Text Book Back Questions and Answers - Chapter 4 Air Term 2 6th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

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On April 24, 2024, 11:35 AM

Textual Evaluation : Chapter 4 - Air - Term 2 - 6th Science Guide Samacheer Kalvi Solutions
I. Choose the appropriate answer:
Question $1 .$

__________is the percentage of nitrogen in air
(a) $78 \%$
(b) $21 \%$
(c) $0.03 \%$
(d) $1 \%$
Answer:
(a) $78 \%$

Question $2 .$
Gas exchange takes place in plants using
(a) Stomata
(b) Chlorophyll
(c) Leaves
(d) Flowers
Answer:
(a) Stomata

Question $3 .$
The constituent of air that supports combustion is
(a) Nitrogen
(b) carbon-di-oxide
(c) Oxygen
(d) water vapour
Answer:
(c) Oxygen

Question $4 .$
Nitrogen is used in the food packaging industry because of it
(a) provides colour to the food
(b) provides oxygen to the food
(c) adds proteins and minerals to the food
(d) keeps the food fresh
Answer:
(d) keeps the food fresh

Question $5 .$

_______ and ________ are the two gases, which when taken together, make up about 99 percentage of air.

I. Nitrogen
II. carbon-di-oxide
III. Noble gases
IV. Oxygen
(a) I and II

(b) I and III
(c) I and II
(d) I and IV
Answer:
(d) I and IV

II. Fill in the blanks:

$1 .$ ________is the active component of air.
2. The gas given out during photosynthesis is________
$3 .$ ________gas is given to the patients having breathing problems.
$4 .$ ________can be seen moving in a beam of sunlight in a dark room.
$5 .$ ________gas turns lime water milky.

Answers:
1. Oxygen
2. Oxygen
3. Oxygen
4. Dust particles
5. Carbon-di-oxide

III. True or False. If False, give the correct statement:
Question 1.
Inhaled air contains a large amount of carbon-di-oxide.
Answer:
False, Inhaled air contains a large amount of Oxygen.

Question $2 .$
Planting trees help in decreasing global warming.
Answer:
True

Question $3 .$
The composition of air is always exactly the same.
Answer:
False, The composition of air changes slightly place to place.

Question $4 .$
Whales come up to the water surface to breathe in oxygen.
Answer:
True

Question $5 .$
The balance of oxygen in atmosphere is maintained through photosynthesis in animals and respiration in plants.
Answer:
False. The balance of oxygen in atmosphere is maintained through photosynthesis in plants and respiration in animals.

IV. Match the following:
Question $1 .$

Answer:

V. Arrange the following statements in correct sequence
Question 1.
1. Plants manufacture food by a process called photosynthesis.
2. Plants require energy for their growth.
3. Plants take in oxygen and release carbon-di-oxide just as animals.
4. Plants take carbon-di-oxide from the atmosphere, use chlorophyll in the presence of sunlight and prepare food.
5. Such oxygen is available to animals and human beings for breathing.
6. During this process, oxygen is released by plants.
Answers:
1. Plants manufacture food by a process called photosynthesis.
2. Plants require energy for their growth.
3. Plants take in oxygen and release carbon di oxide just as animals.
4. Plant take carbon di oxide from the atmosphere use chlorophyll in the presence of sunlight and prepare food.
5. Such oxygen is available to animals and human beings for breathing.
6. During this process oxygen is released by plants.

VI. Analogy:
Question $1 .$
Photosynthesis :_________ $\because$ Respiration : Oxygen.
Answer:
Carbon - dioxide.

Question 2.
$78 \%$ of air : Does not support combustion ::_________ : Supports combustion
Answer:
$21 \%$ of air.

VII. Observe the given figure carefully and answer the questions:
Question 1.
What will happen if we remove plants from the aquarium?
Answer:
If we remove the plants from the aquarium, oxygen percentage will be decreased. So fishes would die.

Question $2 .$
What will happen if we remove the fish from the aquarium and keep it (with green plants) in a dark place?

Answer:
If the aquarium is kept in the dark place, the green plants will not prepare their food due to lack of sunlight and carbon di oxide. So the plants get spoiled.

VIII. Give very short answer:
Question $1 .$
What is the atmosphere? Name the five layers of the atmosphere.
Answer:
Our earth is surrounded by a huge envelope of air called the atmosphere. The atmosphere is made of five different layers - the Troposphere, the Stratosphere, the Mesosphere, the Ionosphere and the Exosphere.

Question $2 .$
How do the roots of land plants get oxygen for breathing?
Answer:
The roots can absorb oxygen from the small air spaces in soil.

Question $3 .$
What should be done if the clothes of a person catch fire accidentally? Why?
Answer:
1. Cover the person in a rug or blanket and Roll him on the floor.
2. This will cut off the air and put out the flames.
3. Suitable fire extinguisher can also be chosen.

Question $4 .$
What will happen if you breathe through mouth?
Answer:
Anyone can develop a habit of breathing through their mouth, but certain conditions increase your risk. These include:-
1. Chronic allergies
2. Hay fever
3. Chronic or recurring Sinus infections
4. Asthma
5. Chronic Stress and Anxiety.

IX. Give short answer:
Question $1 .$
Biscuits kept open on a plate during monsoon days lose it's crispness. Why?
Answer:
Air also contains more water vapour in rainy season (monsoon days). So, Biscuits kept open on a plate during monsoon days loses its crispness.

Question $2 .$
Why do traffic assistants wear a mask on duty?
Answer:
Traffic assistants are continually exposed to smoke emitted out from the vehicles. Inhaling the pollutants in the smoke may cause breathing and lung problems. So they wear a mask on duty.

X. Answer in detail:
Question $1 .$
How do plants and animals maintain the balance of oxygen and carbon-di-oxide in air?
Answer:
Respiration in plants:
During respiration, plants take in oxygen and release carbon-di-oxide, just as animal also do. Gaseous exchange with air in atmosphere takes place in plants with stomata.
Photosynthesis:
During photosynthesis, carbon-di-oxide from the air and water from the soil react in the presence of sunlight to produce food. Plants release oxygen during photosynthesis which is much more than the oxygen consumed by the plants during respiration.

Respiration in animats:
When we breath in air, the oxygen present in the air reacts chemically with digested food within the body to produce carbon-di-oxide gas. The inhaled air contains more oxygen while the exhaled air contains more carbon-di-oxide.
So plants sent out more oxygen during the photosynthesis. Animals sent out more carbon-di-oxide during respiration. Plants take carbon-di-oxide for photosynthesis. Animals take oxygen during respiration. So plants and animals maintain the balance of oxygen and carbon-di-oxide in air.

Question $2 .$
Why is atmosphere essential for life on earth?
Answer:
The atmosphere is essential for life because it maintains an appropriate climate for the maintenance of life by carrying out the following activities:
1. The atmosphere keeps the average temperature of the Earth fairly constant during the day time.
2. It prevents a sudden increase in temperature during the day time.
3. It also slows down the escape of heat from the surface of the Earth into outer space during the night time.

XI. Questions Based on Higher Order Thinking Skills:
Question $1 .$
Can you guess why fire extinguishers throw a stream of carbon-di-oxide while putting - off fire?
Answer:
The reasons behind fire extinguishers throw a stream of $\mathrm{CO}$, while putting-off fire:-
1. $\mathrm{CO}_{2}$ is a colourless and in normal concentrations, odourless gas. It doesn't react with burning materials, so it doesn't create any toxic or other by products while putting-off fire.
2. Carbon dioxide doesn't conduct electricity, making it an ideal fire suppressant for use in the places where a large amount of electricity may be present.
3. $\mathrm{CO}_{2}$ acts on fires in two ways: The release of the gas under pressure has a cooling effect, as can be seen by the resulting mist cloud and ice particles; the gas also displaces the oxygen that's necessary to maintain combustion.

In-Text Activities
Activity 1

Air is everywhere
Let us take an empty glass bottle. Is it really empty or does it have something inside?

Now, shall we turn the glass bottle upside down? Can you agree that there is still something inside the empty glass bottle? Let us do the following activity to find what is there inside an empty glass bottle.
Dip the open mouth of the bottle into the trough filled with water as shown in Fig 1. Observe the bottle. Does water enter the bottle?
$\overline{\text { Now tilt }}$ the bottle slightly. Now again dip the open mouth of the bottle as shown in
Fig 2. Do you think that water will enter the bottle?
Kindly observe the Fig 2 carefully. You can see bubbles coming out of the bottle.
When you perform the experiment, can you hear the bubbly sound? can you now guess what was inside the bottle?
Yes, you are right. It is "air" that was present in the bottle.
The bottle was not empty at all. In fact, it was filled completely with air even when you turned it upside down. That is why we notice that water does not enter the bottle when it is pushed in an inverted position, as there was no space for air to escape.
When the bottle was tilted, the air was able to come out in the form of bubbles, and water filled up the empty space that the air has occupied.
Hence we can see that air fills all the space inside the bottle.
Answer:
Fig. - $1-$ No.
Fig - 2 - Yes.
Yes, I can hear a bubbly sound. Yes the bottle has a full of 'Air'.

Activity 2

Take a healthy branch of Hydrilla and place it in a funnel. Invert the funnel in a beaker of water as shown in the figure. Invert a test tube over the stem of the funnel. The stem of the funnel should be kept immersed inside the water Leave the beaker in sunlight for some time. You will notice some bubbles rising in the test tube. The bubbles contain oxygen released by the plant during photosynthesis. If we show a glowing splinter to the collected air, it burns brightly. This shows that the collected gas is oxygen.

Activity 3
We know that iron undergoes rusting with oxygen and forms iron oxide. This process can be used to estimate the percentage of oxygen in air, which has been removed by the rusting reaction.

Take a small portion of iron wool, press it into a $20 \mathrm{ml}$ graduated test tube and wet it with water. Tip away excess of water. Take a $500 \mathrm{ml}$ beaker and fill half of the beaker with water. Invert the test tube and place it in air. Leave the arrangement at least for a week Without making any disturbance to the test tube.

Observe the changes that had happened in the iron wool and to the level of water inside the test tube. We could see that the water level has increased inside the test tube. The rise in water is because of oxygen in air which has been removed by the rusting reaction. This will be about $20 \%$ which is approximately the percentage of oxygen in the air.

Activity 4
Oxygen is necessary for burning
Place two candles on a table. Ensure that both the candles are of same size and height. Mark them as candle 1 and candle 2 using a chalkpiece. Light both the candles. Now, cover candle 2 with glass tumbler as shown in the figure. Observe the happenings at both the candles.
What does happen to candle 1 ?
What does happen to candle $2 ?$
Can you guess why did the covered candle extinguish?
Let us summarize the happenings.
The candle 1 continues to bum, unless it is blown - off by strong moving air or any other external force. This is because fresh air is continuously available to the candle for its burning process.

Candle 2 glows for a while and then gets put - off. When the burning candle is covered with a glass tumbler, the candle can use the oxygen available in the air inside the glass tumbler. Since only a small amount of air is present inside the glass tumbler - only a small portion of oxygen is available for the candle to continue glowing. When all the oxygen of the air inside the gas jar is used up, then the burning candle gets extinguished.

Now, repeat the candle - glowing experiment taking four containers of different sizes. Lor example, you can take a $250 \mathrm{ml}$ conical flask, a $500 \mathrm{ml}$ bottle, a one - litre jar, a two - litre jar. Cover the burning candle one by one with these containers and find out how long it takes for the candle to extinguish in each case. Record your observations in the following table.
Answer:

The time taken for the candle to extinguish depends upon the volume of the containers. Lor less volume, the time taken is less. Lor more volume, the time taken is more.

Additional Questions
I. Choose the correct answer:
Question $1 .$
Movement of wind takes place in _______layer
(a) Troposphere
(b) ozone
(c) stratosphere
(d) ionosphere
Answer:
(a) Troposphere

Question 2.
A component of air used by green plants to prepare their food is
(a) $\mathrm{N}_{2}$
(b) $\mathrm{O}_{2}$
(c) $\mathrm{He}$
(d) $\mathrm{CO}_{2}$
Answer:
(d) $\mathrm{CO}_{2}$

Question $3 .$
________layer contain ozone layer.
(a) Trophosphere
(b) Stratosphere
(c) Mesosphere
(d) Exosphere
Answer:
(b) Stratosphere

Question $4 .$
The percentage of oxygen in exhaled air of respiration is
(a) $78 \%$
(b) $16 \%$
(c) $4 \%$
(d) $21 \%$
Answer:
(b) $16 \%$

Question $5 .$
During respiration carbon-di-oxide is exhaled out of the body through the
(a) Lungs
(b) Heart
(c) Kidney
(d) Skin
Answer:
(a) Lungs

Question $6 .$ 

________respire using their skin.
(a) Fish
(b) Frogs
(c) Rats
(d) Human beings
Ans:
(b) Frogs

Question $7 .$
__________gas cylinders are used for breathing purpose for a diver going deep into the sea
(a) Hydrogen
(b) Carbon-di-oxide
(c) Oxygen
(d) Nitrogen
Answer:
(c) Oxygen

II. Fill in the blanks:
1. Atmosphere is held in place by the earth's__________
2. The atmosphere is made of __________different layers.
3. A __________shows the direction in which the air is moving at a particular place.
4. The ozone layer protects all life on earth from the harmful rays__________ of the sun.
5. Highly reactive gas was later names 'oxygen' by__________
$6 .$ __________discovered nitrogen.
7. Air contains small amount of $\mathrm{CO}_{2}$, Water vapour and some other gases like__________ etc.
8. Air contains more __________in rainy season
Answers:

1. gravity
2. five
3. weathercock
4. ultraviolet
5. Lavoisier
6. Daniel Rutherford
7. argon, helium
8. water vapour.

III. Find whether the following sentences are true or false. If false Correct the statement:
Question $1 .$
When air is moving with cool and soothing, it is called as cyclone.
Answer:
False. When air is moving with cool and soothing is called as breeze.

Question $2 .$
Exosphere has high temperature.
Answer:
False. Exosphere has low temperature.

Question 3 .
Jan Ingenhousz showed that chlorophyll is essential to the plant to carry out photosynthesis.
Answer:
False. Jan Ingenhousz showed that sunlight is essential to the plant to carry out photosynthesis.

Question $4 .$
The second major component of air is oxygen.
Answer:
True.

Question $5 .$
Air also contains small amount of carbon-di-oxide, water vapour and some other gases like argon, helium etc.
Answer:
True.

Question $6 .$
The amount of water vapour in the air is more in windy places than other areas.
Answer:
False. The amount of dust in the air is more in windy places then other areas.

IV. Match the following:

Answer:
1. $-\mathrm{c}$
2. $-d$
3. $-b$
4. $-\mathrm{a}$

V. Analogy:

Question $1 .$
Cool and soothing wind : Breeze.
uproot trees wind :___________
Answer:
Cyclone

Question 2.
Weather changes : Trophosphere.
Ozone layer:___________
Answer:
Stratosphere

Question $3 .$
Oxygen : Joseph Priestley.
Nitrogen:___________
Answer:
Daniel Rutherford

Question $4 .$
Respire through skin:___________
Respire through gills: Fish
Answer:
Frogs

VI. Give Short Answer:
Question $1 .$
Define - Atmosphere.
Answer:
Our earth is surrounded by a huge envelope of air. It is called atmosphere.

Question $2 .$
The air envelope is thicker near the earth's surface and we go higher the density and availability of air gradually decreases. Why?
Answer:
When altitude increases, number of gas molecules will be decreased. Therefore, the density is also decreased when we go higher. Gravity pulls most of the atmosphere's gas molecules close to the Earth's surface. Air rises as it is heated because it becomes less dense.

Question 3 .
Define troposphere.
Answer:
1. This layer is closest to the earth.
2. It is the layer in which we live.
3. Movement of wind takes place in this layer.
4. It also contains water vapour, which is responsible for making clouds.
5. It is responsible for the weather we experience on earth.

Question $4 .$
Why aircraft usually fly above the troposphere layer?
Answer:
Aircrafts usually fly above the troposphere to avoid strong winds and bad weather.

Question $5 .$
How to show that the presence of carbon-di-oxide in air?
Answer:
Pour some lime water in a glass tumbler Bubble some air using a straw through the litne water. After a few minutes, lime water will produce a white precipitate and that the lime water will turn to a milky white solution. This shows the presence of Carbon- di-oxide in air.

Question $6 .$
Write the composition of air.
Answer:
The major component of air is nitrogen. Almost four - fifth of air is nitrogen. The second major component of air is oxygen. Air also contains small amount of Carbon-di- oxide, water vapour and some other gases like argon, helium etc. The air may also contain some dust particles.

Question $7 .$
The composition of air changes slightly from place to place. Give examples.
Answer:
1. Air over industrial cities has a higher amount of carbon-di-oxide in it.
2. Air in coastal areas may have more water vapour than inland areas.
3. Air also contains more water vapour in rainy season.
4. The amount of dust in the air is more in windy places.

Question $8 .$
What is meant by burning?
Answer:
The process of burning of a substance in the presence of oxygen and releasing a large amount of light and heat is called burning.

Question $9 .$
In Rockets, along with fuel, oxygen is also carried for combustion - why?
Answer:
In Rockets, as they go high in the atmosphere, the availability of oxygen is considerably reduced. So rockets along with the fuel, oxygen is also carried for combustion.

Question $10 .$
Write the equation of photosynthesis.
Answer:

Question $11 .$
What is dry ice? What is its use?
Answer:
1. When carbon-di-oxide is cooled to $-57^{\circ} \mathrm{C}$, it directly becomes a solid, without changing to its liquid state. It is called dry ice.
2. Dry ice is used in trucks or freight cars for refrigerating meat and fish while transporting them.

Question $12 .$
Write the uses of wind mills.
Answer:
The wind mills are used
1. to draw water by running pumps
2. run flour mills
3. to generate electricity.

Question $13 .$
Give the components present in the air with percentage?
Answer:
The components present in the air with percentage Nitrogen $-78 \%$, Oxygen $-21 \%$, Carbon di oxide, Argon, Water vapour and other gases $-1 \%$.

VII. Answer in detail:
Question $1 .$
Prove by an experiment that Oxygen is released during photosynthesis.

Answer:
1. Take a healthy branch of Hydrilla and place it in a funnel. Invert the funnel in a beaker of water as shown in the figure.
2 . Invert a test tube over the stem of the funnel.
3. The stem of the funnel should be kept immersed inside the water Leave the beaker in sunlight for some time.
4. You will notice some bubbles rising in the test tube.

5. The bubbles contain oxygen released by the plant during photosynthesis.
6 . If we show a glowing splinter to the collected air, it bums brightly.
7. This shows that the collected gas is oxygen.

Question $2 .$
Prove by an experiment that oxygen is necessary for burning.
Answer:
1. Place two candles on a table.
2. Ensure that both the candles are of same size and height.
3. Mark them as candle 1 and candle 2 using a chalkpiece.
4. Light both the candles. Now, cover candle 2 with glass tumbler as shown in the figure.
5. Observe the happenings at both the candle.

6. The candle 1 continues to bum, unless it is blown - off by strong moving air or any other external force.
7. This is because fresh air is continuously available to the candle for its burning process.
8. Candle 2 glows for a while and then gets put - off.
9. When the burning candle is covered with a glass tumbler, the candle can use the oxygen available in the air inside the glass tumbler.
10. Since only a small amount of air is present inside the glass tumbler - only a small portion of oxygen is available for the candle to continue glowing.
11. When all the oxygen of the air inside the gas jar is used up, then the burning candle gets extinguished.

Question $3 .$
Compare the composition of inhaled air and exhaled air.
Answer:

Question $4 .$
Write the uses of air.
Answer:
1. Air is used by plants and animals for breathing.
2. Air is used for burning fuels like wood, coal, kerosene, LPG etc.
3. Compressed air is used to fill tyres of various kinds of vehicles.
4. Ozone layer, present in the atmosphere, helps in preventing harmful radiations of the sun from reaching the earth's surface.
5. Under extra - ordinary conditions such as:
- (a) a patient having breathing difficulties,
- (b) a mountaineer climbing a high mountain,
- (c) a diver going deep into the sea, oxygen gas cylinders are used for breathing purposes.
6. Blowing air is used to turn the blades of wind mills. The wind mills are used to draw water by running pumps, run flour mills and to generate electricity.