CBSE Class 8

Sound Class 8 Extra Questions and Answers Science Chapter 13 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 8 Science Question bank on a regular basis.

Class 8 Science Chapter 13 Extra Questions and Answers Sound

Extra Questions for Class 8 Science Chapter 13 Sound with Answers

Sound Class 8 Extra Questions Very Short Answer Type

Question 1.
Name some of the musical instruments which are simply beaten or struck to produce music.
Answer:
Such instruments are manjira, ghatam, kartal, dholak, etc.

Question 2.
What part in humans produces sound?
Answer:
It is voice box in humans, that produces sound.

Question 3.
Can sound travel through solid also?
Answer:
Yes, the sound can travel through solids also.

Question 4.
What is to and fro motion of an object called?
Answer:
The to and fro motion of an object is called vibration or oscillatory motion.

Sound Class 8 Extra Questions Short Answer Type 1

Question 1.
What role does sound play in our life?
Answer:
The sound plays an important role in our life. It helps us to communicate with one another.

Question 2.
Define vibration. What is its other 7 name ?
Answer:
The to and fro or back and forth motion of an object is known as vibration. Its other name is oscillation or oscillatory motion.

Question 3.
How do dolphins and whales communicate?
Answer:
The sound can travel in water as it is also a medium for sound to travel. So, whales and dolphins, which live in water, can easily communicate there.

Question 4.
Why does sound travel through wood or metals?
Answer:
As wood and all metals are solid matters, and all solids are the media for sound to travel, so sound travels through wood or metals.

Question 5.
Why should we never put a sharp, pointed or hard things into our ears?
Answer:
If we put sharp, pointed or hard (things in our ear, the eardrum might get damaged. And damage to eardrum can cause deafness).

Question 6.
Define frequency of oscillation.
Answer:
The number of oscillations or vibrations produced per second is known as frequency of oscillation.

Question 7.
How is frequency of oscillation expressed?
Answer:
The frequency of oscillation is expressed in terms of hertz. Its symbol is Hz. A frequency of one Hz is one oscillation per second.

Question 8.
If an object oscillates 20 times in one second, what would be its frequency?
Answer:
As the frequency is the number of vibrations per second; so in this case, when, an object oscillates 20 times in one second, its frequency would be 20 Hz.

Question 9.
Can we differentiate sounds on the basis of their amplitudes and frequencies?
Answer:
Yes, with the help of amplitude and frequency we can differentiate two sounds easily.

Question 10.
Define amplitude. How is it expressed ?
Answer:
The displacement of the oscillating body is the measure of the amplitude of vibration of the body. It is expressed in terms of metre (m).

Question 11.
How is loudness of a sound determined ?
Answer:
The loudness of a sound is determined by its amplitude. When the amplitude of a vibration is large, the sound produced is loud, and in case of the smaller amplitude, the sound produced is feeble.

Question 12.
What is noise? Do you enjoy the sound produced by horns of buses and trucks? Why?
Answer:
The unpleasant sounds are called noise. We do not enjoy the sounds produced by the horns of buses and trucks because these sounds are loud and harsh and hende are unpleasant sounds.

Question 13.
What are the causes of hearing impairment ?
Answer:
Hearing impairment is generally the result of an ear disease, injury or degeneration of the hearing mechanism with age. The noise pollution also contribute to deafness.

Question 14.
How can one improve hearing impairment ? Is society and technology to contribute towards improving this defect ?
Answer:
Technological devices for the hearing impaired have made it possible for such persons to improve their quality of hearing. Society too, can do much to improve the living environment for the hearing impaired by minimising noise pollution.

Question 15.
What should be done to control noise pollution?
Answer:
To control noise pollution, we must control the sources of noise at home or in the surroundings. We should also plant trees in the surroundings.

Sound Class 8 Extra Questions Short Answer Type 2

Question 1.
What is noise pollution and what are the harms due to it? Mention any two methods to limit noise pollution.
Answer:
Noise pollution: Presence of excessive or unwanted sounds in the environment is called noise pollution.
Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers, etc.

Harms of noise pollution:
(a) The presence of excessive noise in the surroundings causes many health related problems like lack of sleep, hypertension, anxiety, etc.
(b) A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

Methods to control noise pollution :
(a) Use of automobile horns should be minimised.
(b) TV and music systems should be run at low volumes.

Question 2.
What are audible and inaudible sounds ? Describe.
Answer:
Audible sounds: Sounds of frequencies between 20 to 20,000 hertz.
Inaudible sounds:
(i) Sounds of frequencies less than 20 hertz. Such sounds are called infrasonic.
(ii) Sounds of frequencies more than 20,000 hertz. Such sounds are called ultrasonic.

Question 3.
What are the uses of ultrasound?
Answer:
Uses of ultrasound :

1. The ultrasound or ultrasonic sound is used in investigating and tracking many medical problems.
2. In industries, ultrasound is used for detecting flaws and cracks in metallic and other structures.
3. Some operations, like bloodless surgery, can be done by applying this sound.

Question 4.
Write a short note on the children having impaired hearing.
Answer:
A child who has a moderately severe hearing loss and does not use a hearing aid will hear very little conversational speech, because speech develops as the direct result of hearing. A child with a moderately severe hearing loss may have defective speech, minimal expressive vocabulary and inadequate language structure. So, children with impaired hearing need special care. By learning sign language such children can communicate effectively.

Sound Class 8 Extra Questions Long Answer Type

Question 1.
Describe the construction and working of ears with diagram.
Answer:
We hear sound through our ears. The shape of the outer part of ear is like a funnel. When sound enters in it, it travels down a canal at the end of which a thin membrane is stretched tightly. It is called the eardrum.

Sound vibrations make the eardrums vibrate. The eardrum sends vibrations to the inner ear. From there, the signals go to the brain and we hear.

Question 2.
(a) Name the sound box in human being. Explain, how it works ?
(b) A body vibrates 100 times in 20 seconds. Calculate the time period and frequency.
Answer:
(a) The name of the voice box is larynx. The larynx or voice box is responsible for producing sounds in humans were. The voice box consists of two vocal chords. These chords are arranged in such a manner that there is a small gap between them. This small gap allows air to pass through. When we speak, air is forced into this small gap by the lungs. The vibrations in the vocal chords produces the sound.
(b) Number of vibrations = 100
Time taken = 20 s
Time taken to complete one vibration

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Friction Class 8 Extra Questions and Answers Science Chapter 12 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 8 Science Question bank on a regular basis.

Class 8 Science Chapter 12 Extra Questions and Answers Friction

Extra Questions for Class 8 Science Chapter 9 Friction with Answers

Friction Class 8 Extra Questions Very Short Answer Type

Question 1.
The given sentence is true or false:
Rolling friction is greater than sliding friction.
Answer:
False

Question 2.
Rewrite the sentence by correcting the mistakes:
Friction is not caused by the rrregula- rities on the two surfaces in contact. Smooth surfaces also do not have large number of irregularities on them.
Answer:
Friction is caused by the irregularities on the two surfaces in contact. Smooth surfaces don’t have large number of irregularities on them.

Question 3.
Does the distance covered by a moving body depend on the nature of the surface on which it moves?
Answer:
Yes, it does. Smoother the surface, bigger is the distance covered.

Question 4.
Can you imagine being able to walk if there were no Auction at all?
Answer:
No.

Question 5.
Is sliding friction less than static friction ?
Answer:
Yes, sliding friction is slightly less than static friction.

Question 6.
Would it be possible to hold the glass at all if there is no. friction?
Answer:
No.

Question 7.
Why cannot we write on a smooth blackboard with chalk?
Answer:
Because there is not sufficient friction on the blackboard.

Question 8.
Is friction a friend or foe?
Answer:
Friction is both a friend and a foe.

Question 9.
What energy can be produced by friction?
Answer:
Friction can produce heat energy.

Question 10.
What happens when you strike a matchstick against the rough surface on the side of matchbox ?
Answer:
The matchstick catches fire.

Question 11.
How can efficiency of machinery be increased?
Answer:
By reducing friction, the efficiency of the machinery can be increased.

Question 12.
What is the substance which reduces friction called?
Answer:
It is called a lubricant.

Question 13.
What does air cushion between the moving parts of the machine do?
Answer:
It reduces friction.

Question 14.
Can we reduce friction to zero by polishing surfaces or using large amount of lubricants ?
Answer:
No, friction cannot be reduced to zero by any ‘means.

Friction Class 8 Extra Questions Short Answer Type 1

Question 1.
Name factors on which force of friction depends.
Answer:
Factors on which frictional force depends are :

1. Nature of surface in contact.
2. Area of contact of the two surfaces.
3. Relative speed of the surfaces.

Question 2.
When a brick kept on a table is pulled by a string to which a spring balance is attached, what gives the measure of the force of friction?
Answer:
When a brick kept on a table is pulled by a string attached to it and a spring balance is also attached with the string, then the reading on the spring balance gives the measure of the force of friction between the surface of the brick and the floor.

Question 3.
If a body is made to move on the sandy surface, what will happen to its motion?
Answer:
As the frictional force produced by the sandy surface is greater, so the motion of the body will be slower.

Question 4.
What we have to do when we attempt to move any surface over other?
Answer:
When we attempt to move any surface over other, we have to apply a force to overcome the frictional force prevailing in between the surfaces.

Question 5.
Why is there a greater force of friction when a rough surface is involved?
Answer:
On rough surfaces, there are a large number of irregularities (bumps) which facilitates interlocking. So, the force of friction is greater if a rough surface is involved.

Question 6.
How is it possible to write with chalk on black- board?
Answer:
When we write with a chalk on the blackboard, its rough surface rubs off some chalk particles due to friction. So, we can see the writing on the blackboard.

Question 7.
Why are treaded tyres used in automobiles like cars, trucks or bulldozers?
Answer:
The treaded tyres of cars, trucks and bulldozers provide better grip with the ground, due to increased friction. That is why they are used.

Question 8.
Why do Kabaddi players rub their hands with the soil?
Answer:
The Kabaddi players rub their hands with the soil to increase friction for a firm grip of their opponents.

Question 9.
What do gymnasts do to have a better grip?
Answer:
The gymnasts apply some coarse substance on their hands to increase friction for better grip.

Question 10.
When a few drops of oil are poured on the hinges of a door, why does the door move smoothly?
Answer:
When a few drops of oil are poured on the hinges of the door it moves smoothly because oil is one of the lubricants used to minimise or reduce friction.

Question 11.
Define the term lubricant. Where are they used?
Answer:
The substances which reduce friction are called lubricants. That is why, they are used in the machine parts.

Question 12.
In some machines, use of oil or lubricant is not advisable. Why?
Answer:
In some machines, it may not be advisable to use oil or lubricant because they uses air cushion in between the moving parts to reduce friction.

Question 13.
Why do attaches are fitted with rollers?
Answer:
Attaches and other pieces of luggage are fitted with rollers, because they enable the puller to pull them easily as wheels and rollers reduce friction facilitating rolling friction.

Question 14.
Define rolling friction.
Answer:
When one body rolls over the surface of another body, the resistance to its motion is called rolling friction.

Question 15.
Does air exert friction?
Answer:
Although air is very light and thin, yet it exerts frictional force on objects moving through it.

Question 16.
Does water exert friction?
Answer:
Yes, water and other liquids exert force of friction when objects move through them.

Question 17.
Define drag.
Answer:
The frictional force exerted by fluids (gases and liquids) is called drag.

Question 18.
What are the factors affecting friction on an object in fluids?
Answer:
Factors affecting friction on an object in fluids are:

1. Objects speed with respect to the fluid
2. Shape of the object.
3. Nature of the fluid.

Friction Class 8 Extra Questions Short Answer Type 2

Question 1.
Give any two methods each to increase and decrease friction.
Answer:
Methods to increase the friction:
(a) By making the surfaces rough.
(b) By removing the lubrication between the two surfaces.
(c) By changing the rolling friction to sliding friction.

Methods to decrease the friction:
(а) By making the surfaces smooth.
(b) By applying the lubrication between the two surfaces.
(c) By changing the sliding friction to rolling friction.

Question 2.
Following are some of the examples which shows that ‘friction is our friend and foe.’ Choose from the given examples which example is useful for us and which is not.
(а) It allows us to grip and catch any object.
(b) It causes wear and tear in objects.

Helps in writing.
It helps to minimise the speed or to stop any moving objects.
Answer:
(a) Useful,
(b) Not useful,
(c) Useful,
(d) Useful.

Question 3.
What do you mean by lubricants? What is their use?
Answer:
The substances which reduce friction are called lubricants. To increase efficiency, friction has to be reduced. This can be done by applying oil, grease or graphite in between the moving parts of a machine. Then its thin layer is formed there and moving surfaces do not directly rub against each other. In this way, interlocking of irregularities is avoided to a great extent and movement becomes smooth.

Question 4.
Site some examples when we prefer to reduce friction.
Answer:
Some examples where we prefer to reduce friction are:
Item used Used on Used for
(i) Fine powder
Carrom board
For easy movement of sticker.

(ii) Lubricants and air cushion
Moving machine parts

Reduce heat production and hence increasing efficiency. Also decreasing wear-tear rate.
(iii) Ball bearings Machine moving parts
To convert sliding friction to rolling friction.

Friction Class 8 Extra Questions Long Answer Type

Question 1.
What are the different types of friction? Arrange them in the increasing order of their magnitude.
Answer:
Static friction: The friction which acts between the two surfaces in contact when there is not actual relative motion between the two surfaces. It is necessary for walking also because without this static friction, feet would slip out, making it difficult to walk.

Sliding friction: The friction which acts between the two surfaces in contact when there is actual relative motion between the two surfaces. When we push a trunk and the trunk moves, the friction acting in this case is sliding friction.Therfe is sliding friction between the brake pads and bike rims each time we use bike’s brakes. This friction slows the rolling wheels.

Rolling friction: The friction which acts between the two surfaces in contact when one surface rolls over the other surface. The friction in the ball bearings is rolling friction. Rolling friction is much weaker than sliding friction or static friction. This explains why most forms of ground transportation use wheels, including bicycles, cars, 4-wheelers, roller skates and scooters.

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Force and Pressure Class 8 Extra Questions and Answers Science Chapter 11 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 8 Science Question bank on a regular basis.

Class 8 Science Chapter 11 Extra Questions and Answers Force and Pressure

Extra Questions for Class 8 Science Chapter 11 Force and Pressure with Answers

Force and Pressure Class 8 Extra Questions Very Short Answer Type

Question 1.
Force per unit area is called as _____________.
Answer:
Pressure

Question 2.
Fill in the blanks with appropriate word:
While sieving grains, small pieces fell down from sieve due to _______.
Answer:
gravity

Question 3.
Write the answer in one sentence. Where do we apply force while walking?
Answer:
On the ground in backward direction.

Question 4.
Write the name of the force which has changed the shape of the dough and rolled it into flat chapati.
Answer:
Muscular force

Question 5.
What happens when a force acts on an object ?
Answer:
The force acting on an object changes its state, form or direction.

Question 6.
What is magnitude of the state of rest?
Answer:
It is zero.

Question 7.
What is required to keep the bob. moving along a circular path with a constant speed ?
Answer:
Force.

Question 8.
Give an example of change of shape by applying a force.
Answer:
When an inflated balloon is pressed between two palms, it is deshaped.

Question 9.
Which of the following is a contact force: (i) muscular force or (ii) gravitational force ?
Answer:
(i) Muscular force.

Question 10.
Why does a ball rolling along the ground gradually slows down and finally comes to rest ?
Answer:
Frictional force acts on it which opposes the motion of a-body.

Question 11.
Which frictional force is smaller, the force due to friction between two solid surfaces or between liquids, or friction due to air ?
Answer:
The force of friction due to air is very small, nearly negligible.

Question 12.
Is it essential for the agent applying a force on an object to be always in contact with it ?
Answer:
No, magnetic force and electrostatic force are examples where there is no contact.

Question 13.
Why do objects fall from the height?
Answer:
It happens due to the gravitational force of the earth acting on the objects.

Question 14.
How are winds and cyclones caused ?
Answer:
They are caused by the differences in air pressure.

Question 15.
What is the formula of pressure?
Answer:
Pressure = \(\frac{\text { Force }}{\text { Area of surface }}\)

Force and Pressure Class 8 Extra Questions Short Answer Type 1

Question 1.
Is attraction between the piece of iron and a magnet a pull? What about repulsion between two similar poles of two magnets?
Answer:
Yes, attraction between the opposite poles of two magnet is a pull and the repulsion between two similar poles is a push.

Question 2.
What causes motion in objects ?
Answer:
The motion imparted to objects is due to the action of force.

Question 3.
What has to happen for a force to come into play ?
Answer:
At least two objects must interact for a force to come into play.

Question 4.
An airplane is flying in the sky. Identify any two forces acting on it.
Answer:
Weight in downward direction
Lift in upward direction

Question 5.
What happens if the force is applied in the direction of motion of the body ?
Answer:
If the applied force is in the direction of motion of the body, the speed of the body increases.

Question 6.
What happens if the force is applied in the direction opposite to the motion of the body ?
Answer:
If the force is applied in the direction opposite to the motion of a body, then it results in a decrease in the speed of the object. The body may also come in a static state.

Question 7.
What infers the change in state of motion of an object ?
Answer:
A change in either the speed of an object, or its direction of motion, or both, is described as a change in its state of motion.

Question 8.
What does the state of rest mean?
Answer:
The state of rest is considered to be the state of zero speed.

Question 9.
What happens to a body in motion along a circle ?
Answer:
When a force makes a body to move in a circle, then its velocity changes at every point in the circular path due to change in direction.

Question 10.
What do you mean by muscular force ?
Answer:
The force resulting due to the action of muscles is known as the muscular force.

Question 11.
What does muscular force enable us to do ?
Answer:
Muscular force enables us to carry out our physical activities and other tasks. It helps us in movement, locomotion, bending of different parts of our body, lifting, kicking, pushing or pulling objects, etc.

Question 12.
Is muscular force a contact? force? Why?
Answer:
Yes, muscular force is a contact force, since muscular force can be applied only when it is in contact with an object.

Question 13.
Where does friction act and what is its direction?
Answer:
Friction acts on all the moving objects and its direction is always opposite to the direction of motion of the object.

Question 14.
Is friction a contact force? Why?
Answer:
Yes, friction is a contact force. Since the force of friction arises due to contact between surfaces.

Question 15.
What do two magnets do on each other when they are brought close?
Answer:
Two magnets with like poles exert a force of repulsion on each other and two unlike poles attract each other. A magnet can exert forces on another magnet without being in contact with each other.

Question 16.
Can force of gravity act on all distant objects ?
Answer:
Yes, force of gravity is not restricted to the near or distant objects. It acts on all the objects.

Question 17.
Do gases exert pressure? Where ?
Answer:
The gases also exert pressure. They axert pressure on the walls of the container in- which they are filled.

Force and Pressure Class 8 Extra Questions Short Answer Type 2

Question 1.
What are contact and noncontact forces ? Give two examples each.
Answer:
Contact forces: A contact force is a force which acts on an object when comes in physical contact with it. The most familiar examples of a contact force are muscular force and frictional force.

Non-contact forces: A non-contact force is a force which acts on an object without coming physically’in contact with it. The most familiar examples of a non-contact force are gravitational force and magnetic force.

Question 2.
What is meant by the state of motion and the state of rest ?
Answer:
The state of motion of an object is described by its speed and the direction of motion. The state of rest is considered to be the state of zero speed.

Question 3.
Give some examples to support that application of a force on an object may change its shape.
Answer:
Examples are: (1) When a force is applied on an inflated balloon by pressing it between two palms, the shape of the balloon undergoes a change.
(2) The shape of a ball of dough changes when it is rolled to make a chapati. The roller applies the force in this case.

Question 4.
Define friction. How does friction act ?
Answer:
Friction is a kind of force which arises between two surfaces in contact. The two surfaces in contact may be solid, liquid or gaseous. The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion.

Question 5.
What is force of gravity? Give some examples to show that it is an attractive force.
Answer:
Objects or things fall towards the earth because it pulls them. This force is called the force of gravity or just gravity. It is an attractive force.
Examples which show that gravity is an attractive force :
(1) Water begins to flow towards the ground as soon as we open a tap.
(2) Water in rivers flows downward due to the force of gravity.

Question 6.
Discuss the characteristics of force of gravity:
Answer:
Characteristics of force of gravity:

1. The force of gravity is an attractive but non-contact force.
2. This force acts on all objects on or near the surface of the earth.
3. The force of gravity acts On all things including us all the time without their being aware of it.

Question 7.
Why does a car or a scooter come to rest once its engine is switched off?
Answer:
Only frictional force acts immediately after the vehicle is switched off. Vehicles only moves, when their mechanical force exceeds the frictional force. But when engine is switch off, the mechanical force becomes zero but frictional force persist. This brings vehicle (car or scooter) to rest.

Force and Pressure Class 8 Extra Questions Long Answer Type

Question 1.
Write the answer of following questions:
(a) Why is it comfortable to lift a school bag with broad straps than thin straps?
(b) Give an example to show that force can change the shape of an object.
Answer:
(a) Broad straps have larger area and decrease the pressure of the weight of the bag on the shoulders. But if the straps are thin the shoulders will be under large pressure and will be painful. That’s why we feel comfortable with a bag with broad straps.
(b) When we apply a force on an inflated balloon by pressing it between our palms the shape of a balloon changes. When a force is applied on the dough, it is rolled to make a Chapati.

Question 2.
(a) How does the medicine or water enter a dropper? Explain the mechanism.
(b) Name the type of force in the following cases:
(i) Rain drops falling on the earth.
(ii) Running a comb through dry hair.
(iii) A bar magneto suspended freely.
Answer:
(a) When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape-in the form of bubbles. On releasing the pressure on the bulb,water gets filled in the dropper. The rise of water in the dropper is due to atmospheric pressure which is acting on the water or the medicine and make it rise in the dropper.
(b) (i) Gravitational force or gravity
(ii) Electrostatic or electric force
(iii) Magnetic force

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Reaching the Age of Adolescence Class 8 Extra Questions and Answers Science Chapter 10 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 8 Science Question bank on a regular basis.

Class 8 Science Chapter 10 Extra Questions and Answers Reaching the Age of Adolescence

Extra Questions for Class 8 Science Chapter 10 Reaching the Age of Adolescence with Answers

Reaching the Age of Adolescence Class 8 Extra Questions Very Short Answer Type

Question 1.
When do human beings and many other kinds of animals become capable of reproduction?
Answer:
They become capable when they get reproductive maturity.

Question 2.
What brings about changes that make a child grow into an adult?
Answer:
Hormones bring about these changes.

Question 3.
What period covers the “teens”?
Answer:
The years 13 to 18 or 19 covers the ‘teens’.

Question 4.
What is the other name of adolescents?
Answer:
It is ‘teenagers’.

Question 5.
What is the conspicuous change during the puberty?
Answer:
The most conspicuous change during puberty is the sudden increase in height.

Question 6.
Upto what age girls grow in height faster than the boys ?
Answer:
Girls grow in height faster than boys upto 18 years of age.

Question 7.
Do all parts of the body grow at the same rate?
Answer:
No, all parts of the body do not grow at the same rate.

Question 8.
What factor does height depend on?
Answer:
Height depends upon the genes inherited from parents.

Question 9.
What happens to the quality of voice on puberty?
Answer:
Girl’s voiee become high-pitched and that of boys becomes deep or hoarse.

Question 10.
Where do endocrine glands release hormones?
Answer:
Endocrine glands release hormones directly into the blood-stream.

Question 11.
Name the secretion of ovaries on reaching puberty.
Answer:
Ovaries begin to produce female hormone called estrogen.

Question 12.
What makes ova in ovaries and sperms in testes mature?
Answer:
FSH or Follicle Stimulating Hormone makes ova mature in ovaries and sperms in testes.

Question 13.
What marks the beginning of reproductive period when one becomes capable of reproduction ?.
Answer:
It is puberty.

Question 14.
When does menstrual cycle stop?
Answer:
At 45 to 50 years of age, the menstrual cycle stops.

Question 15.
What do you understand by menopause?
Answer:
The stoppage of menstrual cycle is termed as menopause.

Question 16.
How many chromosomes do all humans have ?
Answer:
All humans have 23 pairs of chromosomes.

Question 17.
What determines the sex of unborn baby?
Answer:
Sex chromosomes of father determine the sex of unborn baby.

Question 18.
What are sex chromosomes? How many are they ?
Answer:
Chromosomes carrying genes for different sexual characters are termed as sex chromosomes. There are two sex chromosomes out of 23 pairs of chromosomes.

Reaching the Age of Adolescence Class 8 Extra Questions Short Answer Type 2

Question 1.
What is the hormone produced by pancreas ? What is the disease caused due to the non-production of that hormone ?
Answer:
Pancreas secretes insulin hormone. Insulin hormone regulates the levels of sugar in the blood. Its deficiency in the blood causes diabetes. In diabetic patients it is not secreted in required amount therefore blood sugar level rises and causes various harmful effects.

Question 2.
How do you calculate the probable full height of a adolescent? Give the formula for this purpose and state an example.
Answer:
The formula for calculation of full height (in cm) is given as follows :

Example: A girl is 10 years old and her height is 130 cm. At the end of the growth period, she is likely to be of what height?
Solution: \(\frac {130cm}{78}\) × 100 cm ≈ 166 cm.

Question 3.
By seeing the data of activity 10.1, can you read the graph and say at what age girls grow in height faster than the boys?
Answer:
Initially girls grow faster than boys but by about 18 years of age, both reach their maximum height. The rate of growth in height is different in different individuals. Some grow suddenly at puberty and then slow down, while others grow gradually.

Question 4.
What is the proportion of growth of the body parts in adolescence?
Answer:
All the parts of the body do not grow at the same rate. Sometimes the arms and legs of adolescents, look oversized and out of proportion with the body. But, soon the other parts catch up and result into a proportionate body.

Question 5.
How does body get adequate nourishment for growth?
Answer:
It is very important to eat the right kind of food especially during the growing years. This helps the bones, muscles and other parts of the body get adequate nourishment for growth.

Question 6.
What happens to the sex organs of boys and girls at puberty ?
Answer:
At puberty, male sex organs like the testes and penis develop completely. The testes also begin to produce sperms. In girls, the ovaries enlarge and eggs begin to mature. Also, ovaries start releasing matured eggs.

Question 7.
What are psychological changes in adolescence?
Answer:

1. Adolescence is also a period of change in a person’s way of thinking.
2. Adolescents are more independent than before and are also self-conscious.
3. Intellectual development takes place and they tend to spend considerable time in thinking.
4. It is often the time in one’s life when the brain has the greatest capacity for learning.
5. Sometimes, however, an adolescent may feel insecure while trying to adjust to the changes in the body and mind.

Question 8.
Describe menstrual cycle.
Answer:
Menstrual cycle is controlled by hormones. The cycle includes the maturation of the egg, its release, thickening of uterine wall and its breakdown if fertilization does not occur. In case the egg is fertilized, it begins to divide and then gets embedded in the uterus for further development.

Question 9.
What do you understand by the term ‘chromosomes’? Diseuss.
Answer:
These are the thread-like structures found in the nucleus of a cell. It contains genes. All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are sex chromosomes.

Question 10.
What should one do to keep the body healthy?
Answer:
To keep the body healthy, one needs to:

1. have a balanced diet,
2. observe personal hygiene and cleanliness regularly, and
3. undertake adequate physical exercises.

During adolescence, however, these become even more essential.

Question 11.
What are the required hygienic activities for boys and girls when they become adolescents?
Answer:
Everyday bath is more necessary for teenagers because the increased activities of sweat glands sometimes make the body smelly. If cleanliness is not maintained, there are chances of catching bacterial infection. Girls should keep track of their menstrual cycle and be prepared for the onset of menstruation. Undergarments should be changed every day. Cotton undergarments should be preferred.

Question 12.
How do HIV viruses enter the human bodies?
Answer:
HIV pass on to a normal person from an infected person by :

1. sharing the syringes used for injecting drugs.
2. from the infected mother to an infant through milk.
3. through sexual contact with a person infected with HIV.

Question 13.
What are myths and taboos regarding bodily changes in case of adolescents?
Answer:
There are many myths and taboos regarding bodily changes that adolescents experience. Some of these are given below :

1. A girl becomes pregnant if she looks at boys during menstruation.
2. The mother is responsible for the sex of the child.
3. A girl should not be allowed to work in the kitchen during menstruation. These should be discarded outrightly.

Question 14.
What are the drawbacks of early marriage and motherhood?
Answer:
The followings are the drawbacks of early marriage and motherhood :

1. Teenage girls are not prepared mentally or physically for motherhood.
2. Early marriage and motherhood cause health problems in the mother and the child.
3. It also curtails employment opportunities for a young woman and causes mental agony as she is not ready for the responsibilities of motherhood.

Reaching the Age of Adolescence Class 8 Extra Questions Long Answer Type

Question 1.
Describe the reproductive phase of life in females.
Answer:
Reproductive phase of life in females:

1. In females, the reproductive phase of life begins at puberty (10 to 12 years of age) and generally lasts till the age of approximately 45 .to 50 years.
2. The ova begins to mature with the onset of puberty. One ovum matures and is released by the ovaries once in about 28 to 30 days.
3. During this period, the wall of the uterus becomes thick. This is a natural preparation to receive the egg in case it is fertilized and pregnancy occurs.
4. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is known as menstruation.
5. Menstruation occurs once in about 28 to 30 days. Initially, menstrual cycle may be irregular and takes some time to become regular.
6. In case the egg is fertilized, it begins to divide and then gets embedded in the uterus for further development.

Question 2.
What are the changes appears in boys and girls on reaching the adolescence?
Answer:
Changes in boys:

1. Muscles of the body grow more prominently.
2. Facial hair (beard and moustache) appears.
3. Voice becomes hoarse, as voice box enlarges.
4. Under shoulder hair and pubic hair appears.

Changes in girls :

1. Region below the waist becomes wider.
2. Voice pitch increases.
3. Breast appears.
4. Menstrual cycle begins.
5. Under shoulder hair and pubic hair appears.

Question 3.
Name the various secretions (release) of endocrine glands.
Answer:
Endocrine glands release hormones directly into the bloodstream.

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Reproduction in Animals Class 8 Extra Questions and Answers Science Chapter 9 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 8 Science Question bank on a regular basis.

Class 8 Science Chapter 9 Extra Questions and Answers Reproduction in Animals

Extra Questions for Class 8 Science Chapter 9 Reproduction in Animals with Answers

Reproduction in Animals Class 8 Extra Questions Very Short Answer Type

Question 1.
Indicate whether the following statement is true or false:
A zygote is formed as a result of fertilization.
Answer:
True

Question 2.
Indicate whether the following statement is true or false:
An embryo is made of a single cell.
Answer:
False

Question 3.
Indicate whether the following statement is true or false:
Fertilization is necessary even in asexual reproduction.
Answer:
False

Question 4.
What is the name of reproduction in which fusion of male and female gametes takes place ?
Answer:
It is called as sexual reproduction.

Question 5.
What does testes produce ?
Answer:
The testes produce the male gametes called sperms.

Question 6.
What name is given to the babies born through in vitro fertilisation technique?
Answer:
Test-tube baby.

Question 7.
Draw the figure of a sperm.
Answer:

Question 8.
What happens when sperms come in contact with the egg?
Answer:
Fertilization takes place.

Question 9.
What is the other name of a fertilised egg?
Answer:
Zygote.

Question 10.
What is meant by in vitro fertilisation?
Answer:
It means that fertilisation is done outside the body through artificial meAnswer:

Question 11.
What is the fertilisation called which takes place inside the female body ?
Answer:
It is called internal fertilisation.

Question 12.
Which organisms undergo internal fertilisation?
Answer:
Humans, cows, goats, dogs, horses, elephants, buffaloes, etc.

Question 13.
Where does the external fertilisation take place?
Answer:
It takes place in water.

Question 14.
What happens after fertilisation?
Answer:
The fertilisation results in the formation of zygote, which begins to develop into an embryo.

Question 15.
When does a mother give birth to young one?
Answer:
When the development of the foetus is complete, the mother gives birth to young one.

Question 16.
What name is given to animals which give birth to young ones?
Answer:
They are called viviparous animals.

Question 17.
What name is given to the animals which lay eggs?
Answer:
They are called oviparous animals.

Question 18.
Do the young ones in all animals look alike?
Answer:
No, in some animals, the young ones may look very different whereas in other animals the young ones look alike.

Question 19.
Give the different stages in frog’s life-cycle.
Answer:
It is as follows:
Egg ➝ tadpole (larva) ➝ adult.

Question 20.
State the stages of life cycle of silkworm.
Answer:
It is as follows:
Egg ➝ larva or caterpillar ➝ pupa (cocoon) ➝ adult (moth).

Question 21.
What name is given to the drastic change that takes place during the development of an animal?
Answer:
Metamorphosis.

Question 22.
State the reproduction in which new individual develops from the buds in Hydra.
Answer:
Budding.

Question 23.
What is the name of the process of reproduction in Amoeba?
Answer:
Binary fission.

Question 24.
What name is given to a process in which production of an identical cell or a complete organism is done?
Answer:
Cloning.

Question 25.
Who performed the cloning process for the first time and where?
Answer:
Ian Wilmut and his colleagues at Roslin Institute in Edinburgh, Scotland.

Question 26.
What is the name of the sheep which was cloned for the first time in the world?
Answer:
Dolly.

Question 27.
When was Dolly bom? When and how she died ?
Answer:
It was born on 5th July 1996 and it died on 14th February 2003 due to a certain lung disease.

Reproduction in Animals Class 8 Extra Questions Short Answer Type 1

Question 1.
Define internal fertilization with two examples.
Answer:
Fertilization which takes place inside the female body is called internal fertilization. Examples: Humans, cows, etc.

Question 2.
Define oviparous animals with two examples.
Answer:
The animals which lay eggs are called oviparous animals. We haye seen the eggs of the birds. These animals lay eggs and then the chicks hatch out of the eggs. The examples of oviparous are hen, peacock, crow and parrot, etc.

Question 3.
What is uterus ? Is egg a single cell ?
Answer:
Uterus is the part where development of the baby takes place. Yes, an egg is a single cell.

Question 4.
What happens when oviducts of women are blocked?
Answer:
In some women oviducts are blocked. These women are unable to bear babies, because sperms cannot reach the egg for fertilisation.

Question 5.
Are test-tube babies born in test- tubes?
Answer:
No. Only fertilisation is done in test tubes and then the zygote is placed in the mother’s uterus.

Question 6.
Define foetus.
Answer:
The stage of the embryo in which all the body parts are identifiable is called foetus.

Question 7.
How long does embryo take to develop into chick?
Answer:
The embryo takes three weeks to develop into a chick. During this period hen sits on the eggs to provide sufficient warmth.

Question 8.
Do tadpoles look different from the adult?
Answer:
Yes, tadpoles look very different from the adult frog. In a few days, the tadpoles become frogs after complete metamorphosis.

Question 9.
Do human beings also undergo metamorphosis?
Answer:
In human beings, body parts of the young ones similar to the adults are present from the time of birth. So, human beings do not undergo metamorphosis.

Question 10.
Give examples of organisms undergoing asexual reproduction. Name the type of asexual reproduction in them.
Answer:
The organisms undergoing asexual reproduction are (i) Hydra, and (ii) Amoeba. The process of reproduction in Hydra is called budding and in Amoeba is known as binary fission.

Reproduction in Animals Class 8 Extra Questions Short Answer Type 2

Question 1.
Write a short note on sperms.
Answer:
Sperms are the male gametes produced by testes. Millions of sperms are produced by the testes. Though the sperms are very small in size, each has a head, a middle piece and a tail. Each sperm is a single cell having all the usual cell components. The tail present in the sperm enables it to swim in the oviduct to reach the egg and perform fertilisation process.

Question 2.
Describe briefly the female reproductive organs.
Answer:
The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and the uterus. The ovary produces female gametes called ova (eggs). The egg so produced is a single cell.

In human beings, a single matured egg is released into the oviduct by one of the ovaries every month. Uterus is the part where development of the baby takes place.

Question 3.
How does fertilization take place and how is zygote formed? Is zygote the beginning of a new individual?
Answer:
When the sperms come in contact with the egg, one of the sperms may fuse with the egg. The fusion of the egg and the sperm is known as fertilization, which produce zygote.

The process of fertilization is the meeting of an egg cell from the mother and a sperm cell from the father. So, the new individual inherits some characters from the mother and some from the father and, therefore, zygote is the beginning of a new individual.

Question 4.
Describe in vitro fertilization and production of test-tube babies.
Answer:
When some women are unable to bear babies because of blocked oviduct. In doctors collect freshly released egg and sperms and keep them together for a few hours for in vitro fertilization (fertilisation in test-tube).

After the zygote develops for about a week, it is placed in the mothers uterus. Complete development takes place in the uterus and the baby is born like any other baby.

Reproduction in Animals Class 8 Extra Questions Long Answer Type

Question 1.
Raju has a friend who believes that mother is responsible for the sex of a child because she gives birth to the child.
(a) How will Raju correct him using his knowledge of human chromosomes?
(b) What are the values shown by Raju?
Answer:
(a) No, Raju’s friend has wrong perception as mother is not responsible for the gender of the baby.

The sex of baby is depends upon the chromosome. In human beings 23rd pair are sex chromosomes named X and Y. All unfertilized egg have one X chromosome. But sperms carry different chromosome X as well as Y.

If a sperm containing X chromosome fertilizes the egg then the resulting fertilized egg contains two X chromosomes that will give birth to a baby girl whereas if a sperm containing Y chromosome fertilizes the egg then the resulting egg contains one X and one Y chromosome that gives birth to a baby boy. The value shown by Raju is ‘awareness’.

Question 2.
Describe the process of fertilisation in humans?
Answer:
In humans, the process of fertilisation is internal. For this millions of sperms from the male are transferred into the female body. The sperms swim in the oviduct with the help of their tails to reach the egg, when they come in contact with the egg, one of the sperms may fuse with the egg and fertilisation is completed. During fertilisation, the nuclei of the sperm and the egg fuse to form a single nucleus and zygote is formed.

Fertilisation makes the new individual inherits some characteristics from the mother and some from the father.

Question 3.
Draw a labelled diagram of male reproductive organ of human.
Answer:

Question 4.
Draw a labelled diagram of female reproductive organ of human.
Answer:

Question 5.
Name two animals which undergo metamorphosis. Also name the stages they pass by? Draw a diagram of different stgges of anyone animal.
Answer:
Two animals that undergo metamor­phosis are:
(i) Frog.
(ii) Silkworm.

Different stages of frog’s life-cycle :

Egg ➝ Tadpole (larva) ➝ Frog (adult).
Different stages of silkworm’s life-cycle:
Egg ➝ Caterpillar ➝ Cocoon (pupa) ➝ Moth (adult).

Hope the knowledge provided regarding the Reproduction in Animals Class 8 Extra Questions and Answers has helped you to the possible extent. For more info feel free to reach us and we will guide you at the earliest possibility. Stay connected to our site to avail latest updates on Extra Questions for Various Classes instantly.

Cell Structure and Functions Class 8 Extra Questions and Answers Science Chapter 8 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 8 Science Question bank on a regular basis.

Class 8 Science Chapter 8 Extra Questions and Answers Cell Structure and Functions

Extra Questions for Class 8 Science Chapter 8 Cell Structure and Functions with Answers

Cell Structure and Functions Class 8 Extra Questions Very Short Answer Type

Question 1.
List some of the basic functions carried out by all living organisms.
Answer:
Growth and development, movement, digestion, respiration, excretion, reproduction, etc.

Question 2.
What is a cork?
Answer:
Cork is a part of the bark of a tree.

Question 3.
What is meant by cell in Latin?
Answer:
Cell in Latin means “hollow space”.

Question 4.
What instrument helped in studying the living cells ?
Answer:
Microscope helped in studying the living cells.

Question 5.
How many cells are there in a human body ? What about their shape and size ?
Answer:
Human body has trillions of cells, which vary in shape and size on the basis of their functions.

Question 6.
What is the name of organism made of more than one cell?
Answer:
They are called multicellular.

Question 7.
What is meant by unicellular organisms?
Answer:
The single-celled organisms are called unicellular organisms, (uni = one, cellular = cell).

Question 8.
What is the size of cell of a bacteria?
Answer:
0.1 to 0.5 micrometre (mm).

Question 9.
What is tissue?
Answer:
Tissue is a group of similar cells performing a specific function.

Question 10.
Is cell wall present or absent in animal cell?
Answer:
It is absent.

Question 11.
When can chromosomes be seen?
Answer:
The chromosomes can be seen only when the cell divides.

Question 12.
Name two organisms which are made of single cell.
Answer:
Amoeba and Paramecium.

Cell Structure and Functions Class 8 Extra Questions Short Answer Type 1

Question 1.
When you cut your hair and nail, you do not feel pain. Why?
Answer:
When nail and hair are cut, we do not feel any pain because the cells of nails and hair are dead cells.

Question 2.
Why are we able to know a lot about cell structure today?
Answer:
Today, we know a lot about cell- structure and its functions because of the improved microscopes having higher magnification.

Question 3.
How are cells in the living organisms arranged?
Answer:
The cells in the living organisms are arranged in the similar manner as bricks are arranged to make a building.

Question 4.
What are basic structural units in buildings and living organisms ?
Answer:
Bricks in buildings and cells in the living organisms are the basic structural units.

Question 5.
Does egg of a hen represent a single cell ?
Answer:
Yes, egg of a hen represents a single cell and is big enough to be seen by unaided eye. _

Question 6.
While studying living cells with microscope, why do we use stains ?
Answer:
Stains (dyes) are used to colour the parts of the cell to observe and study their detailed structure clearly under microscope.

Question 7.
What is the difference between the functions of organisms with one cell and the organisms with multi cells?
Answer:
A single-celled organism captures and digests food, respires, excretes, grows and reproduces with its single cell. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues which in turn form organs.

Question 8.
What are the projections in Amoeba called? What do they do?
Answer:
The projections in Amoeba are known as pseudopodia (pseudo = false; podia = feet). These projections are in fact false feet and these appear and disappear as Amoeba moves or feeds.

Question 9.
What is the size of cells in living organisms.
Answer:
The size of cells in living organisms may be as small as a millionth of a metre or a few centimetre. However, most of the cells are microscopic in size and are not visible to the unaided eye.

Question 10.
What is the size of smallest cell? What is the size of red blood cells (RBCs) found in the human body?
Answer:
The size of the smallest cell is 0.1 to 0. 5 micrometres (pm) found in bacteria and that of red blood cells in the human body measure seven micrometres.

Question 11.
Give example of a large cell. State the size of the largest cell.
Answer:
The hen’s egg is an example of large. cell, which is quite large that it can be seen by an unaided eye. The largest cell, measuring 170 x 130 mm, is the egg of an ostrich.

Question 12.
What are white and yellow parts of an egg called?
Answer:
In an egg, a white material surrounds the yellow part. The white material is called albumin, and the yellow component is called yolk.

Question 13.
Define the terms tissue and organ.
Answer:

• Tissue: A tissue is a group of similar cells performing a specific function.
• Organ: It is a group of tissues performing a specific function.

Question 14.
Define nucleus. What is its role?
Answer:
The central dense round body in the centre of the cell is called nucleus. In addition to its role in inheritance, nucleus acts as control centre of the activities of the cell.

Question 15.
Define the term cytoplasm.
Answer:
The jelly-like substance found between the nucleus and the cell membrane is called cytoplasm.

Cell Structure and Functions Class 8 Extra Questions Short Answer Type 2

Question 1.
How do we observe the cell by microscope?
Answer:
To observe the cell by microscope, sometimes an organ has to be cut into sections to observe various smaller components. Some components in these sections are visible through the microscope after staining (dying) with coloured dyes.

Question 2.
What was the observation of a part of the bark of a tree (cork) by Robert Hooke?
Answer:
Robert Hooke in 1665 observed slices of cork under a simple magnifying device. He took thin slices of cork and observed them under a microscope. He noticed partitioned boxes or compartments in the cork slice. These boxes appeared like a honey-comb. He coined the term cell for each box.

Question 3.
Describe the differences and similarities between cell and brick.
Answer:
The cells in the living organisms are arranged and appear like bricks in a building. Both bricks in the building and cells in the living organisms are basic structural units. The buildings, though built of similar bricks, have different designs, shapes and sizes. Similarly, in the living world, organisms differ from one another but all are made up of cells. But, cells in the living organisms are complex living structures unlike non-living bricks.

Question 4.
Which part of the cell gives shape to it?
Answer:
Components of cells are enclosed in a membrane ealled cell membrane. This membrane provides shape to the cells in plants and animals. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity.

Question 5.
Is there any relation between the size of the body of the animal or plant with the size of the cell?
Answer:
The size of the cell, in fact, has no relation with the size of the body of the animal or plant. The size of the cell is related to its function. For example, nerve cells, both in the elephant and rat, are long and branched. They perform the same function of transferring messages in bigger as well as in the smaller organism.

Question 6.
How do cells/groups of cells perform different functions in multicellular organisms?
Answer:
The cell in a living organise is the basic structural unit. Cells combine to form tissues and a group of tissues is called an organ. These organs together constitute different systems in living beings and perform different functions. Each organ in the system performs different functions.

Question 7.
What constitutes cytoplasm?
Answer:
Cytoplasm is a fluid present between the cell membrane and the nucleus and is made up of basic elements like carbon (C), hydrogen (H), oxygen (O) and nitrogen (N). These are found in the form of chemical substances like carbohydrates, proteins and water.

Question 8.
What are the components present in cytoplasm?
Answer:
Besides nucleus, various other components-or organelles of cells are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes, etc. Cytoplasm, along with nucleus, forms the living substance of a cell. This living substance is called protoplasm.

Question 9.
What is nucleolus? Describe its function in brief.
Answer:
Nucleolus is a small, spherical, dense body in the nucleus. The function of nucleolus is to assemble ribosomes.

Question 10.
What are prokaryotic cells and eukaryotic cells ?
Answer:
The cells having nuclear material without nuclear membrane are termed prokaryotic cells. The organisms with these kinds of cells are called prokaryotes (pro = primitive; karyon = nucleus). Examples are bacteria and blue-green algae.

The cells having a well-organised nucleus with a nuclear membrane are designated as eukaryotic cells. The organisms having these cells are called eukaryotes (eu = true; karyon = nucleus). Examples are onion, cells and cheek cells.

Question 11.
What is the function of nucleoplasm?
Answer:
Nucleoplasm of nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance.

Cell Structure and Functions Class 8 Extra Questions Long Answer Type

Question 1.
Define the function of following:
(a) Plasma membrane
(b) Mitochondria
(e) Gene
(d) Vacuole
(e) Plastid

Answer:
(a) Plasma membrane: It is the outer covering of the cell which separates its contents from the surrounding medium. It is made up of lipids and protein. The main function of cell membrane is to regulate the movement of molecules in and out of the cell.

(b) Mitochondria: Mitochondria are the powerhouses of the cell because energy is released from the mitochondria after respiration. They are the sites cellular respiration of or oxidation of food.

(c) Gene: Genes carry information of heredity help in inheritance or transfer of characters from the parents to the offspring.

(d) Vacuoles: Cells contain water-filled, sac-like structures called as vacuoles. They are large-sized in plant cells while either absent or small-sized in animal cells.

(e) Plastids: The coloured bodies in the cytoplasm of the cells are called plastids. Plastids are found in plant cells only. Chloroplast i.e., the green plastids contains chlorophyll for the process of photosynthesis. Through this process, plant cell prepares food which is ultimately stored in the form of starch.

Question 2.
What are the basic components of a cell? Describe their functions.
Answer:
The basic components of a cell are:
(i) Cell membrane
(ii) Cytoplasm
(iii) Nucleus

(i) Cell membrane separates the inside contents of the cell from outside. It being porous, allows movement of substances or materials both inwards and outwards of the cell.
(ii) Cytoplasm contains the cell organelle, which performs different functions.
(iii) Nucleus acts as a control centre of a cell. In addition to it, it also facilitates inheritance.

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