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KSEEB Solutions for Class 8 Science Chapter 15 Some Natural Phenomena Points To Remember

Some objects can be charged by rubbing with other objects. There are two kinds of charges positive charge and negative charge. Like charges repel and unlike charges attract each other. The electrical charges produced by rubbing are called static charges. When charges move, they constitute an electric current An electroscope may be used to detect whether a body is charged or not.

The process of transfer of charge from a charged object to the earth is called earthing. The process of an electric discharge between clouds and the earth or between different clouds causes lightning. A lightning strike could destroy life and property. Protective measures are of utmost importance during lightning strikes, Taking shelter in interiors(houses or other closed places) and vehicles(closed e.g. cars) are the most preferred measures.

Lightning conductors can protect buildings from the effects of lightning. A natural phenomenon that cannot be predicted is an earthquake, which is a sudden shaking or trembling of the earth which lasts for a very short time. The earth consists of three major layers, called the crust, the mantle, and the core. The core is further divided into the inner core and the outer core. The mantle consists of semi-solid material above which the crust floats.

The crust consists of oceans and continents. The crust is divided into several parts, called tectonic plates. The regions where one tectonic plate slides against another are referred to as fault zones, and these are the regions where an earthquake is likely to occur. Hence, these zones are referred to as seismic zones. The place in the interior of the earth where an earthquake occurs is the focus, and the region on the surface of the earth that is the closest to focus is likely to experience the largest damage. This region is called the epicenter of the earthquake.

The instrument that measures the severity of an earthquake is a seismograph. The energy released at the focus of an earthquake propagates outwardly in form of waves known as seismic waves. The destructive energy of an earthquake is measured on the Richter scale. It is a logarithmic scale, ranging from | to 10 for indicating the intensity of an earthquake.
An earthquake measuring 7 or more on the Richter scale can cause severe damage to life and property.

Protective measures for earthquakes:
1. If you are at home: Take shelter under a table and stay there till the shaking stops. Stay away from tall and heavy objects that may fall on you.
If you are in bed, do not get up. Protect your head with a pillow.
2. If you are outdoors: Find a clear spot, away from buildings, trees, and overhead power lines. Drop to the ground. If you are in a car or bus, do not come out. Ask the driver to drive slowly to a clear spot Do not come out till the tremors stop.

Class 8 Science KSEEB Some Natural Phenomena Notes 

Some Natural Phenomena NCERT Textbook Exercises

Question 1. Which of the following cannot be charged easily by friction?
1. A plastic scale
2. A copper rod
3. An inflated balloon
4. A woolen cloth
Answer: 2. A copper rod.

Question 2. When a glass rod is rubbed with a piece of silk cloth the rod
1. And the clothes both acquire a positive charge.
2. Becomes positively charged while the cloth has a negative charge.
3. And the cloth both acquire a negative charge.
4. Becomes negatively charged while the cloth has a positive charge.
Answer: 2. Becomes positively charged while the cloth has a negative charge.

Question 3. Write T against true and F against false in the following statements.
1. Like charges attract each other. (T/F)
2. A charged glass rod attracts a charged plastic straw. (T/F)
3. Lightning conductors cannot protect a building from lightning. (T/F)
4. Earthquakes can be predicted in advance. (T/F)
Answer: 1. F, 2.T, 3. F, 4. F

Question 4. Sometimes, a crackling sound is heard while taking off a sweater during winter. Explain?
Answer: The cracking sound is heard because when the sweater is mobbed while taking it off, it acquires a small charge

Question 5. Explain why a charged body loses its charge.
Answer: Our body is a conductor of electricity. When we touch a charged body with our hand, the charged body loses charge to the earth through our body.

Question 6. Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer: The destructive energy of an earthquake is measured on a scale called the Richter scale. An earthquake measured 3 on this scale will be recorded by a seismograph. Whoever, it s not likely to cause much damage

Question 7. Suggest three measures to protect ourselves
Answer:
1. Hearing thunder, we should rush to a safer place like a house or building. cloth has a negative charge.
2. If no proper shelter is available and in open, never hide under a tree of an electric pole.
3. The telephone cord’s electric wires and metal
4. Becomes negatively charged while the pipes should be avoided from touching. cloth has a positive charge.

Question 8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon.
Answer: A charged balloon is repelled by another charged balloon because both have the same charge and we know that like charges repel each other. But charged balloons attract an uncharged balloon and lose its own charge to the other balloon.

Question 9. Describe with the help of a diagram an instrument that can be used to detect a charged body.
Answer:
A device that is used to test whether an object is carrying charge or not is known as an electroscope It consists of a metal rod on which two leaves of aluminum foil are fixed to one end and a metal disc at the other end. The leaves are kept inside a conical flask and it is corked to isolate them from the atmospheric air. When a charged body comes in contact with the metal disc, the aluminum leaves move away from each other because some charges get transferred to aluminum leaves through the metal rod. This process is called charging by conduction. The charges on the leaves and the charged body are of the same in nature and thus the leaves of aluminum repel each other. If the body is not charged then they would attract each other.

Question 10. List three states in India where earthquakes are more likely to strike.
Answer: The states that fall in seismic zones are Jammu and Kashmir, Himachal Pradesh, and Gujarat.

KSEEB Class 8 Science Solutions For Some Natural Phenomena 

Question 11. Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?
Answer: The following precautions could be taken to protect ourselves ina earthquakes outside the home:
1. First find a clear spot, away from buildings, trees, and overhead wires.
2. If I am in a car or on a bus, I will not come out Instead I will tell the driver slowly to clear the spot and will not come out till the traitors stop.

Question 12. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer: No, I would not carry an umbrella, because the pointed rod of the umbrella can become a target of lightning.

Some Natural Phenomena Activities

Question 1. Take a used ballpen refill and rub it vigorously with a piece of polythene. Bring it close to small pieces of paper. Take care not to touch the rubbed end of the refill with your hand or with a metallic object. Repeat the activity with small pieces of dry leaf, husk and mustard seeds.
Answer: When we rub ballpen refill with polythene, it acquires a small electric charge. On bringing the charged ballpen refill close to small pieces of paper, the bits of paper are attracted to it. A charged plastic refill can attract bits of paper.

Question 2. Collect the objects and the materials listed Try to charge each by rubbing with the materials mentioned in the Table. Record your findings. You can add more items to the Table.
Answer:

Through this activity, it can be concluded that certain objects acquire charge on being rubbed with certain materials. An object possessing a charge will attract bits of paper.

Question 3.
1. Inflate two balloons. Hang them in such a way that they do not touch each other Rub both balloons with a woolen cloth and release them. What do you observe? Now let us repeat this activity with the used pen refills. Rub one refill with polythene. Place it carefully in a glass tumbler using the tumbler as a stand

Rub the other refill also with polythene. Bring it close to the charged refill. Be careful not to touch the charged end with your hand. Is there any effect on the refill in the tumbler? Do the two attract each other, or repel each other? In this activity, we have brought close together the charged objects that were made of the same material. What happens if two charged objects made of different materials are brought close to each other? Let’s find out.

2. Rub a refill and place it gently in a glass tumbler as before Bring an inflated charged balloon near the refill and observe.

Answer:
1. We observed that balloons repelled each other in the first case. Thus, like charges repel each other. In the second case, a charged refill repelled another charged refill due to the presence of like charges on them.
2. A charged balloon attracted a charged refill because the balloon had charges opposite to that on a refill. Thus, opposite charges attract each other.

Question 4. Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle. Pierce a hole in it so that a metal paper clip can be inserted. Open out the paper clip Cut two strips of aluminum foil about 4 cm x 1 cm each. Hang them on the paper clip Insert the paper clip into the cardboard lid so that it is perpendicular to it. Charge a refill and touch it with the end of the paper clip. Observe what happens. Is there any effect on the foil strips? Do they repel each other or attract each other? Now, touch other charged bodies with the end of the paper clip. Do foil strips behave in the same way in all cases? Can this apparatus be used to detect whether a body is charged or not? Can you explain why the foil strips repel each other?

Answer: We observed that aluminum foil strips received the same charge from the charged refill through the metal paper clip as it is a good conductor of electricity. The strips carrying similar charges repelled each other and they became wide open. Such a device that can be used to test the charge on an object is called an electroscope. When we touch the metal paper clip with other charged bodies, the foil strips behave in the same way in all cases. Thus, we find that electrical charges can be transferred from a charged object to another through a metal conductor.

Some Natural Phenomena Class 8 KSEEB Questions And Answers 

Question 5. Ask your parents about the huge damage to life and property caused by these earthquakes. Collect a few pictures showing the damage caused by these earthquakes from newspapers and magazines of those days. Prepare a short report on the suffering of the people during and after the earthquakes.

Answer: An earthquake is a sudden shaking or trembling of the earth which lasts for a short time. It is one of the most dreaded and devastating natural calamities. It causes a huge loss and destruction of our life and property. Some of the damaging effects of an earthquake are as follows It brings the destruction of buildings, dams, railway tracks, roads, etc.
1. There is an outbreak of fire due to the breaking of electrical power or gas lines.
2. It ruptures groundwater pipes disrupting the water supply system.
3. Landslides and tsunamis occur respectively in hilly and coastal areas.
4. There is a bursting of sewer pipes releasing sewage water.
5. Communication is completely cut off and the areas get 5 disconnected from the rest of the world.
6. An earthquake also causes floods.

Question 6. Take an outline map of the world. Locate the eastern coast and Andaman and Nicobar Islands in India. Mark other countries around the Indian Ocean which could have suffered damage. Collect accounts of the devastation caused by the tsunami in India from your parents, or other elders in the family or in the neighborhood.


Answer:
1. An outline map of the world locating the eastern coast and Andaman and the Nicobar Islands in India. Other countries around the Indian Ocean have been marked in the map given which could have suffered damage.
2. Accounts of the devastation caused by the tsunami in India—A major tsunami occurred in the Indian Ocean on 26th December 2004. At 8.38 a.m. quake of 6.1 magnitudes was felt in Andamans. At 9.00 a.m. as it nears the Chennai coast, the tsunami slowed down but rose higher. This affected India’s South-East coast, predominantly in the state of Tamil Nadu as well as the territories of Andaman and Nicobar Island. Thousands of people died, and the coastal area was devastated completely. Many fishing communities were ruined by the tsunami, most notably the fishing town of Nagapattinam. In fact, it was one of the most devastating natural calamities, people have ever witnessed.

Some Natural Phenomena Additional Questions

Question 1. What are the two natural calamities?
Answer: Lightning and Earthquake.

Question 2. Name the two types of charges.
Answer: Positive and Negative.

Question 3. Mention the interactions of two types of charges.
Answer: Like charges repel each other wMe unlike charges attract each other.

Question 4. Name the device used to protect buildings from lightning.
Answer: Lightning conductor.

Explanation Of Some Natural Phenomena In KSEEB Science 

Question 5. In which direction do the shock waves produced by an earthquake travel?
Answer: Both on the surface and inside the earth.

Question 6. Who discovered static electricity or lightning in clouds and when?
Answer: Benjamin Franklin in 1752.

Question 7. What actually causes lightning?
Answer: Lightning is caused by the accumulation of charges in the clouds.

Question 8. What are static &electricity?
Answer: The electrical charge reproduced by rubbing two objects is called static electricity.

Question 9. What are weak zones called?
Answer: Seismic or fault zones.

Question 10. What is the static charge? How does it differ from an electric current?
Answer: The electric charges generated by rubbing are called static charges. The static charges do not move while charges move in electric current.

Question 11. What is earthing? What is the application of earthing?
Answer: The process of transfer of charges from a charged object to the earth is called earthing. It is provided in buildings to protect from electrical shocks due to any leakage of electrical current.

Question 12. How does the electric discharge occur in clouds?
Answer: At the time of thunder negative charges are accumulated near the clouds and positive charges near the ground. When these charges meet, the electric discharge takes place between the ground and clouds. In this process, a large amount of energy is released.

Question 13. What are fault zones? Name the fault zones in India.
Answer: Since earthquakes are caused by the movement of plates, the boundaries of the plates are weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones.

Question 14. What are seismic waves? How are these waves recorded?
Answer: The tremors produce waves on the surface of the earth. These are called seismic waves. These waves are recorded by an instrument called the seismograph.

Question 15. What safety measures should be taken during lightning and thunderstorm?
Answer: The following safety measures are advisable to be adopted to protect from lightning and thunderstorm:
1. No open place is safe. A house or a building is a safe place. If traveling by car or by bus, it is safe to stay inside with the windows and doors of the vehicle shut.
2. If we are outside, the following things are important to be kept in mind
3. Open vehicles, like motorbikes, tractors, construction machinery, fields, tall trees, shelters in parks, and elevated places do not protect us from lightning strikes.
4. Carrying an umbrella is not at all a good idea during thunderstorms.
5. If no shelter is available and we are in an open field, we should keep away from all trees. We should stay away from poles or other metal objects. We should not be on the ground. Sitting in a pose is advisable.
6. If we are inside the house, we should take care as advised further:
7. Lightning can strike telephone cords, electrical wires, and metal pipes. During a thunderstorm, contact with r these should be avoided.
8. It is safer to use mobile phones and cordless phones, However, it is not wise to call up a person with a wired phone. Bathing should be avoided. Electrical appliances should be unplugged.

KSEEB Class 8 Science Chapter 15 Important Questions 

Some Natural Phenomena Multiple Choice Questions

Question 1. An electroscope is a device that is used to find if an object is
1. Charged
2. Magnetic
3. Free of cracks
4. Hot

Answer: 1. Charged
Explanation: An electroscope is a device that is used to find whether the object is charged or not. It consists of two metallic strips which are closely placed.

Question 2. Electric current is to be passed from one body to another. For this purpose, the two bodies must be joined by
1. Cotton thread
2. Plastic string
3. Copper wire
4. Plastic string

Answer: 3. Copper wire
Explanation: Copper is a good conductor of electricity. Plastic, rubber, and cotton are bad conductors of electricity.

Question 3.The movement of the earth’s plates causes
1. Cyclones
2. Lightning
3. Earthquakes
4. Thunderstorms

Answer: 3. Earthquakes
Explanation: When the earth’s plates brush past one another it leads to earthquakes. Earth can cause damage to buildings and dams.

Question 4. Two charged objects are brought close to each other. Choose the most appropriate statement from the following options:
1. They may attract
2. They may repel
3. They may attract or repel depending on the type of charges they carry
4. There will be no effect

Answer: 3. They may attract or repel depending on the type of charges they carry
Explanation: The charges are like charges they repel each other and if the charges are unlike charges they attract each other.

Question 5. Which of the following is not likely to cause Tsunami?
1. A major nuclear explosion undersea
2. Earthquake
3. Volcanic eruption
4. Lightning

Answer: 4. Lightning
Explanation: Tsunami is caused due to disturbances caused deep down the sea. Lightening will not cause any disturbance to the sea whereas earthquakes, major nuclear explosions undersea, and Volcanic eruptions can cause a disturbance in the sea.

Question 6. The earth’s plate responsible for causing earthquakes is
1. The crust of the earth
2. The mantle of the earth
3. The inner core of the earth
4. The outer core of the earth

Answer: 1. The crust of the earth
Explanation: Sudden trembling or shaking of the earth due to disturbance deep down its top layer called the crust.

Question 7. Consider the list of terms given below:
1. Seismic Zone
2. Fault Zone
3. Mantle
4. Inner Core
The boundaries of the earth’s plate are known as

Answer: 1. Seismic Zone,2. Fault Zone
Explanation: An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. Earthquakes are caused due to the movement of plates. Boundaries of the plates are weak zones where earthquakes are most likely to occur.

Question 8. The outermost layer of the earth is called
1. Mantle
2. Outer core
3. Crust
3. Inner core

Answer: 3. Crust
Explanation: Earth’s top layer is called the crust which is followed by the mantle, outer core, and inner core.

Question 9. Major earthquakes are less likely to occur in
1. North East India
2. Rajasthan
3. Rann of Kutch
4. Orissa

Answer: 4. Orissa
Explanation: Major earthquakes are less likely to occur in Orissa. The most threatened areas in India are Kashmir, the Western and Central Himalayas, the whole of North-East, Rann of Kutch, Rajasthan, and the Indo-Gangetic Plain.

Question 10. Consider the list of terms given below
1. Tsunami
2. Landslide
3. Floods
4. Lightning

Earthquakes can cause
Answer:
1. Tsunami
2. Landslide
3. Floods

Detailed Notes On Some Natural Phenomena KSEEB 

Some Natural Phenomena Very Short Answer Type Questions

Question 1. State whether the following are True or False.
1. Earthquakes occur all the time all over the world.
2. The plates of the outermost layer of the earth are always in continuous motion.
3. Tremors on the earth can also be caused by the eruption of a volcano.
4. The process of electric discharge cannot occur between clouds and the earth.
5. Bathing outdoors should be avoided during a thunderstorm.

Answer:
1. True
2. True
3. True
4. False- The process of electric discharge occurs between clouds and the earth.
5. True

Question 2. Is it possible to predict the occurrence of an earthquake?
Answer: No, it is not possible to predict the occurrence of an earthquake.

Question 3. If a charged plastic straw is brought near another uncharged plastic straw, what will happen?
Answer: Plastic straws will attract each other

Question 4. Plastic straws A and B are rubbed with a dry cotton cloth. What will happen if they are brought near each other?
Answer: They will repel each other.

Question 5. During the construction of a building, the lightning conductor was left hanging in the air by mistake. Would the lightning conductor be still effective? Explain.
Answer: It will not be effective because the charge will not pass through to the earth as the lightning conductor was not connected properly to the earth.

Question 6. If air and cloud were good conductors of electricity, do you think lightning could occur? Explain.
Answer: No, lightning will not occur because the separation of charges cannot take place in conductors. Hence charges will not accumulate on clouds and lightning cannot take place.

Question 7. Identify the lightning conductor and the copper plate


Answer: A is the lightning conductor and B is the copper plate.

Question 8. If the materials used for constructing a building were good conductors, do you think lightning will strike the building? Will the lightning conductor be still required to be installed in the building?
Answer: No installing conductor is not required if the materials used for constructing a building were good conductors.

Question 9. You might have observed on a dry day that when you touch the screen of a television or computer monitor (with a picture tube), you get a slight shock. Why does it happen?
Answer: The electric charge gets accumulated on the screen. On touching the screen the charge discharges through our body. Thus, we get a slight shock.

Question 10. Explain how does lightning conductor protect a building from getting struck by lightning.
Answer: Lightning conductor conducts the charge to the earth hence charge will not accumulate on the build. This protects the building from getting struck by lightning.

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions for Class 8 Science Chapter 13 Reaching The Age of Adolescence Points To Remember

Humans become capable of reproduction after puberty sets in. Between the ages of 11 years and 19 years, children are called adolescents.
Puberty: It is the time when sex organs begin to work. The onset of puberty starts much earlier in girls, between 8 and 13 years of age, whereas it starts between 10 and 14 years of age in boys and lasts up to 2 to 4 years
Changes during Puberty:
1. Increase in Height: The bones of the eggs and arms elongate and the individual becomes tall and lanky.
2. Changes in Body Shape: In boys, the body becomes more muscular, and the shoulder becomes wider. In girls, the body shows curves in certain parts, and the region below the waist becomes wider and broader
3. Change in Voice: In boys, the voice becomes hoarse and heavy due to the extra growth of the larynx (voice box). In girls, the voice becomes high-pitched and shriller
4. Sweat and sebaceous glands: They become more active and secrete more sweat and oil. Pimples or acne appear due to the increased action of sebaceous glands or oil glands.
5. Emotional aspects develop.
6. Mental and intellectual development is at its peak.
7. The sex organs grow and become functionally active. The testis starts producing male gametes, called sperms. The ovaries grow and release one mature ovum in a periodic cycle of 28 days.
The onset of puberty and the maturity of reproductive parts are controlled by hormones.
Hormones are secretions of endocrine glands which pour them directly into the bloodstream.
The pituitary gland secretes hormones which include growth hormones and hormones that make other glands such as the testes, ovaries, thyroids, and adrenal, secret hormones. The pancreas secretesnsuinm, and the thyroid produces adrenalin.
Testosterone is the male hormone and estrogen, is the female hormone. The uterine wall in females The uterine wall in females prepares itself to receive the developing fertilised egg.
In case there is no fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood. This is called menstruation.
SpermandOvum fuses together to form a zygote. Sex chromosomes in sperm determine the baby’s gender.
Humans have 23 pairs of chromosomes in each cell pair of chromosome forms the sex chromosomes.
Males carry XY and females carry XX chromosomes. If a sperm carrying X fertilises the ovum with X chromosome, then the resulting baby is a girl.
If a sperm carrying a Y chromosome fertilises the ovum with X chromosome, then the resulting baby is a boy. Hence, males are responsible for the gender of newly formed babies.

Reproductive Health:
1. It is important to eat balanced food and maintain personal hygiene during adolescence. Cleaning of private parts is important to prevent possible infections.
2. The activity of sweat glands increases in puberty and releases bad odor from the body frequent bathing is necessary.
3. Physical exercise keeps the body fit and healthy as it releases a lot of sweat.
4. Peer pressure is best addressed by selfconfidence and a healthy lifestyle.

Class 8 Science KSEEB Reaching The Age Of Adolescence Notes 

Reaching The Age of Adolescence NCERT Textbook Exercises

Question 1. What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer: The term used for the secretion 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: The cyclic flow of blood and mucus along with the inner lining of the uterus in case of no fertilisation of the egg from the female body is called menstruation. Each month uterus prepares itself to receive the fertilized egg. If fertilisation does not occur the immer Imaging breaks away and comes out through the vagina for 3-5 days.

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 growth at various places of the body. Breasts develop in girls and facial hairs appear in boys.
3. Voice of the boys becomes hoarse as the voice box enlarges during adolescence.

Question 5. Prepare a table having two columns depicting the 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: Testes and ovaries secrete sex hormones. This is secreted by endocrine glands, These hormones are responsible for the male and female secondary sexual characteristics. That is why these hormones are called sex- hormones. Further, the sex-hormone are under the control of hormones from pituitary glands.

Question 7. Choose the correct option.

Adolescents should be careful about what they eat, because
1. Proper diet develops their brains.
2. Proper diet is needed for the rapid growth taking place in their body.
3. Adolescents feel hungry all the time.
4. Taste buds are well-developed in teenagers.

Reproductive age in women starts when their
1. Menstruation start.
2. Breast start developing
3. Body weight increases
4. Height increases.

The right meal for adolescents consists of
1. Chips, noodles, coke.
2. Chapatti. dal vegetables.
3. Rice, noodles, and burger.
4. Vegetable cutlets, chips, and lemon drink.

Answer:
Adolescents should be careful about what they eat: 2. Proper diet is needed for the rapid growth taking place in their bodies.
Reproductive age in women starts when their: 1. Mensuration starts.
The right meal for adolescents consists of 2. Chapatti, dal, and vegetables.

KSEEB Class 8 Science Solutions for Reaching The Age Of Adolescence 

Question 8. Write notes on
1. Adam’s apple.
2. Secondary sexual characters.
3. Sex determination in the unborn babies.

Answer:
1. Adam’s apple: 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 the Adam’s apple.
2. Secondary sexual characters: Those changes that take place at puberty in boys and girls are called secondary sexual characters. It includes an increase in the size of breasts in girls and pubic hairs around genital organs in girls. In boys, facial hair and cracking of voice are secondary sexual
features.
3. Sex determination in the unborn baby: Human beings have 23 pairs of chromosomes. One pair of male (XY) and one pair of chromosomes in female (XX) are called sex chromosomes. When the sperm containing the Y chromosome fuse with the egg the sex of the baby is male and when the X chromosome containing the sperm fertilize the egg the sex of the baby is female.

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 thyroxin
3. Another term for teenage
5. Hormone reaches here through the bloodstream
6. Voicebox
7. Term for changes in adolescence

Answer:
ACROSS                                 DOWN
3. ADAMS APPLE               1. TESTOSTERONE
4. ENDOCRINE                   2.THYROID
7. PITUITARY                      3. ADOLESCENCE
8. HORMONE                    5. TARGET SITE
9. INSULIN                         6. LARYNX
10. ESTROGEN                   7.PUBERTY

Question 10. The table below shows the data on the likely height of boys and girls as they grow in age. Draw graphs showing the height and age of both boys and girls on the same graph paper. What conclusions can be drawn from these

Answer:

Reaching The Age of Adolescence Activities

Question 1. Collect information from magazines or from doctors and prepare a note on the importance of consuming iodized salt. You can also look for this information on the internet.
Answer: Iodine is necessary for the thyroid gland to produce thyroxine hormone. It regulates the metabolism of carbohydrates, fats, and proteins, so as to produce the best balance for growth. A deficiency of iodine in our diet leads to a reduction in the formation of thyroxine hormone causing goiter disease.

Question 2. Get ideas from the pictures given Prepare charts or posters and paste them into the class so that you are aware of the diet for adolescents. You may use your creative ideas and present them as an advertisement. You may even organise a competition on this topic.
   

Answer: You have already studied about food and its components and you are aware of the importance of various ingredients of food like vitamins, proteins, carbohydrates, fats, minerals, water, etc. So you can do this activity yourself.

Reaching The Age Of Adolescence Class 8 KSEEB Questions And Answers 

Question 3. Collect data on the number of children in your class who exercise regularly and who do not exercise regularly. Did you notice any difference in their fitness and health? Prepare a report on the benefits of regular exercise.
Answer:
Doing exercises daily keeps one fit and healthy. It is a popular saying that a sound mind resides in a sound body, i.e., if you are healthy or physically fit, you are mentally sound also.
You can collect data on the number of children in your class who exercise regularly and who do not. You will notice the difference clearly in their fitness and health. Also, prepare a note on the benefits of regular exercise.

Reaching The Age of Adolescence Additional Questions

Question 1. What is Adam’s apple?
Answer: The protruding part of the throat in males is called Adam’s apple.

Question 2. Name the hormone in females that is produced by ovaries and helps in the development of mammary glands.
Answer: Estrogen

Question 3. Whose height grows faster initially – boys or girls?
Answer: Girls

Question 4. Name a gland that transports secretions through ducts.
Answer: Sweat glands/salivary glands/oil glands (anyone).

Question 5. What are hormones?
Answer: The chemical substances produced by endocrine glands are called hormones.

Question 6. What is menarche?
Answer: The first menstrual flow begins at puberty and is termed menarche.

Question 7. Name the chromosome present in a female.
Answer: Chromosome

Question 8. What is a vital change which marks puberty in boys and girls?
Answer: During puberty, the human body undergoes several changes, but the most important change which marks puberty is that boys and girls become capable of reproduction.

Question 9. Why do boys have a hoarse voice at puberty?
Answer: The voice box or larynx begins to grow at the onset of puberty. This growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. This leads to the voice becoming hoarse.

Question 10. Why are endocrine glands also called ductless glands?
Answer: Endocrine glands release hormones directly into the bloodstream. So, they are termed ductless glands. For example, pituitary, and thyroid) pancreas, etc.

Question 11. What are secondary sexual characters?
Answer: At puberty, in girls, breasts begin to develop, the region below the waist becomes wider, the voice becomes shriller. Boys begin to grow facial hair, i.e., mustache and beard. Boys also develop hair on their chest, the muscles of the body grow more prominently, and develop a larger voice box which can be seen as a protruding part of the throat called Adam’s apple. In both boys and girls, hair grows under the arms and in the pubic region. As these features distinguish the male from the female they are called secondary sexual characters.

Question 12. What are sex hormones? How do they work in the human body?
Answer:
1. Sex hormones help boys and girls develop sex organs to enable them for reproducing. These hormones lead them to reproductive maturity.
2. In girls, estrogen makes the breasts develop. Milk-secreting glands or mammary glands develop inside the breasts. Ovaries begin to produce eggs.
3. In boys, testosterone is released by the testes. Testes begin to release sperms. Changes in boys are also seen due to this hormone.

Question 13. Explain the terms menarche and menopause.
Answer: The first menstrual flow begins at puberty and is termed as menarche. At 45 to 50 years of age, the menstrual cycle stops. Stoppage of menstruation is called menopause.

Question 14. What do you mean by reproductive health?
Answer: The physical and mental well-being of an individual is regarded as an individual’s health.
1. To keep the body healthy, every human being, at any age,needs to have a balanced diet.
2. The person must also observe personal hygiene and undertake adequate physical exercise.
3. Thus, reproductive health refers to the diseases, disorders, and conditions that affect the functioning of the male and female reproductive system during all stages of life.

Explanation Of Reaching The Age Of Adolescence In KSEEB Science

Question 15. What is the role of hormones in completing the life history of insects and frogs?
Answer:
1. Hormones play an important role in the completion of the life cycle of insects and frogs.
2. Metamorphosis in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by thyroid gland.
3. Thyroxine production requires the presence of iodine in water. In the water in which iodine is not, present, the tadpoles cannot become adults.

Reaching The Age of Adolescence Multiple Choice Questions

Question 1. The belief that the mother is completely responsible for the sex of the child is wrong because the child
1. Gets sex chromosomes only from the mother.
2. Develops in the body of the mother.
3. Gets one sex chromosome from the mother and the other from the father.
4. Gets sex chromosomes only from the father.

Answer: 3. Gets one sex chromosome from the mother and the other from the father.
Explanation: Mother has a pair of the X chromosome on their 23“ chromosome set and she always donates the X chromosome to the offspring. Father has an XY chromosome on the 23rd set. If the father donates the X chromosome, the child will be female. If Father donates the Y chromosome then the child will be male. Hence it is the father who is responsible for the sex of the child.

Question 2. AIDS can spread from an infected person to another person through:
1. Sharing food
2. Blood transfusion
3. Sharing comb
4. A mosquito bite

Answer: 2. Blood transfusion
Explanation: AIDS can be transmitted from an infected person by the following means:
1. Sharing needles and syringes
2. From infected mother to fetus.
3. By sexual means through the exchange of fluids.
4. From infected mother to a baby through breast milk.

Question 3. Given below are events that lead to pregnancy and development of the embryo.
1. Fertilization of the egg
2. Maturation of egg
3. Release of egg
4. Embedding of the embryo in the thickened uterine wall.

Answer:
2. Maturation of egg
3. Release of egg
1. Fertilization of egg
4. Embedding of the embryo in the thickened uterine wall.
Explanation: The sequence of events is as follows:
1. Maturation of egg after puberty.
2. Release of the egg cell.
3. Fertilization of the egg by sperm to form the zygote.
4. Repeated division of zygote to form an embryo.
5. Embryo gets embedded in the wall of the uterus for further development.

Question 4. For the metamorphosis of tadpoles which of the following elements must be available in the water?
1. Chlorine
2. Carbon
3. Sulphur
4. Iodine

Answer: 4. Iodine
Explanation: Metamorphosis is brought by a hormone called thyroxine. The thyroid gland needs Iodine to secrete Thyroxine. Hence Iodine should be present in water for the metamorphosis of tadpoles.

Question 5. The most conspicuous visible change that occurs in boys during puberty is:
1. Development in the voice box.
2. Increase in height.
3. Production of sperm.
4. Increased sweating.

Answer: 2. Increase in height.
Explanation: Most conspicuous change during puberty is the sudden increase in height. At this time the long bones, that is, the bones of the arms and the legs elongate and make a person tall.

KSEEB Class 8 Science Chapter 13 Important Questions 

Question 6. Structures present in a cell which is responsible for determination of the sex of a baby is
1. Cytoplasm
2. Cell membrane
3. Nucleus
4. Chromosome

Answer: 4. Chromosome
Explanation: 23″ set of the chromosome which is called a sex chromosome determines the sex of the child. If the 23″ set of the chromosomes is XX baby will be female and if the sex chromosome is XY then the baby will be a boy.

Question 7. Unscramble the underlined words in the following sentences.
1. Reproductive life of a woman lasts from hacreemn to spauoemen.
2. The development of a caterpillar into an adult butterfly is termed as poommertaish.
3. The overgrowth of sumsele in xalnyr leads to the hoarse voice in adolescent boys.
4. Dannalier helps the body to adjust and fight stress.

Answer:
1. Menarche, Menopause
2. Metamorphosis
3. Muscles, larynx
4. Adrenalin

Question 8. Complete the following sentences.
1. In females, the uterine wall thickens to receive the________.
2. Endocrine glands release hormones directly into _______ for transportation to the______.
3. The sex hormones, and estrogen are responsible for the development of _______ characters.
4. Release of sex hormones is under the control of a hormone secreted from the______.

Answer:
1. In females, the uterine wall thickens to receive the fertilized egg.
2. Endocrine glands release hormones directly into the bloodstream for transportation to the target site.
3. The sex hormones, Testosterone, estrogen, and estrogen are responsible for the development of secondary sexual characteristics.
4. Release of sex hormones is under the control of a hormone secreted from the pituitary gland.

Question 9. Give a suitable word for each of the following statements.
1. The site which response to a hormone.
2. Name of a gland which transports secretions through ducts.
3. Chemicals which control changes at the adolescence stage.
4. It marks the beginning of the reproductive period.

Answer:
1. Target site
2. Sweat glands/salivary glands/oil glands (anyone)
3. Hormones
4. Puberty

Question 10. Name the hormone that is released by testes at the onset of puberty.
Answer: Testosterone is the hormone that is released by testes at the onset of puberty

Question 11. Name the female hormone produced by ovaries that helps in the development of mammary glands
Answer: Estrogen is the female hormone produced by ovaries that helps in the development of mammary glands.

Question 12. Match the hormones given in Column A with their deficiency disease given in 
Column A                             Column B
Thyroxine                           1. Salt imbalance
Growth hormone               2. Diabetes
Insulin                                 3. Goiter
Adrenal hormone              4. Dwarfism
Answer:
Column A                         Column B
Thyroxine                        1. Salt imbalance
Growth hormone            4. Dwarfism
Insulin                             2. Diabetes
Adrenal hormone           1. Salt imbalance

Question 13. Lila always eats only dal and rice at every meal. She often falls ill and has become prone to diseases. Can you suggest changes in her diet that can make her healthy and free from disease?
Answer: Food Lila takes every day consists of only carbohydrates and proteins. To be free from disease Lila should eat food with vitamins and minerals. She should include more vegetables and fruits in her daily diet.

Question 14. Mention any two features each that are seen in boys and girls each to distinguish them from each other at puberty.
Answer: Two features seen in boys at puberty are:
1. Growth of facial hairs
2. The voice becomes hoarse.
Two features seen in girls at puberty are:
1. Breast development.
2. The region below the waist becomes wider.

Detailed Notes On Reaching the Age Of Adolescence KSEEB

Question 15. We should avoid taking medicines/drugs unless prescribed by a doctor. Give reasons.
Answer: We should not take medicines/drugs unless prescribed by a doctor because some medicines have various side effects which may also lead to adverse effects or can get addicted to drugs, which ruin our health and happiness.

Question 16. A few of Paheli’s classmates eat potato chips and burgers regularly during recess at school. Are they healthy eating habits? Give reasons.
Answer: No. Potato chips and burgers are not healthy as it contains very little nutritional value in them and is not good foods to eat regularly.
Flow Chart

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions For Class 8 Science Chapter 12 Reproduction In Animals Points To Remember

Reproduction: This is a process in which organisms produce young ones of their own kind.

There are two modes by which animals reproduce. These are;
1. Sexual reproduction, and
2. Asexual reproduction

Sexual Reproduction

Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.

The reproductive organs in the female include ovaries, oviducts, and uterus.

The reproductive organs in males include the testes, sperm ducts, and penis.

The ovary produces female gametes called ova and the testes produce male gametes called sperms.

The fusion of the ovum and sperm is called fertilisation. The fertilized egg is called a zygote.

Fertilization that takes place inside the female body is called internal fertilization. This is observed in human beings and other animals such as hens, cows, and dogs.

Fertilization that takes place outside the female body is called external fertilization. This is observed in frogs, fish, starfish, etc.

The zygote divides repeatedly to give rise to an embryo.

The embryo gets embedded in the wall of the uterus for further development

The stage of the embryo in which all the body parts are identifiable is called the fetus.

Animals such as human beings, cows, and dogs that give birth to young ones are called viviparous animals.

Oviparous Animals: Animals that lay eggs are called oviparous animals, for example, frogs, lizards, butterflies, etc.

The transformation of the larva into an adult through drastic changes is called metamorphosis.

Asexual Reproduction

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

In hydra, new individuals develop from buds. This method of asexual reproduction is called budding.

Amoeba reproduces by dividing themselves into two. This type of asexual reproduction is called binary fission.

Class 8 Science KSEEB Reproduction In Animals Notes 

Reproduction In Animals NCERT Textbook Exercises

Question 1. Explain the importance of reproduction in organisms.
Answer: The production of new individuals from the parents is known as reproduction. Reproduction is very important as it ensures the continuation of similar kinds of individuals, generation after generation. If this process does not exist, the generation of living beings will vanish from the earth.

Question 2. Describe the process of fertilisation in human beings.
Answer:

In human beings, sexual reproduction occurs in which reproduction results from the fusion of male and female gametes.

Males produce sperm intestines and females produce ovum in the ovary.

Malerelease their sperms in the female reproductive organ during copulation called the vagina from where the sperms move towards the fallopian tube.

Females release one ovum every month in the middle of the menstruation cycle which travels toward the fallopian tube.

The fusion of male and female gametes takes place in the fallopian tube. The fusion of male and female gametes is called fertilisation.

Question 3. Choose the most appropriate answer.

Internal fertilisation occurs
1. In the female body.
2. Outside female body
3. In the male body
4. Outside male body

A tadpole develops into an adult frog through the process of
1. Fertilisation.
2. Metamorphosis
3. Embedding
4. Budding

The number of nuclei present in a zygote is
1. None
2. One
3. Two
4. Four

Answer:

Internal fertilisation occurs: 1. In the female body.

A tadpole develops into an adult frog by the process of 2. metamorphosis.

The number of nuclei present in a zygote is 2. One.

Question 4. Indicate whether the following statements are True or False

1. Oviparous animals give birth to young ones.
2. Each sperm is a single cell.
3. External fertilisation takes place in frogs.
4. The number of nuclei present in a zygote is
5. Egg laid after fertilisation is made up of a single cell.
6. Amoeba reproduces by budding.
7. Fertilisation 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: True/False

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

Question 5. Give two differences between a zygote and Foetus
Answer:

When fertilisation takes place, the nuclei of the sperm and the egg fuse to form a single nucleus, which results in the formation of a fertilized egg or zygote.

The zygote now begins to develop into an embryo.

The embryo continues to develop in the uterus and produces body parts such as hands, legs, head, eyes, etc the stage of the embryo in which all the body parts are identified is called a fetus.

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.

Asexual reproduction takes place in very small animals like Hydra and microscopic organisms like Amoeba.

Budding: New individual develops as outgrowths from a single parent. In hydra small bulges called buds develops into new individuals.

Binary fission: The body of unicellular organisms like amoeba divides into two equal parts and each part develops as a new individual.

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

KSEEB Class 8 Science Solutions For Reproduction In Animals 

Question 8. What is metamorphosis? Give examples.
Answer: The drastic change which takes place during the development of an animal is called metamorphosis The animals that undergo metamorphosis are
1. Silkworm (egg -> caterpillar-> pupa ->adult)
2. Frog (egg —> tadpole —> adult)

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

Internal fertilisation
1. fertilisation takes place inside the female body.
2. Example: human beings, hens, dogs,s, etc.

External fertilisation
1. The fertlilsatlon takes place outside the body of the female.
2. Example: frog, fish, etc.

Question 10. Complete the crossword puzzle using the hints given below.
Across
1. The process of the fusion of the gametes.
6. The type of fertilisation in the hen.
7. 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 the fertilized egg.
4. These animals lay eggs
5. A type of fission in Amoeba

Reproduction In Animals  Additional Questions

Question 1. What is a fertilised egg called?
Answer: Zygote

Question 2. Which mode of reproduction does take place in human beings?
Answer: Sexual reproduction

Question 3. Name two animals in which asexual reproduction takes place.
Answer: Hydra and yeast

Question 4. What is male gamete or sperm?
Answer: The reproductive cell produced by male reproductive organs is called the male gamete or sperm.

Question 5. What is a female gamete or ova?
Answer: The reproductive cell produced by female reproductive organs is called the female gamete or ova.

Question 6. Which organ produces eggs or the ovum?
Answer: A pair of ovaries.

Question 7. Which male reproductive organ produces sperm?
Answer: A pair of testes.

Question 8. In which organ fertillsation take place in female?
Answer: Fallopian tube

Question 9. What are the two methods of asexual reproduction?
Answer:

• Budding
• Binary fission

Question 10. Name two animals which undergo external fertilisation.
Answer: Frog and fish

Question 11. Name two animals which undergo internal fertilisation.
Answer: Human being and cow

Question 12. Which type of reproduction takes place in Amoeba?
Answer: Asexual reproduction through binary fission

Question 13. What type of reproduction is cloning?
Answer: Asexual reproduction

Question 14. What is a fetus?
Answer: Foetus is a well-developed embryo.

Question 15. How is an embryo developed?
Answer: Fertilisation results in the formation of a zygote. The zygote divides repeatedly to give rise to a ball of cells which then begin to form groups that develop into different tissues and organs of the body. This developing structure is called an embryo, It gets embedded in the wall of the uterus for further development.

Reproduction In Animals Class 8 KSEEB Questions And Answers 

Question 16. What is cloning? Explain how the first cloned mammal was born.
Answer: Cloning is the production of an exact or a true copy of a cell, any other living part, or a complete organism by asexual reproduction, Cloning of an animal was successfully performed for the first time by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland. They cloned the sheep named Dolly on July 5, 1996.

In the process of cloning Dolly, a cell was collected from the mammary gland of a female Finn Dorsett sheep. Meanwhile, an egg was obtained from a Scottish blackface ewe.

The nucleus was removed from the egg. Then the nucleus of the mammary gland cell from the Finn Dorsett sheep was inserted egg of the Scottish blackface ewe whose nucleus had been removed.

This egg was implanted into the Scottish blackface ewe. The egg developed normally and finally, Dolly was born.

The cloning of Dolly was a successful attempt. However, many clones often die soon after birth.

Sometimes cloning also leads to certain abnormalities among clones.

Unfortunately, Dolly died on 14th February 2003 due to a certain lung disease.

Question 17. What is budding? Explain.
Answer:

Budding is a type of asexual reproduction in which an organism or new individual develops from an outgrowth of a single parent. This outgrowth is called a bud.

On maturation, this bud gets separated from the parent’s body to grow into a new individual.

This process of reproduction is known as budding. For example, Hydra, yeast, and sponges produce their young ones through the process of budding.

In some organisms, like sponges, buds are not separated from their parent’s body and form a colony.

They remain attached to their parent’s bodies.

Question 18. Why do only male gametes have a tail?
Answer: Male gametes have to reach non-motile female gamete in the oviduct from the vagina. So they have a tail to reach the egg cell.

Reproduction In Animals Multiple Choice Questions

Question 19. Sets of reproductive terms are given below. Choose the set that has an incorrect combination.
1. Sperm, testis, sperm duct, penis
2. Menstruation, egg, oviduct, uterus
3. Sperm, oviduct, egg, uterus
4. Ovulation, egg, oviduct, uterus
Answer: 3. Sperm, oviduct, egg, uterus
Explanation: Sperm is the male gamete, the egg is the female gamete, oviduct, and uterus are part of the female reproductive system. Hence option 3. is an incorrect combination.

Question 20. In humans, the development of the fertilised egg takes place in the
1. Ovary
2. Testis
3. Oviduct
4. Uterus

Answer: 4. Uterus
Explanation: The development of the fertilised egg takes place in the uterus. Embryo gets embedded in the wall of the uterus for development by implantation.

Question 21. In the list of animals given below, the hen is the odd one out. a human being, cow, dog, and hen The reason for this is
1. It undergoes internal fertilisation.
2. It is oviparous.
3. It is viviparous.
4. It undergoes external fertilisation.

Answer: 2. It is oviparous
Explanation: The hen is oviparous, it lays the egg and the young one gets hatched later. The rest of the animals provided are viviparous. They give birth to young ones after they are developed completely.

Question 22. Animals exhibiting external fertilisation produce a large number of gametes. Pick the appropriate reason from the following
1. The animals are small in size and want to produce more offsprings.
2. Food is available in plenty of water.
3. To ensure a better chance of fertilisation.
4. Water promotes the production of a large number of gametes.

Answer: 3. To ensure a better chance of fertilization
Explanation: Because they release gametes in water chances of getting washed away by water, wind and rain are more. Hence To ensure a better chance of fertilisation. A large number of gametes are produced by Animals exhibiting external fertilization.

Question 24. Reproduction by budding takes place in
1. Hydra
2. Amoeba
3. Paramecium
4. Bacteria

Answer: 1. Hydra
Explanation: Paramecium, Amoeba, and bacteria reproduce by binary fission. Hydra reproduces by budding where a bud detaches from the parent and grows into a complete organism.

Question 25. Which of the following statements about reproduction in humans is correct?
1. Fertilisation takes place externally.
2. Fertilisation takes place in the testes.
3. During fertilisation, the egg moves towards the sperm.
4. Fertilisation takes place in the human female.

Answer: 4. Fertilisation takes place in the human female.
Explanation: Male gametes are introduced into a female’s body through the vagina. Sperm reaches the uterus through the oviduct. At the uterus, the egg gets fertilized by sperm to form a zygote.

Question 26. In human beings, after fertilisation, the structure which gets embedded in the wall of the uterus is
1. Ovum
2. Embryo
3. Foetus
4. Zygote

Answer: 2. Embryo
Explanation: The egg fuses with sperm to form the zygote which will divide to form a clump of hundreds of cells that form the embryo. The process of moving down embryo from the oviduct into the uterus is called as implantation.

Explanation Of Reproduction In Animals In KSEEB Science 

Question 27. Aquatic animals in which fertilisation occurs in water are said to be:
1. Viviparous without fertilisation.
2. Oviparous with external fertilisation.
3. Viviparous with internal fertilisation.
4. Oviparous with internal fertilisation.

Answer: 2. Oviparous with external fertilisation.
Explanation: Aquatic animals lay eggs and release sperm into the water for fertilization to take place. Young one is formed outside the body hence it is called external fertilization.

Question 28. After fertilisation, the resulting cell which gives rise to a new individual is the
1. Embryo
2. Ovum
3. Foetus
4. Zygote
Answer: 4. Zygote
Explanation: The zygote is the beginning of the formation of a new individual. All multicellular organisms start their life from the single-celled zygote.

Question 29. In human beings, the correct sequence of events during reproduction is
1. Gamete formation, fertilisation, zygote, embryo
2. Embryo, zygote, fertilisation, gamete formation
3. Fertilisation, gamete formation, embryo, the zygote
4. Gamete formation, fertilisation, embryo, the zygote
Answer: 1. Gamete formation, fertilisation, zygote, embryo
Explanation: In humans, male gametes fuse with female gametes to fertilise in the female ovary. Fertilised sperm and egg form zygote which will divide repeatedly to form the embryo.

Question 30. Although 2 cells called gametes fuse, the product formed is a single cell called the zygote. Justify.
Answer: During fertilization, only the nucleus ofthe sperm gets implanted into the uterus to forma zygote. Then sperm degenerates. Hence fused cell is called gamete. Stages in the lifecycle of silkwormare given below. Write them in sequential order.

Question 31. Stages in the lifecycle of silkworms are given below. Write them in sequential order. pupa, silkworm, egg, silkmoth
Answer:
1. Egg.
2. Pupa.
3. Silkmoth.
4. Silkworm.

Question 32. What is the importance of reproduction?
Answer: Reproduction ensures the continuation of species from generation to generation.

Question 33. In markets, eggs of birds are available but never eggs of dogs. Why?
Answer: Because the dog is viviparous. It does not lay an egg. It gives birth to a new one.

Question 34. The eggs of frogs do not have shells for protection, yet they are safe in the water. How?
Answer: Jelly-like covering on the eggs gives protection Hence frog eggs are safe in the water.

Question 35. The term metamorphosis is not used while describing human development. Why?
Answer: Because body parts of humans will be present by birth. Whereas in metamorphosis parts of adults are different from the young ones.

Question 36. Mother gives birth to a baby but the baby has characteristics of both parents. How is this possible?
Answer: Though the mother gives birth to the baby fertilization involves the fusion of gametes from both parents. Hence character is obtained by both parents.

Question 37. How is reproduction in hydra different from that in amoeba?
Answer: Hydra reproduces by budding where a bud detaches from the parent which grows into a complete organism. Whereas amoeba reproduces by binary fission. The process of reproduction begins with the division of its nucleus into two. This is followed by the division of its body into two.

Question 38. State whether the following statements are True or False. If false, correct the statement:
1. External fertilisation can occur both in water and on land.
2. The eggs of fish are covered by hard shells for protection.
3. The human egg has a head, middle piece and tail.
4. In adult human females, a single mature egg is released into an oviduct every month.

Answer:
1. False: External fertilisation can occur only in water.
2. False: eggs of fish are covered by jelly-like substance for protection.
3. False: Human sperm has a head, middle piece and tail.
4. True

Question 39. Why do only male gametes have a tail?
Answer: Because sperm need to be motile to reach the non-motile egg in the ovary of the female.

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions for Class 8 Science Chapter 11 Cell Structure And Functions Points To Remember

Cell: The smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.

All organisms are made of smaller parts called organs.

Organs are made of still smaller parts. The small- est living part of an organism is a ‘cell’.

Cells were first observed in cork by Robert Hooke in 1665.

Cells exhibit a variety of shapes and sizes.

The number of cells also varies from organism to organism.

Some cells are big enough to be seen with the unaided eye. Hens egg is an example.

Some organisms are single-celled (unicellular), while others contain a large number of cells(multicellular).

The single cell of unicellular organisms performs all the basic functions performed by a variety of cells in multi-cellular organisms.

Size of cells:

The size may be as small as a millionth of a metre or may be as large as a few centimetres.

The size of the cells has no relation with the size of the body of the animal or plant. It is related to its function.

The cell has three main parts:

The cell membrane,

Cytoplasm which contains smaller components called organelles,

The nucleus.

Cell membrane:

The basic component of a cell The cytoplasm and nucleus are enclosed within the cell membrane.

There is an outer thick layer in the cells of plants called a cell wall.

Cytoplasm: The jelly-like substance present between the cell membrane and the nucleus. Various organelles present in the cytoplasm are:
1. Mitochondria
2. Plastids (present only in plant cells)
3. Endoplasmic reticulum (ER)
4. Ribosome
5. Lysosornes
6. vacuole
7. Golgi body
8. Centrosome (present only in animal cells).
Nucleus: The nucleus is separated from the cytoplasm by a nuclear membrane. It is generally spherical in the centre of the cell.
Nuclear membrane: The nucleus is separated from the cytoplasm by a membrane called the nuclear membrane.
Nucleolus: The nucleus contains a still smaller round body known as a nucleolus.
Chromosomes: The nucleus contains thread-like structures called chromosomes. These carry genes and help in the inheritance or transfer of character from the parents to the offspring

Cells without a well-organised nucleus, i.e. lacking a nuclear membrane, are called prokaryotic cells.

Cells with well-organised nuclei with nuclear membranes are called eukaryotic cells.

Plant cells differ from animal cells in having an additional layer around the cell membrane termed the cell wall.

Coloured bodies called plastids are found in plant cells only. Green plastids containing chlorophyll are called -chloroplasts.

Purcell has a big central vacuole unlike a number of small vacuoles in animal cells.

Class 8 Science KSEEB Cell Structure And Functions Ncert Textbook Exercises

Question 1. Indicate whether the following statement is true (T) or false (F ).
1. Unicellular organisms have a one-celled body. (T/F)
2. Muscle cells are branched. (T/F)
3. The basic living unit of an organism is an organ. (T/F)
4. Amoeba has an irregular shape. (T/F)
Answer: 1. T, 2. F, 3. F,4.T

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

The function of nerve cells: The function of the nerve cell is to receive and transfer messages, it helps 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. Cytoplasm: It is the jelly-like substance found between the nucleus and the cell membrane. It contains many cell organelles. Cytoplasm along with the nucleus forms the protoplasm.
2. Nucleus: It is a spherical structure located in the Centre of the cell. It is known as the brain of the cell as it controls the activities of cells. It is separated from the cytoplasm by a membrane called a nuclear membrane.

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

Question 5. Make sketches of animal and plant cells. State three differences between them.
Answer:
Animal cell
1. Cell wall is absent.
2. Plasttds are absent
3. Nucleus is in the middle of the cell.
Plant cell
1. Cell wall present
2. Plastids are present.
3. Nucleus is towards the periphery.

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

1. Eukaryotes have well-organised nuclei with nuclear membranes while prokaryotes do not have well-organized nuclei.
2. A prokaryotic cell is generally smaller in size than a eukaryotic cell.

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

Question 8. Cells are the basic structural units of living organisms Explain.
Answer: All living organisms are made of cells either unicellular or multicellular. The basic functions of life like respiration, assimilation and all major metabolic activities are carried inside the cell. So, the cell is known as the structural and functional unit of a living organism.

Question 9. Explain why chloroplasts are found only in plant cells.
Answer: Chloroplast contains chlorophyll which synthesizes food in plants by the process of photosynthesis. No photosynthesis occurs in animals. So, they do not contain chloroplast.

KSEEB Class 8 Science Solutions For Cell Structure And Functions 

Question 10. Complete the crossword with the help of the clues given below.
Answer:
Across
1. This is necessary for photosynthesis.
3. Term for components 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.

Cell Structure And Functions Additional Questions

Question 1. _____is the outermost layer of an animal cell.
Answer: Plasma membrane/Cell membrane

Question 2. What is the name given to the green plastids?
Answer: The green plastids are called chloroplasts.

Question 3. Name two organelles present in the plant cell but not in the animal cell.
Answer: Cell walls and chloroplast are found in a plant cell but not in an animal cell.

Question 4. Which cell is observable with the unaided eye?
Answer: Ostrich egg.

Question 5. The term cell was coined by _______
Answer: Robert Hooke.

Question 6. Which organism has the smallest cell?
Answer: Bacterium mycoplasma has the smallest cell.

Question 7. Give two examples of unicellular animals.
Answer: Amoeba, paramoecium.

Question 8. What is the jelly-like fluid inside the nucleus called?
Answer: The Jelly – fluid inside the nucleus is called nucleoplasm.

Question 9. Give another name for cell membranes.
Answer: Plasma membrane.

Question 10. Why are mitochondria known as the powerhouse of the cell”?
Answer: Mitochondria is known as the powerhouse of the cell because they perform the function of respiration and provide the cell with energy.

Question 11. Are the cells of an elephant larger than cells of a rat?
Answer: No, the size of the cell has no relation to the size of the body of the animal or plant.

Question 12. What is the difference between tissue and organ?
Answer: Groups of cells of the same type make up the different tissues of the organisms For example muscle tissue.

Several different types of tissues together form an organ, For example, a stomach.

Cell Structure And Functions Class 8 KSEEB Questions And Answers 

Question 13. Name the organelle known as suicide bags. Why is it called so?
Answer: Lysosomes are known as suicide bags. They contain enzymes which help in breaking down or destroying various materials.

Question 14. Give the functions of cell wall.
Answer:

It provides rigidity to the cell wall.

It provides protection against plant viruses and pathogens.

Question 15. Why are plant cells more rigid in shape than animal cells?
Answer: Plant cells are more rigid in shape than animal cells due to the presence of cell wall.

Question 16. Name the largest and the smallest cells in the living world.
Answer: Largest — Ostrich’s egg Smallest— PPLO
Pleuro Pneumonia Like Organisms).

Question 17. Tomatoes are red and leaves are green. Why?
Answer :

Tomatoes are red because of chromoplasts in their cells.

Leaves are green because of chloroplasts in their cells.

Question 18. What are the functions of the cell membrane?
Answer:

It protects the cell.

It provides shape to the cell.

It allows materials to enter and leave the cell through tiny holes.

Question 19. Give the functions of the following
1. Endoplasmic reticulum
2. Golgi complex
3. Ribosornes
Answer:
1. Endoplasmic reticulum is a network of membranes, that provides a large surface area for life functions to take place.
2. Golgi complex collects and distributes the substance made in the cell and it synthesises and secretes many materials.
3. Ribosomes are the site of protein synthesis.

Question 20. Name the different parts of the nucleus and give the function of each part.
Answer:
1. Nuclear membrane: It separates the nucleus from the cytoplasm. It allows the exchange of substances between the nucleoplasm and the cytoplasm.
2. Nucleoplasm: Chromosomes and nucleoli are present in the nucleoplasm.
3. Chromosomes: Play an important role in the inheritance of characters from one generation to another.

Cell Structure And Functions Multiple Choice Questions

Question 21. Choose the correct statement with respect to unicellular organisms:
1. In unicellular organisms, tissues work in coordination to perform different functions.
2. Unicellular organisms do not require food.
3. Unicellular organisms respire and reproduce.
4. All unicellular organisms move by cilia.
Answer: 3. Unicellular organisms respire and reproduce.
Explanation: Unicellular are single-celled organisms where a single cell performs basic functions such as respiration, digestion and reproduction.

Option 1. This is wrong because tissues are a group of cells in unicellular there will be only one cell.

Option 2. This is wrong because organisms require food for their survival like any other organisms. Different unicellular uses different organisms for locomotion Example: Cilia, Pseudopodia.

Question 22. The majority of cells cannot be seen directly with our naked eyes because:
1. Organisms are generally unicellular
2. Cells are microscopic
3. Cells are present only inside the body
4. Cells are grouped into tissues

Answer: 2. Cells are microscopic
Explanation: Cells are basic units of life whose size is very small to be seen by our naked eye. Cell varies from nanometer to micrometre which requires a microscope to visualize. Hence they are called microscopic structures.

Question 23. Read the different combinations of terms given below:
1. Cell wall, cell membrane, nucleus, plastid
2. Cell wall, nucleus, ribosome, chromosome
3. The cell membrane, mitochondria, ribosome, chromosome
4. The cell membrane, ribosome, mitochondria, and chloroplast.
The correct combination of terms with reference to an animal cell is _____

Answer: 3. Cell membrane, mitochondria, ribosome, chromosome
Explanation: Options 1. and 2. are wrong because they have a cell wall which is present only in plant cells. Option 4. is wrong because it has chloroplast which is absent in animal cells. Hence the answer is 3.

Question 24. Which one of the following terms is not a part of the nucleus?
1. Ribosome
2. Nucleolus
3. Chromosome
4. Gene

Answer: 1. Ribosome
Explanation: Ribosomes are the organelles that float in the cytoplasm. Chromosomes are the structures present in the nucleus which are composed of genes. The nucleolus is a part of the nucleus which helps in protein synthesis.

Question 25. A suitable term for the various components of cells is
1. Tissue
2. Cell organelles
3. Chromosomes
4. Genes

Answer: 2. Cell organelles
Explanation: The tissue is a group of cells which work together to perform a certain function.

Chromosomes are thread-like structures present in the nucleus which constitutes all the genes.

Gene is a unit of inheritance in living organisms. It controls the transfer of hereditary characteristics from parents to offspring. Genes are made of DNA.

Question 26. The jelly-like fluid substance present in cells is called
1. Protoplasm
2. Chromosome
3. Chloroplast
4. Cytoplasm

Answer: 4. Cytoplasm
Explanation: It is the jelly-like substance present between the cell membrane and the nucleus. Various other components, or organelles, of cells are present in the cytoplasm. These are mitochondria, Golgi bodies, ribosomes, etc.

Question 27. Read the following pairs of examples of organisms:
1. Moss and Sponge
2. Yeast and Amoeba
3. Bacteria and a blue-green alga
4. Penicillium and Spirogyra
The pair that belongs to the group prokaryotes is _____

Answer: 3. Bacteria and a blue-green alga
Explanation: Prokaryotes are organism which lacks a true nucleus and cell organelles. Other options provided are contained in eukaryotes.

Explanation Of Cell Structure And Functions In KSEEB Science 

Question 28. Read the following terms and select the pair that is related to the inheritance of characters.
1. Cell wall and cell membrane
2. Chromosome and mitochondria
3. Chloroplast and cell membrane
4. Chromosome and genes

Answer: 4. Chromosome and genes
Explanation: Chromosomes and gene are responsible for the inheritance of characters. Chromosomes are present in the nucleus. Genes are the parts of chromosomes which consist of DNA.

Question 29. Choose the correct statement:
1. Genes are located in chromosomes.
2. The cell is located in the nucleus.
3. Chromosomes are located in the nucleolus.
4. Cell membrane surrounds the nucleus.

Answer: 1. Genes are located in chromosomes.
Explanation: Genes are the units of inheritance located in the chromosomes. The nucleus is located in cells but no cell is located in the nucleus. Chromosomes are present in the nucleus, not the nucleolus. The nucleus is surrounded by the nucleus membrane, not cell membrane.

Question 30. The green colour of leaves is due to the presence of the pigment
1. Chlorophyll
2. Ribosomes
3. Mitochondria
4. Chloroplast

Answer: 1. Chlorophyll
Explanation: Chlorophyll is a pigment present in chloroplasts. Chlorophyll is responsible for the green colour of leaves. Chlorophyll can absorb energy from the sun and helps in converting it to chemical energy.

Question 31. The unit of measurement used for expressing the dimension (size) of cells is:
1. Centimetre
2. Millimetre
3. Micrometre
4. Metre
Answer: 3. Micrometre

Question 32. The most important function of the cell membrane is that it:
1. Controls the entry and exit of materials from cells.
2. Controls only the entry of materials into cells.
3. Controls only the exit of materials from cells.
4. Allows entry and exit of materials without any control.

Answer: 1. Controls the entry and exit of materials from cells.
Explanation: Cell membrane facilitates the entry and exit of material from cells. The cell membrane also provides shapes to the cells.

Question 33. Paheli accidentally placed her hand over a flame and immediately pulled it back. She felt the sensation of heat and reacted due to the action of
1. Blood cells
2. Skin surface
3. Nerve cells
4. Nucleus of cells

Answer: 3. Nerve cells
Explanation: Paheli felt the sensation of heat and reacted due to the response to the stimulus by the nerve cells. Nerve cell are specialized cells, which receives and transmits signals from one part to other cells that react to stimuli by generating signals through the axons

Question 34. Which of the following cell organelle is found in all plant cells, animal cells and also in bacterial cells?
1. Chloroplast
2. Cell wall
3. Cell membrane
4. Nucleus

Answer: 3. Cell membrane
Explanation: Chloroplast and cell walls are present only in plant cells. The nucleus is absent in bacterial cells, therefore, the answer is 3. Cell membrane.

Question 35. The thread-like structures present in the nucleus are
1. Nucleolus
2. Chromosomes
3. Genes
4. Ribosomes

Answer: 2. Chromosomes
Explanation: The nucleolus is a spherical body present on the nucleus. Genes are present on chromosomes which help in the inheritance or transfer of characters from the parents to the offspring. Ribosomes are present in the cytoplasm. Hence the answer is 2. Chromosomes.

Question 36. Identify the statement which is true for cells.
1. Cells can be easily seen with the naked eye.
2. Insect’s egg is not a cell.
3. A single cell can perform all the functions in a unicellular organism.
4. The size and shape of cells are uniform in multicellular organisms

Answer: 3. A single cell can perform all the functions in a unicellular organism.
Explanation: Cells can only be seen with microscopes hence

• option 1. is wrong. An insect’s egg is a cell so
• option 2. is wrong. Cells in a multicellular organism are in different size and shape
• option 4. is wrong.

Question 37. Which of the following is not a cell?
1. Red Blood Corpuscle (RBC)
2. Bacterium
3. spermatozoa
4. Virus
Answer: 4. virus
Explanation: The virus is considered as an intermediate between living and non-living. It is not considered a cell because it cannot replicate or perform life processes outside the host cell.

Question 38. Which of the following feature will help you in distinguishing a plant cell from an animal cell?
1. Cell wall
2. Cell membrane
3. Mitochondria
4. Nucleus

Answer: 1. Cell wall
Explanation: The cell wall is present only in plant cell whereas cell wall, mitochondria and nucleus are present in both plant and animal cells. Hence cell wall help in distinguishing a plant cell from an animal cell.

Question 39. Under a microscope Paheli observes a cell that has a cell wall but no distinct nucleus. The cell that she observes is
1. A plant cell
2. An animal cell
3. A nerve cell
4. A bacterial cell

Answer: 4. A bacterial cell
Explanation: Bacterial cell is a prokaryote and it lacks a distinct nucleus and cell organelles. Hence the answer is 4. A bacterial cell.

Question 40. Cheek cells do not have
1. Cell membrane
2. Nucleus
3. Golgi apparatus
4. Plastids

Answer: 4. Plastids
Explanation: Plastids are present only in plant cells. Cheeks cells are present only in animals hence the answer is 4. Plastids.

KSEEB Class 8 Science Chapter 11 Important Questions 

Question 41. Identify the correct statement.
1. Tissue is a group of dissimilar cells.
2. An organ consists of similar cells.
3. Vacuoles are not found in plant cells.
4. Prokaryotes do not have a nucleus.

Answer: 4. Prokaryotes do not have a nucleus.
Explanation: Prokaryotes are organism which lacks a true nucleus and cell organelles.

Question 42. Which of the following statements are not true for eukaryotic cells?
1. They do not have a nuclear membrane.
2. They have a well-organised nucleus.
3. They have a nuclear membrane.
4. Blue-green algae are eukaryotic cells

Answer: 4. Blue-green algae are eukaryotic cells
Explanation: Blue-green algae is a bacteria which comes under prokaryotes hence statement 4. is wrong.

Question 43. Identify the correct statement about cells.
1. All the cells have a nucleus.
2. Cells of an organ have a similar structures.
3. Cells of tissue have a similar structure.
4. The shape of all types of cells is round.

Answer: 3. Cells of tissue have a similar structure.
Explanation: Only eukaryotic cells have well-defined nucleus hence

• Option 1. is wrong. Cells of an organ comprise of different types of the cell
• Option 2. is wrong. Cells are of different shapes and size hence option d) is wrong.

Question 44. The table given below has certain terms and four blank spaces named A, B, C and D.

From the options given below choose the correct combination of terms.
1. A-Pseudopodia; B-Respirations; C-Muscle cell; D-Branched
2. A-Pseudopodia; B-Photosynthesis; C-Muscle cell; D-Branched
3. A-Contractile vacuole; B-Photosynthesis; C-Blood cell; D-Spindle shaped
4. A-Pseudopodia; B-Photosynthesis; C-Cheek cell; D-Spindle shaped

Answer: 2. A-Pseudopodia; B-Photosynthesis; C-Muscle cell; D-Branched
Explanation:
1. The pseudopods are used by Amoeba for movement and as a tool to capture prey.
2. Plastids are major organelles found in plant cells, which contain chlorophyll and can carry out photosynthesis.
3. Muscles are spindle-shaped cells, which are involved in contraction and relaxation.
4. Nerve cells are long, branched and active components of the nervous system, which functions by responding to stimuli.

Question 45. In leaves, name the cell organelle and pigment that is responsible for the green colour.
Answer: Chloroplast and Chlorophyll

Question 46. The instrument used to observe cells is ______
Answer: Microscope

Question 47. We do not sense any pain when we clip our nails or cut our hair. why?
Answer: Nails and hairs are made up of dead cells, which is not connected with nerve cells. Hence we do not feel the pain when we cut our nails or hair.

Question 48. In a cell, where are the genes located?
Answer: Genes are located in Chromosomes present within the nucleus.

Question 49. Amoeba and Paramecium belong to which category of organisms?
Answer: Protozoans

Question 50. What are the functions of the cell wall in plant cells?
Answer: Functions of cell-wall are as follows

1. Acts as a protective layer.
2. Provides shape to the cell.
3. Control the cell expansion
4. Preventing water loss from the cell.
5. Provides strength and rigidity to the cell.

Question 51. Is the following statement correct? If it is wrong, correct the statement Statement :“Unicellular organisms do not respire, only multicellular organisms respire”
Answer: The statement is wrong because all kind of living organisms respire and undergo respiration process.

Question 52. Match the terms given in column I with their functions given in column II and fill the blanks given below the table:

Answer:

Question 53. Classify the following terms into cells, tissues and organs and write in the tabular column given below.
RBC, blood vessels, blood, WBC, Nerve cell, muscle, brain, heart, hand,\ nerve.
Answer:
Cell                           Tissue                Organ
RBC                          Blood                 Blood vessels
WBC                         Muscle               Brain
Nerve Cell                Nerve                 Heart Hand

Detailed Notes On Cell Structure And Functions KSEEB 

Question 54. Read the following statements and write the appropriate term against each statement.
1. I control the functions of a cell. Who am I? _______
2. I am like a policeman. I do not allow anything and everything to get in and out of the cell. Who am I?________
3. I transfer characters from parents to offspring. Who am I? _____
Answer:
1. Nucleus
2. Cell membrane
3. Genes/Chromosomes

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

Combustion And Flame Points To Remember

Combustion: The process of burning a substance in the presence of air (oxygen) and undergoing a chemical reaction to produce heat and light.

The substances which burn in the air are called combustible.

Oxygen (in the air) is essential for combustion.

During the process of combustion, heat and light are given out.

Ignition temperature: This is the lowest temperature at which a combustible substance catches fire.

Types of combustion: The type of combustion differs depending on the type of fuel. Based on nature and intensity combustions are classified into three types. They are:
1. Rapid combustion
2. Spontaneous combustion
3. Explosion

Flame: It is a zone of burning vapour. The substances which vaporise during burning give flames. Example: Kerosene oil and molten wax.

Inflammable substances have very low ignition temperatures.

Fire can be controlled by removing one or more requirements essential for producing fire.

Water is commonly used to control fires.

Water cannot be used to control fires involving electrical equipment or oils.

There are three different zones of flame — dark zone, luminous zone, and non-luminous zone.

Fuel is any material that is burned to obtain energy that can be used to heat or move another object.
A good fuel must
1. Be readily available.
2. Be cheap.
3. Burn easily at a moderate rate.
4. Produce a large amount of heat.
5. Do Not leave behind any undesirable substances.

Fuels differ in efficiency and cost.

Fuel efficiency is expressed in terms of its calorific value which is expressed in units of kilojoules per kg.

Types of Fuels:
1. Solid Fuels: Combustible substances which are solid at room temperature.
Examples: coal, coke, wood, charcoal, etc.
2. Liquid fuels: Volatile liquids. which produces combustible vapour.
Examples: Petrol, kerosene, alcohol, diesel, etc.
3. Gaseous fuels: Combustible gases or a mixture of combustible gases.
Examples: Natural gas, LPG, biogas, coal gas, etc.

Effects of Burning of Fuels:
1. Carbon fuels like wood, and coal petroleum release unburnt carbon particles. These are dangerous pollutants causing respiratory diseases, such as asthma.
2. Incomplete combustion of carbon fuels gives carbon monoxide which is a poisonous gas.
3. Increased concentration of carbon dioxide in the air is believed to cause global warming.
4. Oxides of Sulphur and nitrogen dissolve in rainwater and form acids. Such rain is called acid rain. It is very harmful to crops, buildings and soil.

Unburnt carbon particles in the air are dangerous pollutants causing respiratory problems.

The incomplete combustion of fuel gives poisonous carbon monoxide gas.

An increased percentage of carbon dioxide in the air has been linked to global warming.

Oxides of sulphur and nitrogen produced by the burning of coal, diesel and petrol cause

Acid rain is harmful to crops, buildings and soil.

Combustion And Flame NCERT Textbook Exercises

Question 1. List conditions under which combustion can take place.
Answer: Conditions under which combustion can take place are as follows:
1. Air
2. The ignition temperature
3. Inflammable substance.

Question 2. Fill in the blanks.
1. Burning of wood and coal causes pollution of air.
2. A liquid fuel, used in the home is LPG.
3. Fuel must be heated to its ignition temperature before it starts burning.
4. Fire produced by oil cannot be controlled by water.

Question 3. Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer: The use of CNG in automobiles has reduced pollution in our cities because CNG does not produce any poisonous gas on burning. That is why pollution in our cities is reduced.

Question 4. Compare LPG and wood as fuels.
Answer: LPG burns easily and produces more heat in comparison to wood. Besides, it is a clean fuel, it does not produce fume and ashes as wood do. LPG can be stored and transported easily and conveniently.

Question 5. Give reasons.
1. Water is not used to control fires involving electrical equipment.
2. LPG is a better domestic fuel than wood.
3. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Answer:
1. Water is not used to control fire produced by electrical equipment because water is the conductor of electricity and may result in electric shock.
2. LPG is a substance which is readily available. It is cheaper and burns easily in the air at a moderate rate, It produces a large amount of heat and does not leave behind any undesirable substance.
3. Paper catches fire easily: but when it is wrapped around an aluminium pipe, the ignition temperature does not meet as heat is transferred to aluminium to lower the temperature of paper.

Question 6. Make a labelled diagram of a candle flame.
Answer:

Question 7. Name the unit in which the calorific value of a fuel is expressed
Answer: The calorific value of a fuel is expressed in kilojoules per kg (kj/kg).

Question 8. Explain how CO, is able to control fires.
Answer: Carbon dioxide being heavier than oxygen covers the fire like a blanket. Since the contact between fuel and oxygen is cut off the fire is controlled. The added advantage of carbon dioxide is that in most cases it does not harm electrical appliances.

Question 9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer:

Green leaves contain a lot of water. So, when we try to burn green leaves, water contained in the leaves cools the combustible materials, so that their temperature is brought below its ignition temperature.

This prevents the burning of green leaves.

In the case of dry leaves, water is absent in them so the burning process starts as the temperature is raised above the ignition temperature and the leaves catch fire easily.

Question 10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer: The goldsmith uses the outermost zone of a flame with a metallic blowpipe for melting gold and silver. The flame in the outermost zone has the highest temperature sufficient to melt the gold and silver.

Question 11. In an experiment, 45kg of fuel has completely burnt The heat produced was measured to be 180,000 Kj. Calculate the calorific value of the fuel
Answer: Calorific value of a fuel =Total heat produced/ total mass burnt.
Here, the mass of fuel = 4.5 kg.
The heat produced = 180,000 Kj.
Therefore, the calorific value of fuel = 180,000 / 4.5kg =40,000 kj/kg.

Question 12. Can the process of rusting be called combustion? Discuss.
Answer: Yes, the process of rusting can be called combustion, in fact, slow combustion, because rusting also takes place in the air in presence of humidity in the atmosphere.

Question 13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water, will get heated in a shorter time?
Answer: The water in Ramesh’s beaker will get heated in a shorter time because the outermost part of the flame is the hottest.

Combustion And Flame Additional Questions

Question 1. Name the most common fuel used in homes.
Answer: Liquefied Petroleum Gas. (LPG)

Question 2. What are the states in which fuel may exist?
Answer: A fuel may exist in a solid, liquid or gaseous state.

Question 3. What acts as fuel for our body?
Answer: Food

Question 4. Give two examples of non-combustible substances.
Answer: Water, sand

Question 5. Where were matchsticks first used?
Answer: Egypt

Question 6. What is the composition of the head of a matchstick?
Answer: Antimony trisulphide and potassium chlorate.

Question 7. Comparing the calorific values of coal and petrol, a state which fuel is better.
Answer: The calorific value of coal is about 25000—33,000 kJ/kg, whereas that of petrol is 45,000 kJ/kg. Hence, petrol is a better fuel.

Question 8. What does coal produce during its combustion?
Answer: Coal produces carbon dioxide, heat and light during its combustion.

Question 9. How does a matchstick catch fire?
Answer: By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.

Question 10. What is rapid combustion?
Answer: When a substance burns instantly and produces a huge amount of heat and light, the combustion is called rapid combustion
Example: The instant burning of LPG in a gas stove.

Question 11. Mention any three characteristics of good fuel.
Answer: Any three characteristics of a good fuel are the following:

It has a high calorific value.

It is very easy to transport.

It is cheap, affordable and economic.

Question 12. What is global warming?
Answer: An increase in the average temperature of the earth’s atmosphere, especially a sustained increase that causes climatic changes, is termed as global warming.

Question 13. Why isn’t hydrogen gas used as a domestic or industrial fuel, although it has a very high calorific value? State three reasons for the answer.
Answer: Although hydrogen gas has a very high calorific value, it is not used as a domestic or industrial fuel due to the following reasons:

It is expensive.

It burns with an explosion.

It is extremely inflammable, so it is risky to store and transport hydrogen.

Question 14. It is observed at petrol pumps and airports, that hydrocarbon fire extinguishers are used, instead of soda-acid fire extinguishers. Give reasons why.
Answer: At petrol pumps and airports, there is more probability of a fire breaking out due to oil. In such situations, a soda-acid fire extinguisher does not work as it contains water or uses water to take off the fire by cooling down the place. Water being heavier than oil sinks to the bottom and hence, fire does not get controlled. In such a case, a hydrocarbon fire extinguisher is very useful, as it contains turkey red oil, which causes the foaming of carbon dioxide gas under pressure. The foam covers the surface of the burning substances and dispels the supply of air to control the fire.

Question 15. Explain complete combustion.
Answer: This type of combustion involves the complete burning of the combustible substance. No residue is left behind. Ash or smoke is not given off during or after this type of combustion. Most gases, such as hydrocarbons go through this form of combustion. On combustion, hydrocarbon produces carbon dioxide, water and heat.

Question 16. Can the process of cellular respiration be called combustion? Why?
Answer: Yes. Cellular respiration is a set of metabolic reactions and processes that breaks large molecules into smaller ones with the release of heat. So, this is a slow combustion reaction.

Combustion And Flame  Activities

Question 1. Collect some materials like straws, matchsticks, kerosene oil, paper, iron nails,” stone pieces, glass, etc. Under the supervision of your teacher try to burn each of these materials one by one. If combustion takes place mark the material combustible, otherwise mark it non-combustible.
Answer: Combustible and Non-combustible Substances

Question 2. (Caution: Be careful while handling burning candles).
Fix a lighted candle on a table. Put a glass chimney over the candle and rest it on a few wooden blocks in such a way that air can enter the chimney Observe what happens to the flame. Now remove the blocks and let the chimney rest on the table Again observe the flame. Finally, put a glass plate over the chimney Watch the flame again. What happens in the three cases? Does the flame flicker off? Does it flicker and give smoke? Does it burn unaffected? Can you infer anything at all about the role played by air in the process of burning?


Answer: The candle burns freely

when air can enter the chimney from below.

when air does not enter the chimney from below, the flame flickers and produces smoke.

The flame finally goes off because the air is not available.

Question 3. Place a piece of burning wood or charcoal on an iron plate or Tawa. Cover it with a glass jar or a tumbler, or a transparent plastic jar. Observe what happens. Does charcoal stop burning after some time? Can you think of a reason why it stops burning?
Answer: After burning under the jar for some time, the wood/charcoal stops burning due to the discontinuous supply of air (or oxygen present in the air).

Question 4. (Caution: Be careful while handling burning candles) Make two paper cups by folding a sheet of paper. Pour about 50 ml. of water into one of the cups. Heat both cups separately with a candle What do you observe?

Answer: It is observed that the empty cup catches fire immediately and begins to burn, whereas the cup containing water does not burn; instead, the water present in it becomes hot.

Question 5. Light a candle (Caution: Be careful). Hold a glass tube with a pair of tongs and introduce its one end in the dark zone of a non-flickering candle flame Bring a lighted matchstick near the other end of the glass tube. Do you see a flame? If so, what is it that produces a flame?


Answer: When we bring a lighted matchstick near the other end of the glass tube then we observe a flame. The vapourised wax from candles produces this flame.

Question 6. Make a model of a fire extinguisher. Place a short candle and a slightly taller candle in a small dish filled with baking soda. Place the dish at the bottom of a large bowl and light both candles. Then pour vinegar into the dish of baking soda. Take care. Do not pour vinegar on the candles. Observe the foaming reaction. What happens to the candles? Why? In what order?
Answer: It is observed that the candles go off. The shorter candle blows off first, and then the longer one. It happens because of the production of carbon dioxide gas, which reaches the shorter candle first, and then the longer candle.

Combustion And Flame Ncert textbook exercises Multiple Choice Questions

Question 1. A substance which reacts with oxygen giving heat is called a combustible substance. Which one of the following is a combustible substance?
1. Iron nail
2. Glass
3. Stone piece
4. Wood
Answer: 4. Wood
Explanation: Glass, iron nails and stone pieces will not burn like wood hence they are not combustible. Wood burns in the air and it is called a combustible substance.

Question 2. Which one of the following has the highest calorific value?
1. Kerosene
2. Biogas
3. LPG
4. Petrol
Answer: 3. LPG
Explanation: Calorific represents the amount of heat generated when fuel burns completely.
The calorific value of LPG is 55000-kilo joules/ Kg, which is high when compared to the calorific value of Kerosene, Biogas and petrol.

Question 3. Magnesium ribbon on burning in air produces:
1. Magnesium oxide, water and light.
2. Magnesium oxide and heat.
3. Magnesium oxide, heat and light.
4. Magnesium oxide, water and heat.
Answer: 3. Magnesium oxide, heat and light
Explanation: Magnesium reacts with atmospheric oxygen to get magnesium oxide by liberating heat and light.
The chemical reaction is Mg+O₂ MgO₂ + Heat+ Light

Question 4. Which of the following is not a combustible substance?
1. Camphor
2. Glass
3. Straw
4. Alcohol
Answer: 2. Glass
Explanation: Camphor, glass, and straw can burn in the air and they are combustible substances. Glass will not burn in the air and it is a non-combustible substance.

Question 5. The substance that does not burn with flame is
1. LPG
2. Camphor
3. Dry grass
4. Charcoal
Answer: 4. Charcoal
Explanation: The charcoal will not vaporize on heating. Hence charcoal will not burn by producing a flame. Charcoal glows on combustion.

Question 6. On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of the non-availability of
1. Oxygen
2. Water vapours
3. Carbon dioxide
4. Wax
Answer: 1. Oxygen
Explanation: Oxygen is necessary for combustion. When we place an inverted tumbler over a burning candle, the oxygen supply will be stopped, this extinguishes the flame.

Question 7. If a person’s clothes catch fire, the best way to extinguish the fire is to:
1. Throw water on the clothes
2. Use the fire extinguisher.
3. Cover the person with a woollen blanket.
4. Cover the person with a polythene sheet.
Answer: 3. Cover the person with a woollen blanket.
Explanation: By covering a person’s clothes with a woollen blanket we are cutting off the oxygen required for the burning of clothes. Hence fire will be distinguished.

Question 8. The substance expected to have the highest ignition temperature out of the following is
1. Kerosene
2. Petrol
3. Coal
4. Alcohol
Answer: 3. Coal
Explanation: Ignition temperature is the lowest temperature at which a substance catches fire. Among the given options coal have the highest ignition temperature.

Question 9. Choose the correct statement about inflammable substances from the following. They have:
1. Low ignition temperature and cannot catch fire easily.
2. High ignition temperature and can catch fire easily.
3. Low ignition temperature and can catch fire easily.
4. High ignition temperature and cannot catch fire easily.
Answer: 3. Low ignition temperature and can catch fire easily.
Inflammable substances are substances that easily catch fire. They are substances, which have very low ignition temperatures and when exposed to air, they catch fire easily.

Question 10. Choose the incorrect statement from the following. Forest fires are usually due to:
1. Carelessness of humans
2. Heat of the sun
3. Cutting of trees
4. Lightning strike
Answer: 3. Cutting of trees.
Deforestation or Cutting of trees is not the cause of the forest fire. Forest fires are usually caused due to heat of the sun, lightning strikes and the carelessness of humans

Question 11. The calorific value of a fuel is expressed in a unit called
1. Kilojoule per litre
2. Kilogram per millilitre
3. Kilojoule per gram
4. Kilojoule per kilogram
Answer: 4. Kilojoule per kilogram

Question 12. In villages, people use wood as fuel because:
1. It is considered to be an ideal fuel.
2. Of its easy availability and low cost.
3. It is environment-friendly.
4. It catches fire easily.
Answer: 2. Of its easy availability and low cost.

Question 13. Which among the following is considered the cleanest fuel?
1. Cow dung cake
2. Petrol
3. Kerosene
4. Hydrogen gas
Answer: 4. Hydrogen gas
Explanation: Hydrogen gas is called a clean fuel as it does not produce any dangerous gases. It can only produce heat and water as products.

Question 14. Choose the incorrect statement from the following. A good fuel is one that:
1. Is readily available.
2. Produces a large amount of heat.
3. Leaves behind many undesirable substances.
4. Burns easily in the air at a moderate rate.
Answer: 3. Leaves behind many undesirable substances.
Explanation: Good fuel is readily available and produces a large number of meat. Good fuel burns easily in the air at a moderate rate and will not leave behind any undesirable substances.

Question 15. Shyam was cooking potato curry on a chulha. To his surprise, he observed that the copper vessel was getting blackened from the outside. It may be due to:
1. Proper combustion of fuel.
2. Improper cooking of potato curry.
3. Improper combustion of the fuel.
4. Burning of the copper vessel.
Answer: 3. Improper combustion of the fuel.
The copper vessel was blackened from the outside because of the insufficiency of oxygen.

Question 16. Two glass jars A and B are filled with carbon dioxide and oxygen gases, respectively. In each jar, a lighted candle is placed simultaneously. In which jar will the candle remain lighted for a longer time and why?
Answer: The candle remains in jar B because it is filled with oxygen which is necessary for the combustion and flame. In Jar A candle will not burn due to lack of oxygen.

Question 17. Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity.
Answer: Anu should use the outermost zone of the flame which is the hottest part of the flame.

Question 18. Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Gas (CNG) in big cities?
Answer: Compared to petrol and diesel CNG is a clean fuel. It produces very less amount of gases which are poisonous hence in big cities CNG is used in place of petrol and diesel.

Question 19. Boojho wants to separate the following materials as combustible and non-combustible. Can you help him?
Charcoal, chalk, stone, iron rod, copper coin, straw, cardboard, glass, paper, and wood.
Answer:
Combustible

Straw

Paper

Wood

Charcoal

Cardboard

Non-Combustible

Chalk

Stone

Iron rod

Copper coin

Glass

Question 20. If you hold a piece of iron wire with a pair of tongs inside a candle flame or a Bunsen burner flame, what will you observe? Will it produce a flame?
Answer: Iron will not produce flame rather it glows red hot.

Question 21. People usually keep Angethi/burning coal in their closed rooms during the winter season. Why is it advised to keep the door open?
Answer: The burning of coal produces carbon monoxide which is poisonous for the people inhaling it. If the door is closed, the oxygen level will be less and the carbon-monoxide level will be high. This is harmful to the person sleeping in the room. Hence the door should be closed.

Question 22. The cracker on the ignition produces sound. Why?
Answer: Upon ignition, the cracker releases gas is released out and the gas is heated by the amount of heat generated by the cracker. This led to an explosion resulting in the production of sound.

Question 23. What do you understand by fuel efficiency?
Answer: Fuel efficiency is determined by its calorific value which is the amount of heat energy produced on the complete combustion of 1 kg of fuel. The calorific value of a fuel is expressed in kJ/kg.

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions Class 8 Science Chapter 9 Sound Points To Remember

Sound: Vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear.

Musical Sound: The sound that produces a pleasing effect on the ear. Noise: The sounds that produce a jarring or unpleasant effect.

Types of Sound:

1. Audible Sound: Vibrations whose frequency lies between 20 Hz to 20,000 Hz (20 kHz) are heard by the human ear.
2. Inaudible Sound: The sounds having frequencies above 20,000 Hz and below 20 Hz cannot be heard by the normal human ear.

Low-frequency sounds that cannot be heard are called infrasonics.

High-frequency sounds that cannot be heard are called ultrasonics. In human beings, the

vibration of the vocal cords produces sound. Sound travels through a medium (gas, liquid, or solid). It cannot travel in a vacuum.

The eardrum senses the vibrations of sound. It sends vibrations to the inner ear. From there, the signal goes to the brain. That is how we hear.

Higher the frequency of vibration, the higher the pitch, and the shriller the sound.

Unpleasant sounds are called noise.

Excessive or unwanted sounds lead to noise pollution. Noise pollution may pose health problems for human beings.

Lack of sleep, hypertension (high blood pressure), anxiety, and many more health disorders may be caused by noise pollution.

A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

Attempts should be made to minimize noise pollution. Silencing devices must be installed in aircraft engines, transport vehicles, industrial machines, and home appliances.

Plantation on the roadside and elsewhere can reduce noise pollution.

Amplitude: The maximum extent of vibration of the vibrating body from its mean position is known as its amplitude.

Time Period: One complete to-and-fro movement of the pendulum around its mean position is called one oscillation. The time taken by the vibrating particle to complete one oscillation is called the time period.

Frequency:
1. The number of vibrations made by the vibrating body in one second is known as its frequency.
2. The SI unit of frequency is the hertz (Hz).

Characteristics of Sounds:
1. Loudness: The sensation produced in the ear which enables us to distinguish between a loud and a faint sound. The larger the amplitude of the vibration, the louder the sound is produced. It is proportional to the square of the amplitude.
2. Pitch: The characteristics of sound which distinguishes between a shrill sound and a soft sound. The higher the frequency of vibration, the higher the pitch and shrillness.
3. Quality: Characteristic which enables us to distinguish between musical notes emitted by different musical instruments or voices even though they have the same pitch and Loudness.

Class 8 Science Sound KSEEB Notes 

Sound Ncert Textbook Exercises

Question 1. Sound can travel through
1. Gases only
2. Solid only
3. Liquid only
4. Solids, liquids, and gases
Answer: 4. Solids, liquids, and gases

Question 2. Voice of which of the following is likely to have a minimum frequency?
1. Baby girl
2. Baby boy
3. A man
4. A woman
Answer: 1. Baby girl.

Question 3. In the following statements, tick ‘T against those which are true, and “F” against those which are false.
1. Sound cannot travel in a vacuum. (T/F)
2. The number of oscillations per second of a vibrating object is called its time period.T/F)
3. If the amplitude of the vibration is large, the sound is feeble. (T/F)
4. For human ears, the audible range is 20 Hz. To 20,000 Hz. (T/F)
5. The lower the frequency of vibration, the higher the pitch. (T/F)
6. Unwanted or unpleasant sound is termed as music. (T/F)
7. Noise pollution may cause partial hearing impairment. (T/F)
Answer: 1.T, 2. F, 3. F, 4.T, 5. F, 6. F, 7.T

Question 4. Fill in the blanks with suitable words.
1. Time is taken by an object to complete one oscillation called a time period.
2. Loudness is determined by amplitude.
3. The unit of frequency is hertz.
4. Unwanted sound is called noise.
5. Shrillness of a sound is determined by the pitch of vibration.

Question 5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
No. of oscillations = 40.
Time- taken= 4 sec.
Frequency = no. of oscillation / time-taken
Frequency = 40/4 = 10 Hz.

Question 6. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 per second. What is the time period of the vibration?
Answer:
No- of vibration in 1 second = 500.
Therefore, frequency= 500Hz.
Time-period = 1/frequency
Time Period = 1/500 = 0.002 seconds.

Question 7. Identify the part which vibrates to produce sound in the following instruments.
1. Dholak
2. Sitar
3. Flute
Answer:
1. Dholak- Stretched membrane.
2. Sitar- Stretched string
3. Flute- Air column.

Question 8. What is the difference between noise and music? Can music become noise sometimes?
Answer: The unpleasant sound’s called noise. Whereas pleasant sound is called music. Noise can produce so many health hazards, whereas noise\ music brings about a soothing effect. Yes, music can become a noise sometimes when the musical instruments produce very high-volume sounds.

Question 9. List sources of noise pollution in your surroundings.
Answer: The sources of noise pollution are:
1. The sound produced by buses and trucks.
2. The sound produced at the construction site.
3. The sound produced by playing on TV., radio and loudspeaker.
4. Bursting of crackers, and the sound of big machines in the factories.

Question 10. Explain in what way noise pollution is harmful to humans.
Answer: Noise pollution may cause many health-related problems. Lack of sleep, hypertension, anxiety, etc. is some of the problems that may cause due to noise pollution. Moreover, a person who is exposed to a loud sound continuously may get temporary or permanent deafness.

Question 11. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer: I would suggest my parents buy the house which is three lanes away from the roadside. This would protect us from noise pollution which is maximum at the roadside buildings.

Question 12. Sketch the larynx and explain its function in your own words.
Answer: The larynx is also known as the voice box. It is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air When the lung forces air through the slit the vocal cords vibrate producing sound. Muscles attached to the vocal cords can make the cords tight or loose.

When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.

Question 13. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightening is seen earlier and thunder is heard later. Can you explain why?
Answer: Light travels at the speed of 3,00,000 km/s which is very large in comparison to the speed of sound which travels at the rate of 330 m/s in the air That is why lightning is seen earlier and thunder is heard later.

KSEEB Class 8 Science Chapter 9 Sound Questions 

Sound Activities

Question 1. Take a metal plate (or a shallow pan). Hang it at a convenient place in such a way that it does not touch any wall. Now strike it with a stick Touch the plate or pan gently with your finger. Do you feel the vibrations? Again strike the plate with the stick and hold it tightly with your hands immediately after striking. Do you still hear the sound? Touch the plate after it stops producing sound. Can you feel vibrations now?


Answer: When we touch the pan gently with our finger after striking we feel the vibration. When we hold the pan tightly after striking it, we do not hear the sound. When the pan stops producing sound it also stops vibrating. Thus, we can conclude that the vibrating body produces sound.

Question 2. Take a rubber band. Put it around the longer side of a pencil box Insert two pencils between the box and the stretched rubber. Now, pluck the rubber band somewhere in the middle. Do you hear any sound? Does the band vibrate?


Answer: Yes, we hear the sound of plucking the rubber band. Also, we find that the band is vibrating. Thus, all vibrating bodies produce sound.

Question 3. Take a metal dish. Pour water into it. Strike it at its edge with a spoon Do you hear a sound? Again strike the dish and then touch it. Can you feel the dish vibrating? Strike the dish again. Look at the surface of the water. Do you see any waves there? Now hold the dish. What change do you observe on the surface of the water? Can you explain the change? Is there a hint to connect sound with the vibrations of a body?


Answer: Onstriking the metal dish we hear sound and on touching it we feel the dish vibrating. Striking the dish with water we see circular waves produced. Thus vibrating object produces sound.

Question 4. Take a hollow coconut shell and make a musical instrument ektara. You can also make it with the help of an earthen pot Play this instrument and identify its vibrating part.

Answer: We observed that the vibrating part of the musical instrument ektara is stretched string.

Question 5. Take 6-8 bowls or tumblers. Fill them with water up to different levels, increasing gradually from one end to the other. Now take a pencil and strike the bowls gently. Strike all of them in succession. You will hear pleasant sounds.

Answer: We can hear a pleasant sound. This is due to different levels of water in the bowls. Thus, we find that the shorter the length of the vibrating air column, the higher the pitch of the sound produced.

Question 6. Take two rubber strips of the same size. Place these two pieces one above the other and stretch them tight. Now blow air through the gap between them. As the air blows through the stretched rubber strips, a sound is produced. You can also take a piece of paper with a narrow slit and hold it between your fingers as shown in Now blow through the slit and listen to the sound.

Answer: This activity shows that vocal cords also produce sound in a similar manner when they vibrate.

Question 7. Take a metal or glass tumbler. Make sure that it is dry. Place a cell phone in it. Ask your friend to give a ring on this cell phone from another cell phone. Listen to the ring carefully. Now, surround the rim of the tumbler with your handspun your mouth on the opening between your hands. Indicate to your friend to give me a ring again. Listen to the ring while sucking air from the tumbler. Does the sound become fainter as you suck air? Remove the tumbler from your mouth. Does the sound become loud again?
Answer: We observed that sound becomes fainter than earlier when we try to suck air. But when we remove the tumbler from our mouths the sound again becomes loud. Thus, sound needs a medium to travel.

Question 8. Take a bucket or a bathtub. Fill it with clean water. Take a small bell in one hand. Shake this bell inside the water to produce sound. Make sure that the bell does not touch the body of the bucket or the tub. Place your ear gently on the water’s surface Can you hear the sound of the bell? Does it indicate that sound can travel through liquids?
Answer: We can hear the sound of the bell which indicates that sound can travel through liquids.

Question 9. Take a meter scale or long metal rod and hold its one end to your ear. Ask your friend to gently scratch or tap at the other end of the scale Can you hear the sound of the scratching? Ask your friends around you if they were able to hear the same sound.
Answer: Yes, we find that we can hear the sound of the scratch. But, the people standing around us cannot hear the same sound or we can say that it is limping not audible to them.

KSEEB Class 8 Sound Textbook Solutions 

Question 10. Take a plastic or tin can. Cut its ends. Stretch a piece of rubber balloon across one end of the can and fasten it with a rubber band. Put four or five grains of dry cereal on the stretched rubber. Now ask your friend to speak” Hurrey, Hurrey” from the open end Observe what happens to the grain. Why does the grain jump up and down?
Answer: The grain jumps up and down because of the vibration caused underneath the stretched rubber. Thus when sound waves fall on the eardrum, it starts vibrating back and forth rapidly.

Question 11. Take a metallic tumbler and a tablespoon. Strike the tablespoon gently at the brim of the tumbler. Hear the sound produced. Now bang the spoon on the tumbler and hear the sound produced again. Is the sound louder when the tumbler is struck hard? Now suspend a small thermal coal ball touching the rim of the tumbler Vibrate the tumbler by striking it. See how far the ball is displaced. The displacement of the ball is a measure of the amplitude of the vibration of the tumbler. Now, strike the tumbler gently and then with some force. Compare the amplitudes of vibrations of the tumbler in the two cases. In which case is the amplitude larger?
Answer: The sound produced is louder when the tumbler is struck hard. The amplitude of vibration of the tumbler is larger when the glass is struck hard. Thus the loudness of sound depends upon the amplitude of vibration.

Sound Additional Questions

Question 1. Define vibration.
Answer: Vibration is the to-and-fro or back-and-forth motion of an object.

Question 2. Which part of the human body is responsible for producing sound?
Answer: In humans, the sound is produced by the voice box or larynx

Question 3. Can Sound travel in a vacuum?
Answer: No, sound cannot travel in a vacuum.

Question 4. What is meant by oscillatory motion?
Answer: The to and fro motion of an object is known as oscillatory motion.

Question 5. Define 1 hertz.
Answer: A frequency of | hertz means one oscillation per second.

Question 6. What is a range of audible sounds?
Answer: Sound of frequency 20Hz to 20,000 Hz is the audible range.

Question 7. What is meant by noise pollution?
Answer: The presence of excessive or unwanted sound in the atmosphere is called noise pollution.

Question 8. How do plants help in reducing noise pollution?
Answer: Plants absorb sound and so help us in minimizing noise pollution.

Question 9. How can a hearing-impaired child communicate?
Answer: A hearing-impaired child can communicate effectively by using sign language.

Question 10. Which characteristic of a vibrating body determines
1. Loudness
2. What pitch of the sound is produced by it?
Answer: 1. Amplitude 2. Frequency.

Question 11. Why do we not hear echoes in our ordinary surroundings?
Answer: We do not hear echoes in our ordinary surroundings because the distance to hear echoes should be more than 17 m.

Question 12. We cannot hear the sound of the exploding meteors in the sky, though we can see them. Why?
Answer: Sound cannot travel through a vacuum. In space, there is a vacuum. Light can travel through a vacuum, so we can see the exploding meteor but cannot hear the explosion.

Question 13. When does a thud become music?
Answer: When thuds are repeated at regular intervals, it becomes music, For Example, the beating of drums or wood.

Question 14. Give an example of each of the:
1. Stringed instrument
2. Percussion instrument
3. Wind instrument
4. Striking instrument
Answer:
1. Violin
2. Drums
3. Flute
4. Jal Tarang

Question 15. What is the difference between noise and music? Can music become noise sometimes,?
Answer: Unpleasant sounds are called noise. Music is a sound that produces a pleasing sensation. If the music is too loud, it becomes noise.

Question 16. Draw a labeled diagram showing the structure of the human ear?
Answer:

Question 17. What are ultrasounds? How are they useful to us?
Answer: Sound having a frequency higher than 20kHz is known as ultrasound, and is used for

• Detecting finer faults in metal sheets.
• Scanning and imaging the body for stones, tumors, and fetuses.

Sound Class 8 KSEEB Exercise Solutions 

Sound Multiple Choice Questions

Question 18. A list of mediums is given below.
1. Wood
2. Water
3. Air
4. Vacuum
In which of these mediums can sound travel?

Answer:
1. Wood
2. Water
3. Air
Explanation: Sound required a medium to travel. In a vacuum there is no medium to transmit sound waves hence sound cannot travel in a vacuum.

Question 19. The loudness of a sound depends on:
1. Its amplitude
2. Its frequency
3. Its time period
4. Its speed.
Answer: 1. Its amplitude.
Explanation: Loudness is directly proportional to the amplitude of sound waves. If the amplitude is high then the sound will be louder and the sound will be feeble if the amplitude is low.

Question 20. Which of the following statements is correct?
1. Sound is produced by vibrations.
2. Sound requires a medium for propagation.
3. Light and sound both require a medium for propagation.
4. Sound travels slower than light.

Answer:
1. Sound is produced by vibrations.
2. Sound requires a medium for propagation.
4. Sound travels slower than light.
Explanation: Statement 3. is wrong because light and sound are two different entities.

Question 21. An object is vibrating at 50 hertz. What is its time period?
1. 0.02 s
2. 2s
3. 0.2 s
4. 20.0 s

Answer: 1. 0.02 s
Explanation: If an object is vibrating at 50 hertz
50=1/1T
T=1/50
T=0:02s
Its time period will be 0.02 sec

Question 22. In order to reduce the loudness of a sound, we have to
1. Decrease the frequency of vibration of the sound.
2. Increase the frequency of vibration of the sound.
3. Decrease the amplitude of the vibration of the sound.
4. Increase the amplitude of the vibration of the sound.

Answer: 3. Decrease the amplitude of the vibration of the sound.
Explanation: Sound is directly proportional to the loudness of sound. Hence by decreasing amplitude loudness of the sound decreases.

Question 23. The loudness of sound is measured in units of
1. Decibel (dB)
2. Hertz (Hz)
3. Metre (m)
4. Metre/Second (m/s)
Answer: 1. Decibel (dB)

Question 24. The loudness of sound is determined by the
1. Amplitude of vibration
2. The ratio of amplitude and frequency of vibration
3. Frequency of vibration
4. Product of amplitude and frequency of vibration

Answer: 1. Amplitude of vibration
Explanation: Loudness is directly proportional to the amplitude of sound waves. If the amplitude is high then the sound will be louder and the sound will be feeble if the amplitude is low.

Question 25. Lhertzis equal to
1. 1 vibration per minute
2. 10 vibrations per minute
3. 60 vibrations per minute
4. 600 vibrations per minute

Answer: 3. 60 vibrations per minute
Explanation: 1Hz= | vibration/second
1 minute=60 seconds hence 1 hertz = 60 vibrations /minute

Question 26. The Pitch of sound is determined by its
1. Frequency
2. Amplitude
3. Speed
4. Loudness
Answer: 1. Frequency

Question 27. Ultrasound has a frequency of vibration
1. Between 20 and 20,000 Hz
2. Below 20 Hz
3. Above 20,000 Hz
4. Between 500 and 10,000 Hz
Answer: 3. Above 20,000 Hz

Question 28. Lightning can be seen the moment it occurs. Paheli observes lightning in her area. She hears the sound 5s after she observed lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s).
Answer: Distance=330ms x 5s= 1650m

Question 29. Does any part of our body vibrate when we speak? Name the part.
Answer: The larynx or vocal cords vibrate when we speak.

Question 30. Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give the reason for the delay in hearing the sound.
Answer: The speed of light is faster than the speed of sound, hence Boojho heard the sound of the cracker a little later after seeing the cracker burst.

Question 31. When we hear a sound, does any part of our body vibrate? Name the part.
Answer: When we hear a sound our eardrum vibrates.

Question 32. Name two musical instruments which produce sound by vibrating strings.
Answer: Sitar and Veena

Question 33. A simple pendulum makes 10 oscillations in 20 seconds. What is the time period and frequency of its oscillation?
Answer:
Time period: 2 s
Frequency: 0.5 oscillations/sec
Explanation: A pendulum makes 10 oscillations in 20 seconds.
So it makes 1 oscillation in 20/10 = 2sec
Time period=2 sec
Frequency= 1/t = 1/2 = 0.5Hz

Question 34. We have learned that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us.
Answer: Everybody has their own range of frequency. But we can only hear frequencies in the range of 20hz to 2000 Hz so we cannot hear the sound of a few vibrating bodies.

Question 35. Suppose a stick is struck against a frying pan in a vacuum. Will the frying pan vibrate? Will we be able to hear the sound? Explain.
Answer: The frying pan will vibrate. We will not be able to hear the sound of vibration because sound cannot travel in a vacuum.

Question 36. Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.
Answer: In space, there will be no medium for sound waves to travel and it will be the vacuum. Sound cannot travel in a vacuum hence sound cannot be heard without any special device.

Question 37. List three sources of noise pollution in your locality.
Answer: Industrial sirens, Vehicle honking, and bursting crackers.

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions Class 8 Science Chapter 8 Friction Points To Remember

• Friction: A force that opposes the relative motion between two surfaces of objects in contact. The force of friction always acts in a direction opposite to that of the applied force.
• Causes of Friction: Friction exists between two surfaces due to irregularities on the surfaces of the objects in contact, interlocking of micro-level irregularities of the two surfaces and ploughing of harder surfaces into smoother surfaces. Factors That Affect Friction
  1. Roughness of the surface
  2. The extent to which the two surfaces pressed together
  3. Nature of the surface
• Types of Friction:
  1. Static Friction: When a body is at rest, the force of friction is called static friction and is always equal and opposite to the applied force. The force of friction which acts when the body is just on the verge of sliding on the surface is called limiting friction.
  2. Sliding friction: The friction force which opposes the actual relative sliding motion between two contact surfaces. Sliding friction is smaller than static friction.
  3. Rolling Friction: The frictional force that exists between two surfaces when a body rolls over the other. Rolling friction is smaller than sliding friction.
• Effects of Friction
  1. Friction produces heat.
  2. Friction causes wear and tear
  3. Friction opposes motion.
• Advantages of Friction
  1. Friction between pen and paper enables us to write on paper.
  2. Friction between our feet and the ground allows our movements like standing, walking and running.
  3. Friction between the surface of the road and the tyres of our vehicles allows the vehicles to move without slipping.
• Disadvantages of Friction
  1. Friction causes moving objects to stop or slow down.
  2. Friction produces heat causing waste of energy in machines.
  3. Friction causes wear and tear on moving parts of machinery, soles of shoes, etc.
• Friction is a necessary Evil: As friction is advantageous to us it is considered a friend but due to its disadvantages it is a foe. Depending on the circumstance, friction can be a help or a hindrance. Thus it is a necessary evil.
• Increasing Friction: By pressing the surfaces together more strongly. For Example: when brakes are applied on a bicycle or car, the brake pads press
  against a moving part of the wheel and the force of friction increases. Friction can be increased by increasing the roughness of the surfaces in contact.
  For example, The Treading of shoes and tyres is done to increase friction.
• Reducing Friction: Friction between the sliding surfaces of two objects can be reduced by making the surfaces in contact smooth by polishing them. Sliding friction between the moving parts of vehicles and machinery can be reduced by using oil, grease, graphite or any other lubricant. Rolling friction is less than sliding friction. Hence, sliding friction is replaced by rolling friction by using rollers, like ball bearings between the hub and the axles in the moving parts of machines and vehicles. Friction is reduced by providing wheels:
  Example: suitcase, school bags of kids, etc.
  Aeroplanes, boats, fishes, and birds which move through fluids have bodies of special shape called streamlined shape, so as to reduce the friction due to fluid and avoid energy loss.

Class 8 Science Friction KSEEB Ncert Textbook Exercises

Question 1. Fill in the blanks.
Answer:
1. Friction opposes the relative motion between the surfaces in contact with each other.
2. Friction depends on the nature of surfaces.
3. Friction produces heat.
4. Sprinkling of powder on the carom board reduce friction.
5. Sliding friction is less than static friction.

Question 2. Four children were asked to arrange forces due to rolling, static and sliding frictions in decreasing order. Their arrangements are given below.
1. Rolling, static, sliding
2. Rolling, sliding, static
3. Static, sliding, rolling
4. Sliding, static, rolling
Answer: 2. Rolling, sliding, static.

Question 3. Alida runs her toy car on the dry marble floor, wet marble floor, and newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be
1. Wet marble floor, dry marble floor, newspaper and towel
2. Newspaper, towel, dry marble floor, wet marble floor
3. Towel, newspaper, dry marble floor, wet marble floor
4. Wet marble floor, dry marble floor, towel, newspaper
Answer: 1. Wet marble floor, dry marble floor, newspaper and towel.

Question 4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of the frictional force acting on it.
Answer: The frictional force will act parallel to the inclined surface, opposite to the direction of the sliding of the book.
Question 5. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Answer: Soapy floor reduces the frictional force applied by the floor to a maximum. That is why; it is difficult to walk on a soapy floor.

Question 6. Explain why sportsmen use shoes with spikes.
Answer: Sportsmen use shoes with spikes because spikes produce the desired frictional force and thus help in holding the ground firmly.

Question 7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Answer: Seema will have to apply a larger force because her box is heavier and heavier objects will have to undergo greater frictional force from the surface of contact.

Question 8. Explain why sliding friction is less than static friction.
Answer: Suppose a box kept on the surface has to be pushed. If the box is slided then, when the box starts sliding, the contact points on its surface do not get enough time to lock into the contact point on the floor. So, the sliding friction is slightly less than the static friction and we find it easier to move the box already in motion than to get it started.

Question 9. Give examples to show that friction is both a friend and foe.
Answer:
1. Friction as a friend:

• To hold a glass, we have ridges on our palms, which increase the friction between palm and the glass.
• We do write anything with a pen or pencil because there is friction between the surfaces of paper and the point of the pen or pencil.
• The teacher writes on black —the board with chalk because of friction between the blackboard surface and the chalk.
• If there is no friction, then a moving body would never stop.

2. Friction as a foe:

• Friction wears out materials, whether they are screws, ball-bearing or soles of shoes.
• Friction can also produce heat, which increases the wear and tear of machine parts. It also causes much wastage of energy because this heat is not utilized.

Question 10. Explain why objects moving in fluids must have special shapes.
Answer: Birds and fishes have to move about in fluids all the time. Their bodies must have evolved to shapes which would make them not lose much energy in overcoming friction. Such shapes are called streamlined. Cars are also designed so that their shapes resemble the streamlined shapes of birds, fishes, etc.

KSEEB Class 8 Science Chapter 8 Friction Questions 

Friction Activities

Question 1. Gently push a book on a table. You observe that it stops after moving for some distance. Repeat this activity pushing the book from the opposite direction Does the book stop this time, too? Can you think of an explanation? Can we say that a force must be acting on the book opposing its motion? This force is called the force of friction.

Answer: Yes, the book stops this time too. After sliding for some time, the book stops. The surface of the table provides the frictional force to oppose the sliding of the book. Yes, we can say that a force must be acting on the book opposing its motion.

Question 2. Tie a string around a brick. Pull the brick by a spring balance You need to apply some force. Note down the reading on the spring balance when the brick just begins to move. It gives you a measure of the force of friction between the surface of the brick and the floor.

Now wrap a piece of polythene around the brick and repeat the activity. Do you observe any difference in the readings of the spring balance in the above two cases? What might be the reason for this difference? Repeat this activity by wrapping a piece of jute bag around the brick. What do you observe?
Answer:

• It is observed that the reading of the spring balance in the case when a brick is wrapped with a piece of polythene is less than in the other cases.
• The reason for this difference could be that in the first case, since the brick surface in contact with the ground is rough, the surface gets the greater force of friction. But in the second case, when the brick is wrapped with polythene, the surface gets The pencil cell covers different distances on smoother.
• Hence, less frictional force is required for different surfaces Repeat this activity by moving it. spreading a thin layer of sand over the table.
• By wrapping a piece of jute bag around the hi Von on the same slope throughout the brick, it is observed that the reading of spring balance is more than the second case when the brick was wrapped with polythene.

Question 3. Make an inclined plane on a smooth floor, or on a table. You may use a wooden board supported by bricks, or books. Put a mark with a pen at any point A on the inclined plane. Now let a pencil cell move down from this point. How far does it move on the table before coming to rest? Note down the distance, Now spread a piece of cloth over the table. Make sure that there are no wrinkles in the cloth. Try the activity again.
The pencil cell covers different distances on different surfaces Reapt this activity by spreading a thin layer of sand over the table. Maintain the same slope throughout the activity.
Answer: The distance covered by the pencil cell is
brick wrapped with polythene. different every time because of the different

Question 4. Take a few pencils which are cylindrical down from this point. How far does it move shape? Place them parallel to each other on
the table before coming to rest. Note a table. Place a thick book over it down the distance. Now spread a piece of Now push the book. You observe the pencil cloth over the table. Make sure that there roll as the book moves. Do you feel it are no wrinkles in the cloth? Try the activity easier to move the book in this way than to again slide it. Do you think that resistance to the motion of the book has been reduced? Have you seen heavy machinery being moved by placing logs under it?


Answer: It is observed that the book moves efficiently when placed on cylindrical pencils or rollers. It can be concluded that rolling friction is smaller than sliding friction.

KSEEB Class 8 Friction Textbook Solutions 

Friction Additional Questions

Question 1. What is the force of friction?
Answer: The force acting on a moving object equal and opposite to the direction of motion is called the force of friction.

Question 2. What is the cause of friction?
Answer: The irregularities on the two surfaces in contact is the cause of friction.

Question 3. Why are the wheels of vehicles made circular?
Answer: Rolling friction is less than sliding friction.

Question 4. What is the direction of the force of friction acting on a moving object?
Answer: Opposite to the direction of moving objects.

Question 5. What is the name of a special shape given to objects moving in fluids?
Answer: Streamlined

Question 6. Give one example where ball bearings are used.
Answer: Ceiling fan

Question 7. Which surface does produce more friction smooth or rough surface?
Answer: Rough surface

Question 8. What is drag?
Answer: The frictional force exerted by fluids is called drag.

Question 9. What are fluids?
Answer: Commonly gases and liquids are called fluids.

Question 10. How can fluid friction be minimised?
Answer: By giving suitable shapes to bodies moving in fluids.

Question 11. If we push the book on the table, it stops after some time. Why?
Answer: When we push a book on a table, a force is applied to it in the opposite direction of the motion called the force of friction. This force opposes the movement and the book stops.

Question 12. What is a spring balance?
Answer: A spring balance is a device which measures the force acting on an object. It contains a coded spring. When a force is applied to it, the spring gets stretched. The pointer moves on the scale showing the magnitude of the force.

Question 13. What are the two factors on which the force of friction depends?
Answer: These two factors are:

• The nature, i.e., smoothness or roughness of the surfaces in contact.
• How the surfaces in contact pressed together.

Question 14. Explain increasing and decreasing friction with suitable examples.
Answer: In our daily life, in many cases, we increase or decrease friction for our own convenience. Some examples are given below:
Increasing friction:

• The soles of our shoes are grooved to provide the shoes better grip on the floor so that we can move safely. Similarly, the tyres of vehicles are treaded to increase friction to provide better grip.
• We increase friction by using brake pads in the brake system of bicycles and automobiles.
• Gymnasts apply some coarse substance on their hands to increase friction for better grip.
• Kabaddi players rub their hands with soil for a better grip on their opponents.
• Roads are made rough to prevent from slipping.
• Handles of cricket and tennis are made of rough materials to get a better grip.

Decreasing friction:

• In some situations, however, friction is undesirable and we would want to minimise it. For example:
• A few drops of oil are poured on the hinges of a door, the door moves smoothly.
• A bicycle and motor mechanic uses grease between the parts of these machines to reduce friction.
• By polishing surfaces, and sprinkling powder on carrom board, we reduce friction.
  Wheel and ball bearings are used in machines and vehicles to reduce friction.

Question 15. What do you mean by fluid friction? How can fluid friction be reduced?
Answer: The gases and liquids are called fluids. All of them exert a force of friction on solid bodies moving in either of them. The force exerted by fluid is called drag.

• It depends on the speed of the object with respect to the fluid.
• It also depends on the shape of the object and the nature of the fluid.
• It is obvious that when objects move through fluids, they have to overcome friction acting on them. In this process, they lose energy.
• Efforts are, therefore, made to reduce friction. So, the objects are given special shapes, Birds and fishes have to move about in fluids all the time.
• Their bodies must have evolved to shapes which would make them lose less energy in overcoming friction. Such shapes are called streamlined.
• This is why the shapes of aeroplanes, ships and all vehicles are designed to have shapes which minimise fluid friction.

Question 16. A toy to play with: Take an empty matchbox. Take out its tray.
Cut a used refill of a ball pen of the same width as the tray as shown in the figure. Fix the refill with two pins on the top of the tray in Fig. Make two holes on the opposite sides of the tray. Make sure that the holes are large enough to allow a thread to pass through them easily. Take a thread about a metre long and pass it through the holes as shown. Fix beads at the two ends of the thread so that it does not come out Insert the tray in the outer cover of the matchbox.
Suspend the matchbox by the thread. Leave the thread loose. The matchbox will start falling down due to gravity. Tighten the thread now and observe what happens. Explain your observation. Can you relate to friction?

Answer: The matchbox will not fall further due to the friction between the thread and the matchbox.

Friction Class 8 KSEEB Exercise Solutions 

Friction Multiple Choice Questions

Question 1. Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play
1. Only if the objects are solid.
2. Only if one of the two objects is liquid.
3. Only if one of the two objects is gaseous.
4. Irrespective of whether the objects are solid, liquid or gaseous.

Answer: 4. Irrespective of whether the objects are solid, liquid or gaseous.
Explanation: Force of friction acts in solids, liquids and gasses and opposes each other’s motion.

Question 2. A boy is shown pushing the box from right to left. The force of friction will act on the box
1. From right to left ( !)
2. From left to right (’!)
3. Vertically downwards (“!)
4. Vertically upwards (‘!)
Answer: 2. From left to right (*!)
Explanation: Friction always acts in the opposite direction to the motion, hence the force of friction will be from left to right.

Question 3. To sharpen the blade of a knife by rubbing it against a surface, which of the following will be most suitable?
1. Stone
2. Plastic block
3. Wooden block
4. Glass block

Answer: 1. Stone
Explanation: Stone exerts a greater frictional force which sharpens the blades upon rubbing.

Question 4. A toy car released with the same initial speed will travel farthest on
1. Muddy surface
2. Polished marble surface
3. Cemented surface
4. Brick surface

Answer: 2. Polished marble surface
Explanation: Polished marble surface has the least frictional force and least inertia, hence car will travel farther on a marble floor.

Question 5. If we apply oil to door hinges, the friction will
1. Increases
2. Decreases
3. Disappear altogether
4. Will remain unchanged

Answer: 2. Decreases
Explanation: Because oil acts as a lubricant and reduces friction.

Question 6. Which of the following statements is incorrect?
1. Friction acts on a ball rolling along the ground.
2. Friction acts on a boat moving on water.
3. Friction acts on a bicycle moving on a smooth road.
4. Friction does not act on a ball moving through air.

Answer: 4. Friction does not act on a ball moving through air.
Explanation: Friction acts on the body moving in the air as fluid friction

Question 7. A boy rolls a rubber ball on a wooden surface. The ball travels a short distance before coming to rest. To make the same ball travel a longer distance before coming to rest, he may
1. Spread a carpet on the wooden surface.
2. Cover the ball with a piece of cloth.
3. Sprinkle talcum powder on the wooden surface.
4. Sprinkle sand on the wooden surface

Answer: 3. Sprinkle talcum powder on the wooden surface.
Explanation: Applying talcum powder will reduce the frictional force, which will make the ball to travel a longer distance.

Question 8. In a large commercial complex, there are four ways to reach the main road. One of the paths has loose soil, the second is laid with polished marble, the third is laid with bricks and the fourth has a gravel surface. It is raining heavily and Paheli wishes to reach the main road. The path on which she is least likely to slip is
1. Loose soil.
2. Polished marble.
3. Bricks.
4. Gravel.

Answer: 4. Gravel.
Explanation: The only path will have the sufficient frictional force to walk easily, hence the answer is 4. Gravel.

Question 9. Two blocks of iron of different masses are kept on a cemented floor Which one of them would require a larger force to move it from the rest position?


Answer: The larger force will be required to move the heavier block.

Question 10. Will the force of friction come into play when a raindrop rolls down a glass window pane?
Answer: Yes, the force of friction comes into play when a raindrop rolls down a glass window pane.

Question 11. Two boys are riding their bicycles on the same concrete road. One has new tyres on his bicycle while the other has tyres that are old and used. Which of them is more likely to skid while moving through a patch of the road which has lubricating oil spilt over it?
Answer: The bicycle with worn-out tyres is more likely to skid.

Question 12. Shows two boys applying force on a box. If the magnitude of the force applied by each is equal, will the box experience any force of friction?


Answer: Force of friction will be zero as the net force on the box is zero.

Question 13. Imagine that an object is falling through a long straight glass tube held vertically; the air has been removed completely from the tube. The object does not touch the walls of the tube. Will the object experience any force of friction?
Answer: No, the object will not experience any force of friction.

Question 14. You might have noticed that when used for a long time, slippers with rubber soles become slippery. Explain the reason.
Answer: After using slippers for a long time, the soles become smooth. This decreases the friction between the sole and the floor. Therefore, slippers become slippery.

Important Questions For KSEEB Class 8 Friction 

Question 15. Is there a force of friction between the wheels of a moving train and iron rails? If yes, name the type of friction. If an air cushion can be introduced between the wheel and the rail, what effect will it have on the friction?
Answer: Yes, there exists a rolling force between the wheels of a moving train and iron rails. If an air cushion is introduced between the wheel and the rails, the friction will decrease.

Question 16. Cartilage is present in the joints of our body, which helps in their smooth movement. With advancing age, this cartilage wears off. How would this affect the movement of joints?
Answer: With advancing age, this cartilage wears off. This increases friction, which will lead to difficulty in movement and will cause joint pain.

Question 17. While playing tug of war Preeti’s hands. Suggest a way out for her to prevent this.


Answer: She may rub soil to increase friction between the rope and her hand.

Question 18. The handle of a cricket bat or a badminton racquet is usually rough. Explain the reason.
Answer: To have a better grip on the bat it should be rough because a rough surface decreases friction and allow you to have a firm grip on the bat.

Question 19. Explain why the surface of the mortar and pestle (ciabatta) used for grinding is etched again after prolonged use.
Answer: To increase friction to make it more effective for grinding again.

Question 20. A marble is allowed to roll down an inclined plane from a fixed height. At the foot of the inclined plane, it moves on a horizontal surface
1. Covered with silk cloth
2. Covered with a layer of sand and
3. Covered with a glass sheet. On which surface will the marble move the shortest distance? Give the reason for your answer.
Answer: A marble moves to the shortest distance on the floor covered with sand as it offers maximum friction against its motion.

Question 21. A father and son pushed their car to bring it to the side of the road as it had stalled in the middle of the road. They experienced that although they had to push with all their might initially to move the car, the push required to keep the car rolling was smaller, once the car started rolling. Explain.
Answer: Initially they had to apply force to set the card in motion but once the car started rolling, they had to apply force only to balance the rolling friction of the car, the value of which is very less.

Question 22. When the cutting edge of a knife is put against a fast-rotating stone to sharpen it, sparks are seen to fly. Explain the reason.
Answer: Heat is produced as a result of friction between a knife and the rotating stone. As the speed of rotation increases the amount of heat generated also increases which results in the sparks.

Question 23. We have two identical metal sheets. One of them is rubbed with sandpaper and the other with ordinary paper. The one rubbed with sandpaper shines more than the other. Give reason.
Answer: The friction between plane paper and the metal sheet is less compared to the friction between sandpaper and metal. This friction acts on the top layer of the metal sheet which will remove the top layer to make the metal shine.

Question 24. While travelling on a rickshaw, you might have experienced that if the seat cover is very smooth, you tend to slip when brakes are applied suddenly. Explain.
Answer: If the seat cover is very smooth then the friction between the seat and our body is very less. Because of this, we tend to slip when brakes are applied in a rickshaw.

Question 25. Two friends are trying to push a heavy load Suggest a way which will make this task easier for them.

Answer: Their work can be made easy by putting rollers below the heavy load because the rolling friction is smaller than the sliding friction.

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water