose content of blood rises. This stimulates P-cells of islets of Langerhans to secrete insulin. Insulin promotes glucose absorption by individual cells, formation of glycogen in liver and muscles. As the glucose level in the blood decreases, secretion of insulin is also reduced.

Question 33.
(a) Identify the enducrine glands a, b, c and d in the given diagram.

(b) List the functions of parts d and f (CCE 2012, 2013)
Answer:
(a) a—pituitary,
b—parathyroids,
c—adrenal,
d—kidney.
(b) Kidney:

1. Produces erythropoietin that stimulates bone marrow to form more RBCs.
2. Produces renin that raises blood pressure to increase ulfrafiltration.
3. Formation of urine by extracting metabolic wastes from blood.

Testes:

1. Formation of sperms,
2. Secretion of testosterone that stimulates formation and maintenance of male sex traits.

Question 34.
In the given diagram of reflex arc

(a) Name the parts labelled A, B, C and D.
(b) Write the function of B and E. (CCE 2012)
Answer:
(a) A—receptor
B—sensory neuron
C—relay neuron
D—motor neuron.
(b)

1. Function of B: To pick up impulse from receptor and.pass it to CNS (here spinal cord).
2. Function of E: It is effector muscle which is activated by motor impulse to provide response or relfex action.

Question 35.
Name a hormone secreted by
(a) Pancreas
(b) Pituitary
(c) Thyroid. State one function of each of the hormones.
(CCE 2012)
Answer:
(a) Pancreas. Insulin. Control of glucose absorption by individual cells and formation of glycogen in liver as well as muscles.
(b) Pituitary. Follicle stimulating hormone (FSH). Formation of ova and sperms in sex organs.
(c) Thyroid. Thyroxine. Control of basal metabolism, regulation of protein, fat and carbohydrate metabolism, consumption of energy, development and differentiation.

Question 36.
(a) Name the hormone which is secreted by growing plants when they detect light. Mention its site of secretion in plant,
(b) Explain why plants appear ro bend towards light ?
(c) Name the diseases caused by deficiency of

1. Iodine
2. Insulin. (CCE 2012)

Answer:
(a) Auxin. Site of Secretion. Stem tip.
(b) Shoot bends towards light as more auxin accumulates on the darker side as compared to illuminated side.
(c)

1. Deficiency of Iodine. Goitre,
2. Deficiency of Insulin. Diabetes mellitus.

Question 37.
(a) How is brain protected from injury and shock ? (CCE 2013)
(b) Name two parts of hind brain and state the function of each. (CCE 2012)
Answer:
(a) Protection of Brain. Brain is protected by

1. Bony cranium
2. Meninges
3. Cerebrospinal fluid present in subarachnoid space and ventricles of brain.

(b)

1. Medulla Oblongata: It regulates rate of breathing, rate of heart beat, blood pressure and reflexes like swallowing, vomiting, coughing, sneezing, salivation and peristalsis.
2. Cerebellum: Maintaining equilibrium or posture in various activities of the body and coordinating muscular activity of the body.

Question 38.
Name the property that causes tendril to circle around the object ? Explain how it happens and how is plant benefitted by it. (CCE 2012)
Answer:
(a) Property: Thigmotropism.
(b) Mechanism: Less auxin occurs on the side of contact as compared to the free side. More growth occurs on the free side.
As a result of more growth on the free side, the tendril coils around the support.
(c) Benefit: As the tendrils encircle the support, the plant can climb higher and higher to expose its leaves properly to sun.

Question 39.
Smitas father has been advised by a doctor to reduce his sugar intake;

1. Name the disease he is suffering from and name the hormone whose deficiency causes it.
2. Identify the gland that secretes it and mention the function of this hormone.
3. Explain how the time and amount of secretion of this hormone is regulated in human system. (CCE 2012)

Answer:

1. Diabetes mellitus: Hormone Deficiency. Insulin.
2. Gland: Pancreas ((3-cells of islets of Langerhans). Insulin activates glucose receptors of body cells for its absorption. In liver and muscles, it stimulates conversion of glucose to glycogen.
3. As glucose level in blood rises after a meal, the [3-cells of islets of Langerhans are stimulated to secrete insulin. As glucose level falls in blood, insulin secretion is reduced.

Question 40.
(a) Name the part of brain which controls

1. Voluntary actions
2. Involuntary actions,

(b) What is the significance of peripheral nervous system ? Name the components of this nervous system and distinguish between the origin of the two. (CCE 2012)
Answer:
(a) Voluntary Actions. Cerebellum. Involuntary Actions. Medulla oblongata. Fore brain has controls over many involuntary and voluntary actions.
(b) Peripheral Nervous System: It is soild lateral part of nervous system that develops from CNS and connects different parts of the body with CNS. Peripheral nervous system has two components, voluntary and involuntary. Voluntary peripheral nerous system is under the control of will. It consists of cranial nerves from brain and spinal nerves from spinal cord. Involuntary peripheral nervous system works independent of will. It develops from some cranial and spinal nerves. Involuntary peripheral nervous system is also called autonomic nervous system. It has two parts, sympathetic (for emergency) and parasympathetic (for moderation). They control the functioning of various internal body parts.

Question 41.
Brain and spinal cord are two vital organs of our body. How is our body designed to protect them ?
(CCE 2013)
Answer:

1. They lie inside bony cases, brain inside cranium and spinal cord inside vertebral column,
2. Both are covered by meninges—duramen, arachnoid and piamater.
3. Cerebrospinal fluid occurs both inside and outside them.

Question 42.
(a) How do muscle cells move ?
(b) Name any two types of tropism.
(c) Define tropism.
(d) Which type of impulses are generally shown by human cells ? (CCE 2013)
Answer:
(a) Excitation of neuron is transferred to muscle at the neuromuscular junction by the release of acetylcholine from the knobs of its motor end plate. Acetylcholine is picked up by Ach receptors present on the surface of muscle fibre. This induces the mucles fibre to contract.
(b) Geotropism, Phototropism
(c) Tropism: It is the phenomenon of directional paratonie growth movement of curvature in which the direction of movement is determined by the direction of stimulus, e.g., phototropism, geotropism, hydrotropism.
(d) Electrical.

Question 43.
(a) Complete the following table

(b) Give an example of chemotropism. (CCE 2013)
Answer:
(a)
(i) Inhibits growth and induces dormancy
(ii) Cytokinin
(iii) Controls basal metabolic rate (BMR)
(iv) Adrenaline.
(b) Movement of pollen tube in style and ovary.

Question 44.
After consuming a lot of alcohol, Manish could not walk properly and was vomiting. His friend Sunil stopped his car and tried to help him by dropping him home
(a) Which part of the brain gets affected by consuming alcohol ?
(b) Which part of the nervous system controls the reflex action ?
(c) Which two values are shown by Sunil by helping him. (CCE 2013)
Answer:
(a) Cerebellum
(b) Central nervous system like spinal cord
(c)

1. Sunil knows the after-effects of excessive alcohol intake,
2. He is trying to protect his friend from any mishap on the way. Sunil is showing both comradeship and social sense.

Question 45.
(a) Name the major parts of the brain.
(b) Name the part of brain responsible for maintaining the posture and balance of the body.
(c) Which tropic movement is responsible for the growth of pollen tubes towards ovules ? (CCE 2013)
Answer:
(a) Major Parts of Brain
Fore-Brain: Olfactory lobes (2), Cerebral hemispheres (2) or cerebrum, Diencephalon.
Mid-Brain: Cerebral peduncles, Corpora quadrigemina.
Hind Brain: Pons, Cerebellum, Medulla oblongata.
(b) Cerebellum
(c) Chemotropism.

Question 46.
(a) How does tendril coil around the support ?
(b) Define geotropism. (CCE 2013, 2014)
Answer:
(a) Thigmotropism or curvature movement that occurs in response to contact. Less auxin is present in the region of contact. The free side having more auxin shows more growth. This causes the tendril to coil over the support.
(b) Geotropism : It is directional growth movement of curvature which occurs in response to force of gravity. Main root shows positive geotropism while main stem shows negative geotropism.

Question 47.
(a) Define nerve impulse and reflex arc.
(b) Which structure in a neuron helps to conduct a nerve impulse

1. towards the cell body
2. away from cell body. (CCE 2013)

Answer:
(a) Nerve Impulse. It is a self propagated electrical current that travels from one end to another end of a neuron/nerve for the passage of a message.
Reflex Arc: The pathway taken by a stimulus to travel from receptor organ to effector organ in a reflex action is called reflex arc.
(b)

1. Dendrites
2. Axon.

Question 48.
(a) What is significance of reflex actions ?
(b) Which signals will get disrupted in case of a spinal cord injury. (CCE 2013)
Answer:
(a) Significance of Reflex actions:

1. It checks overloading and overtaxing of brain.
2. Survival Value. Reflex actions have survival value.
3. Quick Response. There is an immediate response to otherwise harmful stimuli without the brain having analysed the same.
4. Conditioned Reflexes. With the help of conditioned reflexes we perform a number of our activities, g., reading, writing, typing, pedalling, playing a musical instrument.

(b)

1. Sensory impulses from the area innervated by injured portion,
2. Transmission of motor impulses through the injured portion,
3. Reflex action in the area of injury. Sensations and movements are restricted.

Question 49.
With the help of schematic diagram trace the events which occur when you suddenly touch a hot pan. What is the path followed by reflex action known as ?
Answer:

For Events: Control of reflex arcs is carried out by CNS, chiefly spinal cord.
Sequence of Events. The hot object functions as a stimulus. The stimulus is received by receptors present in the skin. Sensory neurons carry the information as electrical impulse from the receptors to the CNS. CNS possesses relay neurons that transfer the information as electrical impulse to motor neurons. The motor neurons conduct the impulse to effector organs which in this case are muscles that pull away the arm before the information reaches brain.
Path. Reflex arc.

Question 50.
Two examples of plant movements are shown

(a) State the stimulus which is common for movement in both the cases
(b) Mention separately for both, whether the movement takes place away or at the point where stimulus is received.
(c) State one reason for movement in each case.
Answer:
(a) Stimulus. Touch.
(b) In Sensitive Plant, the leaf shows movement away from place of contact, at the bases of pinnules, pinnae (pulvinules) and petiole (pulvinus). In tendril the movement takes place in the region of contact.
(c) In Sensitive Plant movement occurs due to loss of water or turgidity by certain cells. In tendril it is due to auxin induced greater growth of cells on the side not in contact with object.

Question 51.
Write three points of difference between reflex action and walking. (CCE 2014, 2015)
Answer:

Question 52.
Illustrate with the help of a diagram the effect of auxin in different parts of a plant. (CCE 2014)

Answer:
In stem auxin stimulates more growth when its concentration reaches above Root 10 ppm. In roots the optimum concentration required for growth is 0-0001 ppm. Higher value is inhibitory.

Question 53.
How does the plant detect the touch and how do the leaves move in response ? (CCE 2015)
Answer:
The stimulus of touch is converted into electro-cheftiical potential or synthesis of chemical called turgarin.
The same travels to the bases of pinnules, pinnae and petiole. The thin walled cells present on upper side of pinnule bases and lower side of pinna bases and petiole are stimulated to eject K⁺ ions and then water. They shrink in size and cause folding and drooping movements.

Question 54.
(a) Write two points of difference between enzymes and hormones.
(b) Name one endocrine gland in our body which performs dual function. Write its functions.
Answer:
(a)

(b) Testis :

1. Secretion of hormone testosterone,
2. Formation of sperms.

Question 55.
Name the system which facilitates communication between central nervous system and other parts of the body. Mention two types of nerves it consists of alongwith their organs of origin. (CCE 2015)
Answer:

1. Peripheral nervous system.
2. It has two components, cranical nerves and spinal nerves. There are 12 pairs of cranial nerves which arise from brain. Spinal nerves are 31 pairs. They develop from spinal cord.

Question 56.
Write two different types of movements shown by the plants. Explain them by giving one example for each.
(CCE 2015)
Answer:
Response of Plants to External Stimuli. Plants are fixed. They cannot run away from stressful conditions nor move to area of favourable conditions. They respond to external stimuli by

1. Turgor movements and
2. Growth movements.

Turgor Movements: Change in hydration of certain cells gives rise to these movements, e.g, closure and opening of stomata, nyctinasty or sleep movements in legumes, hydronasty in many grasses, seismonasty in Sensitive Plant.
Growth Movements: They are of two types, nondirectional or nastic and directional or tropic.
Nondirectional growth movement is related to struture of the responding organ and not the direction of stimulus, e.g, opening and closing of flowers. Directional growth movement is related to the direction of stimulus, e.g, phototropism, geotropism.

Question 57.
(a) An old man is advised by his doctor to take less sugar in his diet. Name the disease from which the man is suffering. Mention the hormone due to imbalance of which he is suffering from this disease. Which endocrime gland secretes this hormone ?
(b) Name the endocrime gland which secretes growth hormone. What will be the effect of the following on a person :

1. Deficiency of growth hormone,
2. Excess secretion of growth hormone. (CCE 2015)

Answer:
Ans.
(a)

1. Diabetes mellitus. Hormone Deficiency. Insulin.
2. Gland. Pancreas ((3-cells of islets of Langerhans). Insulin activates glucose receptors of body cells for its absorption. In liver and muscles, it stimulates conversion of glucose to glycogen.
3. As glucose level in blood rises after a meal, the [3-cells of islets of Langerhans are stimulated to secrete insulin. As glucose level falls in blood, insulin secretion is reduced.

(b) Pituitary gland

1. Dwarfism
2. Gigantism.

Question 58.
Draw a diagram showing the correct position of pancreas, thyroid gland, pituitary gland, adrenal gland in human being. (CCE 2015, 2016)
Answer:

Question 59.
Name and state briefly one function each of any three phytohormones. (CCE 2016)
Answer:
Five types — auxin, gibberelin, cytokinin, ethylene and abscisic acid.
Auxin: Cell enlargement, root formation, apical dominance, inhibition of abscission, fruit growth.
Gibberellin: Growth in stem and leaves, higher fruit yield, overcoming dormancy.
Cytokinin: Essential for cell division, differentiation, prevention of senescence and overcoming apical dominance.
Ethylene: Promotes transverse growth, fruit ripening and overcoming dormancy of some parts.
Abscisic Acid (ABA): Induces dormancy, senescence and abscission, checking excessive activity of growth promoting hormones, closure of stomata under water stress.

Question 60.
Mention the part of the brain which

1. Enables us to ride a bicycle
2. Changes the size of the pupil of eye
3. Maintains blood pressure of the body
4. Maintains posture and equilibrium of the body
5. Regulates respiration
6. Detects the smell of agarbatti. (CCE 2016)

Answer:

1. Cerebellum
2. Superior corpora quadrigemina
3. Medulla oblongata
4. Cerebellum
5. Medulla oblongata
6. Temporal lobe.

Question 61.
How does the plant shoot bends when the plant is placed in a room having only one open window ? Explain briefly. (CCE 2016)
Answer:
The plant will be receiving light from one side. The unidirectional light caues positive phototrophic response from the shoot. More auxin is formed on the shaded side of the shoot apex. As a result more growth occurs on the shaded side than the illuminated side. This results in bending of the shoot towards the direction of light.

Question 62.
“As the blood sugar level in our body falls, insulin secretion is reduced”.
Justify the statement in the reference of feedback mechanism that regulates the timing and amount of hormone released. (CCE 2016)
Answer:
Insulin secretion by pancreas is linked to the concentration of sugar in the blood. After a meals, as the glucose concentration becomes high in the blood, insulin is secreted. It activates glucose receptors of the body cells. They absorb glucose for their use. In liver and muscles, the absorbed glucose is converted into glycogen. This reduces the glucose concentration in blood. Insulin secretion by pancreas is also reduced because the P-cells of its endocrine region are not being stimulated to secrete.

Question 63.
Draw a nerve cell and label on it the following : Nucleus, Dendrite, Axon. (CCE 2016)
Answer:

Question 64.
Write two different types of movements shown by plants. Explain them by giving one example for each. (CCE 2016)
Answer:
Nastic and trophic
Nastic Movements: They are non-directional curvatures movements of turgor or growth where the movements are determined by the structure of the responding organ irrespective of the direction of stimulus which is generally diffuse. Ex. Drooping and folding of leaves in Sensitive Plant in response to shock (seismonasty).
Tropic Movements: It is the phenomenon of directional paratonie growth movement of curvature in which the direction of movement is determined by the direction of stimulus, e.g., phototropism, geotropism, hydrotropism.

Long Answer Questions (5 Marks Each)

Question 1.
(a) What is reflex action ? Give its two examples. Illustrate the pathway followed by a message from the
receptor in a reflex arc. (CBSE Delhi 2006 C, CCE 2010, 2015)
(b) Name the actions of sympathetic and parasympathetic systems on eye. (CBSE Delhi 2006 C)
Answer:
(a) Reflex Action: It is an automatic, spontaneous nerve mediated response to a stimulus without consulting the will of the individual.
e.g., withdrawal of hand on being pricked or coming in contact with hot surface.
(b) Effect on Pupil,

1. Sympathetic—dilation
2. Parasympathetic—constriction.

Question 2.
(a) What are “hormones” ?
(b) List four characteristics of hormones
(c) Name the hormone required for the following :

1. Functioning of mammary glands
2. Regulation of calcium and phosphate
3. Lowering of blood glucose
4. Development of moustache and beard in human malc.(CBSE A.I. 2006 C, CCE 2015)

Answer:
(a) Definition: Hormones (Gk. hormein— to excite) are chemical messengers or informational molecules produced by ductless glands which are translocated by circulatory system to other body parts for inducing and coordinating their activities including growth. First hormone, secretin, was discovered by Bayliss and Starling (1902). The term hormone was coined by Starling (1905)
(b) Characteristics:

1. Hormones are produced by endocrine or ductless glands.
2. They are poured into circulatory system for passage to different body parts.
3. Target Sites. Hormones act on specific cells, tissues and organs called target sites, generally away from the place of their synthesis.                                                                              ‘
4. They function as chemical messengers or informational molecules that trigger specific chemical and physiological processes of target cells.
5. Slow Action. Since hormones reach the target sites through blood, their effect appears after a lag period. They are slow acting with the exception of adrenaline.
6. Chemical Nature. Hormones are small sized organic molecules which are of diverse origin— proteins, peptides, amino acids, amines and steroids.
7. Non-nutrient Nature. Hormones are nonnutrient in nature. They have no role in providing energy or body building materials. Hormones take part in stimulation or inhibition of physiological processes.
8. The hormones are effective in very low concentration, e.g., adrenaline one in 300 million parts.
9. It is very specific. TSH acts only on thyroid while thyroxine affects all body parts.
10. Hormones are generally produced in response to specific stimuli.
11. Hormones are ultimately broken down or consumed during their activity in target cells.
12. Deficiency or Excess. Both deficiency and excess of hormone are harmful, often leading to serious disorders.

(c)

1. Functioning of Mammary Glands. Prolactin.
2. Regulation of Calcium and Phosphate in Blood. Parathormone.
3. Lowering of Blood Glucose. Insulin.
4. Development of Moustache and Beard in Human Male. Testosterone.

Question 3.
(a) What is

1. Phototropism and
2. Geotropism ?

With labelled diagrams describe an activity to show that light and gravity change the direction that plant parts grow in.
(b) Mention the role of each of the following plant hormones :

1. Auxin
2. Abscisic acid. (CBSE A.I. 2008, CCE 2011)

Answer:
(a)

1. Definition of Phototropism: It is directional growth movement of curvature which occurs in plants in response to stimulus of unilateral light.
2. Definition of Geotropism: It is directional growth movement of curvature which occurs in response to force of gravity. Main root shows positive geotropism while main stem shows negative geotropism.

Activity: Phototropism and Geotropism- Take two potted plants. Place one plant near a window. Keep the other pot tilted horizontally in the open. Water the plants on alternate days. Observe after a week. Potted plant kept near the window shows bending of young stems towards the window. They are positively phototropic. In the horizontal pot, the stem bends upward as it is negatively geotropic. Its root if taken out, shows downward bending indicating its positive geotropic nature.
(b)

1. Role of Auxin. It promotes cell enlargement, fruit growth, apical dominance, rooting of cuttings, prevention of abscission and differential growth during tropic movements.
2. Role of Abscisic Acid. It checks excessive activity of auxin and gibberellins, closes stomata in water deficiency, induces dormancy of buds and seeds.

Question 4.
(a) Name the hormone which is injected to a diabetic patient.
(b) Why should we use iodised salt in our diet ?
(c) If iodine is insufficient in one’s diet, what might be the deficiency disease and its symptoms.
(CCE 2010, 2011)
Answer:
(a) Diabetic Patient. Hormone injected is insulin.
(b) Iodised Salt. Iodine is essential for synthesis of hormone thyroxine in thyroid gland. Thyroxine controls basal metabolic rate, metabolism of protein fat and carbohydrates, activity, body temperature, heart beat and body development.
(c) Deficiency of Iodine. Reduced thyroxine which causes goitre, cretinism and myxoedema. In goitre, there is enlargement of thyroid that results in swelling of neck.

Question 5.
(a) What is reflex arc ?
(b) What are the components of reflex arc ?
(c) How do muscle cells move ?
(CCE 2010, 2011)
Answer:
(a) Reflex Arc: The pathway taken by a stimulus to travel from receptor organ to effector organ in a reflex action is called reflex arc.
(b) Components of Reflex Arc:

Stimulus —> Receptor —> Sensory neuron —> Relay Neuron (CNS) —> Motor neuron —> Effectors —> Response.

(c) Movement of Muscle cells:
It is the place of apposition of motor end plate of a neuron with the surface of the muscle. Motor end plate consists of a number of knobbed branches. A knob or bouton is plugged into shallow depression present on surface of muscle fibre called sole plate. A narrow space or synaptic cleft occurs between the two.
On excitation the knob of motor end plate passes out acetylcholine which reaches the Ach receptors on the surface of muscle. The excitation spreads over the whole muscle fibre. The latter contracts.

Question 6.
Mention the part of brain involved in the following :

1. Walking in a straight line,
2. Picking up a pencil.
3. Blood pressure
4. A question is being asked by the teacher in a class.
5. Change in size of the pupil in response to intensity of light. (CCE 2014, 2015)

Answer:

1. Walking in Straight Line. Cerebellum.
2. Picking up a Pencil. Cerebellum.
3. Blood Pressure. Medulla oblongata.
4. Question being Asked by Teacher. Frontal (Broca’s motor area of speech) lobe of fore brain.
5. Change in Pupil. Superior corpora quadrigemina.

Question 7.
Define tropism. Explain four kinds of tropism with one example each. (CCE 2014)
Answer:
Tropism: It is the phenomenon of directional paratonie growth movement of curvature in which the direction of movement is determined by the direction of stimulus, e.g., phototropism, geotropism, hydrotropism.
Four Kinds

1. Geotropism: It is directional growth movement of curvature which occurs in response to force of gravity. Main root shows positive geotropism while main stem shows negative geotropism.
2. Phototropism: It is directional growth movement of curvature which occurs in plants in response to stimulus of unilateral light.
3. Thigmotropism: Thigmotropism or curvature movement that occurs in response to contact. Less auxin is present in the region of contact. The free side having more auxin shows more growth. This causes the tendril to coil over the support.
4. Hydrotropism: It is directional growth movement of curvature which occurs in response to unilateral stimulus of water. Roots are positively hydrotropic.

Question 8.
(a) Define reflex action. State its significance.
(b) How do plants respond to external stimuli ? (CCE 2014)
Answer:
(a) Reflex Action: It is an automatic nerve mediated response to a stimulus without consulting the will of the individual, e.g., withdrawal of hand on being pricked or coming in contact with hot surface.
Significance,

1. It provides very quick response to stimuli which require immediate remedy,
2. Reflex action relieves the brain of overloading or overtaxing.
3. It has survival value.

(b) Response of Plants to External Stimuli. Plants are fixed. They cannot run away from stressful conditions nor move to area of favourable conditions. They respond to external stimuli by

1. Turgor movements and
2. Growth movements.

Turgor Movements: Change in hydration of certain cells gives rise to these movements, e.g, closure and opening of stomata, nyctinasty or sleep movements in legumes, hydronasty in many grasses, seismonasty in Sensitive Plant.
Growth Movements: They are of two types, nondirectional or nastic and directional or tropic.
Nondirectional growth movement is related to struture of the responding organ and not the direction of stimulus, e.g, opening and closing of flowers. Directional growth movement is related to the direction of stimulus, e.g, phototropism, geotropism.

Question 9.
(a) Name one organ each where growth hormone is synthesised in man and plant.
(b) List the sequence of events that occur when a plant is exposed to unidirectional light leading to bending of a growing shoot. Also name the hormone and the type of movement. (CCE 2014)
Answer:
(a)

1. Growth Hormone in Man (GH, Somatotrophic Hormone). Anterior pituitary.
2. Growth hormone in Plants (Auxin). Shoot tip.

(b) A plant exposed to unidirectional light shows bending of shoot towards the source of light. It is due to higher growth on the shaded side as compared to the illuminated side.
Hormone. Higher growth is caused by hormone auxin which is synthesised at the shoot tip. More of it is synthesised on the shaded side. Some auxin also diffuses from illuminated to shaded side.
Type of Movement. Positive phototropism.

Question 10.
(a) State two points of difference between cerebrum and cerebellum.
(b) Explain the mechanism of reflex action. (CCE 2014)
Answer:
(a) Differences between Cerebrum and Cerebellum.

(b) Mechanism of Reflex Action:
Mechanism. The stimulus for reflex action is picked up by a receptor located in the organ on which stimulus is acting. One or more sensory neurons carry the impulse from receptor to the central nervous system (e.g., spinal cord). CNS functions as modulator. It transfers the sensory nerve impulse to one or more motor neurons. The motor neurons carry the impulse to effectors which provide a proper response to the stimulus.

Stimulus Receptor ——–>Sensory neurons ———>CNS ——–>Motor neurons ———-> Effectors ———->Response.

Question 11.
Name the hormone which is secreted by the adrenal gland. Explain the function of this hormone when we have to deal with scary situation. (CCE 2015)
Answer:
Adrenaline: It works in co-ordination with sympathetic nervous system to deal with scary situation. Function.
Both sympathetic nervous system and hormone adrenaline of adrenal medulla work together in preparing the body for protection from a scary or dangerous situation.

1. Heart beats faster so as to provide more blood and its contained oxygen and glucose to muscles,
2. Blood supply to peripheral vessels and digestive tract is reduced. More blood becomes available to skeletal muscles.
3. Breathing rate increases due to dilation of bronchioles, increased activity of diaphragm and rib-muscles.

Question 12.
(a) Define reflex arc. Draw a flow chart showing the events which occur during sneezing.
(b) List four plant hormones. Write function of each. (CCE 2015)
Answer:
(a) Reflex arc: The pathway taken by a stimulus to travel from receptor organ to effector organ in a reflex action is called reflex arc.
Flow chart of Sneeze Reflex :

(b) Plant hormones : Five types — auxin, gibberelin, cytokinin, ethylene and abscisic acid.
Auxin: Cell enlargement, root formation, apical dominance, inhibition of abscission, fruit growth.
Gibberellin: Growth in stem and leaves, higher fruit yield, overcoming dormancy.
Cytokinin: Essential for cell division, differentiation, prevention of senescence and overcoming apical dominance.
Ethylene: Promotes transverse growth, fruit ripening and overcoming dormancy of some parts.
Abscisic Acid (ABA): Induces dormancy, senescence and abscission, checking excessive activity of growth promoting hormones, closure of stomata under water stress.

Question 13.
Define phytohormones. How do plants respond to external stimulus ? (CCE 2015)
Answer:
Phytohormones : Phytohormones are chemical substances other than nutrients produced naturally in plants which regulate growth, development, differentiation and a number of physiological processes, e.g., auxin, gibberellins, abscisic acid, cytokinins.
Response of plants to external stimuli: Plants are fixed. They cannot run away from stressful conditions nor move to area of favourable conditions. They respond to external stimuli by

1. Turgor movements and
2. Growth movements.

Question 14.
(a) Name the hormone which is released into blood when its sugar level rises. Name the organ which produces the hormone and its effect on blood sugar level. Also mention the digestive enzymes secreted by this organ with one function each.
(b) Explain the need of chemical communication in multicellular organisms. (CCE 2016)
Answer:
(a)

1. Insulin,
2. It is secreted by pancreas ((3-cells of islets of Langerhans).
3. Insulin activates glucose receptors of body cells for its absorption. It also stimulates liver and muscles to convert absorbed glucose into glycogen,
4. Pancreas secretes three enzymes— trypsin (as trypsinogen), lipase and amylase. Trypsin breaks down proteins, peptones and proteeses into peptides. Pancreatic lipase hydrolysis lipids into fatty acids and glycerol. Pancreatic amylase acts on complex carbohydrates to form maltose.

(b) Multicellular organisms require a system of chemical communication as it can reach every cell of the body and stimulate the cells to perform particular functions. Different cells respond to particular chemicals for which they have receptors. This helps different structures of the body to perform particular functions, e.g., glucose absorption with the help of insulin, glycogen breakdown and glucose formation with the help of glucagon, cell division by cytokinin, cell growth by auxin, etc.

Question 15.
(a) Define nerve impulse. Name the structure that helps to conduct a nerve impulses

1. Towards cell body
2. Away from cell body.

(b) Why have organisms adapted to use electrical impulse to transmit messages.
(c) State two limitations about the use of electrical impulses. (CCE 2016)
Answer:
(a) Nerve Impulse. It is a self propagated electrical current that travels from one end to another of a neuron for the passage of message,

1. Dendrites
2. Axon.

(b) Electrical impulses are fast, hardly taking 1 msec for passage. There is no spill-over to external medium, nor any after-effect. As a result the same nerve can carry a new impulse soon after.
(c) In electrical impulse there is one type of transmission while certain messages are to be blocked or inhibited. This is carried out at synapse by means of different types of neurotransmitters.

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Chapter 5 Periodic Classification of Elements Class 10 Science Important Questions and Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Periodic Classification of Elements Class 10 Important Questions and Answers Science Chapter 5

Very Short Answer Questions

Question 1.
Indicate the elements which belong to the same group from their atomic numbers as 9, 17, 24, 30, 35, 45.
Answer:
Elements with atomic numbers 9, 17 and 35 belong to the same group i.e. halogen family.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
Arrange the following in decreasing atomic size :
(i) Na, Mg, K
(ii) N, F, O
(iii) N, S, P
Answer:
(i) K, Na, Mg
(ii) N, O, F
(iii) P, S, N.

Question 3.
Give the name and electronic configuration of second alkali metal.
Answer:
The second alkali metal is sodium (Na). Its electronic configuration is 2, 8, 1.

Question 4.
What is the similarity in the electronic configuration of Mg, Ca and Sr ?
Answer:
All the elements belong to group 2 and have two electrons in their valence shell.

Question 5.
Name the members of alkaline earth family. Which out of them is radioactive in nature ?
Answer:
The members of alkaline earth family (group 2) are : Be, Mg, Ca, Sr, Ba, Ra. The last element radium (Ra) is radioactive in nature.

Question 6.
The two isotopes of chlorine have atomic mass 35 u and 37 u. Should they be placed in separate slots in the periodic table ?
Answer:
No, they should be placed in the same slot (or position) because the periodic table is based on the atomic numbers of the elements. Both the isotopes of the element chlorine have the same atomic number (Z = 17).

Question 7.
An element “X” has mass number 35 and number of neutrons is 18.
Identify group number and period of the element “X”.
Answer:
Atomic number of X = Mass No. – No. of neutrons = 35 – 17 = 18.
Electronic configuration = 2, 8, 7;
Group No. = 17, Period No. = 3.

Question 8.
Flow does metallic character of the elements vary
(i) in a group
(ii) in a period ?
Answer:
(i) The metallic character of the elements increases downwards in a group.
(ii) The metallic character of the elements decreases from left to the right along a period.

Question 9.
Name three elements which behave as metalloids.
Answer:
The elements are : arsenic (As), antimony (Sb) and germanium (Ge).

Question 10.
Which property do all the elements possess which are present in the same period as the element boron ?
Answer:
In all the elements, the last electron is present in the same shell i.e., L-shell or second shell.

Question 11.
Which common property do all the elements present in the same group have as the element fluorine ?
Answer:
All the elements have the same number of electrons (seven) in their valence shells.

Question 12.
Write the electronic configuration of the element present in the third period and seventeenth group of the periodic table.
Answer:
The group 17 consists of halogens. The halogen present in third period is chlorine (Cl) with atomic number (Z) = 17.

Question 13.
What is the basic difference in the electronic configuration of the elements belonging to group 1 and group 2 ?
Answer:
All elements belonging to group 1 have one electron in the valence shell while all elements belonging to group 2 have two electrons in their valence shell.

Question 14.
Three elements X, Y and Z belong to 17th group but to 2nd, 3rd and 4th period respectively. Number of valence electrons in Y is 7. Find the number of valence electrons in X and Z.
Answer:
All the elements present in a group have same number of valence electrons whatever may the periods to which they belong. Since element Y has 7 valence electrons, the elements X and Z have also 7 valence electrons.

Question 15.
Element ‘Y’ with atomic number 3 combines with element A’ with atomic number 17. What would be the formula of the compound ?
Answer:
The electronic distribution in elements A’ and ‘Y’ are 2, 1 and 2, 8, 7 respectively. Both have valency equal to 1. The formula of the compound is AY.

Question 16.
Name two other elements which belong to the same family as.
(i) fluorine
(ii) calcium
(iii) carbon.
Answer:
(i) chlorine, bromine
(ii) magnesium, strontium
(iii) silicon, germanium.

Question 17.
On the basis of the periodic classification, identify each set belonging to either a group or a period :
(a) Na, Mg, Al
(b) Na, K, Rb
(c) B, C, N
(d) He, Ne, Ar.
Answer:
(a) period
(b) group
(c) period
(d) group.

Question 18.
The formula of magnesium oxide is MgO. Write the formula of magnesium chloride.
Answer:
Oxygen is divalent in nature. The valency of magnesium in magnesium oxide is +2. The formula of magnesium chloride is MgCl₂ since chlorine has valency equal to one.

Question 19.
The electronic configuration of an element is 2, 8, 7. What is its expected valency ?
Answer:
The expected valency of the element is 1. It may be calculated as 8 – 7 = 1

Question 20.
Two elements A and B belong to the same period. What is common in them ?
Answer:
They have the same number of shells.

Question 21.
The electronic configuration of an element is 2, 8, 6. Identify the element and name of the family to which it belongs.
Answer:
The element with configuration 2, 8, 6 (Z= 16) is sulphur. It belongs to oxygen family (group 16).

Question 22.
How would tendency to gain electrons change as you go down a group ?
Answer:
It is expected to decrease since atomic size increases down the group and the tendency of the element to gain electrons decreases.

Question 23.
Why do elements present in a group show similar characteristics after definite gaps of atomic numbers 8, 8, 18, 18, 18, 32 ?
Answer:
This is because of the reason that the same valence shell configuration of the atoms gets repeated after definite gaps of atomic numbers.

Short Answer Questions

Question 24.
Identify the non-metals from the elements given below.
(a) 2, 8, 1
(b) 2, 8, 7
(c) 2, 8, 3
(d) 2, 8, 5.
Answer:
The element chlorine (Cl) corresponding to configuration (b) and the element phosphorus (P) corresponding to configuration (d) are both non-metals.

Question 25.
Identify the elements X and Y from the following information.
(a) X has 17 protons and 18 neutrons
(b) Y has 17 protons and 20 neutrons.
Answer:
Both the elements X and Y are the isotopes of the same element chlorine because they have the same number oi protons (17).
Remember : Two different elements cannot have the same number of protons. Therefore, X and Y are the isotopes of the same element.

Question 26.
Identify the elements from the following characteristics and arrange them in increasing order of metallic character.
(a) An element which imparts golden yellow colour to the flame.
(b) An element whose oxide is used as a white wash.
(c) An element which is constituent of chlorophyll i.e. green colouring matter in plants.
Answer:
(a) Sodium
(b) Calcium
(c) Magnesium.
Sodium (Na) belongs to group 1. Both calcium (Ca) and magnesium (Mg) are present in group 2. The element Ca is placed below Mg in the group. Since the metallic character of the elements decreases along a period and increases down the group, in the light of these observations, the increasing order of metallic character is : Mg < Na < Ca.

Question 27.
(a) Atomic numbers of Mg and Al are 12 and 13 respectively. “Write their electronic configuration.
(b) Mention the period of the Modern Periodic Table to which the above two elements belong. Give reason for your answer.
Answer:
(a) The electronic configuration of the elements are
Mg(Z = 12) 2, 8, 2 ;
Al (Z = 13) 2, 8, 3.
(b) Both these elements belong to third period since their atoms have three shells.

Question 28.
From the part of a periodic table, answer the following questions

(a) Atomic number of oxygen is 8. What would be the atomic number of, Fluorine ?
(b) Out of ‘X’ and ‘Q’ which element has larger atomic size ? Give reason for your answer.
(c) Out of ‘Y’ and ‘Z’ which element has smaller atomic size ? Give reason for your answer.
Answer:
(a) Atomic number of Fluorine is (8 + 1) = 9.
(b) Since the atomic size of the elements decreases along a period the element ‘Q’ has a smaller size than element ‘X’.
(c) Since the atomic size of the elements increases down the group, the element ‘Y’ has a smaller size than element ‘Z’.

Question 29.
Calcium is an element with atomic number 20.
(i) Is it a metal or non-metal ?
(ii) Will its size be more or smaller than that of potassium?
(iii) Write the formula of its chloride.
Answer:
The electronic configuration of calcium (Z = 20) is 2, 8, 8, 2.
(i) Since it has only two valence electrons, it is present in group 2. It is a metal.
(ii) Both potassium (K) and calcium (Ca) are present in fourth period. Since atomic size decreases along a period, calcium is smaller in size.
(iii) The valency of calcium is 2. The formula of its chloride is CaCl₂.

Question 30.
An element ‘X’ has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’.
Answer:
Atomic number of the element ‘X’ = 35 – 18 = 17
Electronic configuration of the element ‘X’ = 2, 8, 7
Group number = 17;
Period number = 3.
Valency of the element ‘X’ = 8 – 7 = 1.

Question 31.
Given below are some of the elements of first group Li, Na, K
(Their atomic numbers are 3, 11, 19 respectively and they belong to 2nd, 3rd and 4th period respectively). Arrange these in the decreasing order of metallic character exhibited by them.
Answer:
All the three elements belong to the group (1) of alkali metals. Since the metallic character of the elements increases down a group, the decreasing order of metallic character is K > Na > Li.

Question 32.
Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the modern periodic table do these two elements belong ? What type of bond will be formed between them and why ?
Answer:
Electronic configuration : X (Z = 12); 2, 8, 2 Electronic configuration : Y (Z = 16); 2, 8, 6
Both these elements are present in third period since they have three electron shells.
These are likely to form an ionic bond as a result of transference of two electrons from element X to the element Y. The compound will form compound XY.

Question 33.
An element has electronic configuration 2, 8, 3. What is the atomic number of the element ? To which
(i) group and
(ii) period does this element belong ?
Answer:
(i) Atomic number of the element (Z) = 2 + 8 + 3= 13
(ii) Group to which the element belongs =13

Question 34.
(a) What is common in the elements belonging to the same period in the periodic table ?
(b) Why are chlorine and bromine kept in the same group in the periodic table ?
Answer:
(a) The elements belonging to the same period have same number of shells. For example, the elements placed in the second period have two shells (K, L). Similarly, the elements included in the third period have three shells (K, L, M). ‘
(b) Both the elements have same number of valence electrons (7) in their atoms.
Chlorine (Z = 17) 2, 8, 7;
Bromine (Z = 35) 2, 8, 18, 7
That is why these are placed in the same group in the periodic table.

Question 35.
An element belongs to third period and second group in the periodic table.
(a) State number of valence electrons in it.
(b) Is it a metal or non-metal ?
(c) Name the element
(d) Write the formula of its oxide
Answer:
The element belonging to third period and second group is calcium (Z = 20). Its electronic configuration is 2, 8, 8, 2
(a) It has two valence electrons
(b) The element is a metal
(c) The element is calcium (Ca)
(d) The formula of calcium oxide is CaO.

Question 36.
(a) The elements of the second period along with their atomic numbers in parentheses are given below ;
B (5), Be (4), O(8), N(7), Li (3), C (6), F (9)

1. Arrange them in the same order as they appear in the periodic table.
2. Which element has the largest and smallest atom ?

(b) Why does atomic radius change as we move from left to right in a period ?
Answer:
(a)

1. Li (3), Be (4), B (5), C (6), N (7), O(8), F (9)
2. The element Li has the largest atom. The element F has the smallest atom.

(b) Along a period, the nucleus charge increases and the electrons are attracted more towards the nucleus.
Therefore, the atomic size or atomic radius decreases as we move from left to the right along a period.

Question 37.
Account for the following :
(a) Elements C, N, O and F are placed in the second period of the periodic table. .
(b) Elements of group 17 are monovalent.
Answer:
(a) All these elements have two electron shells. Therefore, these are placed in the second period.
C (Z=6) 2, 4 ;
N (Z = 7) 2, 5 ;
O (Z = 8) 2, 6 ;
F (Z = 9) 2, 7
(b) All the elements included in the group 17 have 7 valence electrons in their atoms. These atoms need only one electron to acquire the electronic configuration of nearest noble gas atom. Therefore, these are monovalent.

Question 38.
Chlorine (atomic number 17) is more electronegative than sulphur (atomic number 16). Explain.
Answer:
Chlorine (Z = 17) is placed after sulphur (Z = 16) in the same period i.e. third period. The size of chlorine is smaller than that of sulphur and its atom needs only one electron to have noble gas electronic configuration while sulphur atom needs two electrons. Therefore, chlorine has greater attraction for electrons than sulphur. It is more electronegative than sulphur.

Question 39.
The atomic numbers of three elements X, Y and Z are 9, 11 and 17 respectively. Which of these two elements will show similar characteristics and why ?
Answer:
The elements X and Z will show similar characteristics because they differ in their atomic numbers by 8 (9, 17). Both these are halogens and belong to group 17 (halogen family). These are fluorine (Z= 9) and chlorine (Z = 17) .

Question 40.
The atomic number of three elements are given below :

Write the symbol of the element which belongs to
(i) group 13,
(ii) group 15, of the periodic table. State the period of the periodic table to which these elements belong. Give reason for your answer.
Answer:
Electronic configuration of the elements A, B and C are as given :

Element (Symbol) A B C
Atomic number 5 (2, 3) 7 (2, 5) 10(2, 8)
(i) Element A belongs to group 13 (Group No. = 10 + 3 = 13). It is boron (B)
(ii) Element B belongs to group 15 (Group No. = 10 + 5 = 15). It is nitrogen (N)
Both these elements belong to second period since they have two shells.

Question 41.
Write two reasons responsible for the late discovery of noble gases.
Answer:
(i) Noble gas elements were not present in earth crust as minerals like other elements and were present in air to a very small extent.
(ii) Their atoms have stable electronic configuration of their outermost shells also called valence shells. (2 in case of He and 8 for other elements). They do not combine with atoms of other elements.
That is why noble gas elements were discovered at a later stage.

Long Answer Questions

Question 42.
Three elements A, B and C have atomic numbers 7, 8 and 9 respectively.
(a) What would be their positions in the modern periodic table ? (Mention group and period both)
(b) Arrange A, B and C in decreasing order of their size.
(c) Which one of the three elements is most reactive and why ?
Answer:
The electronic configuration of these elements are :
(a) A ( Z = 7) 2, 5;
B (Z = 8) 2, 6;
C (Z = 9) 2, 7
Position of element A = 15th group and 2nd period
Position of element B = 16th group and 2nd period ‘
Position of element C = 17th group and 2nd period.
(b) In general, atomic size decreases along a period. Therefore, decreasing order of size is A > B > C
(c) The element C (Z = 9) is fluorine. It is the most reactive element since it needs only one electron to acquire a noble gas configuration.

Question 43.
The elements with atomic number 3 to 10 belong to the second period. Taking into account the trends in the general periodic properties, predict.
(a) The most electronegative element
(b) The most electropositive element
(c) The element belonging to noble gas family
(d) The element which constitutes large number of organic compounds.
Answer:
(a) The most electronegative element has atomic number (Z) = 9. It is fluorine (F).
(b) The most electropositive element has atomic number (Z) = 3. It is lithium (Li)
(c) The element belonging to noble gas family has atomic number (Z) = 10. It is neon (Ne)
(d) The element which constitutes large number of organic compounds has atomic number (Z) = 6. It is carbon (C).

Question 44.
“Elements in Periodic Table show periodicity of properties”. List any four properties.
Answer:
Periodicity i.e., repetition of similar properties is shown by the elements present in a group and separated by definite gaps of atomic number. For example,

1. Elements in a group have same number of valence electrons and same valency.
2. Elements present in a group show similar chemical properties.
3. The atomic sizes of the elements in a group increase regularly.
4. The m.p. and b.p. of the elements in a group increase regularly.

Question 45.
The electronic configuration of three elements X, Y and Z are given below ;
X = 2 ; Y = 2, 6 ; Z = 2, 8, 2.

1. Which element belongs to the second period ?
2. Which element belongs to the eighteenth group ?
3. Which element belongs to the second group ?
4. What is the valency of Y ?
5. Are Y and Z metals or non-metals ?

Answer:

1. The element ‘Y’ belongs to second period.
2. The element ‘X’ belongs to eighteenth group also called zero group.
3. The element ‘Z’ belongs to second group.
4. Element ‘Y’ has valency equal to 2(8 -6 = 2).
5. The element ‘Y’ is a non-metal while element ‘Z’ is a metal.

Question 46.
The atomic numbers of elements A, B, C, D and E are given below :

From the above table, answer the following questions
(a) Which two elements are chemically similar ?
(b) Which is an inert gas ?
(c) Which element belongs to 3rd period of periodic table ?
(d) Which element among these is a non-metal ?
Answer:
The electronic configuration of the elements are as follows :

(a) Elements C and D are chemically similar since they have same number of valence electrons.
(b) Element B is an inert gas element since it has complete octet.
(c) Element C belongs to third period since it has three shells.
(d) Element A is a non-metal since it has five valence electrons.

Question 47.
Using the part of the periodic table given below, answer the questions that follow.

(i) Na has physical properties similar to which elements and why ?
(ii) Write the electronic configuration of N and P.
(iii) State one property common to fluorine and chlorine.
Answer:
(i) Na has physical properties similar to Li and K. All the three elements have one electron each in the valence shell of their atoms. These are known as alkali metals. However, the element hydrogen has different physical properties.
(ii) Electronic configuration of N (Z = 7) = 2, 5
Electronic configuration of P (Z = 15) = 2, 8, 5
(iii) Both the elements have seven electrons in the valence shells as their atoms and have valency equal to one.
Fluorine (Z = 19) 2, 7 ;
Chlorine (Z = 17) 2, 8, 7.

Question 48.
Atomic radii of the elements present in second period are given :

1. Arrange them in decreasing order of their atomic radii.
2. Are these elements arranged in the pattern of a period in the periodic table ?
3. Which elements have the largest and the smallest atoms ?
4. How does the atomic radius change as you move from left to right in a period ?

Answer:

1. The decreasing order of atomic radii is :
   Li(152) > Be (111) > B (88) > C(77) > N(74) > O(66)
2. No, the arrangement of the elements is not systematic. The correct arrangement is as given above.
3. The element Li has the largest atoms while the element O has the smallest atoms.
4. The atomic radii of the elements decrease in moving from left to the right.

Question 49.
“The atomic number of Cl is 17. On the basis of this information, answer the questions that follow :
(a) Write the electronic configuration of Cl.
(b) Find its valency.
(c) To which group does it belong ?
(d) Identify the type of ion it will form.
(e) Write down the formula of the compound it forms with other elements.
Answer:
(a) Electronic configuration of Cl (Z = 17) = 2, 8, 7.
(b) Valency of Cl = 8 – 7 = 1
(c) Group to which Cl belongs =17 id) Type of ion formed bly Cl = Anion (Cl^–).
(e) Formula of compound with other elements (M) = MCI_x.
∴ Here x is the valency of the element.

Question 50.
The list of the elements present in the same period but in different groups is given :
1           2            13            14               15             16           17             18
(a) Do these groups represent modern periodic table ?
(b) Which element will belong to oxygen family ?
(c) Which element will not take part in chemical combination ?
(d) The elements belonging to which groups will form ionic bonds most readily ?
Answer:
(a) Yes, these groups of elements represent modern periodic table.
(b) The element present in group 16 belongs to oxygen family.
(c) The element included in group 18 (noble gas elements) will not take part in chemical combination.
(d) The elements belonging to group 1 and group 17 will form ionic bonds most readily.

Question 51.
An element E has following electronic configuration :

(a) To which group of the periodic table does element E belong ?
(b) To which period of the periodic table does element E belong ?
(c) State the number of valence electrons present in element E.
(d) State the valency of the element E.
Answer:
The element with atomic no. (Z) = 16 is sulphur (S).
(a) It belongs to group 16 of the periodic table,
(b) It belongs to third period since it has three shells.
(c) The element has six valence electrons.
(d) The valency of the element is 2 (8 – 6 = 2).

Question 52.
From the part of the periodic table given, answer the following questions.

(a) Which is the most reactive metal ?
(b) Name the family of L, Q, R, T.
(c) Name one element of group 2 and 15,
(d) Name one member of group 18 other than neon.
(e) Give the name of the element S placed below carbon in group 14.
Answer:
(a) The element Z is the most reactive metal.
(b) The elements are present in group 17. The family is that of halogens.
(c) One element belonging to group 2 is calcium (Ca) while one present in to group 15 is nitrogen (N).
(d) The element argon (Ar) is also present in group 18.
(e) The element is silicon (Si)

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 5 Periodic Classification of Elements helpful to you.

If you have any doubts, please comment below. We try to provide online math tutoring for you.

Chapter 10 Light Reflection and Refraction Class 10 Science Important Questions with Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Light Reflection and Refraction Class 10 Important Questions and Answers Science Chapter 10

Very Short Answer Questions (1 Mark)

Based on Reflection of light

Question 1.
Define reflection of light ?
Answer:
The process of returning or bouncing back the light to the same medium after striking the surface is called reflection of light.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
What is a reflector ?
Answer:
A surface which reflects the light is called reflector.

Question 3.
State laws of reflection.
Answer:

1. Angle of incidence is equal to the angle of reflection. That is , ∠i = ∠r .
2. Incident ray, reflected ray and normal to the reflecting surface at the point of incidence lie in the same plane.

Question 4.
What are the values of angle of incidence ∠i and angle of reflection ∠r for normal incidence of light on a plane mirror ? [CBSE (All India) 2005]
Answer:
For normal incidence, ∠i = 0. Therefore, according to law of reflection ∠r = ∠i = 0.

Question 5.
What is real image ?
Answer:
When rays of light from an object actually meet at a point after refraction, then image formed is real.

Question 6.
What is virtual image ?
Answer:
When rays of light from an object do not meet at a point but appears to meet at a point, then image formed is virtual.

Question 7.
Mention the nature of image produced by a plane mirror. (CBSE 2014)
Answer:
Image is virtual, erect and of the same size as that of the object.

Based on curved or spherical mirrors

Question 8.
Define centre of curvature of a spherical mirror.
Answer:
The centre of a hollow sphere of which the spherical mirror forms a part is called the centre of curvature of the spherical mirror.

Question 9.
Define radius of curvature of a spherical mirror.
Answer:
The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature of the spherical mirror.

Question 10.
Define aperture of a spherical mirror.
Answer:
The part of spherical mirror exposed to the incident light is called the aperture of the spherical mirror.

Question 11.
Define pole of a spherical mirror.
Answer:
The mid point of the spherical mirror is called the pole of spherical mirror.

Question 12.
Define principal axis of the spherical mirror.
Answer:
The line joining the centre of curvature and pole of the spherical mirror and extended on either side is called the principal axis of the spherical mirror.

Question 13.
Define the principal focus of a convex mirror.
Answer:
A point on the principal axis, where rays of light parallel to the principal axis appear to meet after reflecting from the convex mirror.

Question 14.
Define the principal focus of a concave mirror.
Answer:
A point on the principal axis, where the rays of light parallel to the principal axis meet after reflection from the concave mirror is called the principal focus of the concave mirror.

Question 15.
Define focal length of a spherical mirror.
Answer:
The distance between the pole and principal focus of a spherical mirror is called focal length of the spherical mirror.

Question 16.
Write down the relation between the focal length (f) and radius of curvature (R) of a spherical mirror.
Answer:
f = R/2.

Question 17.
Name the mirror which acts as
(i) a convergent mirror and
(ii) divergent mirror.
Answer:
(i) concave mirror,
(ii) convex mirror.

Question 18.
Copy the figure in your answer-book and show the direction of light after reflection. [CBSE (Delhi) 2008]

Answer:

Question 19.
Copy the figure in your answer-book and show the direction of light after reflection. Also write the angle of reflection.

Answer:

Question 20.
No matter how far you stand from a mirror, your image always appears erect and diminished. Identify the type of mirror. [CBSE (All India) 2005; CBSE (Foreign) 2016]
                                                                                              Or
If the image formed by a mirror for all positions of the object placed in front of it is always diminished, erect and virtual. State the type of mirror. (CBSE 2017)
Answer:
Convex mirror.

Question 21.
Where should an object be placed on the principal axis of a concave mirror so that its real image is of the same size as that of the object ?
Answer:
Object should be placed at the centre of curvature of the concave mirror.

Question 22.
Where should an object be placed on the principal axis of a concave mirror so that a magnified and virtual image of the object is formed ?
Answer:
Object must be placed between the pole and focus of the concave mirror.

Question 23.
Where will the image be formed by a convex mirror if object is placed between infinity and pole of the mirror r.
Answer:
Between pole and focus of the convex mirror and behind the convex mirror.

Question 24.
Name a mirror that gives an erect and magnified (enlarged) image of an object.
Answer:
Concave mirror.

Question 25.
Write mirror formula.
                  Or
Write relation between u,v and ffor mirrors. (CBSE 2014, 2016)
Answer:

where u is the object distance from the spherical mirror, v is the image distance from the mirror and f is the focal length of the mirror.

Question 26.
Define linear magnification of a mirror.
Answer:
It h defined as the ratio of the size (or height) of the image to the size (or height) of the object.

Question 27.
What is the magnification of the images formed by plane mirrors and why ? (CBSE 2015)
Answer:
Magnification, m = 1 because size of image is equal to size of object in case of a plane mirror.

Question 28.
An object of size 2 cm is placed at 25 cm in front of a concave mirror. If the magnification produced by the mirror is 4, what is the size of the image ?
Answer:

Question 29.
Name the mirror used by a dentist to examine the teeth of a patient.
Answer:
Concave mirror.

Question 30.
Name the rear view mirror used in vehicles.
                                 Or
Which type of mirror is usually used as a rear-view mirror in motor-cars ?
[CBSE (Foreign) 2008, CBSE 2011]
Answer:
Convex mirror.

Question 31.
Name the type of mirrors used in head lights of buses and cars. (CBSE 2012)
                                Or
Which kind of mirrors are used in the head lights of a motor-car and why ?
Answer:
Concave mirrors. This is because these mirrors send the reflected light as a parallel beam of light to illuminate the road.

Question 32.
Name the type of mirror used in solar furnaces. (CBSE 2013)
Answer:
Concave mirror.

Question 33.
Why does a ray of light passing through the centre of curvature of a concave mirror after reflection, is reflected back along the same path ? (CBSE 2011)
Answer:
A ray of light passing through the centre of curvature of a concave mirror falls perpendicular to the surface of the mirror i.e. ∠i = 0. According to the law of reflection ∠r = ∠i = 0. Therefore, the ray is reflected along the same path.

Question 34.
What kind of mirrors are used in big shopping stores to watch the activities of customers ? [CBSE (All India) 2009)]
Answer:
Convex mirrors.

Question 35.
State the relation between the height of an object (h), height of image (h) object, distance (u) and image distance (v) in case of a spherical mirror.
Answer:

Question 36.
In the following diagram, MM’ is a concave mirror and AB is an object. Draw on your answer-sheet a ray diagram to show the formation of image of this object.
[CBSE (Foreign) 2017]

Answer:

Based on refraction of light

Question 37.
What is refraction of light ?
Answer:
The bending of light when it passes obliquely from one medium to light.

Question 38.
What is the cause of refraction of light ?
Answer:
The refraction of light is due to the fact that speed of light is different in different media.

Question 39.
Define refractive index and express it mathematically. (CBSE 2011, 2012)
                                         Or
Define absolute refractive index of a medium. (CBSE 2012, 2013, 2015, 2016)
Answer:
Refractive index is defined as the ratio of the speed of light in vacuum (c) to the speed of light in medium (v).
That is, n = c/v .

Question 40.
Define relative refractive index of a medium.
Answer:
Relative refractive index of a medium (2) w.r.t. medium (1) is defined as the ratio of speed of light in medium (1) to the speed of light in medium (2).

Question 41.
Write Snell’s law. (CBSE 2011)
Answer:

where i = incident angle, r = refracted angle and n₂₁ = constant and is the refractive index of medium 2 with respect to medium 1.

Question 42.
If refractive index of water for light going from air to water is 1.33, what will be the refractive index of air for light going from water to air ? (CBSE 2011)
Answer:

Question 43.
Why does a ray of light bend when it travels from one medium into another ? [CBSE (Delhi) 2009]
Answer:
This is because speed of light changes when light goes from one medium to another medium.

Question 44.
Why is the absolute refractive index of a medium always greater than one ? (CBSE 2011, 2016)
Answer:
Absolute refractive index, n = c/v . Since c > v, therefore, n > 1.

Question 45.
The refractive index of glass is 1.5. What is the meaning of this statement in relation to speed of light ?
[CBSE (Delhi) 2008]
Answer:

Question 46.
A ray of light PQ is incident on a glass slab as shown. Write the values of angle of incidence and angle of refraction for this ray of light.
(CBSE Sample Paper 2010)

                                                                             Or
A ray of light is incident normally to the surface of a glass slab placed in air. Find the angle of incident and angle of refraction in this case. (CBSE 2011, 2013)
Answer:

Question 47.
Name the physical quantity which remains the same when light goes from one medium to another medium.
Answer:
Frequency of light remains the same when light goes from one medium to another medium.

Question 48.
What happens when a ray of light strikes the surface of separation between the two media at right angle ? (CBSE 2011)
Answer:
There is no refraction of light and the ray of light continues to travel along the same path.

Question 49.
What is the angle between the incident ray of light and the emergent ray of light, when incident ray of light falls obliquely on the glass slab ?
Answer:
When incident ray of light falls obliquely on the glass slab, then the emergent ray of light is parallel to the incident ray of light. Therefore, angle between the incident and emergent rays of light is zero.
A ray of light falls obliquely on the glass slab. The perpendicular distance between the emergent ray of light and the original path of the incident ray is 2 mm.

Question 50.
What is the lateral displacement of the ray of light ?
Answer:
Lateral displacement of the ray of light = 2 mm. on Refraction by spherical lens

Question 51.
What do you understand by optical centre of a lens ?
Answer:
A point in a lens through which rays of light pass without deviation in their original path.

Question 52.
Define principal axis of a lens.
Answer:
A line joining the centres of curvature of two spherical surfaces forming a lens is called principal axis of the lens.

Question 53.
Define principal focus of a convex lens.
Answer:
A point on the principal axis of a convex lens where all rays of light parallel to the principal axis meet after refracting through the lens is called principal focus of the convex lens.

Question 54.
Define principal focus of a concave lens.
Answer:
A point on the principal axis of a concave lens where all rays of light parallel to the principal axis appear to meet after refracting through the lens is called principal axis of the concave lens.

Question 55.
Define focal length of a lens. [CBSE (All India) 2005]
Answer:
The distance between the optical centre and principal focus of a lens is called the focal length of the lens.

Question 56.
Write lens formula.
                     Or
Write relation between u, v and ffor a lens. (CBSE 2014, 2016)
Answer:

Question 57.
State the relation between the height of an object (h), height of image (h), object distance (u) and image distance (v) in case of a lens. (CBSE 2011)
Answer:

Question 58.
Incident ray AB falls on a lens. The refracted ray is BC as shown in figure. Name the lens.

Answer:
Since the ray AB converges along BC after passing

Question 59.
Incident ray AB falls on a lens. The refracted ray BC is shown in figure. Name the lens.

Answer:
Since the ray AB diverges along BC after passing through the lens, so the lens is diverging or concave lens.

Question 60.
If on applying cartesian sign conventions for spherical lenses, the image distance obtained is negative, state the significance of the negative sign. (CBSE 2011)
Answer:
Negative sign with image distance signifies that image is formed on the same side in which the object lies or image is formed in front of the lens.

Question 61.
Define power of a lens and write its SI unit. [CBSE Saniple Paper 2010, 2012, 2015, 2016)]
Answer:
Power of a lens is its ability to converge or diverge the rays of light falling on it. Power of a lens is equal to reciprocal of the focal length of the lens.
SI unit of power is dioptre (D).

Question 62.
In what SI unit is the power of lenses stated ? [CBSE (Foreign ) 2005)]
Answer:
Dioptre (D).

Question 63.
A convex lens forms a virtual and magnified image. What should he the position of the object on the principal axis ?
Answer:
Between focus and the optical centre of the lens.

Question 64.
State the relation between the focal length (f) and power of a lens.
                                              Or
How are power and focal length of a lens related ? [NCERT Question Bank; CBSE 2016]
Answer:

Question 65.
A lens has -4D power. Is the lens concave or convex ?
Answer:
Lens is concave.

Short Answer Questions( 2 & 3 Marks)

Based on Reflection of Light

Question 1.
List two differences between real and virtual images
Answer:

Question 2.
State the laws of reflection of light.
Answer:

1. Angle of incidence is equal to the angle of reflection. That is , ∠i = ∠r .
2. Incident ray, reflected ray and normal to the reflecting surface at the point of incidence lie in the same plane.

Based on curved or spherical mirror

Question 3.
With the ray diagram show that angle of incidence is equal to the angle of reflection when a ray is incident on the concave mirror. (CBSE 2015)
Answer:

Question 4.
An object is placed at the following distances from a concave mirror of focal length 15 cm.
(a) 10 cm
(b) 20 cm
(c) 30 cm
(d) 40 cm
Which position of the object will produce

1. Virtual image
2. A diminished real image
3. An enlarged real image
4. An image of same size. (CBSE 2011, 2012)

Answer:

1. Concave mirror forms virtual image if object is placed between the focus and pole of the mirror. Therefore, for the position of object at 10 cm mirror forms the required image.
2. A real and diminished image is formed when object lies beyond C i.e. beyond 2F. So, for the position of object at 40 cm, mirror forms the required image.
3. An enlarged real image is formed when object lies between F and 2 F. So, for the position of object at 20 cm, mirror forms the required image.
4. An image of same size of the object is formed when object lies at C or 2F. So, for the position of object at 30 cm, mirror forms the required image.

Question 5.
Draw ray diagram to show the formation of images when the object is placed in front of a concave mirror
(i) between its pole and focus point,
(ii) on the centre of curvature. (CBSE 2014, 2016)
Answer:
(i)

(ii)

Question 6.
State three uses of a concave mirror. (CBSE 2012)
Answer:

1. Reflector: Concave mirrors are used in motor head lights, search lights and torches etc. to produce an intense parallel beam of light. A bulb is placed at the focus of concave mirror or concave reflecting surface. The beam of light from the bulb after reflecting from the concave mirror goes as a parallel beam (figure 24).
   
   This parallel beam of – light illuminates the road ahead of the vehicle.
2. Shaving and make up mirror: When an object is placed close to a concave mirror (i.e between the pole and focus of the concave mirror), an erect and enlarged (large in
   size) image of the object is formed. Because of this fact, concave mirror is used by men to see their enlarged faces while shaving. Similarly, a lady can see her face better with the help of a concave mirror while doing make up.
3. In solar cookers: When a parallel beam of sun light falls on a concave mirror, this beam is brought to the focus of the concave mirror. As a result of this, the temperature of an object (say a container containing un-cooked food) placed at this focus increases considerably. Hence the food in the container is cooked (figure 25).
   

Question 7.
State two uses of a convex mirror. (CBSE 2012)
Answer:

1. Rear view or driver’s mirror. Convex mirror is used as a rear view mirror in vehicles because this mirror forms an erect and diminished image of an object behind the vehicle. Since the image of the object formed is small in size, so the field of view is increased. It means, the driver of a vehicle can see the traffic over large area behind his vehicle. This mirror is also known as driver’s mirror.
2. In street lights. Convex mirror is used in street lights to diverge light over a large area (figure 28).
   

Question 8.
Parallel rays of light incident on a concave mirror and a convex mirror as shown in figure,
(i) Redraw the reflected rays in both the cases,
(ii) Name the points where the reflected rays meet or appear to meet on the principal axis.

Answer:
(i) Reflected rays are shown in figures.

(ii) The point where the reflected rays of light meet or appear to meet on the principal axis is known as principal focus F of the concave mirror or convex mirror.

Question 9.
A ray of light LM is incident on a mirror as shown in the figure. The angle of incidence for this ray is the angle between it and the line joining two other points in the figure. Name these two points.

Answer:
The angle of incidence for a ray falling on a spherical mirror is the angle between the incident ray and the normal to the point of incidence. A line joining the centre of curvature and the point of incidence is a normal to the point of incidence. Thus, the given two points are C and M as shown in figure.

Question 10.
A ray of light AM is incident on a spherical mirror as shown in the diagram. Redraw the diagram and show the reflected ray. Also indicate and mark the angle of incidence and angle of reflection in the diagram. (CBSE 2012)

                                                                        Or
Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray of light parallel to the principal axis of a concave mirror. Mark the angle of incidence and angle of reflection on it.
(CBSE 2014, 2017)
Answer:
Incident ray AM is parallel to the principal axis of a concave mirror. Hence, it will pass through the principal focus (F) of the mirror after reflection as shown in figure.

Question 11.
Incident ray AB passes through the focus (F) of a concave mirror and strikes the mirror at B as shown is figure. Trace the reflected ray and also mark the angle of incidence and angle of reflection in the figure. (CBSE 2012)
                                                                          Or
Copy the figure in your answer-book and show the direction of the light after reflection.

Answer:
Incident ray passing through the focus (F) of a concave mirror goes parallel to the principal axis after

Question 12.
Draw the ray diagram to show reflected ray by a concave mirror when the incident ray
(a) passes through its centre of curvature
(b) passes through its focus
(c) is incident on pole of the concave mirror. (CBSE 2015)
Answer:
(a)

(b)

(c)

Question 13.
Name the type of mirror used in a solar furnace. How is high temperature achieved by this device ?
(CBSE 2011, 2013)
Answer:
Concave mirror. The sun rays are focused at a point by the concave mirror. The concentrated beam of sun light at a point increases the temperature at that point.

Question 14.
Draw ray diagrams to describe the nature, position and relative size of the image formed by a concave mirror for the object
(i) When the object is placed between the centre of curvature and the focus of the concave mirror,
(ii) When the object is placed between the pole and the focus of the concave mirror.
(CBSE 2004, 2011, 2012, 2013)
Answer:
(i)

(ii)

Question 15.
A spherical mirror produces an image of magnification -1.0 on a screen placed at a distance of 30 cm from the pole of the mirror.
(i) Write the type of mirror in this case.
(ii) What is the focal length of the mirror ?
(iii) What is the nature of the image formed ?
(iv) Draw the ray diagram to show the image formation in this case. (CBSE 2014)
Answer:
(i) Concave mirror

(iii) Image is real, inverted and of the same size as that of the object.
(iv)

Question 16.
The magnification produced by a mirror is -1.5. What does it signify about the image formed ?
(CBSE 2011)
Answer:

It means, size of image =1.5 times the size of the object. Negative sign signifies that the image is inverted. Inverted image is real image.

Question 17.
Identify the nature of the mirror and mention two characteristics of the image formed when magnification (m) = + 6. (CBSE 2011)
Answer:
m = + 6 means size of image formed = 6 times the size of the object and the image is erect. Such image is formed by a concave mirror when object is placed between the focus and pole of the mirror. The image is virtual and magnified.

Question 18.
Mention two properties of image formed by a convex mirror. (CBSE 2011)
Answer:
Image formed by a convex mirror is

1. virtual and erect,
2. smaller in size as compared to the size of the object.

Question 19.
Why does a ray of light passing through the centre of curvature of a concave mirror after reflection, is reflected back along the same path ? (CBSE 2011)
Answer:
A ray of light passing through the centre of curvature of the concave mirror strikes the surface of the mirror . normally i.e. ∠i = 0. According to the law of reflection, ∠r = ∠i = 0.
Thus, the reflected ray retraces its path.

Question 20.
How can you identify the three types of mirrors without touching ? (CBSE 2011)
Answer:
We can identify the three types of mirrors by looking at them. If the size of the image of an object is of the
same size as that of the object, then mirror is plane mirror. If the size of the image of an object increases as the object is brought closer to the mirror and the size of image is highly magnified when the object is very close to the mirror, then the mirror is concave mirror. If the size of the image is smaller and full length of the image of an object is seen, then the mirror is convex mirror.

Question 21.
Name the mirror that
(a) can give real as well as virtual image of an object
(b) will always give virtual image of same size of an object
(c) will alway give virtual and diminished image of an object
(d) is used by a doctor in examining teeth. (CBSE 2011)
Answer:
(a) Concave mirror
(b) Plane mirror
(c) Convex mirror
(d) Concave mirror.

Question 22.
What should be the position of the object, when a concave mirror is to be used :
(i) as a shaving mirror, and
(ii) in torches producing parallel beam of light ? (CBSE 2011, 2012)
Answer:
(i) between the focus and pole of the concave mirror
(ii) at the focus of the concave mirror.

Question 23.
A man standing in front of a mirror finds his image having a very large head and legs of normal size. What type of mirrors are used in designing such a mirror ? (CBSE 2011)
Answer:
The upper part of such a mirror is concave mirror and lower part is a plane mirror.

Question 24.
A concave mirror of focal length ft can form a magnified erect as well as an inverted image of an object
placed in front of it. ” Justify this statement stating the position of the object with respect to the mirror in each case for obtaining these images. (CBSE 2013)
Answer:

1. When object is placed between the focus (F) and pole (P) of a concave mirror, magnified and erect image of the object is formed on the back of the mirror.
2. When object is placed between the centre of curvature and the principal focus of a concave mirror, magnified and inverted image is formed in front of the mirror.

Based on Refraction of light

Question 25.
State laws of refraction of light. [CBSE (Foreign) 2004, 2012, 2013, 2014, 2015]
Answer:
Refraction of light follows the following two laws :

1. 1. The incident ray, the refracted ray and the normal to the surface separating the two media all lie in the same plane.
      
   2. The ratio of the sine of the incident angle (∠i) to the sine of the refracted angle (∠r) is constant for a pair of two media.
      
      This constant is known as the refractive index of the medium in which refracted ray travels with respect to the medium in which incident ray travels. Refractive index is denoted by n.
   3. Refractive index of second medium with respect to the first medium is denoted by
      Thus, eqn. (1) can be written as
      

This law is also known as Snell’s law as it was stated by Prof. Willebrord Snell (Dutch mathematician and astronomer).

Question 26.
Prove that if a ray of light enters a rectangular glass slab obliquely and emerges from the opposite face of the glass slab, the emergent ray will be parallel to the incident ray. [CBSE (Foreign) 2004]
                                                                         Or
(a) With the help of a diagram, show that when light falls obliquely on a side of a rectangular glass slab, the emergent ray is parallel to the incident ray. (CBSE 2013)
(b) Show the lateral displacement of the ray on the diagram. (CBSE 2008)
Answer:
Perform an experiment to demonstrate that light bends from its path, when it falls obliquely on the surface of a glass slab. Also show that angle of incidence is about equal to the emergent angle.

1. Take a glass slab and place it on a white sheet of paper fixed on a drawing board.
2. Mark the boundary ABCD of the glass slab.
3. Fix two pins P₁ and P₂, vertically on the drawing board such that line joining the pins is inclined to the edge AB of the glass slab (Figure 37).
   
4. Now, look through the glass slab from opposite side so that the images of pins P₁ and P₂ are seen exactly in line. Fix two pins P₃ and P₄, vertically on the drawing board such that pins P₃, P₄ and image of P₁ and P₂ are exactly in one line.
5. Remove the glass slab and all pins. Join the points P₁ and P₂ with a line and extend this line to touch the edge AB at P. Similarly join the points P₃ and P₄ with a line and extend the line to touch the edge DC at Q.
6. Join points P and Q with a straight line.
7. Draw normal NN’ at P on the edge AB and a normal N₁N₁‘ at Q on the edge DC.
8. Measure ∠P₂ PN and ∠P₃ QN₁‘ using a protractor or dee.

This experiment shows that when light falls obliquely on a glass slab, it bends along PQ from its original path along PL.
Also ∠P₂PN ≈ ∠P₃QN₁‘. That is, angle of incidence is about equal to the emergent angle.
Note : Distance between pins P₁ and P₂, and between P₃ and P₄ must be large.

Question 27.
For the same angle of incidence 45°, the angle of refraction in two transparent media : I and II is 20° and 30° respectively. Out of I and II, which medium is optically denser and why ? (CBSE 2011)
Answer:

Question 28.
A ray of light falls normally on the surface of a transparent glass slab. Draw a ray diagram to show its path and also mark angle of incidence and angle of emergence. (CBSE 2013)
Answer:
Angle of incidence = 0, angle of emergence = 0.

Based on Refraction by spherical lens

Question 29.
What is the difference between a convex lens (converging lens) and a concave lens (diverging lens) ?
(CBSE 2012)
Answer:

 Question 30.
Study the ray diagram given below and answer the following questions :

(i)State the type of lens used in the figure.
(ii) List two properties of the image formed.
(iii) In which position of the object will the magnification be – 1 ? (Sample Paper 2012-13)
Answer:
(i) Lens is convex lens.
(ii) Image formed is real, inverted and enlarged.

If object is placed at 2F₁ Size of image = Size of object, then in this case, m = – 1.

Question 31.
Draw ray-diagrams to describe the nature, position and relative size of the image formed
(i) by a convex lens for the object when it is placed at 2F₁
(ii) by a concave mirror for the object when it is placed between pole P and focus F.
(CBSE 2008, 2009, 2011, 2016)
Answer:
(i)

(ii)

Question 32.
Draw ray diagrams to describe the nature, position and’relative size of the image formed by a convex lens for the object
(i) When the object is placed at F₁ and
(ii) When the object is placed between F₁ and optical centre of the lens. (CBSE 2011, 2016)
Answer:

Question 33.
Draw ray diagrams to describe the nature, position and relative size of the image formed by a concave lens for the object
(i) When the object is placed at infinity and
(ii) When the object is placed to between infinity and optical centre of the lens. (CBSE 2011, 2012)
Answer:

Question 34.
A ray of light, incident obliquely on a face of a rectangular glass slab placed in air, emerges from the opposite face parallel to the incident ray. Draw labelled diagram to show it. State two factors on which the lateral displacement of the emergent ray depends. [CBSE (Foreign) 2008, 2013]
Answer:
Perform an experiment to demonstrate that light bends from its path, when it falls obliquely on the surface of a glass slab. Also show that angle of incidence is about equal to the emergent angle.

1. Take a glass slab and place it on a white sheet of paper fixed on a drawing board.
2. Mark the boundary ABCD of the glass slab.
3. Fix two pins P₁ and P₂, vertically on the drawing board such that line joining the pins is inclined to the edge AB of the glass slab (Figure 37).
   
4. Now, look through the glass slab from opposite side so that the images of pins P₁ and P₂ are seen exactly in line. Fix two pins P₃ and P₄, vertically on the drawing board such that pins P₃, P₄ and image of P₁ and P₂ are exactly in one line.
5. Remove the glass slab and all pins. Join the points P₁ and P₂ with a line and extend this line to touch the edge AB at P. Similarly join the points P₃ and P₄ with a line and extend the line to touch the edge DC at Q.
6. Join points P and Q with a straight line.
7. Draw normal NN’ at P on the edge AB and a normal N₁N₁‘ at Q on the edge DC.
8. Measure ∠P₂ PN and ∠P₃ QN₁‘ using a protractor or dee.

This experiment shows that when light falls obliquely on a glass slab, it bends along PQ from its original path along PL.
Also ∠P₂PN ≈ ∠P₃QN₁‘. That is, angle of incidence is about equal to the emergent angle.
Note : Distance between pins P₁ and P₂, and between P₃ and P₄ must be large.

Question 35.
A convex lens is placed in contact with a concave lens so that the power of the combination is positive. Name the type of the lens, this combination of lenses behaves.
Answer:
Power of a convex lens is positive and the power of a concave lens is negative. Since the power of combination of lenses is positive, so the combination of lenses behaves as a convex lens.

Question 36.
An object is placed at the following distances from a convex lens of focal length 15 cm.
(i) 35 cm
(ii) 30 cm
(iii) 20 cm
(iv) 10 cm
Which position of the object will produce an image of same size as that of the object ? (CBSE 2011)
Answer:
When object is placed at 2 F i.e at 2 f= 30 cm from a convex lens, then the image of same size as that of the object is formed.

Question 37.
A lens X has focal length 20 cm and lens Y has focal length 40 cm. Which lens would you select to obtain a more convergent beam of light ? (CBSE 2011)
Answer:

Thus, a lens of less focal length has large power of converging a parallel beam (in cm) of light. Therefore, lens X will be used to obtain a more convergent beam of light.

Long Answer Questions ( 5 Marks)

Question 1.
A thin converging lens forms a :
(i) real magnified image
(ii) virtual magnified image of an object placed in front of it.
Answer:
(a) Write the positions of the objects in each case.
(b) Draw labelled diagrams to show the image formation in each case.
(c) How will the following be affected on cutting this lens into two halves along the principal axis ?

1. focal length,
2. intensity of the image formed by half lens. (CBSE 2011)

Answer:
(a)

1. A converging or convex lens forms real and magnified image of an object, when the object is placed between F₁ and 2F₁
2. A converging lens forms a virtual magnified image of an object, when the object is placed between the focus and optical centre of the converging lens.

(b)


(c)

1. Focal length of each half will be equal to the focal length of the lens. If converging lens of focal length f is cut into two equal halves as shown in figure
   
   then the focal length of each half = f.
2. Intensity of the image formed ∝ (aperture of the lens)2. Aperture of each cut half of the lens is ½ times aperture of the lens. Hence, intensity of the image formed by half lens will decrease.

Question 2.
For the given data showing object distance and focal length of three concave mirrors, answer the following questions :

1. Out of the three in which case the mirror will form the image having same size as the object ?
2. Which mirror is being used as a make-up-mirror ?
3. Draw the ray diagram for part (1) and part (2) (CBSE 2011, 2015)

Answer:

1. Concave mirror forms the image having same size as the object if object is placed at the centre of curvature
   of the mirror i.e. object distance = 2 f Therefore, for S.No. 3, concave mirror forms the required image.
2. Concave mirror is used as a make-up mirror if the image of the face is magnified. This happens if the face or object is placed between F and 2 F. Therefore, for S. No. 2, concave mirror is used as a make-up mirror.
3. 
   

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 10 Light Reflection and Refraction are helpful to complete your science homework. If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.