CBSE Class 6 Science Air Around Us Worksheet

Match the Column

DIRECTIONS : Match Column-I with Column-II and select the correct answer using the codes given below the columns.

Question.
Column-I (Name of gas in Air)        Column-II (% age of gas in air)
(A) Oxygen                                                   (p) 20%
(B) Nitrogen                                                  (q) 79%
(C) Carbon dioxide                                         (r) 0.04%
(D) Other gases                                             (s) Less than 1%
(a) A → (p); B → (q); C → (r); D → (s)
(b) A → (q); B → (p); C → (r); D → (s)
(c) A → (p); B → (q); C → (s); D → (r)
(d) A → (q); B → (p); C → (s); D → (r)
Answer : A

Question.
Column-I                                            Column-II
(A) Nitrogen                         (p) Produced when fuel is burnt
(B) Oxygen                          (q) Supporter of combustion
(C) Carbon dioxide               (r) Not a supporter of combustion
(D) Smoke                           (s) Colourless, odourless gas that may cause suffocation
(a) A → (p); B → (q); C → (r); D → (s)
(b) A → (q); B → (r); C → (s); D → (p)
(c) A → (r); B → (q); C → (s); D → (p)
(d) A → (s); B → (q); C → (p); D → (r)
Answer : C

Question.
Column-I                                                        Column-II
(A) Oxygen                          (p) Consumed by plants and animals during photosynthesis
(B) Carbon dioxide               (q) Produced by plants during photosynthesis
(C) Atmosphere                   (r) Animals that live under water
(D) Aquatic animals             (s) Thin layer of air that surrounds the earth
(a) A → (p); B → (q); C → (r); D → (s)
(b) A → (q); B → (p); C → (s); D → (r)
(c) A → (p); B → (q); C → (s); D → (r)
(d) A → (q); B → (p); C → (r); D → (s)
Answer : B

Passage Based Questions

DIRECTIONS : Read the passage(s) given below and answer the questions that follow.

Passage-1
Until eighteenth century, people thought that air was just one substance.
Now it has been experimentally proved that it is really not so.
Air is a mixture of gases.

Question. Air is
(a) a mixture of liquids
(b) a mixture of liquid and gases
(c) a mixture of gases
(d) None of these
Answer : C

Question. Air
(a) contains gases and solids
(b) contains gases and liquids
(c) contains no solid or liquid
(d) All of the above
Answer : A

Question. Which of the following statement(s) is/are correct?
(a) Water is present in air in vapour form
(b) Water is not present in air
(c) Water is present in air in liquid form
(d) Water is present in air in solid form
Answer : A

Passage-2
The earth is surrounded by a thin layer of air.
Thin layer extends upto many kilometers above the surface of earth and is called atmosphere.

Question. Which of the following statement(s) is/are correct?
(a) The air surrounds the earth.
(b) The thin layer of air that surrounds the earthextends only upto 2 kilometres above thesurface of earth.
(c) The thin layer of air that surrounds the earth extends upto 2 kms below the surface of earth.
(d) All of the above are correct.
Answer : A

Question. Which of the following statement(s) is/are correct?
(a) Atmosphere is essential for plants.
(b) Atmosphere is essential for human beings.
(c) Atmosphere is essential for life.
(d) None of these
Answer : C

Question. Which of the following statement(s) is/are correct?
(a) Atmosphere is the envelope of air that surrounds the earth.
(b) Atmospheric gases contain nitrogen and oxygen.
(c) Both the above are correct.
(d) None of these
Answer : C

Passage-3
If in a closed room there is some material that is burning, you may have felt suffocation.
This is due to excess carbon dioxide that may be accumulating in the room.
Plants and animals consume oxygen for respiration and produce carbon dioxide.

Question. Which of the following is produced by animals during respiration?
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
(d) All of these
Answer : C

Question. Which of the following is consumed by plants and animals during respiration?
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
(d) None of these
Answer : A

Question. Plants consume which of the following during photosynthesis?
(a) Oxygen
(b) Nitrogen
(c) Carbondioxide
(d) All of these
Answer : C

Assertion/ Reason Based Questions

DIRECTIONS : The questions in this segment consists of two statements, one labelled as “assertion A” and the other labelled as “reason R”. You are to examine these two statements carefully and decide if the assertion A and reason R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Question. Assertion (A) : Air is a homogeneous mixture of gases.
Reason (R) : The composition of every part of a homogeneous mixture is same.
Answer : A

Question. Assertion (A) : The gases nitrogen and oxygen together make 90% (by volume) of air.
Reason (R) : Air contains some dust particles.
Answer : D

Question. Assertion (A) : Oxygen helps in burning of substances.
Reason (R) : Burning of substances is a combustion process.
Answer : B

Question. Assertion (A) : Atmosphere is essential for life on earth.
Reason (R) : Carbon dioxide is a colourless, odourless gas present in air.
Answer : B

Question. Assertion (A) : Aquatic animals use dissolved air (or oxygen) in water for respiration.
Reason (R) : When fuel is burnt, a smoke is produced.
Answer : B

Figure Based Questions

Question. The gas produced in the closed container is

(a) air
(b) oxygen
(c) nitrogen
(d) carbon dioxide
Answer : D

Question. Which of these show the uses of air?

(a) (i) only
(b) (ii) only
(c) (i), (ii) and (iii)
(d) (i) and (ii) only 
Answer : C

Question.

Which of the following statement is correct?
(a) 2/3 part is nitrogen and (1/3)rd part is oxygen
(b) 3/4 part is oxygen and 1/4 part is nitrogen
(c) 1/2 part is oxygen and 1/2 part is nitrogen and other
(d) 1/5 part is oxygen and 4/5 part is nitrogen and other gases
Answer : D

Short question answers -.

Question 1: What do you mean by 'atmosphere'?
Answer : Atmosphere is a layer or blanket of air surrounding the earth. It extends up to 1000 kilometres above the earth's surface.

Question 2: Carbon dioxide is present to the extent of only 0.03% by volume in air. Why then is it considered to be so important?
Answer : Though carbon dioxide is present in lesser amount, it is very essential for both plants and animals. Plants require carbon dioxide to prepare their food. All animals in turn depend upon plants either directly or indirectly for their nutrition.

Question 3: What is humidity?
Answer : The amount of water vapours present in the air is called as humidity.

Question 4: What is the difference between breathing in and respiration?
Answer : Breathing in
Breathing in is inhaling air.
It involves the diaphragm, lungs, nose, wind passages and the chest
Breathing in is simply a physical process of taking in air.
Respiration
Respiration is the process which involves breathing in and breathing out.
Respiration happens in every cell.
Respiration is a chemical process where the oxygen in air reacts with digested food to give energy.

Question 5: How do fish breathe?
Answer : Fish have gills, with the help of which they breathe in the oxygen present in water. The water containing the dissolved oxygen passes through the gills and the oxygen gets absorbed by the gills.

Question 6: Do plants require nitrogen? Why?
Answer : Yes, plants require nitrogen because it is involved in the growth of the plant.

Question 7: What is the importance of the ozone layer in the atmosphere?
Answer : Ozone layer is a protective layer of gases which is present in the upper atmosphere. This layer blocks harmful ultraviolet rays from the sun and prevents them from reaching the earth.

Question 8: When is air said to be polluted?
Answer : Air is said to be polluted when the composition of different gases in the air is dramatically altered. Moreover, addition of gases that are not normally found in the air also leads to air pollution.

1- Fill In The Blanks.
a) Plants gives out oxygen gas and breathe in carbon dioxide
b) Nitrogen gas cannot be used directly from the atmosphere.
c) Earth is protected from the harmful rays of sun by ozone layer.
d) Atmosphere is important for the water cycle.

2- Write True Or False.
a) Oxygen gas protects us from the harmful UV rays of the sun. (False)
b) Carbon dioxide gas is required for the burning of fuel. (False)
c) Composition of air always remain the same. (False)
d) Air contains equal amount of oxygen and nitrogen. (False)
e) Aquatic animals breathe carbon dioxide which is dissolved in water.(False)

3- Match The Column:-
Column A                                                                  Column B
1. Most abundant gas in the air                                   a. Ozone
2. Gas required for photosynthesis                              b. Water vapour
3. Gas used for respiration                                          c. Carbon dioxide
4. Form of water present in the air                              d. Nitrogen
5. Layer that protect us from harmful rays of the sun    e. Oxygen
Answer : 1-d,2-c,3-e,4-b,5-a

4. Choose The Correct Answer.

Question. Air contains highest percentage of which gas?
a) Oxygen
b) Nitrogen 
c) Smoke
d) Carbon dioxide
Answer : B

Question. Which gas is a supporter of combustion?
a) Nitrogen
b) Carbon dioxide
c) Smoke
d) Oxygen
Answer : D

Question. Moving air is known as:
a) Wind
b) Water vapour
c) Ozone
d) Wind mill
Answer : A

Question. Earthworms come out of soil during:
a) Heavy rains
b) Cold weather
c) Snow
d) Hot weather
Answer : A

 5- Very Short Answer Type Questions.

Question. Which gas is essential for breathing of animals?
Answer : Oxygen.

Question. Name one component of air that does not support burning.
Answer : Carbon dioxide.

Question. Name the components of air.
Answer : Air consists of various gases like nitrogen (78%), oxygen (21%), carbon dioxide (0.03%), some noble gases and water vapours etc.

6- Short Answer Type Questions.

Question. Which gas in the atmosphere is essential for respiration?
Answer : Oxygen gas.

Question. Why does a lump of cotton wool shrink in water?
Answer : Lump of cotton wool has air among gaps of cotton fibres. When water replaces the air from these gaps, the cotton lump becomes heavy and also shrinks due to removal of air gaps..

Question. How will you show that air dissolves in water?
Answer : Heat the glass vessel filled with water. Before they start boiling bubbles occur, these bubbles are due to air present in water. This experiment concludes air is present in the water.

7- Long Answer Type Questions.

Question. How will you show that air supports burning?
Answer : (a) Take a small burning candle. (b) Cover the burning candle with a glass jar. After few minutes the candle is extinguished. This experiment proves that air supports burning.

Question. How is the balance of carbon dioxide and oxygen gases are maintained in the atmosphere?
Answer : Animals and plants use oxygen from air during respiration and release carbon dioxide gas in air. But green plants release oxygen gas by using carbon dioxide during photosynthesis.

More Question

Q1) Fill in the blanks:

1. The envelope of air that surrounds the earth is known as __________.

2. Air is a __________of many gases.

3. Burning of a substance can occur only in the presence of __________.

4. The major component of air is __________.

5. Plants use __________ for photosynthesis and __________ for respiration.

6. All living organisms take in_________and give out_____________during respiration.

7. The burning of fuels produces __________ gas.

8. __________ contains few gases and fine dust particles.

9. Animals and plants living in water use oxygen __________ in water.

10. __________ and __________ present inside the nose prevent dust particles to enter into the respiratory system.

11. Two processes which maintain balance of carbon dioxide and oxygen in nature are __________ and __________.

12.Air in motion is called__________.

Q2) Why do mountaineers carry oxygen cylinders with them?

Q3) What is the composition of air.

Q4) The process in which water vapour changes into water droplets is called condensation. What conditions are required for this process to occur?

Q5) What happens when burning continues in a closed room?

Q6) Why long chimneys are built in factories?

Q7) Name two variable components of air.

Q8) Describe an activity to show that
(a) Water has air dissolved in it.
(b) Soil has air in it.

Q9) Why do earthworms come out of the soil when it rains heavily?

Q10) Why should we breathe through our nostrils and not through our mouth?

Q11) How does air help plants in various activities?

Q12) Write three uses of windmill.

Q13) Explain how plants and animals are interdependent.

Q14) Why are we advised not to sleep under a tree during the night?

Q15) In a school, students thought of planting trees in and around the school, to reduce air pollution. What values can you infer from the planting of trees.

Multiple Choice Questions

Question. Farmers plough their fields before they plant seeds because
(a) it loosens the soil and allows the air to enter into the spaces between soil particles
(b) the sprouting seed will be able to use the trapped air
(c) plants will absorb some air through their roots and also take in water and minerals from the soil
(d) All of the above
Answer : D

Question. Which of the following statement(s) is/are correct?
(a) The percenage of oxygen in air inhaled and exhaled by us remains same
(b) Plants use more of oxygen in respiration and produce no oxygen in any of its processes
(c) Plants do not need oxygen for respiration
(d) All of the above
Answer : D

Question. Which of the following statement(s) is/are correct?
(a) Air is a mixture of many gases
(b) Air is a homogeneous mixture
(c) Air is a pure substance
(d) Only (a) and (b) are correct
Answer : D

Question. Which of the following statement(s) is/are correct?
(a) We cannot observe the presence of dust particles in air
(b) Amount of dust particles in air vary from time to time
(c) Both the above are correct
(d) All of the above
Answer : B

Question. Which of the following statement(s) is/are correct?
(a) The planet earth is surrounded by a thin layer of air.
(b) The thin layer of air that surrounds earth extends only upto two kilometres below the surface of earth.
(c) This thin layer of air that surrounds earth is no importance for living beings.
(d) All of the above
Answer : A

Question. Which of the following statement(s) is/are correct?
(a) The percentage of nitrogen in air varies from place to place on the earth.
(b) The percentage of oxygen in air varies from place to place on the earth.
(c) Both the above are correct
(d) All of the above
Answer : C

Question. Which of the following statement(s) is/are correct?
(a) Air is present everywhere
(b) We can feel air
(c) Both the above
(d) None of these
Answer : C

Question. Which of the following statement(s) is/are correct? 
(a) The moving air is called wind.
(b) We can find the direction in which air is moving at a place.
(c) Weather cock is used to find the direction in which air is moving at a particular place.
(d) All of the above
Answer : D

Question. Which of the following statement(s) is/are correct?
(a) Plants and animals are interdependent.
(b) Plants and animals depend on each other for exchange of oxygen.
(c) Plants and animals depend on each other for exchange of carbon dioxide.
(d) All of the above
Answer : D

Question. Guess who am I?
I am present in air. I enter your lungs when you inhale air. You cannot live without me. I give energy to your body.
(a) Hydrogen
(b) Oxygen
(c) Nitrogen
(d) Carbondioxide
Answer : B

Question. Which of the following statement(s) is/are correct?
(a) Smoke contains suspended solid particles
(b) Smoke is generally harmful
(c) Both the above are correct
(d) None of the above
Answer : C

Question. Which of the following statement(s) is/are correct?
(a) Plants consume more oxygen and produce less oxygen.
(b) Plants consume less oxygen and produce more oxygen.
(c) Plants consume the same amount of oxygen as they produce.
(d) Plants consume a large amount of oxygen during photosynthesis and produce a large amount of carbondioxide during photosynthesis.
Answer : B

Question. Which of the following statement(s) is/are correct?
(a) The animals that live under water cannot use the atmospheric air for their respiration.
(b) The aquatic animals do not need air for respiration.
(c) The aquatic animals use carbondioxide dissolved in water for their respiration.
(d) All the above are incorrect.
Answer : D

Question. Which of the following statements is correct?
(a) Air helps in pollination and in dispersal of seeds.
(b) Air becomes denser as we go on mountains.
(c) Air does not contain dust particles.
(d) Water contains dissolved carbon dioxide.
Answer : A

Question. When charcoal is burnt in a closed room, it gets suffocating. The gas that is mainly responsible to cause suffocation is
(a) Nitrogen
(b) Carbon monoxide
(c) Carbondioxide
(d) None of these
Answer : B

Question. Which of the following statement(s) is/are correct?
(a) Carbondioxide is a colourless gas
(b) Oxygen is an odourless gas
(c) Air contains both oxygen and carbondioxide
(d) All of the above
Answer : D

Question. Which of the following statement(s) is/are correct?
(a) We make use of wind energy to rotate a wind mill
(b) Windmill is used to generate electricity
(c) Windmill is used to run flour mills
(d) All of the above
Answer : D

Question. Which of the following statement(s) is/are correct?
(a) In air percentage of nitrogen by volume is 77%
(b) In air percentage of oxygen by volume is 20%
(c) In air percentage of carbondioxide is only 2.0%
(d) In air percentage of water and argon is 1.0%
Answer : B

Question. The percentage of which gas is maximum in inhaled air?
(a) Nitrogen
(b) Oxygen
(c) Carbondioxide
(d) Other gases
Answer : A

Question. The percentage of which gas is maximum in exhaled air?
(a) Nitrogen
(b) Oxygen
(c) Carbondioxide
(d) Other gases
Answer : A

Question. Why do the earthworms come out of soil during heavy rains?
(a) They come out of soil so as to stay at some dry place.
(b) They come out of soil for respiration.
(c) They come out to see the nature when it is raining heavily.
(d) None of the above
Answer : B

Question. Which of the following statements is wrong?
(a) Air contains dust, water vapour and smoke.
(b) Ozone depletion causes skin cancer.
(c) Acid rain is caused due to air pollution.
(d) None of these
Answer : D

Question. Why are plants called oxygen producer?
(a) They consume oxygen for respiration.
(b) They consume oxygen for photosynthesis.
(c) They produce more oxygen during photosynthesis as compared to that they consume for respiration.
(d) All of the above
Answer : C

Question. Which of the following can reduce air pollution?
(a) Planting more trees on roadsides
(b) Using CNG in vehicles
(c) Reducing the number of vehicles
(d) All of the above
Answer : D

Question. If you take water in a glass tumbler and put some ice in it, you will observe some water droplets on the outer surface of tumbler. This shows that
(a) air occupies space
(b) air contains dust particles
(c) water vapours are present in air
(d) air has mass
Answer : C

Question. Which of the following plants do not have stomata?
(i) Hydrilla
(ii) Water lily
(iii) All of these
(a) Only (ii) is correct
(b) Both (i) and (iii)
(c) Only (i) is incorrect
(d) Only (iii) is correct
Answer : A

Question. Which of the following statement(s) is/are correct?
(a) Air is not a matter as it cannot be seen
(b) Air is incompressible
(c) Air exerts pressure
(d) All of the above
Answer : C

Question. Which of the following statement(s) is/are correct?
(a) Air plays an important role in water cycle.
(b) Birds can fly due to presence of air.
(c) Both the above are correct
(d) None of these
Answer : C

Question. A gas that is present in air and makes about 4/5th (by volume) of air. It is also not a supporter of combustion?
(a) Oxygen
(b) Nitrogen
(c) Water vapours
(d) Hydrogen
Answer : B

Question. The gas used by aquatic animals for respiration?
(a) Dissolved nitrogen
(b) Dissolved oxygen
(c) Dissolved air
(d) None of these
Answer : C

Question. Why are chimneys provided in factories?
(a) So as to locate the factories easily.
(b) To take the harmful smoke and gases away from us.
(c) To absorb the dust particles present in smoke before being released to the atmosphere.
(d) All of the above
Answer : B

Question. Which gas protects us from ultraviolet rays of the sun?
(a) Oxygen
(b) Carbondioxide
(c) Ozone
(d) Nitrogen
Answer : C

Air around Us

Fill in the blanks :-

1. Air occupies _________________________.

2. Harmful gases and smoke in the air causes _________________________.

3. The _______________________ and ______________________ within the nasal passage prevents entry of dust particles into our respiratory system.

4. Air helps in _________________________ of sound.

5. Nitrogen present in the air is used for making _________________________.

Choose the correct answer :-

1. The height of the atmosphere is (120 km/240km)

2. The volume of oxygen (increases/decreases) with increase in altitudes.

3. (Carbondioxide/Oxygen) is taken in by the plants for photosynthesis.

4. Air contain approximately (78 percent/80 percent) of Nitrogen.

Name the following :-

1. The two scientists who proved air is a mixture of gases :

2. The lightest gas in the air.

3. The gas essential for combustion and respiration.

4. The substance in presence of which photosynthesis takes place :

Define the following :-

(a) Atmosphere

(b) Respiration

Air around Us

I. Fill in the blanks :

1. Air is really not one substance but a __________________.

2. The component of air that supports burning is called ________________.

3. The aquatic animals use dissolved Oxygen in water for respiration, this is possible because Oxygen ________________ in water.

4. Nitrogen of the air is used on a large scale to manufacture ________________.

5. ________________ is the place in nature for gaseous exchange.
 

II. True or False statements :

1. Air is a compound but not an element.

2. Air is an opaque material.

3. Air contains water vapour.

4. The major part of air is Nitrogen.

5. Plants produce Oxygen through photosynthesis.

Learning Objectives
1. Air is a natural resource
2. We cannot see air but can feel it
3. Role of atmosphere
4. Oxygen cycle
5. Composition of air
6. Usefulness of air
7. Pollution of air

Air is also an important natural resource. Air is present everywhere, in water, around us, in soil and within plants and animals. Life on Earth is not possible without air. Air cannot be seen but it can be felt. When air blows hard, leaves and branches start moving. This movement signifies presence of air. Strong moving air is called wind and strong winds cause storms.

Presence of Air : We can feel air when we switch on a fan. We feel the cool breeze (air).

Atmosphere : The thin layer of air surrounding the Earth is called the atmosphere. All plants and animals need air to breathe.

Properties of air
→ Air occupies space.
→ Air exerts pressure.
→ Air cannot be seen but it can be experienced.
The atmosphere extends upto 1000 km above the surface of Earth. However this air gets thinner and thinner as we go up. That is why mountaineers have to carry their own oxygen supply in oxygen in cylinders. Ninety nine percent of air is found up to a height of 30 km above the surface of Earth.

Composition of air
Air is a mixture of gases, water vapour and dust particles. Lavoisier was the first scientist to prove that air is a mixture of gases and not a compound.

He found that
(1) Air is a mixture of gases. Oxygen is the active part of air and make up about one fifth of air by volume.
(2) When certain substances are burnt in air, they combine with oxygen. So air is a mixture and not a compound.

Interesting Fact : Until the 18th century, people thought that air uses a single substance. In 1774, Joseph Priestly showed that part of air has oxygen. This proved that air is a mixture and not a single substance. The combustion of petrol releases poisonous gases like carbon monoxide, nitrogen dioxide, nitrogen monoxide, lead, dust etc. which mixes with air and pollute it. Impurities from factories like sulphur dioxide, dust and smoke get mixed up with air.

Constituents of air

(a) Nitrogen : Air contains 78% of nitrogen. It occupies about 4/5th of volume of dry air. Nitrogen is an inert gas but it is needed by plants and animals for making amino acids.

(b) Oxygen : Air contains about 21% oxygen. To show that plants produce oxygen during photosynthesis Take a beaker half filled with water and place a water plant (say, Hydrilla) in the beaker. Invert a glass funnel and place it over the plant and cover the open end of the funnel with a test tube. (Before doing so, fill the test tube with water and cover its opening with your thumb. Then, invert the tube into the funnel.). Place the beaker in sunlight and observe. You will notice bubbles of gas escaping from the leaves of the plant and filling the test tube. Introduce a glowing splint near the mouth of the test tube. It continues to glow, proving the presence of oxygen gas in the air.

Conclusion:
Plants produce oxygen during the process of photosynthesis and liberate it into the atmosphere.

To show oxygen is used in burning
Fix a candle in the centre of a trough. Fill the trough with water more than half. Light the candle. Place a gas jar over the burning candle upside down as shown in the figure alongside. Observe and say what is happening? Does burning candle burns continuously or gets extinguished? It extinguishes after a while and at the same time, the level of water in the gas jar rises. Can you explain why this happens? After putting the gas jar on the burning candle, the candle burns for while, because there is some oxygen in the air, which helps burning. When all oxygen is consumed in burning, the candle extinguishes.

Conclusion: Oxygen helps in burning.

Uses of oxygen
1. Oxygen is necessary for breathing and burning.
2. It is needed in hospitals for artificial respiration.
3. Mountaineers, sea divers and astronauts carry oxygen cylinders with them as supply of oxygen decreases as we go up.
4. Oxygen is needed by aquatic plants and animals.
5. It is used for welding purposes and for cutting of metal at high temperatures.
6. Liquid oxygen is needed in rockets for combustion of fuels.

(c) Carbondioxide : Carbondioxide occupies a very small percentage of air but is very important for existence of all plant life. It occupies 0.02 - 0.04% of air by volume. It is released during
(i) combustion of fuels like coal, diesel, petrol, etc.
(ii) the process of respiration.
(iii) decomposition of vegetable matter and fermentation.

Uses of carbondioxide
1. It is used as a fire extinguisher since it is heavier than air and does not burn.
2. Solid carbondioxide is called dry ice. It is used as a refrigerant.
3. It is used in preparation of aerated drinks like soda water etc.
4. Plants use carbon dioxide to prepare their own food by the process of photosynthesis. Oxygen is given out during the process.

(d) Water Vapour : Air contains water vapour. We know this because when air comes in contact with a cool surface, water drops are seen.
Water vapour is important for water cycle  The clothes dry on clothesline. The water from wet clothes evaporates and form water vapour. This mixes with air. Amount of water vapour in air is called humidity.

(e) Dust and Smoke : Dust particles can be seen in a beam of sunrays.
These dust particles are present in air. Content of dust particles vary from time to time from place to place. When it rains, dust particles in the atmosphere settles down. That is why weather is clean after rainy season. Air also contains smoke released from factories and vehicles.

Respiration : It is process by which air rich in oxygen is breathed in by an organism and air rich in carbon dioxide is breathed out.
Air support life – All living things breathe in oxygen. Oxygen is needed to get energy from food. Living things on land breathe in oxygen present in air. The air that is taken in through nose enters the lungs. Here the oxygen is absorbed from the air and used by the body.
Living things that live under the soil breathe in air present in soil. If you put water on the soil you may see some bubbles of air. This is because air is trapped between soil particles which escape when water is added. Plants that live in water logged soil such as mangroves, have roots that grow out of the soil to get ir.

Activity 8
To prove that the soil also entraps air (oxygen).
Take a lump of dry soil in a beaker. Add some water to it. Do you observe bubbles start coming out from the soil. Yes, it is air entrapped in soil. Organisms living in burrows and holes formed in deep soil get this entrapped air. But, when it rains heavily, these burrows and holes are filled with water, air is expelled. It becomes very difficult for these animals to remain there. So they come out of burrows and holes.
Some animals that live in water, e.g., whales come up to the surface to breathe in oxygen from air. Fish have organs called gills. They breathe in oxygen dissolved in water. When water enters the gills, oxygen dissolved in water is absorbed.

Activity 7
How do fishes and other aquatic animals breathe in water?
Where from the aquatic animals get oxygen?
Have some water in a beaker. Heat is slowly on a tripod stand. After sometime, you can observe lot of bubbles at the bottom of the beaker, which start rising up and break up at the outer surface of water. Where do these bubbles come from? These bubbles are mainly of oxygen present in air which has been dissolved in water. Aquatic animals use this oxygen and survive.
Plants have small openings called stomata on the lower side of leaves through which air is taken in. Plants that float on water like water lily have stomata on the upper surface. Underwater plants like tape grass have no stomata. They breathe in oxygen dissolved in water through their body surface.
Amphibians like frog, newt and salamander need systems for breathing both in air and water. Crocodile and aligator swim with the snout above water surface to breathe easily through nostrils.
Frogs have lungs to breathe in air when they are on land. In weather they breathe through moist skin.
Birds have an efficient respiratory system. They need high levels of oxygen during flight. Their lungs have air sacs that remain open all the time.
Mammals breathe with the help of lungs. They take in oxygen and give out carbon dioxide.

Balance of oxygen : The amount of oxygen in the atmosphere remains constant because of oxygen and carbon dioxide cycle that operate together in nature. All animals breathe out carbon dioxide. Plants take in carbon dioxide and exhale oxygen. Humans and other animals inhale oxygen. This process goes on forever. Plants and animals are interdependent on each other. Some human activities however disturb this balance. Such activities include deforestation, use of fossil fuels, pollution, industries, etc.

Other uses of Air
1. Windmill runs with the help of air. It is used to generate electricity.
2. Gliders, parachutes, yachts and aircraft all need air to sail and fly.
3. Insects, birds and bats need air to fly.
4. Some fruits and seeds need air to disperse their seeds.
5. Air is needed for winnowing.
6. Tyres are filled with air to run vehicles.
7. Air helps in pollination of several flowers.

Ozone : There is another layer of gas called ozone in the upper atmosphere. It prevents harmful rays of the sun from reaching Earth. These are ultraviolet rays and may cause skin cancer and eye problems.
Role of Atmosphere : Atmosphere causes weather changes. When the sun shines brightly, it heats the Earth. The air also gets heated. Hot air rises and cold air pushes in to take it place. This is how wind blows. Blowing of storms and cyclones is also due to movement of air. The water vapour in the air is responsible for rainfall and snowfall. Thus the atmosphere is responsible for weather changes. The atmosphere helps to maintain the temperature of the
Earth. The heat of the sun is partly absorbed by the atmosphere, and partly is reflected back. This prevents the Earth from becoming very hot during the day. At night the trapped heat prevents the Earth from cooling down too much
Thus the atmosphere acts as a blanket around the earth and helps to keep the earth’s surface at right temperature for life to exist.

Air pollution : Air is getting polluted day by day due to some human activities.
Some major causes of contamination of air are
(i) Burning of fossil fuels like coal, petroleum
(ii) Smoke from vehicles
(iii) Harmful gases from industries
(iv) Burning of wood, plastic tyres
(v) Deforestation
Due to poor quality of air, people find it difficult to breathe. It may cause diseases like asthma and lung cancer. It also affects plant life and crops. In order to protect our environment we should plant more trees, recycle plastics, avoid using fossil fuels.

Keywords

• Atmosphere : It is the thick blanket of air surrounded the Earth’s surface.

• Gravity : The pull of the earth on bodies

• Humidity : Amount of water vapour present in air at any place and time.

• Ozone : A gas present in upper atmosphere that prevents us from harmful ultraviolet rays of the sun.