CBSE Class 10

On this page, you will find Human Eye and Colourful World Class 10 Notes Science Chapter 11 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 11 Human Eye and Colourful World will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 11 Notes Human Eye and Colourful World

Human Eye and Colourful World Class 10 Notes Understanding the Lesson

1. The human eye: The human eye an extremely valuable and a sensitive sense organ, which enables us to see objects and colours around us.

2. Parts of the human eye:

• Cornea: A thin membrane through which light enters the eye, maximum refraction occurs at the outer surface of cornea.
• Iris: A dark muscular membrane which controls size of pupil.
• Pupil: Regulates and controls the amount of light entering the eye.
• Eye lens: Composed of fibrous, jelly-like material, with adjustable curvature, forms an inverted and real image of object on retina.
• Retina: It is a light sensitive screen on which image is formed.

3. Power of Accommodation:

• The ability of the eye lens to adjust its focal length is called accommodation.
• Least distance of distinct vision: Minimum distance at which object can be seen distinctly without any strain from normal eye, i.e, 25 cm for normal vision.
• Far point of the eye: The farthest point upto which the eye can see objects clearly is called far point of the eye. It is infinity for normal eye.

4. Defects of Vision:
(i) Cataract: Crystalline lens of people at old age becomes milky and cloudy. This condition is called cataract. It is possible to restore vision through cataract surgery.
(ii) Myopia: (Near sightedness)

A person with myopia can see nearby objects clearly but cannot see distant objects clearly. Cause

• Due to excessive curvature of the eye lens.
• Elongation of the eyeball.

(iii) Hypermetropia (far-sightedness)
A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.
Cause

• The focal length of the eye lens is too long.
• The eyeball has become too small.

Correction
Convex lens of suitable power.

(iv) Presbyopia
The power of accommodation of the eye usually decreases with ageing. In this eye defect it is difficult to see nearby objects comfortably and distinctly without corrective eye glasses.

Cause:Weakening of cilary muscles and diminishing flexibility of eye lens.

Correction: By using bifocal lens. Upper portion consists of concave lens and lower part is convex lens.

5. Refraction of Light through Prism

(i) The refraction of light takes place at two surfaces firstly when light enters from air to prism and j secondly when light emerges from prism.
(ii) Angle of prism: The angle between the two lateral faces of the prism is called angle of prism.
(iii) Angle of deviation: The angle between incident ray (produced forward) and emergent ray I (produced backward).

6. Dispersion of White Light by a Glass Prism
Dispersion:

• The splitting of light into its component colours is called dispersion.
• Red light bends the least while violet bends the most.

Spectrum: The band of the coloured components of a light beam is called spectrum, i.e., VIBGYOR

When an inverted prism is kept a little distance away from the prism causing dispersion or basically in the path of splitted beam, the spectrum recombines to form white light.

7. Rainbow Formation
A rainbow is a natural spectrum appearing in the sky after rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. The water droplet act like small prism. They refract and disperse the incident sunlight, then reflect it internally and finally refract it again.

Due to dispersion of light and internal reflection different colours appears.

8. Atmospheric Refraction
If physical conditions of the refracting medium (air) are not stationary, the apparent position of the object fluctuates.

Twinkling of stars

• The twinkling of stars is due to atmospheric refraction of starlight.
• When starlight enters the earth’s atmosphere, it suffers refraction continuously. Since the physical conditions of the earth’s atmosphere are not stationary the stars appear twinkling.

Advance sunrise and delayed sunset

Advance sunrise and delayed sunset is due to atmospheric refraction.
When the sun is slightly below the horizon, the sunlight coming from the less dense (vacuum) to the more dense (air) medium is refracted downwards. Therefore the Sun appears to be above the horizon. Similarly, even after sunset, the Sun can be seen for sometime due to refraction of sunlight.

9. Tyndall Effect

The phenomenon of scattering of light by colloidal particle gives rise to Tyndall effect.
Tyndall effect can be observed when sunlight passes through a canopy of a dense forest. Here tiny droplets in mist scatters light.
The colour of the scattered light depends on the size of the scattering particles. Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths.

Colour of the clear sky is blue: The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. When sunlight passes through the atmosphere, the fine particles in air scatter the blue colour more strongly than red.

Danger signal lights are red in colour: Because red colour is least scattered by fog or smoke.

Sun appears reddish early in the morning: In the morning and evening, the Sun lies near the horizon. Sunlight travels through a larger distance in the atmosphere and most of the blue light and shorter wavelengths are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelength. This gives rise to the reddish appearance of the Sun.

Class 10 Science Chapter 11 Notes Important Terms

Eye: The human eye is an extremely valuable and sensitive sense organ, which enables us to see objects and colours around us.

Power of accommodation: The ability of the eye lens to adjust its focal length is called accommodation.

Myopia: A person with myopia can see nearby objects clearly but cannot see distant objects clearly.

Cataract: Crystalline lens of people at old age becomes milky and cloudy. This condition is called cataract.

Hypermetropia: A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.

Presbyopia: The power of accommodation of the eye usually decreases with ageing. In this eye defect, it is difficult to see nearby objects comfortably and distinctly without corrective eye glasses.

Dispersion: The splitting of light into its component colours is called dispersion.

Atmospheric refraction: Refraction of light by the constituent particles of the atmosphere. Tyndall effect: The phenomenon of scattering of light by colloidal particles gives rise to Tyndall effect.

On this page, you will find Light Reflection and Refraction Class 10 Notes Science Chapter 10 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 10 Light Reflection and Refraction will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 10 Notes Light Reflection and Refraction

Light Reflection and Refraction Class 10 Notes Understanding the Lesson

1. Light: It is a form of energy which produces the sensation of sight.

• Light exhibits dual nature i.e. wave as well as particle nature.
• It travels with a speed of 3 x 10⁸ m/s in vacuum. However speed is inversely proportional to optical density of the medium.

2. Reflection: When light falls on a surface, it bounces back to the medium. The phenomena is called reflection.

3. Beam: A beam is a bundle of rays, which originates from a common source and travels in the same direction.

4. Laws of Reflection:
Terminology

• Incident ray: Ray of light coming from a source towards the reflecting surface.
• Reflected ray: Ray of light which is reflected back by a reflection surface.
• Normal: Perpendicular drawn to the reflecting surface.
• Angle of incidence: The angle between incident ray and normal at the point of incidence.
• Angle of reflection: The angle between reflected ray and normal at the point of reflection

Laws:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, the normal to the mirror at the point of incidence and reflected ray, all lie in the same plane.
  These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces.

5. Types of mirror
1. Plane mirror
2. Spherical mirror

• Concave mirror
• Convex mirror

Concave Mirror: A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of sphere, is called a concave mirror.
Convex Mirror: A spherical mirror whose reflecting surface is curved outwards, is called a convex mirror.

6. Basic terms of Spherical Mirrors:

• Centre of curvature: The centre of a hollow sphere of which the curved or spherical mirror forms a part is called centre of curvature.
• Radius of curvature (R): The radius of sphere of which the reflecting surface of a spherical mirror forms a part is called the radius of curvature of the mirror.
• Pole: The centre of the reflecting surface of spherical mirror. The pole is usually represented by the letter P.
• Principal axis: Its an imaginary line passing through the centre of curvature and pole.
• Aperture: The diameter of the reflecting surface of the spherical mirror is called its aperture.
• Principal focus: A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appear to meet after reflection from the spherical mirror is called principal focus.
• Focal length (f): The distance between the pole and principal focus (F) of a spherical mirror is called the focal length of the mirror. It is denoted by f.
• \(f=\frac{\mathrm{R}}{2}\)

7. Type of image

Representation of images formed by spherical mirror using ray diagrams:

• In order to locate the image of an object, an arbitrarily large number of rays emanating from a point could be considered.
• The intersection of reflected ray gives the position of image.

8. Rules for obtaining image:
(i) A ray parallel to the principal axis, after reflection, will pass through the principal focus in case of concave mirror or appear to diverge from the principal focus in case of a convex mirror.

(ii) A ray passing through principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror after reflection will emerge parallel to the principal axis.

(iii) A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror after reflection, is reflected back along the same path.

(iv) A ray incident obliquely to the principal axis, towards point P (pole of the mirror) on the concave or convex mirror is reflected obliquely.

9. Formation of image by concave mirror
Image formation by a concave mirror for different positions of the object

Ray diagram for the image formation by a concave mirror

10. Formation of image by convex mirror

Ray diagram for image formation by convex mirror

11. Uses of mirrors
(a) Uses of concave mirrors:

• Concave mirrors are commonly used in torches, search lights and vehicles headlights to get powerful beam of light.
• It is used in shaving mirrors to see large image of the face.
• The dentists use concave mirror to see large images of the teeth of patients.
• Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

(b) Uses of convex mirrors:

• Convex mirrors are used as rear-view (wing) mirrors in vehicles.
• Convex mirrors are used as street reflectors because they are able to spread light over a bigger area.

12. Sign convention for reflection by spherical mirrors:

• The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.
• All distances parallel to the principal axis are measured from the pole of the mirror.
• All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.
• Distances measured perpendicular to and above the principal axis (along +y-axis) are taken as positive, (u)

13. Mirror formula and Magnification
Mirror formula
\(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

Refractive index:
Refractive index: The ratio of speed of light in vacuum (c) to the speed of light in any medium (v) is called refractive index of the medium.

Relative refractive index:
The relative refractive index of a medium with respect to other medium is the ratio of speed of light in the second

Here, n₂₁ = Relative refractive index of medium 1 with respect to medium 2.

14. Some applications of refraction:

• Bottom of a tank or a pond containing water appears to be raised due to refraction.
• When a thick glass slab is placed over some printed matter, the letters appear raised when viewed through the glass slab.
• When a pencil is partly immersed in water, it appears to be displaced at the interface of air and water.
• A lemon kept in water in a glass tumbler appears to be bigger than its actual size, when viewed from sides.
  Lens: A transparent medium bound by two surfaces, of which one or both surfaces are spherical.

15. Convex lens: A lens may have two spherical surfaces, bulging outwards. Such a lens is called a double convex lens or convex lens.

• It is thicker at the middle as compared to the edges.
• Convex lens converges light as shown in Figure above.

Hence, convex lenses are called converging lens.

16. Concave lens: A double concave lens is bounded by two spherical surface curved inwards.

• It is thicker at the edges than in the middle.
• Concave lens diverges light and is called diverging lens.

17. Basic terms of spherical lens:

• Principal axis: A line joining the centre of curvatures of two spherical surfaces forming a lens is called principal axis. The line joining C₁ and C₂ is the principal axis (see figure below).
• Principal focus: A point on the principal axis of a lens where all rays of light parallel to the principal axis meet (figure a) or appears to meet (figure b) after passing through the lens is called principal focus of the lens.
• Optical centre: The central point of a lens (O) through which a ray of light pass undeviated is called optical
  
• Focal length: The distance between the principal focus and optical centre of a lens is called focal length of lens. It is denoted by f.
• Aperture of lens: The effective diameter of circular outline of a spherical lens is called its apperture.

18. Rules for making ray diagram

1. A ray of light from the object, parallel to the principal axis, after refraction from a lens passes through the principal focus or appears to diverge from the principal focus

2. A ray of light passing through the principal focus or appearing to meet at the principal focus after refraction, will emerge parallel to the principal axis.

3. A ray of light passing through the optical centre of lens will emerge without any deviation.

19. Image formation by convex lens. Nature, position and relative size of the image formed by a convex lens for various positions of the object.

20. Ray diagram for the image formation by convex lens:

21. Image formation by concave lens:

Position of the objectPosition of the imageRelative size of the imageNature of the imageAt infinityAt focus F₁ Highly diminished, point-sizedVirtual and erectBetween infinity and optical 1 centre 0 of the lensBetween focus F₁ and optical centre 0DiminishedVirtual and erect

22. Sign convention of spherical lens:

• Sign conventions of lens is same as sign convention of mirrors
• The focal length of convex lens is positive and concave lens is taken as negative.

23. Lens formula and magnification:
\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

u = object distance
v = image distance
f= focal length

24. Magnification (m)
Magnification is defined as the ratio of the height of image to the height of object.
\(m=\frac{\text { Height of the image }}{\text { Height of the object }}=\frac{h^{\prime}}{h}=\frac{v}{u}\)
h’ = height of image
h = height of object

25. Power of a lens
The power of a lens is defined as reciprocal of its focal length.
\(P=\frac{1}{f}\)
f = focal length (in metre)

• The SI unit of power is ‘dioptre’. It is denoted by the letter D.
• 1 dioptre is the power of a lens whose focal length is 1 metre, 1 D = 1 m^-1
• Power of convex lens is positive and concave lens is negative.

26. Combination of lens
\(\frac{1}{f_{\text {net}}}=\frac{1}{f_{1}}+\frac{1}{f_{2}}\)
f_net ⁼ Net focal length f_x = focal length of lens 1 f₂ = focal length of lens 2
P net = Power of combination
P₁ = Power of lens 1
P₂ = Power of lens 2.

Class 10 Science Chapter 10 Notes Important Terms

Reflection: When light falls on a surface and bounces back to the medium, the phenomenon is called reflection.

Concave mirror: A spherical mirror, whose reflecting surface is curved inwards.

Convex mirror: A spherical mirror, whose reflecting surface is curved outwards.

Magnification: Magnification is expressed as a ratio of the height of image to the height of object.

Refraction: The deviation of light rays from its path when it travels from one transparent medium to another transparent medium is called refraction of light.

Lens: A transparent medium bound by two surfaces, of which one or both surfaces are spherical, forms a lens.

On this page, you will find Heredity and Evolution Class 10 Notes Science Chapter 9 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 9 Heredity and Evolution will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 9 Notes Heredity and Evolution

Heredity and Evolution Class 10 Notes Understanding the Lesson

1. Heredity: Transmission of characters/traits from parents to their offspring. Variation: The degree by which progeny differ from their parents.

2. Genetics: The branch of science which deals with the study of heredity and variation.

3. Inheritance: It is the process by which characters are passed on from parent to progeny.

4. Gregor Mendel and his Contributions: Mendel is called as the Father of genetics. Mendel used a number of contrasting characters for garden pea. The seven pairs of contrasting characters taken by Mendel in garden pea are given in the figure.

5. Monohybrid Cross: Cross between two pea plants for one pair of contrasting trait of a character. Example: Tall/Short Plants for Stem height. Results of Monohybrid Cross for the character Height

6. In monohybrid cross for character height; Mendel crossed a homozygous tall pea plant (TT) with a homozygous dwarf pea plant (tt) to obtain all heterozygous tall pea plants (Tt) in the F₁ generation. On selfing the heterozygous pea plants (Tt) obtained in the F₁ generation, he obtained F₂ progeny which showed a phenotypic ratio of 3 : 1 for tall and dwarf plants respectively and a genotypic ratio of 1: 2 : 1 for TT : Tt: tt pea plants respectively.

7. Conclusions:

• TT and Tt both are tall plants while tt is a short plant.
• A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
• Characters/Traits like T are called dominant trait (because it express itself) ‘t’ are recessive trait (because it is not expressed in the presence of the dominant trait)

8. Dihybrid Cross: A cross made between two plants having two pairs of contrasting characters is called dihybrid cross.

9. Observations:

• When pea plant with round-yellow seeds (RRYY) was crossed with wrinkled-green seeds (rryy), all the progeny obtained in F₁ generation was RrYy (round and yellow seeds).
• Self pollination of F₁ plants (RrYy) gave the phenotypic ratio of 9 : 3 : 3 : 1 for round-yellow, round- j green, wrinkled-yellow and wrinkled-green pea seeds respectively.

10. Conclusions:

• Round and yellow seeds are dominant characters.
• Occurrence of new phenotypic combinations shows that genes for round and yellow seeds are inherited independently of each other.

11. Sex Determination
Sex is determined either by environmental factors or by the genetic factors.
Determination of sex due to environmental factors: In some animals, the temperature at which fertilised eggs are kept determines whether the animals developing in the eggs will be male or female. For example, Turtle.
In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined.

Determination of sex due to genetical factors:
In human beings, the sex of the individual is largely genetically determined. The genes inherited from parents decide the sex of the child. Sex is determined by a pair of chromosome called sex chromosome.

In human beings there are 23 pairs of chromosomes.
Out of these 22 pairs are called autosomes and the last pair of chromosomes that help in deciding gender of that individual are called sex chromosome. Females have XX as sex chromosome while males have XY as sex chromosome.

A cross between a male with XY sex chromosomes and a female with XX as sex chromosome shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.

12. Evolution
The process by which different kinds of living organism have developed from earlier life forms during the history of the Earth is called evolution. The essence of idea of evolution is the change in the frequency of certain genes in a population over generations.

Situation I shows Natural Selection: A group of twelve red beetles living in bushes with green leaves are easily spotted by their predator crows. So, red colour does not have any selective advantage in bushes with green beetles than red ones in the beetle population. Hence due to natural selection, the green beetles have better survival chances in green colour bushes. Thus natural selection directs evolution in this case.

Situation II shows Genetic Drift: In the second situation also red coloured beetle live in bushes with leaves. Variations arise as the beetles reproduce sexually and one beetle that is green in colour is produced which has selective advantage in green coloured bushes as crows cannot spot it easily. This beetle passes the colour on to its progeny, so that all its progeny beetles are green. The progeny of green beetles is not eaten, while the progeny of red beetles continues to be eaten. As a result, there are more and more green

which kill the red beetles but leaves the blue beetles. The blue beetles which survive increase in numbers. Though blue colour does not have survival advantage in green coloured bushes, still it survives accidentally or by chance. Such situation where change in the frequency of some genes arises accidentally or by chance without any survival advantage is called genetic drift.

green coloured leaves, are easily spotted and eaten by crows. A colour variation arises during reproduction i and results in a beetle that is blue in colour. This beetle passes the blue colour on to its progeny, so that all its progeny beetles are blue which are again easily spotted in the green coloured bushes by the crows like the red ones. There are a few blue beetles, but most are red. An elephant comes by and stamps on the bushes

the bushes start suffering from a plant disease due to which the beetles are poorly nourished as the amount of leaf material for the beetles is reduced. No genetic change occurs but the average weight of the beetles.

Situation III shows the effect of availability of resources: The beetle population begins to expand but gets decreased. After a few years when the plant disease gets eliminated the average weight of the beetle increases again as lot of leaf food is available.

Mechanism of heredity: A section of DNA called genes present on chromosome provides information for the synthesis of proteins. Proteins control the formation of a character.

Acquired and Inherited Traits
Inherited traits: The traits which are passed on from the parents to their progeny by transfer of genes. For example, Eye colour.
Acquired traits: The traits acquired by individual during its lifetime. For example, Riding a bicycle, playing cricket, etc.

13. Speciation
The process of formation of new species from the existing species is called speciation. The factors which lead to the formation of new species are:
(i) Reproductive Isolation:

• Allopatric speciation: Caused by the various types of barriers like mountain ranges, rivers, seas, etc. It leads to reproductive isolation between members of the species and this is also called geographical isolation.
• Sympatric speciation: It occurs when populations of a species that share the same habitat become reproductively isolated from each other.

(ii) Genetic drift: It is caused by change in the frequency of particular genes by accident or by chance alone.
(iii) Natural selection: The process by which a group of organisms adopts to fit their environment in a better way.
(iv) Migration: When movement of a section of population to another place and population occurs.
(v) Mutation: Sudden changes in the sequence of DNA.

14. Evidences for Evolution
Homologous organs: Organs having the same basic structure but different functions are called homologous organs. They have a common origin (common ancestor). Example: Forelimbs of man, a lizard, a frog, elephant tusk and a bird have the same basic structure and design but perform different functions.

15. Analogous organs: Organs which perform the same function but have different basic structure are called as analogous organs. They have a different origin (different ancestors).
Example: the wings of insect and the wings of bird have different structure but perform the same function of flying.

16. Fossils: The remains or impressions of the dead animals or plants that lived in the remote past are called fossils.

17. Estimation of age of Fossils: There are two ways to estimate the age of the fossils:

18. Relative method: On digging the Earth, the fossils we find closer to the surface are more recent than the fossils we find in deeper layers.

19. Carbon-dating method: By detecting radioactivity of Carbon-14 isotope left in the fossil.

20. Evolution by Stages
Evolution of eye: The complex body designs have been created in stages over many generations. The flatworm named Planaria has very simple ‘eyes’ that are just eye-spots which detect light. But later on more complex eyes evolved in various organisms from them.

(i) Evolution of feathers: Evolutionary change produced in an organism for one purpose became more useful for a different function. Feathers first arose for insulation in cold weather but later they became more useful for flying.

(ii) Evolution by artificial selection: Evolution of wild cabbage is an example of evolution by artificial selection. Humans, cultivated wild cabbage as a food plant, and generated different vegetables from it by artificial selection.

21. Evolution should not be equated with ‘progress’: Natural selection and genetic drift cause evolution but that does not mean that

• one species is eliminated to form the new one, or
• the new species is better than the older one. So, evolution should not be equated with progress as multiple branches are possible at each and every stage of evolution.

Example: Human beings have not evolved from chimpanzees. Both have evolved in their own separate ways from a common ancestor a long time ago.

Only progressive trend in evolution: More and more complex body designs have emerged overtime. The older forms still survive along with the newer forms. Example: Bacteria are most primitive forms which are able to survive even in harsh habitats like hot springs or polar ice caps.

22. Human Evolution
Tools for tracing evolutionary relationships: Excavating, time-dating, studying fossils and determining DNA sequences. These tools have been used to study human evolution. Due to different forms and features of human were distinguished on the basis of skin colours into various races. But evidence points out that all human beings are a single species and there is no biological notion of human races.

Earliest members of human species (Homo sapiens) came from Africa. Some of our ancestors stayed back in Africa while others moved and spread across to West Asia, Central Asia, Eurasia, South Asia, and East Asia. They moved from the islands of Indonesia and the Philippines to Australia, and some crossed the Bering land bridge to reach the Americas. They did not go in a single line but went forwards and backwards, with groups sometimes separating from each other, sometimes coming back to mix with each other, even moving in and out of Africa.

Class 10 Science Chapter 9 Notes Important Terms

Heredity: Transmission of characters/traits from parents to their offspring, either through asexual reproduction or sexual reproduction.

Variation: The degree by which progeny differ from their parents.

Inheritance: It is the process by which characters are passed on from parent to progeny. Monohybrid cross: Cross between two pea plants for one pair of contrasting trait of a character.

Dihybrid cross: A cross made between two plants having two pairs of contrasting characters is called dihybrid cross.

Evolution: The process by which different kinds of living organism have developed from earlier life forms during the history of the Earth.

Inherited traits: The traits which are passed on from the parents to their progeny by transfer of genes. For example, Eye colour.

Acquired traits: The traits acquired by individual during its lifetime. For example, Riding a bicycle, playing cricket, etc.

Speciation: The process of formation of new species from the existing species is called speciation. Homologous organs: Organs having the same basic structure but different functions are called as homologous organs. They have a common origin (common ancestor).
Example: Forelimbs of man, a lizard, a frog and a bird have the same basic structure and design but perform different functions.

Analogous organs: Organs which perform the same function but have different basic structure are called as analogous organs. They have a different origin (different ancestors).
Example: The wings of insect and the wings of bird have different structure but perform the same function of flying.

Mutation: Sudden changes in the sequence of DNA.

Sympatric speciation: It occurs when populations of a species that share the same habitat become reproductively isolated from each other.

Allopatric speciation: Speciation caused by the various types of barriers like mountain ranges, rivers, seas, etc.

Fossils: The remains or impressions of the dead animals or plants that lived in the remote past are called as fossils.

On this page, you will find How do Organisms Reproduce Class 10 Notes Science Chapter 8 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 8 How do Organisms Reproduce will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 8 Notes How do Organisms Reproduce

How do Organisms Reproduce Class 10 Notes Understanding the Lesson

1. Reproduction: It is the process by which organisms produce their own kind.

2. Importance of Reproduction: Reproduction enables the continuity of the species, generation after generation.

3. Basic Event in Reproduction for transmission of hereditary information: Copying of DNA
(Deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell.

4. DNA copying is accompanied by the creation of an additional cellular apparatus: As keeping one copy of DNA in the original cell and simply pushing the other one out would not work, because the copy pushed out would not have any organised cellular structure for maintaining life processes.

5. Importance of Variation: Process of copying the DNA is not completely accurate every time, so variations occur. The useful variations are retained while the harmful ones are eliminated. So, the variations enable the organism to survive under unfavourable conditions. This inbuilt tendency for variation during reproduction is the basis for evolution.

6. Difference between Sexual reproduction and Asexual Reproduction

6. Different Types of Asexual Reproduction
Fission

• Binary fission: The parent cell divides/splits equally into two daughter cells. For example, Amoeba
• Multiple fission: The parent cell splits into many cells. For example, Plasmodium (Malarial parasite)
• Binary fission: The splitting of the two cells into two equal halves during division can take place in any plane; it occurs in Amoeba.

Binary fission in Leishmania (which cause kala-azar), occurs in definite orientation/plane due to presence of whip-like structure at one of the cell

7. Fragmentation:
The process by which the broken pieces of an organism (fragments) grow into a complete organism. For example, Spirogyra

8. Regeneration: Some simple animals can develop into a new individual from their broken older parts by a process called regeneration. For example, Planaria, Hydra, Starfish.

9. Budding: In this process a new organism is produced as an outgrowth of the parent body part. For example, Hydra, Yeast.

10. Spore Formation: Small, bulb-like structures called spores develop at the top of the erect hyphae of the fungus. Spores released into the air, germinate into new individuals

11. Vegetative Propagation: A mode of reproduction in which the vegetative parts of the plant like the stem, root and leaves develop into new plant under favourable conditions.
Advantages of Vegetative Propagation

• Plants can bear flowers, fruits earlier than those produced from seeds.
• Enables us to grow banana, orange, rose, jasmine that have lost the capacity to produce seeds.
• Maintains genetical similarity in the plants.

Example: Layering or grafting done in sugarcane, rose and grapes; buds produced in the notches along the leaf margin of Bryophyllum which fall on the soil and develop into new plants.

Disadvantages of Vegetative Propagation

• Plants gradually lose their genetic variation.
• Since many plants are produced, it results in overcrowding and lack of nutrients.

12. Tissue culture: In this technique, the cells removed from the tip of the plant are placed in an artificial medium where they divide rapidly to form a small group of cells or callus which forms plantlets when placed in a medium containing hormones for growth and differentiation. The plantlets are then placed in the soil to grow into mature plants. This technique can be used to obtain disease free plants from virus infected plants.

13. Sexual Reproduction
The process of sexual reproduction involves the fusion of gametes called fertilisation. During sexual reproduction, exchange of chromosomal (genetic) fragments between homologous chromosomes occur causing genetic recombination which leads to variation.

14. Sexual Reproduction in Flowering Plants Stamen: Male reproductive part of the flower made of filament and anther. Pollen grains are produced inside anthers.

Carpel: Female reproductive part of the flower made of three parts—Stigma, style and ovary. Ovules are present inside ovary.

16. Types of flowers

• Unisexual flowers: Flowers bear either stamen or carpel. For example, papaya and Watermelon.
• Bisexual flower: Flowers bear both stamen and carpel. Example: Hibiscus, Mustard.
• Pollination: The transfer of pollen grains from the anther to the stigma of a flower. The transfer occurs by agents like wind, water or animals.

17. Types of pollination
(i) Self-pollination: Transfer of pollen grains to the stigma of the same flower.

(ii) Cross-pollination: Transfer of pollen grains to the stigma of another flower.
The ovary contains ovules and each ovule has an egg cell. After the pollen lands on a suitable stigma, a pollen tube grows out of the pollen grain which bears male germ cells and travels through the style to reach the ovary. Male germ cells reach female gamete and fuse with it by process of fertilisation to form zygote. The zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is converted into a seed which forms a seedling/new plant by the process of seed germination. Ovary develops into fruit. Ovules develop into seed. Petals, sepals, stamens, style and stigma may shrivel and fall off in most cases but sepals may persist in the case of brinjal, tomato, etc.

18. Reproduction in Human Beings: Humans use a sexual mode of reproduction. The period when the reproductive organs become mature and functional in humans is called puberty. Many changes occur during puberty:

19. Changes common to both boys and girls: Thick hair growing in armpits and the genital area between the thighs; Thinner hair appear on legs, arms and on the face; skin frequently becomes oily and might begin to develop pimples.

Changes different in boys and girls: In girls, breast size begins to increase, with darkening of the skin of the nipples at the tips of the breasts. Girls begin to menstruate at around this time.
Boys begin to have new thick hair growth on the face and Seminal vesicle their voices begin to crack. The penis occasionally begins to become enlarged and erect, either in daydreams or at night.

20. Male Reproductive System
The male germ cells (sperms) are formed in a pair of testes (male reproductive organ) which are located inside scrotum situated outside the abdominal cavity. It helps to keep relatively a low temperature needed for the production of sperms by testes.

Testes release a male sex hormone called testosterone whose function is to:

• Regulate the formation of sperms.
• Bring about changes in appearance seen in boys at the time of puberty.

The sperms formed in testes are delivered through the vas deferens which unites with a tube coming from the urinary bladder. Urethra is a common passage for both the sperms and urine. Glands like the prostate and the seminal vesicles add their secretions to make transport of sperms easier and provide nutrition to them.

21. Female Reproductive System
The female germ-cells or eggs are made in the ovaries. Some hormones are formed inside ovaries. Thousands of immature eggs are already present in the ovary of a newly born girl which start maturing on reaching puberty. Every month one egg produced by one of the ovaries is carried from the ovary to the womb through a thin oviduct or fallopian tube. The two oviducts unite into an elastic bag-like structure known as the uterus which opens into the vagina through the cervix.

23. Fertilisation: During sexual intercourse the sperms enter through the vaginal passage, travel upwards and reach the oviduct where they may fertilise the egg to form zygote. The process of fusion of male and female gamete to form a zygote is called as fertilisation. The zygote formed gets implanted in the lining of the uterus, and starts dividing. The uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo.

24. Placenta and its functions: A disc shaped structure embedded in the uterine wall called the placenta provides nutrition to the embryo from the mother’s blood. It contains villi on the embryo’s side of the tissue which are surrounded by blood spaces on the mother’s side.

Following are the roles of placenta:

• It provides a large surface area for glucose and oxygen to pass from the mother to the embryo.
• It removes waste substances produced by the developing embryo.

25. Gestation Period: The development of the child inside the mother’s body takes approximately nine months. This period is called as gestation period. The child is born as a result of rhythmic contractions of the muscles in the uterus.

26. Fate of Unfertilised egg: The ovary releases one egg every month, the lining of the uterus becomes thick and spongy every month to receive a fertilised egg and nourish the embryo. If the egg is not fertilised, it lives for about one day. But if it remains unfertilised then the lining of the uterus slowly breaks and comes out through the vagina as blood and mucous. This cycle is called menstruation which takes place every month and lasts for about two to eight days.

27. Menopause: The sexual cycle in a woman continues upto the age of 45 to 50 years after which eggs are not released by the ovary and menstruation gets stopped. This stage is called Menopause.

28. Reproductive Health: The total well-being in all aspects of reproduction, i.e., physical emotional, social and behavioural is called reproductive health.

29. Sexually transmitted diseases: Bacterial infections like gonorrhoea and syphilis; viral infections like warts and HIV-AIDS. Transmission of many sexually transmitted diseases can be prevented by condoms.

30. Contraceptive methods: The methods to avoid pregnancy are called as contraceptive methods. The different methods are:
Physical methods: Prevent union of sperm and egg. For example, condoms, diaphragm and cervical caps Chemical methods: Act by changing the hormonal balance of the body so, that eggs are not released and fertilisation cannot occur. They may have side-effects too.

For example, Oral pills Surgical methods:

• Vasectomy: The vas deferens of male is blocked to prevent sperm transfer.
• Tubectomy: The fallopian tube of female is blocked to prevent egg to reach uterus.
• Copper-T or loop is placed in uterus to prevent pregnancy.

31. Pre-natal sex determination: The determination of the sex of the child before birth is called as pre-natal sex determination. It is prohibited by law as it is a major cause of illegal sex-selective abortion of female foetuses. The female-male sex ratio must be maintained for a reproductively healthy society.

Class 10 Science Chapter 8 Notes Important Terms

Reproduction: It is the process by which organisms produce their own kind.

Binary Fission: The parent cell divides/splits equally into two daughter cells. For example, Amoeba

Multiple Fission: The parent cell splits, into many cells. For example, Plasmodium (Malarial parasite)

Vegetative Propagation: A mode of reproduction in which the vegetative parts of the plant like the stem, root and leaves develop into new plant under favourable conditions.

Statement: Male reproductive part of the flower made of filament and anther. Pollen grains are produced inside anthers.

Carpel: Female reproductive part of the flower made of three parts stigma, style and ovary.

Pollination: The transfer of pollen grains from the anther to stigma of a flower.

Testosterone: Male sex hormone released by the testes.

Estrogen and Progesterone: These are the sex hormones released by the ovaries in the human females.

Placenta: A disc shaped structure embedded in the uterine wall which provides nutrition to the embryo from the mother’s blood.

Menopause: The sexual cycle in a woman continues upto the age of 45 to 50 years after which eggs are not released by the ovary and menstruation stops. This stage is called Menopause.

Contraceptive Methods: The methods to avoid pregnancy are called as contraceptive methods.

Vasectomy: The process by which the vas deferens of male is blocked to prevent sperm transfer.

Tubectomy: The process by which the fallopian tube of female is blocked to prevent egg to reach the uterus.

Pre-natal sex determination: The determination of the sex of the child before birth is called pre-natal sex determination.

On this page, you will find Control and Coordination Class 10 Notes Science Chapter 7 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 7 Control and Coordination will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 7 Notes Control and Coordination

Control and Coordination Class 10 Notes Understanding the Lesson

1.Growth related movements: A seed germinates and grows and seedling comes out by pushing the soil aside. Such a movement is related to growth as these movements would not happen if growth of seedling is stopped.

2. Growth unrelated movements: A cat running, children playing on swings, buffaloes chewing cud – these are not movements caused by growth. These are growth independent movements. When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. This movement of its leaves are independent of growth.

3. Movement is an attempt by living organisms to use changes in their environment to their advantage: Plants grow to get sunshine. Buffaloes chew cud to enable digestion of tough food. Swinging gives pleasure to the children. We try to protect ourselves by detecting the change in the environment and showing movement.

4. Control and coordination in animals is regulated by two systems: Nervous system and hormonal system.

5. Animals – Nervous System
The specialised tips of some nerve cells detect all information from our environment with help of receptors usually located in our sense organs, such as the inner ear, the nose, the tongue, etc. Gustatory receptors: Detect taste (present on tongue).

6. Olfactory receptors: Detect smell (present in nose).

7. Stimulus: Any agent, factor, chemical or change in external or internal environment which elicits reaction in an organism.

8. Response: A change in an organism (an action) resulting from a stimulus.

9. Mode of transmission of nerve impulse:

• An electrical impulse is generated when information is acquired at the end of the dendritic tip of a nerve cell.
• This impulse travels from the dendrite to the cell body, and then along the axon to its end.
• At the end of the axon, the electrical impulse sets off the release of some chemicals called neurotransmitters at synapse. Synapse is the junction between two neurons where axon ending of one neuron is placed close to dendrites of the next neuron.
• These chemicals (neurotransmitters) cross the synapse, and start a similar electrical impulse in a dendrite of the next neuron.
• A similar synapse finally allows delivery of such impulses from neurons to effectors.

10. Effectors are muscles, glands, tissues, cells, etc., which respond to the stimulus received from nervous system.

Nervous tissue is made up of an organised network of nerve cells or neurons, and is specialised for conducting information via electrical impulses from one part of the body to another. Neuron (Nerve cell) is the structural and functional unit of the nervous system.

11. Parts of a neuron

• where information is acquired—Dendrites
• through which information travels as an electrical impulse—Axon
• Impulse converted into a chemical signal for onward transmission—Synapse.

12. Reflex Action and Reflex Arc
(i) A reflex action is a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain.

(ii) In such reactions we do something without thinking about it, or without feeling in control of our reactions. Reflex actions are very fast response of nervous system to dangerous situations. Example: We withdraw our hand immediately if we prick our finger or touch a hot object.

(iii) Reflex actions are involuntary actions as they cannot be controlled as per our will. They occur automatically.

(iv) The stimulus received by receptors present on sense organ is sent through sensory neuron to spinal cord. Spinal cord sends messages through motor neuron to muscles (effectors) to cause movement of the part and avoid damage. The arc formed in such case is called as the reflex arc.

13. Human Brain

• Brain is the main coordinating centre of the body.
• The brain and spinal cord constitute the central nervous system and are composed of nerves.
• They receive information from all parts of the body and integrate it.
• The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system.
• The nerves arising from the brain (cranial nerves) and nerves arising from spinal cord (spinal nerves) constitute the peripheral nervous system.
• The brain allows us to think and take actions based on that thinking.
• The actions based on our will are called voluntary actions. Example: Writing, talking, clapping at the end of a programme.
• Brain also sends messages to muscles. This is the second way in which nervous system communicates with muscles.

14. Parts of Brain:

• The brain has three major parts/regions: fore-brain, mid-brain and hind-brain.
• The fore-brain is the main thinking part of the brain. It has regions (sensory area) which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing (auditory area), smell (olfactory area), and sight (optic area) and so on.
• There are separate association areas where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in brain.
• A separate part of fore-brain associated with hunger gives a sensation of feeling full.
• Many involuntary actions are controlled by mid-brain and hind-brain.
• Hind-brain comprises of cerebellum, pons and medulla oblongata.
• Cerebellum is responsible for precision of voluntary actions and maintaining the posture and balance of the body. Activities like walking in a straight line, riding a bicycle, picking up a pencil.
• Pons connects cerebellum and medulla oblongata and helps in regulation of respiration rate.
• Medulla controls the involuntary actions like blood pressure, salivation and vomiting.

15. Protection of Brain and spinal cord

• Human brain is present inside a bony box called skull or cranium.
• A fluid-filled inside the skull called cerebrospinal fluid, helps in shock absorption.
• The spinal cord is protected by the vertebral column.

16. How does the Nervous Tissue cause Action?
Muscle cells have contractile proteins, actin and myosin which change both their shape (by getting shortened) and their arrangement in the cell in response to nervous electrical impulses received by them. This results in movement of the part of the body.

17. Coordination in Plants
The touch-me-not plant moves its leaves in response to touch as its cells change shape by changing the amount of water in them, resulting in swelling or shrinking. Such movement is growth independent movement.

18. Movement Due to Growth: Pea plant climbs up by means of tendrils which are sensitive to touch. The part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.

19. Tropism/Tropic movements: Movements in plants which occur in direction of the stimulus. They are directional movements. These directional, or tropic, movements can be either towards the stimulus, or away from it.

20. Phototropism: Growth of plant in response to light. Shoots respond by bending towards light while roots respond by bending away from it.

21. Geotropism: Growth of plant in response to gravity. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the Earth.

22. Hydrotropism: Growth of plant in response to water. Roots always grow towards water and show hydrotropism.

23. Chemotropism: Growth of plant in response to chemicals. Example: Growth of pollen tubes towards ovules.

24. Thigmotropism: Growth of plant in response to touch. Example: Climbers coil around support.

25. Limitations to the use of electrical impulses
Firstly, they do not reach each and every cell in the animal body. They reach only those cells that are connected by nervous tissue.
Secondly, the cell takes some time to reset its mechanisms before it can generate and transmit a new impulse. They cannot continually create and transmit electrical impulses.

26. Way to overcome limitations to the use of electrical impulses
Most multicellular organisms use chemical communication to overcome the limitations of electrical impulse. Chemical compounds (hormones) released by stimulated cells diffuses all around it and is detected by other cells with help of special molecules on their surfaces.

27. How do Plants coordinate their activity?
Plants do not have nervous system. They respond to stimuli with help of chemicals called as plant growth regulators or plant hormones like auxin, gibberelin, cytokinin, abscissic acid, etc.

28. Auxin: It is synthesised at shoot tips and helps in bending of plant towards light. When light comes from one side of the plant, auxin diffuses towards the shady side of shoot. This higher concentration of auxin stimulates the cells to grow longer on the side of shoot which is away from light. Thus, plant appears to bend towards light.

29. Gibberellins: They help in the growth of the stem.

30. Cytokinins: This hormone promotes cell division. It occurs in higher concentration in areas of rapid cell division, such as in fruits and seeds.

31. Ethylene: It is a gaseous hormone which helps in ripening of fruits.

32. Abscissic acid: This hormone inhibits growth. Its effects include wilting of leaves. It is also called as stress hormone as it helps to overcome stress conditions.

33. Hormones in Animals
Hormones are non-nutrient chemicals which act as intercellular messengers, are produced in trace amounts, directly poured in the blood stream and act only on a specific target organ. They are secreted by endocrine glands (ductless glands).

34. Functions of Animal Hormones:
(i) Thyroxin hormone: Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck.

(ii) Adrenaline hormone: It is secreted by adrenal gland in response to stress of any kind and during emergency situations fear, joy, emotional stress, etc. Adrenaline increases breathing rate and the blood supply to heart and muscles. It constricts arterioles. Its target organ is heart and arteries. It is also called as emergency hormone or stress hormone.

(iii) Growth hormone is secreted by the anterior pituitary gland. If there is a deficiency of this hormone in childhood, it leads to dwarfism. Its excess causes gigantism.

(iv) Testosterone in males secreted by testis and oestrogen in females secreted by ovary causes changes in body of males and females during puberty.

(v) Insulin hormone is produced by the pancreas and helps in regulating blood sugar levels. Its deficiency causes diabetes due to increase in blood glucose level.

35. Feedback Mechanisms:
The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the blood glucose level rises, it is detected by the cells of the pancreas which respond by producing more insulin to promote absorption of glucose and formation of glycogen in liver and muscles. When the blood sugar level falls and comes to normal, insulin secretion is stopped by the pancreas.

Class 10 Science Chapter 7 Notes Important Terms

Gustatory receptors: The receptors present in the tongue which help to detect taste.

Olfactory receptors: The receptors present in the nose which help to detect smell.

Neuron (Nerve cell): It is the structural and functional unit of the nervous system.

Synapse: The junction between the two neurons which helps to transmit the electrical or chemical signal to the next neuron.

Reflex action: A reflex action is a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain.

Tropism/Tropic movements: Tropism is a growth movement whose direction is determined by the direction from which the stimulus strikes the plant.

• Positive = Growth towards the stimulus
• Negative = growth away from the stimulus.

Phototropism: The response of a plant or its part to light. Roots are negatively phototropic while shoots are positively phototropic.

Geotropism: The response of a plant or its part to gravity. Roots are positively geotropic while shoots are negatively geotropic.

Hydrotropism: The response of a plant or its part to water. Roots always grow towards water and show positive hydrotropism.

Chemotropism: The response of a plant or its part to chemical stimulus. Pollen tubes grow towards ovule due to chemicals secreted by them.

Thigmotropism: The response of a plant or its part to stimulus of touch.

Hormones: Hormones are chemical messengers that are secreted directly into the blood, which carries them to the specific target organs and tissues of the body to exert their functions.