CBSE Class 8

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure.

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure

NCERT TEXTBOOK EXERCISES

Question 1.
Give two examples of each of situations in which you push or pull to change the state of motion of objects.
Answer.
(1) If a rubber ball or marble is placed on a very smooth surface and given a small push, it starts moving with some speed. If we keep an obstacle in the way of motion of the marble/ball, the marble/ball will stop moving at the obstacle. Here a push is given to the marble/ball at rest to change its state of rest to motion.

(2) If a child is placed on a hanging swing in the state of rest and the swing is pulled again and again by a rope, the swing will move to and fro with a speed. If the pull is bigger, the swing will move at a bigger distance. This is an example of a pull that changed the state of an object from the rest of the motion.

Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer.

1. If an inflated balloon is taken and pressed from two sides with a hand, its shape changed, i.e., the figure is disturbed. If the inflated balloon is pressed with more force, the balloon will burst.
2. If a plate of steel is beaten with a hammer, after four-five big blows the plate’s shape will change.

Question 3.
Fill in the blanks in the following statements:

1. To draw water from a well, we have to ……….. at the rope.
2. A charged body………….an uncharged body towards it.
3. To move a loaded trolley, we have to…………...it.
4. The north pole of a magnet…………….the north pole of another magnet.

Answer.

1. pull
2. attracts
3. pull/push
4. repels.

Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms: muscular, contact, non-contact, gravity, friction, shape, attraction.

1. To stretch the bow, the archer applies a force that causes a change in its……..
   
2. The force applied by the archer to stretch the bow is an example of.………..force.
3. The type of force responsible for a change in the state of motion of the arrow is an example of a…………….force.
4. While the arrow moves towards its target, the forces acting on it are due to……….and that due to of air.

Answer.

1. shape
2. muscular
3. contact
4. gravity, friction.

Question 5.
In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer.

Question 6.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer.
The shape of the hot piece of iron changes. It flattens and becomes thinner than earlier. This is the effect of force due to hammering the piece of iron.

Question 7.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer.
Electrostatic force.

Question 8.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer.
The forces that act on the bucket are as follows:

1. The pressure of water contained in it exerted on its wall and on the base of the bucket.
2. Force of gravity exerted by earth.
3. Muscular force by my hand.

The water is contained in a bucket and the pressure is exerted by water on the walls of the bucket, which is sufficient to take it as a force. This force is counterbalanced by the force exerted by the walls of the bucket on water. As the bucket (with water) is held in my hand, so I overcome the force of gravity of the earth.

Thus, it can be concluded that there is no net effect of forces acting on the bucket full of water. That is why these forces do not bring a change in its state of motion.

Question 9.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer.
The two forces that are acting on the rocket immediately after leaving the launching pad are:

1. Force of gravity of earth acting down-ward
2. The frictional force produced by air particles.

Question 10.
When we press the bulb of a dropper with its nozzle kept in water, the air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
(a) pressure of water
(b) the gravity of the earth
(c) the shape of a rubber bulb
(d) atmospheric pressure
Answer.
(a) the pressure of water.

We hope the NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence.

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence

NCERT TEXTBOOK EXERCISES

Question 1.
What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?
Answer.
The term used for secretions of endocrine glands is hormones, which are responsible for various changes taking place in the body.

Question 2.
Define adolescence.
Answer.
The period of life when the body undergoes changes, leading to reproductive maturity is called adolescence.

Question 3.
What is menstruation? Explain.
Answer.
When the uterus receives the egg and it is fertilized, pregnancy occurs. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off: This causes bleeding in women, which is called menstruation.

Question 4.
List changes in the body that take place at puberty.
Answer.
The onset of puberty brings about:

1. Growth of the reproductive organs which begin to function.
2. Hair grows at various places of the body. Breasts develop in girls and facial hair (mustache and beard) appear in boys.
3. The voice of the boys becomes hoarse as the voice box enlarges during adolescence.

Question 5.
Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer.

Question 6.
What are sex hormones? Why are they named so? State their function.
Answer.
Hormones secreted by testes and ovaries are termed as sex-hormones.

• They are named so because they are secreted by the reproductive organs.

Functions of sex-hormones.

• These hormones are responsible for the secondary sexual characters of males and females.

Question 7.
Choose the correct option.
(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
Answer.
(ii) proper diet is needed for the rapid growth taking place in their body. Reproductive age in women starts when their

(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
Answer.
(i) menstruation starts.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
Answer.
(ii) Chapati, dal, vegetables.

Question 8.
Write notes on:

1. Adam’s apple.
2. Secondary sexual characters.
3. Sex determination in the unborn baby.

Answer.

1. At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. This makes a boy’s voice hoarse.
2. In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, mustaches and beards. As these features help to distinguish the male from the female, they are called secondary sexual characters.
3. Sex Determination in the Unborn Baby: All human beings have 1 pair of sex chromosomes, as the names X and Y. A female has two X chromosomes,

while male has one X and one Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote, that will have ‘XT would develop into a male child. Now you know that the sex chromosomes of the father determine the sex of a baby.

Question 9.
Word game: Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through the bloodstream
6. Voicebox
7. Term for changes at adolescence.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals.

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Explain the importance of reproduction in organisms.
Answer.
The production of new individuals from their parents is known as reproduction. Reproduction is very important as it ensures the continuation of a species. If the process of reproduction does not exist, the species would get vanished from the earth.

Question 2.
Describe the process of fertilisation in human beings.
Answer.
The first step in the process of reproduction is the fusion of a sperm and an ovum. Millions of sperms from the male are transferred into the female body. The sperms swim in the oviduct with the help of their tails to reach the egg. When they come in contact with the egg, one of the sperms may fuse with the egg.

Such fusion of the egg and the sperm is called fertilization. During fertilization, the nucleus of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote.

Question 3.
Choose the most appropriate answer:
(a) Internal fertilisation occurs
(i) in female body.
(ii) outside the female body.
(iii) in male body.
(iv) outside male body.
Answer.
(i) in female body.

(b) A tadpole develops into an adult frog by the process of
(i) fertilisation.
(ii) metamorphosis.
(iii) embedding.
(iv) budding.
Answer.
(ii) metamorphosis.

(c) The number of nuclei present in a zygote is
(i) none
(ii) one
(iii) two
(iv) four.
Answer.
(ii) one.

Question 4.
Indicate whether the following statements are True (T) or False (F):

1. Oviparous animals give birth to young ones. ( )
2. Each sperm is a single cell. ( )
3. External fertilisation takes place in frogs. ( )
4. A new human individual develops from a cell called gamete. ( )
5. Egg laid after fertilisation is made up of a single cell. ( )
6. Amoeba reproduces by budding. ( )
7. Fertilization is necessary even in asexual reproduction. ( )
8. Binary fission is a method of asexual reproduction. ( )
9. A zygote is formed as a result of fertilisation. ( )
10. An embryo is made up of a single cell. ( )

Answer.

1. False
2. True
3. True
4. False
5. True
6. False
7. False
8. True
9. True
10. False

Question 5.
Give two differences between a zygote and a foetus.
Answer.

Question 6.
Define asexual reproduction. Describe two methods of asexual reproduction in animals. ‘
Answer.

The type of reproduction in which only a single parent is involved is called asexual reproduction.

Budding: The asexual reproduction in which an individual develops from buds, which is detached from a parent body is known as budding. For example, Hydra reproduces by this method. Many bulges are found in the parent body of hydra. These bulges called buds to develop into new individuals.

Budding fission: It is a type of asexual reproduction in which an animal reproduces by dividing into two individuals. This type of reproduction is observed in the microscopic organism, amoeba. The reproduction in Amoeba begins by a division of its nucleus into two nuclei. This is followed by a division of its body into two with each part receiving a nucleus. Finally, two amoebae are produced from a single Amoeba.

Question 7.
In which female reproductive organ does the embryo get embedded?
Answer.
The embryo gets embedded in the wall of the uterus (of the female) for further development.

Question 8
What is metamorphosis? Give examples.
Answer.
The drastic change that transforms a larva into an adult is called metamorphosis. Frog, SilkWorm, Honeybee, are some animals in which metamorphosis occurs.

Question 9.
Differentiate between internal fertilisation and external fertilisation.
Answer.

Question 10.
Across
1. The process of the fusion of the gametes.
6. The type of fertilisation in the hen.
7. The term used for bulges observed on the sides of the body of Hydra.
8. Eggs are produced here.
Down
2. Sperms are produced in these male reproductive organs.
3. Another term for in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions.

NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions

NCERT TEXTBOOK EXERCISES

Question 1.
Indicate whether the following statements are True (T) or False (F):
(a) Unicellular organisms have a one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has an irregular shape. (T/F)
Answer.
(a) True
(b) True
(c) False
(d) True.

Question 2.
Make a sketch of the human nerve cell. What function do nerve cells
perform?
Answer.

The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

Question 3.
Write short notes on the following:

1. Cytoplasm
2. Nucleus of a cell.

Answer.

1. It is the jelly-like substance found between the nucleus and the cell membrane. It contains the nucleus and many small structures called organelles. Cytoplasm, along with nucleoplasm, forms the living substance of the cell, called the protoplasm.
2. It is an important component of the living cell. It is generally spherical and located in the center of the cell. The Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. The liquid substance of the nucleus is termed nucleoplasm. There is a smaller spherical body in the nucleus which is called the nucleolus. The Nucleus also contains thread-like structures called chromosomes. These carry genes and help in inheritance. The Nucleus acts as the control center of the activities of the cell.

With a microscope of higher magnification, we can see a smaller spherical, dense body in the nucleus. It is called the nucleolus. In addition, the nucleus contains thread-like structures called chromosomes. These carry genes and help in the inheritance or transfer of characters from the parents to the next generation. The chromosomes can be seen only when the cell divides. The nucleus, in addition to its role in inheritance, acts as the control centre of the activities of the cell.

Question 4.
Which part of the cell contains organelles?
Answer.
The Cytoplasm contains organelles of the cell.

Question 5.
Make sketches of animal and plant cells. State three differences between them.
Answer.

Question 6.
State the difference between eukaryotes and prokaryotes.
Answer.

Question 7.
Where are chromosomes found in a cell? State their functions.
Answer.
Chromosomes are found in the nucleus of the cell. They carry genes and help in inheritance i.e., transfer of characters from the parents to the offspring.

Question 8.
‘Cells are the basic structural units of living organisms. Explain.
Answer.
All organisms are made up of cells. They have different designs, shapes and sizes in the living organism. All the life processes take place inside a cell. Many similar cells aggregate together to make tissue. So many tissues are organised to form organs and finally, many organs are organised to form a system. So we can say that cells are the basic units of living organisms.

Question 9.
Explain why chloroplasts are found only in plant cells?
Answer.
Chloroplasts contain chlorophyll which synthesizes food in plants by the process of photosynthesis. As photosynthesis does not occur in animals, it does not contain chloroplasts.

Question 10.
Complete the crossword with the help of clues given below:
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down
1. Green plastids.
2. Formed by a collection of tissues.
4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals.

NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Fill in the blanks:

1. A place where animals are protected in their natural habitat is called………….
2. Species found only in a particular area is known as…………
3. Migratory birds fly to faraway places because of…………… changes.

Answer.

1. wildlife sanctuary
2. endemic species
3. climatic.

Question 2.
Differentiate between the following:

1. Wildlife sanctuary and biosphere reserve
2. Zoo and wildlife sanctuary
3. Endangered and extinct species
4. Flora and fauna

Answer.

1. Wildlife Sanctuary: The area that is reserved in a forest for the protection and preservation of wild animals. It also provides suitable living conditions.
   Biosphere Reserve: The area that is meant for the conservation of biodiversity. It also helps to maintain the culture of that area. One biosphere reserve may also contain other protected areas in it.
2. Zoo: A place where animals are protected in an artificial habitat.
   Wildlife Sanctuary: The area, that is reserved in a forest for the protection and preservation of wild animals.
3. Endangered Species: The animal species whose numbers are diminishing to a level that they might face extinction.
   Extinct Species: The animal species, whose numbers are nil (zero), because of changes in their habitat and other calamities.
4. Flora: The plants that are found in a particular area are called flora. For example, Sal, teak, jamun etc.
   Fauna: The animals that are found in a particular area are called fauna. For example, Chinkara, cheeta, leopard etc.

Question 3.
Discuss the effects of deforestation on the following:

1. Wild animals
2. Environment
3. Villages (Rural areas)
4. Cities (Urban areas)
5. Earth
6. The next generation

Answer.

1. They won’t get their natural habitat and surroundings, as well as food. So either they will extinct or reach the verge of extinction or they will migrate to another forest. In course of their migration, they might be killed by humans.
2. Climatic changes disturb the environment. Global warming is caused due to accumulation of carbon dioxide. Because of deforestation and an increase in the temperature on earth, the water cycle will get disturbed and the reduced rainfall will cause droughts.
3. Villagers cannot grow food (crops) because of no rain as drought situations will prevail. Many poor villagers may die for want of food. The villagers will move to towns and cities. On one hand, villages will be completely deserted and on the other hand, the towns and cities will be overcrowded.
4. Cities flooded with drought-affected villagers will disturb the environment. Food-grains will either not available or if available, they will be costlier. People will also not get wood for making furniture and buildings.
5. Deforestation is a major cause, which leads to change in soil properties. Gradually the land will get converted into a desert. On the other hand, the snow of the mountains will melt due to global warming, and many coastal cities will be flooded causing disaster.
6. The next generation will either be extinct or if at all it exists, it will suffer from diseases and face life scarcity of food in life. So, the next generation will be ill, weak, and, consequently, face extinction.

Question 4.
What will happen if:

1. we go on cutting trees.
2. the habitat of an animal is disturbed.
3. the top layer of soil is exposed.

Answer.

1. If we go on cutting trees, then:
   • The survival of mankind will become a threat, because of the low oxygen concentration in the atmosphere.
   • We have to face high temperatures and increased pollution levels.
   • Natural calamities will disrupt our life.
   • The water cycle will be disturbed.
2. If the habitat of an animal is disturbed, then:
   • The animals will lose their natural habitat and ultimately will be at the periphery to become endangered.
   • The survival of animal will be difficult, because of the drought and the rise in temperature.
3. If the top layer of soil is exposed, then:
   • The exposed top layer loses all its nutrients, especially the hummus.
   • It leads to a decrease in the water holding capacity of the soil.
   • The vegetation will go off from the field, and desertification will be the result.

Question 5.
Answer in brief.

1. Why should we conserve biodiversity?
2. Protected forests are also not completely safe for wild animals. Why?
3. Some tribals depend on the jungle. How?
4. What are the causes and consequences of deforestation?
5. What is Red Data Book?
6. What do you understand by the term migration?

Answer.

1. Biodiversity refers to the variety in life existing on Earth, their interrelationships, and their relationship with the environment, so we should conserve as the food chain should not get disturbed, otherwise the whole ecosystem will be affected.
2. Protected forests are also not completely safe for wild animals, because poaching or capturing of the animal takes place in these areas. Wild animals are killed by poachers.
3. Tribes, usually the residents of the jungle, are dependent on the jungle for the fulfillment of their daily needs of life.
4. The causes and consequences of deforestation are:
   • It increases the temperature and pollution level on earth.
   • It decreases the level of oxygen in the atmosphere and groundwater level is also lowered.
   • The rainfall and the fertility of the soil will decrease.
   • The chances of natural calamities are more because of deforestation.
   • It changes the soil properties.
   • It affects the top layer of the soil, which exposes the lower hard and rocky layers.
5. The Red Data Book is the only source as a book, which keeps a record of all the endangered animals and plants.
6. The term migration means the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for some specific purposes like breeding or to overcome unfavourable conditions.

Question 6.
In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.
Answer.
Of course, to meet the ever-increasing demand in factories and for shelter, trees are being continually cut, which is hot justified at all. If one tree is cut, at least five trees should be grown so that the reforestation process may remain continuous.

But, if trees are cut blindly and no trees are planted then the earth may face global warming, no rainfall, climatic change, soil erosion, and desertification, etc. So, cutting trees for any reason at all is not justified.

Question 7.
How can you contribute to the maintenance of the green wealth of your locality? Make a list of actions to be taken by you.
Answer.
For the contribution to maintain of green wealth in my locality, the different actions to be taken are:

1. not to allow anybody to cut any trees;
2. always try to plant saplings in the residing area;
3. never ever show the neglection to water the plants;
4. always trimming the plants from time to time for their better growth.

Question 8.
Explain how deforestation leads to reduced rainfall.
Answer.
Deforestation leads to the accumulation of CO₂ in the atmosphere which results in global warming as CO₂ traps the heat of the sunrays. The increase in temperature on earth will disturb the water cycle and reduce rainfall, causing drought in the region.

Question 9.
Find out about national parks in your state. Identify and show their location on the outline map of India.
Answer.
Do yourself.

Question 10.
Why should the paper be saved? Prepare a list of ways by which you can save paper.
Answer.
Manufacturing paper needs trees. By cutting trees, deforestation is caused which disturbs the balance in nature. If the paper is saved or recycled, many trees can be saved. Paper can be saved by recycling. Paper can be recycled.5-7 times and can be used. If everyone who uses paper, could save at least one sheet of paper in a day, we can save many trees in a year.

We should save and reuse the used paper and recycle it. By following these steps we can save not only the trees but also the energy and water needed for manufacturing paper.

Question 11.
Complete the word puzzle:
Down
1. Species on the verge of extinction.
2. A book carrying information about endangered species.
5. Consequence of deforestation.
Across
1. Species which have vanished.
3. Species found only in a particular habitat.
4. Variety of plants, animals, and microorganisms found in an area.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals, drop a comment below and we will get back to you at the earliest.