Selina ICSE Solutions

Selina Concise Physics Class 6 ICSE Solutions – Light

by

Selina Concise Physics Class 6 ICSE Solutions – Light

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Physics ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Physics Chapter 5 Light

  • Synposis
  • Light itself is not visible, but in the presence of light other objects become visible A.
  • Light is defined as the external physical cause that affects the eye to produce the sensation of vision.
  • Two types of sources of light are:
    (1) Natural sources such as sun, stars andjugnu.
    (2) Artificial sources such as fire, electric lamp, electric tube light, a burning candle, a kerosene lamps heated bodies, etc.
  • The bodies which themselves emit light are called luminous bodies. Examples: torch, electric lamps electric tube light, burning candle, kerosene lamp, sun, stars. Jugnu etc.
  • The bodies which do not emit light by their own, but they become visible because of the light falling on them from a luminous body, are called non-luminous bodies. Examples: moon, earth, table, book, chair etc.
  • A medium which allows the passage of light through it easily, is called a transparent medium. Examples: glass, air, water etc.
  • A medium which allows only a small amount oflight to pass through it, is called a translucent medium. Examples: ground glass, tracing paper etc.
  • A medium which does not allow anydight to pass tough it, is called an opaque medium. Examples: wood, metals etc.
  • Light travels in a straight line path. This is called the rectilinear propagation oflight.
  • The pin hole camera is a simple application of the rectilinear propa – gation oflight.
  • The image (or picture) formed in a pin hole camera is upside down (i.e. inverted). On increasing the distance of screen from the pin hole, the size of image increases.
  • The shadow of an opaque object is the dark patch obtained on the screen when that opaque object is placed in the path of light.
  • Shadow is formed because light travels in a straight line path.
  • The shadow is similar to the shape of the object.
  • The part of the shadow where no light reaches from the source is completely dark and is called the umbra.
  • The part of the shadow where light reaches from only a portion of the source is partially dark and is called the penumbra.
  • There is only umbra in the shadow of an opaque object due to a point source. The umbra is bigger in size than that of the obj ect. The umbra increases in size if the screen is moved away from the object.
  • The shadow of an object due to a light source smaller than the object contains an umbra surrounded by a penumbra. The umbra is bigger in size than that of the object. Both the umbra and penum¬bra increase in size as the screen is moved away from the source.
  • The shadow of an opaque object due to a light source bigger than the object contains an umbra (which is much smaller in size than the object) surrounded by a penumbra. The umbra diminishes while the penumbra increases in size if the screen is moved away from the object.
  • Lunar and solar eclipses are the examples of formation of shadows in nature.
  • A lunar eclipse is caused on a certain full moon night when the earth comes in between the sun and the moon so that the earth casts its shadow on the moon.
  • A solar eclipse is caused on a certain new moon’s day when the moon comes in between the sun and the earth so that the moon casts its shadow

Test yourself

A. Short Answer Questions

1. Write true or false for each statement

(a) The moon is a natural source of light.
Answer. False

(b) The moon is self luminous.
Answer. False

(c) We can see an object through an opaque medium.
Answer. False

(d) Light passes through glass.
Answer. True

(e) Light travels in a straight line path. .
Answer. True

(f) Image formed in a pin hole camera is real.
Answer. True

(g) The image in a pin hole camera gets blurred if the hole is made bigger.
Answer. True

(h) A shadow is formed because light travels in a straight line path.
Answer. True

(i) Solar eclipse occurs when the sun comes in between the earth and the moon.
Answer. False

(j) If the shadow of earth falls on the moon, the eclipse is called the lunar eclipse.
Answer. True

2. Fill in the blanks

(a) Light gives us the sensation of vision.
(b) The sun is a natural source of light.
(c) A medium through which light cannot pass is called the opaque medium.
(d) A medium which allows light to pass through it easily is called the transparent medium.
(e) Moon is a non-luminous body.
(f) Light travels in a straight line path.
(g) In a pin hole camera, the image formed is inverted and real.
(h) The darkest portion of a shadow is called the umbra.
(i) The less dark portion of a shadow is called the penumbra.
(j) Lunar eclipse occurs when the earth comes in between the moon and the sun.

3. Match the following columns
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 1
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 2

4. Select the correct alternative

(i) The natural source of light is

  1. candle flame
  2. electric lamp
  3. sun
  4. kerosene lamp

(ii) The formation of inverted image in a pin hole camera shows that

  1. light enables us to see
  2. light travels in a straight line path
  3. light can pass through the pin hole
  4. light does not pass through the pin hole

(iii) The luminous body is

  1. a lighted bulb
  2. earth
  3. noon
  4. table

(iv) Umbra is a region of

  1. complete darkness
  2. partial darkness
  3. complete brightness
  4. partial brightness

(v) Penumbra is a region of

  1. complete darkness
  2. complete brightness
  3. partial brightness
  4. none of the above

(vi) Solar eclipse occurs on

  1. every new moon’s day
  2. certain new moon’s day
  3. every full moon’s day
  4. certain full moon’s day

(vii) Lunar eclipse occurs on

  1. every full moon’s night
  2. certain full moon’s night
  3. every new moon’s day
  4. certain new moon’s day

B. Short/Long Answer Questions

Question 1.
What is light ? Define it.
Answer:
Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

Question 2.
How does light make an object visible ?
Answer:
An object becomes visible to us when the light after striking the object reaches our eyes. Light itself is not visible, but light makes objects visible to us.

Question 3.
Name two natural sources of light.
Answer:
Sun, stars,jugnu, firefly.

Question 4.
List two artificial sources of light.
Answer:
Electric bulb, torch, an oil lamp, fluorescent tube, candle.

Question 5.
Differentiate between the luminous and non-luminous bodies. Give two examples of each.
Answer:
Difference Between
Luminous
The bodies which have light of their own e.g. sun stars, bulb, candle, oil lamp, torch, a lantern.
Non-Luminous
The bodies-which do not have their own Iight.e.g. moon, chair, table. When light falls on them, they become visible.

Question 6.
Is the moon a luminous object ?
Answer:
Moon is not a luminous body, it is nbn-luminous body. It has no light of its own.

Question 7.
What do we call a body that shmes on its own ?
Answer:
The bodies that shines onits ownor whichthemselves emittheir own light are called the luminous bodies.

Question 8.
What do we call an electric bulb producing light ?
Answer:
Luminous object.

Question 9.
What is a transparent medium ? Give two examples.
Answer:
Amedium which allows the passage of light through it easily,is called a transparent medium.
Examples: glass, air, water etc.

Question 10.
Explain the difference between a transparent, a translucent and an opaque medium. Give two examples of each.
Answer:

  1. Transparent objects — Those objects through which light can pass easily are called transparent obj ects. e.g. Water, glass, air.
  2. Translucent object— The ohj ect through which light can pass partially are called translucent object, e.g. tracing paper, waxed paper.
  3. Opaque object— The objects which do not allow the light to pass through are called opaque objects, e.g. wood.

Question 11.
What do we call a substance through which we cannot see light ? Give an example of such a substance.
Answer:
A substance through which we cannot see light is called an opaque medium.
Examples:  Wood, metals, butter paper and black paper etc.

Question 12.
What do we call a substance through which light passes ? Give an example of such a substance.
Answer:
A substance through which light passes is called a transparent substance.
Examples: glass, air, water etc.

Question 13.
Can a transparent medium form an image ? Explain your answer.
Answer:
No, a transparent medium cannot form image. All the light that passes through a transparent medium completely pass through the substance. For the formation of image it is must that the light rays get reflected through the surface.

Question 14.
How can you obtain a point source of light ?
Answer:
A point source of light is obtained either by placing a screen having a fine hole, in front of die luminous body or by placing the luminous body inside a box having a fine hole on one of its side.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 3

Question 15.
Define the terms : a ray of light and a beam of light.
Answer:
The light travelling in any one direction in a straight line is called a ray of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 4
A group of light rays given out from a source is called a beam of light
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 5

Question 16.
What do you mean by ‘rectilinear propagation of light’ ?
Answer:
Light travels in a straight line path. This is called the rectilinear propagation of light.

Question 17.
Describe an experiment to show that light travels in a straight line path.
Answer:
Take three cardboards A, B and C each about 25 cm square. Take a pin and make a small hole in each cardboard at the same height. Suspend the cardboard pieces by separate threads vertically from a support such that each hole is at the same height, as shown. Pass a string through the holes and pull it taut. This makes the three holes in a straight line. Now take out the string.
Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen.
Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the cardboard C. You do not see the candle flame. The reason is that light travels in a straight line and now the holes in the cardboards A, B and C are not in a straight line.
Conclusion: Light travels in a straight line path called the rectilinear propagation of light.

Question 18.
In which of the following two arrangements (a) and (b) shown in the diagram, you can see the light of the bulb ? Explain Your answer
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 6
Answer:
We can see the light of the bulb in the arrangement (a).
This is so because in arrangement ‘a’ the rod is straight and light travels in a straight line path.
Whereas in arrangement ‘b’ the rod is bent. So the light cannot pass through it.

Question 19.
Name a simple application of the rectilinear propagation of light
Answer:
The simple applications of rectilinear propagation of light are pin hole camera, formation of shadows and elipses.

Question 20.
What is a pin hole camera ? Draw a neat and labelled diagram to show the formation of image of a lighted candle by it.
Answer:
The pin hole camera is a simple application of the rectilinear propagation of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 7

Question 21.
Explain the formation of image of a luminous object in a pin hole camera with the aid of a neat diagram.
Answer:
When a luminous object AB, such as a lighted candle, is placed in front of the pin hole, an inverted picture A’ B’ of the candle is
obtained on the tracing paper. This picture A’ B’ is called the image. The image obtained is upside down (i. e. inverted). The reason is that the light travels in a straight line path. Hence light from the upper point A of the candle passes through the pin hole and strikes
the tracing paper at A’. Similarly, light from the lower point B of the candle passes through the pin hole and strikes the tracing paper
(or screen) at B’. Light from all the other points between A and B, on passing through the pin hole strikes the tracing paper in between
A’ and B’. As a result, an inverted image of the candle is seen on the tracing paper Fig shows the simple ray diagram for die formation of image.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 8

Question 22.
State two factors which affect the size of image formed in a pin hole camera.
Answer:
Factors affecting the size of the image :
The size of image depends on the following two factors:

  1. The distance of screen (i.e. tracing paper) from the pin hole, and
  2. The distance of obj ect (i.e. candle) in front of the pin hole.

Question 23.
Is the image obtained in a pin hole camera erect or inverted ? Give reason for your answer.
Answer:
Image obtained in a pin hole camera is inverted.
The reason is that the light travels in a straight line path. Hence light from the upper point of the candle passes through the pin hole and strikes the tracing paper in the lower point. Similarly light from the lower point of the candle passes through the pin hole and strikes the tracing paper at the upper point.

Question 24.
How is the image affected in a pin hole camera when another fine hole is made near the first pin hole ?
Answer:
If another pin hole is made near the first pin hole, two images are formed on the screen, one due to each of the two pin holes. If the holes are very close, the two images tend to overlap each other. As a result, a blurred image will be seen.

Question 25.
State the effect on the image in a pin hole camera if

  1. The hole is made bigger.
  2. The luminous object is moved towards the pin hole.
  3. The length of the pin hole camera is increased (le. the screen is moved away from the pin hole).

Answer:

  1. If the hole is bigger than a pin hole, again a blurred image in seen. The reason is that a bigger hole is equivalent to a large number of pinholes. Each pin hole produces one image. These images overlap each other resulting in a blurred image.
  2. If the object is moved towards the pin hole the size of the image increases.
    The size of image / The size of object = Distance of screen from pin hole / Distance of object from pin hole
  3. When the length of the pin hole camera is increased. C is the screen is moved away from the pinhole, the size of image also increases.

Question 26.
What is a shadow ? Give a reason for its formation.
Answer:
Shadow : When light falls on an opaque object, light is obstructed and a dark patch on a screen kept behind is called shadow. This is because light propagates in straight line. If distance between obj ect and screen is less, the shad o w will be (umbra) dark and smaller.
If the distance is increased shadow will be dim and larger.

Question 27.
Draw a ray diagram to show the formation of shadow of an opaque object by a point source of light. How is the size of shadow affected if the screen is moved away from the object?
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 9
If we move the screen away from the object, the shadow increases in size.

Question 28.
State two differences between an umbra and a penumbra.
Answer:
Umbra

  1. It is the portion of shadow where no light reaches from the source of light due to the opaque object.
  2. It is completely dark.

Penumbra
It is the portion of shadow where a portion of light from the source of light reaches the shadow even in the presence of the opaque object in between them.
It is not completely dark, but is dim (or less bright).

Question 29.
Draw a ray diagram to show the formation of umbra alone.
Answer:
Formation of umbra alone.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 10

Question 30.
Draw a ray diagram to show the formation of umbra and penumbra both. Label the parts umbra and penumbra in your diagram.
Answer:
If your move the screen away from the object, the shadow increases in size. Formation of umbra and penumbra both.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 11

Question 31.
In each of the following diagrams, draw rays to form umbra and penumbra on the screen.
(a)

Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 12
(b)

Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 13
Answer:
(a)A’B’—umbra
Umbra alone is obtained on the screen when the opaque object is illuminated by a point source of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 14
(b)
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 15
EF is Penumbra CD is umbra.

Question 32.
State the conditions when only the penumbra of an opaque object is obtained on the screen.
Answer:
If the size of source of light is bigger than the size of the opaque object, the size of umbra is very small. If the screen is moved away from the object, the umbra vanishes and only the penumbra remains.

Question 33.
Why is it that the birds flying in the sky do not cast their shadow on the earth ?
Answer:
We do not see the shadow of a bird flying high up in air because in their shadow, the umbra is absent and the penumbra is too large and too faint that it is not visible as the distance of screen (i.e. earth) is very large from the object (i.e. bird).

Question 34.
Why are shadows at noon shorter than in the morning or in the evening ?
Answer:
At noon the sun is directly overhead. So, the sun rays fall vertically on the body. Hence the shadow is very short. In the morning and evenings, the sun rays fall in an inclined position. So, the shadows are long.

Question 35.
What is an eclipse ? Name the two types of eclipses.
Answer:
Eclipses are the examples of formation of shadows in nature. There are two kinds of eclipses:

  1. Lunar eclipse (the eclipse of the moon), and
  2. Solar eclipse (the eclipse of the sun).
    Lunar eclipse is due to the formation of shadow of earth on moon and solar eclipse is due to the formation of shadow of moon on earth.

Question 36.
When does a lunar eclipse take place ? Does it occur on every full moon’s night ?
Answer:
A lunar eclipse occurs when the earth comes in between the sun and moon and casts its shadow on moon. On a full moon night, the moon rises in the east after sun sets in the west. On such a night, the sun and moon are on the opposite sides of the earth. The shadow of the earth falls on the surface of the moon therefore moon is not visible to us. This is lunar eclipse as shown in the figure.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 16

Question 37.
Draw a diagram to show the formation of lunar eclipse.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 17

Question 38.
When does a solar eclipse take place ? Does it occur on even’ new moon’s day ?
Answer:
Solar eclipse— On a certain moon’s day the moon, happens to come in between the sun and the earth. They come in a straight line. In such a situation, the moon being smaller in size casts its shadow only on a limited region on the earth. In these regions of the earth, the solar eclipse occurs.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 18

Question 39.
Draw a diagram to show the formation of solar eclipse.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 19

Question 40.
What is annular solar eclipse ? Draw a labelled diagram to show its formation.
Answer:
An annular solar eclipse occurs when only the tip of the umbra of the moon falls on the earth. From the point D, the sun will appear to be completely obstructed by the moon, only the outer rim of the sun, called corona, is then visible for a very short time which is known as the diamond ring. The formati on of annular solar eclipse is shown below.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 20

Selina Concise Physics Class 6 ICSE Solutions – Force

by

Selina Concise Physics Class 6 ICSE Solutions – Force

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Physics ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Physics Chapter 3 Force

  • Synposis
  • A body not changing position with time with respect to a nearby fixed object is said to be at rest.
  • A body changing position with time with respect to a nearby fixed object is said to be in motion.
  •  Force is a push or pull which can change the state of rest or motion of the body or can change the size and shape of the body (i.e. it can deform a body).
  • A force applied on a body can
    (a) move it, if it is not in motion
    (b) stop it, if it is moving
    (c) increase or decrease its speed
    (d) change its direction of motion
    (e) change its shape or size if it is not free to move.
  • Force is defined as that cause which changes the state of rest or the state of motion of a body and can also deform it.
  • A force has both the magnitude and the direction.
  • When two forces act in opposite directions, the net force is equal to the difference of these forces, in the direction of the bigger force.
  • When two forces act on a body which are equal in magnitude but opposite in direction, the net force on the body is zero.
  • Forces are of two types :
    1. contact forces and
    2. non-contact forces (or forces at a distance).
  • Contact forces are
    1. the muscular force applied as push or pull,
    2. force of friction
    3. the force of reaction normal to the surface and
    4. the force of tension in a string pulled by a load.
  • Non-contact forces are
    1. gravitational force
    2. electrostatic force and
    3. magnetic force
  • The weight of a body is the force with which the earth pulls the body.
  • The unit of weight (or force) is kgf not kg which is unit of mass.
  • Friction is a force that opposes the motion.
  • Friction always acts in a direction opposite to the direction of motion.
  • The cause of friction is the interlocking of the irregular projections on the two surfaces in contact. ‘
  • The force of friction depends on:
    (a) the smoothness (or roughness) of the surfaces in contact, and
    (b) the weight of the sliding (or rolling) body.
  • The force of friction does not depend on the area of the surfaces in contact.
  • The disadvantages of friction are :
    (a) Friction opposes the motion
    (b) Friction produces heat
    (c) Friction causes wear and tear
    (d) Friction reduces efficiency
  • Friction can be reduced by
    (a) making the surfaces smooth
    (b) the use of lubricants
    (c) the use of ball bearings
    (d) streamlining the shape of the moving body.
  • The maximum force exerted by a surface on a body so long as it remains stationary is called the force of static friction.
  • The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction.
  • The minimum force required to roll a body on a surface is called the force of rolling friction.
  • Rolling friction is less than the sliding friction and sliding friction is less than the static friction.
  • Friction is advantageous to us in almost all activities of our life.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) The frictional force acts in the direction of motion of body
Answer. False

(b) The unit of weight is kilogram
Answer. False

(c) A force can change the direction of motion of a moving body.
Answer. True

(d) A force increases the mass of the body when applied on it.
Answer. False

(e) The force of friction is always disadvantageous.
Answer. False

(f) The sliding friction is more than the rolling friction.
Answer. True

(g) Liquids offer more friction than the gases.
Answer. True

(h) A wet oily road offers more friction than a dry rough road.
Answer. False

2. Fill in the blanks

(a) Force is applied as push or pull.
(b) On squeezing a gum tube, its shape changes.
(c) On pulling a string, its length increases.
(d) A moving football when kicked, its direction of motion changes.
(e) On applying brakes on a moving car, its speed slows down.
(f) We use ball bearings to reduce the friction.
(g) Friction opposes the motion.
(h) Lubricants are used to reduce friction.
(i) Friction causes wear and tear of moving parts of machine.

3. Match the following columns

Selina Concise Physics Class 6 ICSE Solutions Chapter 3 Force 1

Answer.

Selina Concise Physics Class 6 ICSE Solutions Chapter 3 Force 2

4. Select the correct alternative 
(a) A body falls downwards because of

  1. electrical force
  2. gravitational force
  3. mechanical force
  4. magnetic force.

(b) A force does not change

  1. mass
  2. length
  3. shape
  4. state of motion.

(c) A force to be expressed correctly requires

  1. only the magnitude
  2. only the direction
  3. both the magnitude and direction
  4. none of the above.

(d) Friction

  1. promotes motion
  2. opposes motion
  3. acts in the direction of motion
  4. is always a nuisance.

(e) Friction is reduced by

  1. making the surfaces wet
  2. making the surfaces dry
  3. making the surfaces rough
  4. sprinkling sand on the surface.

(f) Friction

  1. causes wear and tear
  2. produces heat
  3. stops a moving body
  4. has all the above disadvantages

(g) Friction is increased if

  1. an oil is sprayed
  2. the surfaces are made wet
  3. the surfaces are made dry
  4. the surfaces are polished

B. Short/Long Answer Questions

Question 1.
Name the term used for the push or pull ?
Answer:
Force

Question 2.
Give one example each of a force as

  1. a push
  2. as pull
  3. a stretch and
  4. a squeeze.

Answer:

  1. a push — To1 open a door, we push it.
  2. as pull — To move a grass roller on a lawn, it is pulled by a gardener.
  3. a stretch — Stretching a rubber string.
  4. a squeeze —Change in shape of a sponge on squeezing.

Question 3.
Explain the meaning of the term force.
Answer:
Force: Force is a physical cause that changes or may tend to change the state of rest or the state of motion of an object. The S.I. unit of force is Newton.

Question 4.
What effect can a force have on a stationary body ?
Answer:
When a force is applied on a stationary body, it begins to move.

Question 5.
What effects can a force have on a moving body ?
Answer:
When a force is applied on a moving body, it can be made to stop or it can change the direction of motion.

Question 6.
What effect can a force produce on a body which is not allowed to move ?
Answer:
When a force is applied on a body which is not free to move, it gets deformed i. e., the shape or size of the body changes.

Question 7.
Give one example each to indicate that the application of a force

  1. produces motion
  2. stops motion
  3. slows down motion
  4. changes the direction of motion
  5. deforms a body

Answer:

  1. A car originally at rest when pushed, begins to move.
  2. A moving bicycle is stopped by applying the brakes.
  3. The speed of a moving vehicle is slowed down by applying the brakes.
  4. A player kicks a moving football to change its direction of motion.
  5. On stretching a rubber string, its length increases.

Question 8.
State the effect produced by a force in the following cases :
(a) The sling of a rubber catapult is stretched
(b) A man pushes a heavy cart
(c) A player uses his stick to deflect the ball .
(d) A cyclist applies brakes
(e) A spring is compressed.
Answer:
(a) The shape and size of catapult changes i.e., its length increases.
(b) The heavy cart begins to move.
(c) The direction of the ball changes.
(d) The speed of the moving cycle is slowed down.
(e) There is change in size and shape of spring.

Question 9.
Name the two kinds of forces in nature.
Answer:
Two kinds of forces in nature are :

  1. Contact forces
  2. Non contact forces

Question 10.
Name the type of force which acts in the following cases:
Answer:
(a) A coolie lifts a luggage
Answer. Muscular force
(b) A bicycle comes to rest slowly when the cyclist stops pedalling
Answer. Frictional force
(c) A stone falls from a roof
Answer. Gravitational force.
(d) A comb rubbed with silk attracts the bits of paper
Answer. Electrostatic force
(e) A string hangs with a load
Answer. Force of tension.
(f) A horse moves a cart
Answer. Muscular force
(g) A magnet attracts an iron pin
Answer. Magnetic force
(h) A boy opens the door
Answer. Muscular force
(i) An apple falls from a tree
Answer.Gravitational force
(j) A man rows a boat.
Answer. Muscular force.

Question 11.
What do you mean by the gravitational force ? Give an example to illustrate it.
Answer:
The force of attraction on a body by earth is called gravitational force.
Example : The leaves and fruits fall from a tree downwards towards the ground, water in a river flows down streams, a ball thrown up goes to a height and then returns back on ground are some examples of motion due to gravitational force.

Question 12.
Define the term “weight of a body”
Answer:
Weight: The weight of the body is the force with which the earth attracts it towards the centre. It depends on acceleration due to gravity.

Question 13.
What do you understand by the term friction ?
Answer:
Friction: Friction is that force which opposes the relative motion between the two surfaces that are in contact with each other.

Question 14.
Give an example to illustrate the existence of force of friction.
Answer:
If we stop paddling our bicycle, it gradually slows down and ultimately it stops after travelling a certain distance. This is due to frictional force between bicycle and ground.

Question 15.
What is the cause of friction ?
Answer:
The cause of friction is the interlocking of the irregular projections on the two surfaces in contact.

Question 16.
State two factors which directly affect the force of friction.
Answer:
Two factors which directly affect the force of friction are :

  1. The smoothness of the surface.
  2. The presence of solid, liquid or gas around the moving body.

Question 17.
In which case will there be more friction between the truck and the road : when the truck is empty or when it is loaded ?
Answer:
When the truck is loaded there will be more friction between the truck and the road.

Question 18.
Which offers more friction on a body : a glass surface or a wooden surface ?
Answer:
Wooden surface offers move friction on a body.

Question 19.
Name the three kinds of friction.
Answer:
Friction is of three kinds :

  1. Static friction
  2. Sliding friction,
  3. Rolling friction

Question 20.
List three disadvantages of friction.
Answer:
Disadvantages of friction:

  1. Friction produces heat which damages the moving parts of a machine.
  2. Friction produces wear and tear on the contacting surfaces. This reduces the life of machine parts, tyres and shoe soles.
  3. A lot of energy is wasted due to friction to overcome it before moving.

Question 21.
When you apply the brakes, the bicycle stops and the rim of the wheel becomes hot. Explain the reason.
Answer:
It is due to friction between the brakes and the rim of the wheel that it becomes hot.

Question 22.
The eraser gets smaller and smaller as you use it more and more. Explain the reason.
Answer:
The eraser gets smaller and smaller as we use it more and more due to frictional force causing wear and tear of the eraser.

Question 23.
List three ways of reducing friction.
Answer:
Ways to reduce friction:

  1. Providing ball bearings or wheels between the moving parts of machine or vehicles reduce friction and allow smooth movement as rolling friction is less than sliding friction.
  2. Oiling or lubricating (with graphite or grease) the moving parts of a machine reduces friction. Fine powder like talcum powder also works as a lubricant to reduce friction.
  3. Polishing the rough surface reduces friction offered by it.
  4. Streamlining (giving special shape to experience minimum drag) the bodies of aeroplanes, cars, boats and ships help reduce drag (fluid friction) while travelling through air or water.

Question 24.
It is difficult to open an inkpot with greasy or oily hands. Explain.
Answer:
When the hands are oily, then the oil acts as lubricant and reduces the friction.
As the friction force is less, it is difficult to get grip of the inkpot and it becomes difficult to open it.

Question 25.
It is difficult to walk on a wet road. Explain.
Answer:
When the road becomes wet after rain, friction is reduced and hence, the road becomes slippery.

Question 26.
Give three examples to illustrate that friction is a necessary evil.
Answer:
The examples to illustrate that friction is a necessary evil are:

  1. If friction were absent, we would not be able to walk.
  2. Friction is necessary to burn a matchstick.
  3. It is due to friction that we can write on a board by a chalk.

Question 27.
Define

  1. static friction
  2. sliding friction and
  3. rolling friction

Answer:

  1. The maximum force exerted by a surface on a body so long as it remains stationary is called the force of static friction.
  2. The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction..
  3. The minimum force required to roll a body on a surface is called the force of rolling friction.

Question 28.
Arrange the following in descending order :

  1. static friction
  2. sliding friction and
  3. rolling friction?

Answer:
Static friction > Sliding friction > Rolling friction.

Question 29.
A body needs a force F1 just to start motion on a surface, a force F2 to continue its motion and a force F3 to roll on the surface. What is

  1. the static friction
  2. sliding friction and
  3. rolling friction ? State whether F2 is equal, less than or greater than (1) F1 and (2) F3.

Answer:

  1. F1 = Static friction
  2. F2 = Sliding friction
  3. F3 = Rolling friction
    F1 > F2 > F3
    F2 is less than F1 but greater than F3.

Selina Concise Biology Class 6 ICSE Solutions – Respiratory System

by

Selina Concise Biology Class 6 ICSE Solutions – Respiratory System

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Biology. You can download the Selina Concise Biology ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Biology for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Biology Chapter 5 Respiratory System

Synopsis —

  • The energy released during respiration is stored as chemical energy in the form of ATP — adenosine tri-phosphate.
  • Aerobic respiration —
    C6H12O6 + 6O2   →  6CO2 + 6H2O + 38 ATP
    Anaerobic respiration —
    Selina Concise Biology Class 6 ICSE Solutions - Respiratory System 1
  • During vigorous exercise, the cells respire anaerobically and form lactic acid which accumulate in the muscle cells causing fatigue and pain.
  • The respiration in humans occur in three phases:

    1. Breathing
    2. Gaseous Transport
    3. Cellular respiration
  • The oxygen inhaled in combines with haemoglobin present in the red blood cells forming an unstable compound called oxyhaemoglobin.
  • The nasal chamber has got hairy lining to prevent dust particles from reaching the lungs. The lining also has mucous to trap germs and dust.
  • The common passage for the food and air is the pharynx.
  • Trachea is also called the wind pipe.
  • The voice box or the Adam’s apple is the larynx which contains ligamentous folds called vocal cords.
  • Incomplete closure of epiglottis during swallowing causes coughing.
  • The trachea is formed of incomplete C-shaped cartilaginous rings which keep them permanently distended.
  • The lungs are protected outside by the two membranes called outer and inner pleura.
  • Left lung is slightly smaller than the right lung.
  • Left lung has two lobes while the right lung has three lobes.
    Selina Concise Biology Class 6 ICSE Solutions - Respiratory System 2
  • Breathing is an involuntary act.
  • Even after maximum forced expiration, some air is left in the lungs called residual volume.
  • In normal adults, the breathing rate is 12-18/minute while a newborn breathes at about 60 breaths per minute.
  • Asphyxiation is a condition in which blood becomes venous by the accumulation of excess carbon dioxide and the oxygen supply is diminished.
  • The gas composition in artifical respiration is 95% oxygen, 5% carbon-di-oxide.
  • Snoring: Vibration of soft palate during breathing when mouth is kept open while sleeping.
  • Sneezing: It is a protective mechanism through which a foreign irritant particle is thrown out of the lungs suddenly and forcefully.
  • Hiccups: Jerky incomplete inspiration due to blockage of the respiratory tract.

Review Questions

Multiple Choice Questions

1. Put a tick (✓) against the most appropriate alternative in the following statements.

(i) In humans, taken in of the air through nostrils into the nasal cavity is called
(a) Inhalation
(b) Exhalation
(b) Cellular respiration
(d) Internal respiration

(ii) The front opening of the wind pipe is guarded by —
(a) Glottis
(b) Exoglottis
(c) Epiglottis
(d) Trachea

(iii) The process during which food is oxidised and energy is released is called
(a) Cellular respiration
(b) Excretion
(c) Digestion
(d) Transpiration

Short Answer Questions

1. Answer briefly the following:

  1. Why do our body cells require oxygen ?
    Ans. Body cells require oxygen for the break down of glucose and release energy for carrying out various life functions.
  2. What is the difference between breathing and respiration?
    Ans. Breathing is a simple physical process of drawing in air through the nostrils and expelling it out.
    Respiration is a chemical process which involves the breakdown of food and release energy.
  3. Name the by-product formed during the oxidation of food.
    Ans. The by- products formed are
    1. carbon-di-oxide
    2. water
  4. Name the agency which transports oxygen to all parts of the body.
    Ans. Blood .
  5. What is the role of epiglottis during swallowing ?
    Ans. Epiglottis closes the wind pipe at the time of swallowing.

Question 2.
Describe in brief the function of ribs and diaphragm in breathing.
Answer:

  1. Ribs muscles—During inhalation, the ribs muscles contract and push the ribs upward and outward.
    During exhalation these relax and cause the ribs to return to original position.
  2. Diaphragm: During inhalation it becomes flattened while during exhalation it relaxes and moves up and back into convex (dome) shape.

Question 3.
Name the gas which is expelled out during expiration. Where is it originally produced in our body ?
Answer:
The gas which is expelled during expiration is carbon-di¬oxide. It is produced as a result of oxidation of glucose in the tissues. (Cellular respiration)

Question 4.
Name the following:

  1. Respiratory process
  2. in which oxygen is not utilized.
    Ans. Cellular respiration
  3. Respiratory process in which oxygen is utilized.
    Ans. Gaseous transport
  4. The microscopic air-sacs of the lungs.
    Ans. Alveoli
  5. The two membranes which protect the lungs.
    Ans. Outer pleura, inner pleura

Long Answer Questions:
Question 1.
Why is a respiratory system necessary ?
Answer:
Respiratory system is very important for the body. Respiration in human beings is divided into two distinct parts. The first part involves taking in oxygen from the air or what we commonly call breathing. The respiratory system is responsible for breathing in and out of air, and exchange of gases. The main parts of the respiratory system consist of the nostrils, trachea or wind pipe and lungs.
The blood, then, transports the oxygen to the individual cell where it is used for the chemical process of respiration. This is known as cellular respiration.The second part involves taking out carbon dioxide, which is a waste product of cellular function.

Question 2.
What factors are most likely to affect the breathing rate ?
Answer:
Breathing is a necessary function for human beings. It supplies oxygen for a process called cellular respiration, which is how cells manufacture the energy they need for their life functions.
There are lots of things that can affect the rate of breathing in humans and they are:

  1. Exercise is one of those things, particularly aerobic exercise. Aerobic exercise is any exercise that causes the person to breathe more, such as running jogging, playing basketball, football, running track, or playing soccer.
  2. Even Breathing rate also changes while the person is sleeping, sitting at rest or even after climbing the stairs.
  3. Another factor that can influence breathing rate is allergic reactions to stimuli from the environment, such as pollen. This can inflame the passageways leading to the lungs, making them smaller, requiring more air.
  4. Smoking is a habit that can influence the development of lung cancer, which in turn influences the rate a person breathes.
  5. Nervous conditions and reactions to stimuli also influence the breathing rate, such as the fumed “fight or flight” syndrome.

Question 3.
What happens to the energy liberated during respiration?
Answer:
The energy liberated during respiration is utilised for carrying out various life processes.
Some of the energy liberated during the breakdown of the glucose molecule, is in the form of heat, but a large part of it is converted into chemical energy called Adenosine Triphosphate (ATP). Any activity inside the cell is carried out by the energy released by these ATP molecules.

Question 4.
What do you understand by inhalation and exhalation ? How are they different from each other ?
Answer:
The physical process, by which the air containing oxygen is drawn into the lungs and air containing carbon dioxide is forced out from lungs is called breathing. Breathing involves two steps, inhalation (inspiration) and exhalation (expiration).

Inhalation (Inspiration)

  1. Ribs move upwardsand outwards.
  2. Diaphragm is pushed downwards and flattens.
  3. Volume of chest cavity increases.
  4. Lungs expand, air pressure becomes low.
  5. Atmospheric air at higher pressure rushes into the lungs

Exhalation (Expiration)

  1. Ribs move downwards and inward.
  2. Diaphragm moves upwards and becomes dome shaped.
  3. Volume of chest cavity decreases.
  4. Lung size reduces, air pressure becomes high.
  5. Air rushes out of lungs as atmospheric air pressure is lower.

Question 5.
What do you understand by the term respiratory diseases ? Name any three common respiratory diseases.
Answer:
Any of the diseases and disorders that affect human respiration are called Respiratory diseases. Diseases of the respiratory system may affect any of the structures and organs that have to do with breathing, including the nasal cavities, the pharynx (or throat), the larynx, the trachea (or windpipe), the bronchi and bronchioles, the tissues of the lungs, and the respiratory muscles of the chest cage.

  1. Bronchitis — It is a respiratory infection in which the lining of the bronchi becomes inflamed. As this irritated membrane begins to swell, it narrows or shuts off the bronchial passages, resulting in breathlessness and coughing spells.
  2. Asthma — It is a chronic disease that also causes inflammation and swelling in the airways. But this happens periodically. During an asthmatic attack, a patient experiences tightness in the chest, shortness of breath and wheezing. This condition improves considerably with medication.
  3. Pneumonia — It is a respiratory infection caused by a bacteria. This bacteria enters the air sacs, multiplies there and the air sacs may get filled with fluid. This disease causes chest pain, chills and high fever.

Question 6.
State the cause and treatment for the following diseases

  1. Tuberculosis
  2. Pneumonia
  3. Bronchitis

Answer:

  1. Tuberculosis — Cause: Caused by bacteria that can spread by air, dust or sputum.
    Treatment: BCG vaccine, antibiotic — Streptomycin.
  2. Pneumonia — Cause: Mainly caused by bacteria inhaled through air or by contact.
    Treatment: Antibiotics—Penicillin.
  3. Bronchitis — Cause: This respiratory infection is mainly caused by a virus. Air pollution and smoking can also cause bronchitis.
    Treatment: Drinking plenty of fluids, following a well balanced diet, frequent hand washing and adequate rest can prevent and improve bronchitis.

Selina Concise Biology Class 6 ICSE Solutions – Cell – The Structure and Functions

by

Selina Concise Biology Class 6 ICSE Solutions – Cell – The Structure and Functions

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Biology. You can download the Selina Concise Biology ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Biology for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Biology Chapter 3 Cell – The Structure and Functions

Synopsis

  • The single-celled organisms are called unicellular and if the organisms are made up of more than one cell are called multicellular.
  • The simple microscope was developed by Antony Von Leeuwenhoek.
  • The compound microscope was developed by Robert Hooke.
  • The branch of biology which deals with the study of cells is called cytology.
  • The living substance of the cell is called protoplasm.
  • Examples of
    (a) unicellular organisms:

    1. bacteria
    2. amoeba
    3. yeast
    4. chlamydomonas etc.
  • (b) multicelluar organisms: plants like rose, neem, animals like man, hydra etc.
  • Examples of different cellular shapes.
    1. irregular — amoeba
    2. oval — chlamydomonas (slipper organism)
    3. oblong — paramecium
    4. elongated — striated muscle cells
    5. very long or thread like — nerve fibre cells
    6. cubical or rectangular — plant cell
  • The smallest cell — Bacterial cell
    The longest cell — Nerve cells
    The largest cell — Ostrich egg
  • Cell theory explains
    1. Every living organism is made up of one or many cells.
    2. The structural unit of all the living organisms is the cell.
    3. The functional unit of all the living organisms is the cell.
    4. All cells arise from the pre-existing cells.
  • The three scientists who contributed in the cell theory are:

    1. M.J. Schleiden
    2. Theodor Schwann
    3. Rudolph Virchow
  • Animal cells have no cell walls.
  • The cell wall is made up of cellulose which is rigid and gives shape to the cell.
  • The cell wall is freely permeable while the cell membrane is semi-permeable.
  • The supportive framework which helps in the distribution of various product across the cell is endoplasmic reticulum.
  • Power house of the cell — Mitochondria
  • Synthesise proteins — Ribosomes.
  • The organelle found only in the animal cell which initiate and regulate cell division is Centrosome.
  • The organelle found only in the plant cell is plastid.
    Green plastids are chloroplasts
    Other plastids are amyloplasts.
  • Cell organelles are concerned with specific functions.
  • The importance of cell division is.
    1. Production of new cells.
    2. For growth and repair.
    3. Replacement of the dead and worn out cells. –
    4. For reproduction.
  • The process of fusion of sperm and an egg is called fertilisation.
  • The result of fertilisation is Zygote.

Review Questions

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(i) Identify the part which contain pigment:
(a) cell membrane
(b) plastid
(c) centrosome
(d) cell wall

(ii) The organelle that controls all activities in
(a) nucleus
(b) vacoule
(c) plastids
(d) cytoplasm

(iii) A cell that is spherical in shape is:
(a) white blood cell
(b) nerve cell
(c) red blood cell
(d) amoeba

(iv)The vacuole contains:
(a) water
(b) cell sap
(c) salts
(d) food

Short Answer Questions:

Question 1.
 Name the scientist who invented the first microscope.
Answer :
Antony Von Leeuwenhoek.

Question 2.
Who coined the term “cell” ?
Answer :
The term “cell” was coined by Robert Hooke.

Question 3.
Briefly describe the three essential basic parts of a cell.
Answer :
The essential basic parts of a cell are:

  1. Cell membrane
  2. Cytoplasm
  3. Nucleus
    1. Cell membrane — It is a very thin, delicate and flexible membrane which surrounds each cell. It is also called plasma membrane. It consists of fine pores which allow only certain molecules to pass through it and prohibit the others and therefore, due to its function, also called selectively permeable membrane.
    2. Cytoplasm: This is the living portion of the cell which is a semi-liquid, translucent and colourless liquid. It is the portion of the cell where major functions of the cell are carried out through various finer parts of the cell. The finer structures which are contained in this are called the cell organelles.
    3. Nucleus: The small spherical dark coloured body usually located in the centre of the cell. It is the most important part of the cell which regulates and co-ordinates various life processes. Its major role is during cell division. It contains hereditary factors called the genes.

Question 4.
The cell membrane is called selectively permeable. Why?
Answer :
The cell membrane of the cell is composed of fine pores through which only certain molecules of the different substances can pass into the cell. Since it allows only specific molecules to enter prohibiting the other it is referred to as Selectively Permeable.

Question 5.
State the difference between
Answer :
(i) Nucleus and nucleolus
Nucleus

  1. It is a cell organelle.
  2. It is the most important part of the cell.
  3. It is present in the cytoplasm of the cell.
  4. It is bounded by a delicate nuclear membrane

Nucleolus

  1. It is a component of the nucleus.
  2. It is the most important part of the nucleus.
  3. It is present in the nucleoplasm.
  4. It does not have any such membrane around it

(ii) Cytoplasm and protoplasm
Answer :
Cytoplasm

  1. The living portion of the cell inside the cell except the nucleus.
  2. It has many finer parts contained in it like golgi bodies, mitochondria etc.

Protoplasm
The living substance of a cell is called the protoplast.
It consists of two main parts

  1. cytolasm
  2. nucleus.

(iii) Cell wall and cell membrane.
Answer :
Cell wall

  1. It is made up of cellulose.
  2. It gives shape and rigidity to the plant cell.
  3. It is a non-living structure.
  4. It protects the cell from the entry of disease-causing agents, as well the underlying protoplasm against mechanical injuries.

Cell Membrane

  1. It is very thin, delicate and flexible.
  2. This allows the entry of certain molecules only, while holding back the others.
  3. It is living structure.
  4. It has fine pores in it, through which only certain substances carfpass in and out, while others cannot.

Question 6.
 List the major differences between a plant cell and an animal cell.
Answer :
Plant cell

  1. Cell is comparatively larger with distinct outlines.
  2. Has a definite and rigid cell wall.
  3. Has negligible amount of cytoplasm.
  4. Cytoplasm is not very dense.
  5. Contains plastids.
  6. No centrosome.
  7. Have prominent one or more vacuoles.
  8. Has simple golgi apparatus composed of units called dictyosomes.

Animal cell

  1. Size is small with less distinct outlines.
  2. Cell wall absent.
  3. Cytoplasm fills almost the entire cell.
  4. Cytoplasm is granular and relatively dense.
  5. Do not contain plastids
  6. Centrosomes are present.
  7. Have temporary vacuoles which are small and concerned with secretion or excretion.
  8. Have complex and prominent golgi apparatus.

Question 7.
Briefly discuss the importance of chromosomes to an organism.
Answer :
The most important feature of a living cell is that it can divide or reproduce of its own kind and this function is regulated by the nucleus of the cell. The nucleus in its nucleoplasm contain a network of dark stained thread like structures called chromatin fibres. These fibres during cell division become thick and ribbon like which are then called chromosomes. The chromosomes are the actual hereditary factors. These are unique for each species both in number and in character.
Human body has 46 chromosomes which occur in pairs.
They are further categorised as:

  1. Chromosomes specific for determining the sex of the species called the sex chromosomes.
  2. Other chromosomes are called autosomes.

8. Fill up the blanks with the terms given below in the box.
Pigments, wall, pre-existing, cell, vacoules

  1. The cell is the structural unit of all living things.
  2. All cells arise from pre-existing cells.
  3. Animal cells have no cell wall.
  4. Plastids contain pigments.
  5. Vacoules are filled with water and dissolved substance

Question 9.
Try to find the names of four cell organells hidden in this maze, (hint: The hidden words can appear horizontally or vertically; forwards or backward or even mixed up). Write them in the lines provided. For example :
“NUCLEUS” in the last row, seven backward letters.
Selina Concise Biology Class 6 ICSE Solutions - Cell - The Structure and Functions 1
Answer :
Selina Concise Biology Class 6 ICSE Solutions - Cell - The Structure and Functions 2

  1. Vacuole
  2. Leucoplast
  3. Chromoplast
  4. Nucleus, Plastid

Selina Concise Biology Class 7 ICSE Solutions – Excretion in Humans

by

Selina Concise Biology Class 7 ICSE Solutions – Excretion in Humans

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Biology. You can download the Selina Concise Biology ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Biology for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 7 Biology Chapter 5 Excretion in Humans

Synopsis —

  •  The substances which should be excreted are :
    1. urea, uric acid
    2.  Bile pigments
    3. water
    4. extra salts such as sodium
    5. chloride extra vitamins.
  • The vitamins passed out into urine if in excess are vitamin B and C.
  •  The kidneys are situated towards the back of the abdomen at the level of last two ribs.
  •  Right kidney is located at slightly lower level than the left kidney.
  • The ureters run from the kidney to the urinary bladder and urethra runs from urinaiy bladder to the exterior.
  • Accessory excretory organs are
    1.  skin
    2. lung
    3. liver
  •  The main function of the skin is to cool the body.
  •  Liver converts highly toxic ammonia produced in the body to less toxic urea.
  •  Liver eliminates cholesterol, bile pigments, extra vitamins, and many durgs.
  •  The amount of urine produced by the glomerular filtrate after reabsorption per day is 1.2 litre.

(Review Questions)

MULTIPLE CHOICE QUESTIONS :
1. Put a tick mark (✓) against the most appropriate alternative in the
following statements :

(i) The kidneys are made up of tiny tubular units called :
(a) glomerulus
(b) nephrons
(c) capillaries
(d) neurons

(ii) In human beings, urea is produced in :
(a) liver
(b) kidney
(c) spleen
(d) urinary bladder

(iii) Besides water, the urine mainly contains :
(a) urea
(b) nitric acid
(c) glucose
(d) bile pigments

(iv) Filtration of excretory wastes from the blood occurs in:
(a) collecting tubule
(b) ureter
(c) urinary bladder
(d) nephrons

Short Answer Questions
1. Fill in the blanks :

  1. Nitrogenous wastes in the urine are in the form of urea and uric acid.
  2. The unit of human kidney is called nephron.
  3.  Evaporation of sweat from skin surface has cooling effect.

2. Define the following:
(i) Excretion:
(ii) Excretory organs :
(iii) Dialysis :
(iv) Nephron:
Ans.
(i) Excretion : During different metabolic activities taking place in our body, the body produces many substances of which some are useful and some are useless.
The process of removal of useless and harmful metabolic waste substances is called excretion.
(ii) Excretory organs : During different metabolic activities taking place in our body, the body produces many substances of which some are useful and some are useless.
If retained in the body the unwanted substances may become poisonous and cause much harm and in severe cases, even death. The organs which remove these unwanted and toxic substances from the body are called excretory organs.
(iii) Dialysis : The artificial process which cleans and filters the blood in a person where one or both the kidney may stop working properly is called dialysis.
(iv) Nephron : Inside the kidney, there are millions of microscopic tubes called renal tubules or nephrons. It is the structural and functional unit of kidney.

3. Write True (T) or False (F) for the following statements in the spaces provided. Rewrite the false statements in correct form.

  1. Removal of solid undigested food is excretion
    False
    Correct: Removal of solid undigested food is egestion.
  2.  Medulla of kidney passes urine into urinary bladder.
    False
    Correct: Medulla of kidney passes urine into funnel-like pelvis.
  3.  Excess sugar in blood is a symption ofdiabetes.
    True
  4.  Urine is devoid of blood cells.
    True

4. Name the blood vessel that brings blood to the kidneys.
Ans. Renal Artery

5. Where in the urinary system do the following processes take place ?
Ans.

  1. Urine formation: kidneys.
  2.  Transport of urine away from kidney: urethra.
  3.  Temporary storage of urine : urinary bladder.

Long Answer Questions

Question 1.
Define excretion. Write the four organs of human urinary system in their correct sequence.
Answer:
The process of elimination of unwanted and toxic products from the body is called excretion.
The four organs of the urinary system from above to downward are:

  1. kidneys
  2.  ureter .
  3. urinary bladder
  4.  urethera.

Question 2.
Why is excretion necessary in living beings ?
Answer:
The excretion is necessary because the toxic products if allowed to be retained in the body act as poison and cause great harm to the body. If they exceed the threshold, they may even cause death.

Question 3.
What is meant by osmoregulation ?
Answer:
The process of maintaining accurate concentration of water and salts in the body is called osmoregulation.
This is done by the kidneys.

Question 4.
Describe the structure of kidney with the help of a labelled diagram.
Answer:
Selina Concise Biology Class 7 ICSE Solutions - Excretion in Humans 1

Section through the kidney to show different regions The kidneys is composed of:

  1.  an outer darker area called Cortex
  2.  an inner lighter area called Medulla.

The microscopic structure of kidney is formed of millions of tubules called renal tubules or nephrons.

Question 5.
What are the two ways by which a person can get relief in case of kidney failure ?
Answer:
The two ways by which a person can get relief in case of kidney failure are:

  1. Dialysis: this is a method in which an artificial machine cleans and filters the blood.
  2.  The patient can undergo kidney transplant.

Question 6.
Draw a diagram of human excretory system and label the following parts : Kidney, ureter, urinary bladder and urethra.
Answer:
Selina Concise Biology Class 7 ICSE Solutions - Excretion in Humans 2

Question 7.
How are kidney stones formed ?
Answer:
Kidney stones are formed when crystal forming substances such as calcium oxalate, calcium phosphate and uric acid are
more than the fluid in the urine. When these chemicals start sticking together, they from crystals, commonly called kidney stones. They may be formed and cause severe plain.

Question 8.
 What are the symptoms of an urinary tract infection ?
Answer:
 Common symptoms include a strong and frequent urge to urinate, and a painful and burning sensation while urinating.