Questions Answers

Evaluation

I. Choose the appropriate answer

1. __________ is the percentage of nitrogen in air.

a. 78%

b. 21%

c. 0.03%

d. 1%

Answer: (a) 78%

2. Gas exchange takes place in plants using ___________.

a. Stomata

b. Chlorophyll

c. Leaves

d. Flowers

Answer: (a) Stomata

3. The constituent of air that supports combustion is __________.

a. Nitrogen

b. carbon-di-oxide

c. Oxygen

d. water vapour

Answer: (c) Oxygen

4. Nitrogen is used in the food packaging industry because 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

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. II and IV

d. I and IV

Answer: (d) I and IV

II. Fill in the blanks

1. Oxygen is the active component of air.

2. The gas given out during photosynthesis is Oxygen.

3. Oxygen gas is given to the patients having breathing problems.

4. Dust particles can be seen moving in a beam of sunlight in a dark room.

5. Carbon dioxide gas turns lime water milky.

III. True or False. If False, give the correct statement

1. Inhaled air contains a large amount of carbon-di-oxide. [False]

Inhaled air contains a large amount of oxygen.

2. Planting trees help in decreasing global warming. [True]

3. The composition of air is always exactly the same. [False]

The composition of air varies from place to place.

4. Whales come up to the water surface to breathe in oxygen. [True]

5. The balance of oxygen in atmosphere is maintained through photosynthesis in animals and respiration in plants. [False]

The balance of oxygen in atmosphere is maintained through photosynthesis in plants and respiration in plants. 

IV. Match the following

1. Moving Air - Photosynthesis

2. Layer in which we live - Troposphere

3. Stratosphere - Wind

4. Oxygen - Ozone layer

5. carbon-di-oxide – Combustion

 Answer:

1. Moving Air - Wind

2. Layer in which we live - Troposphere

3. Stratosphere - Ozone layer

4. Oxygen - Combustion

5. carbon-di-oxide – Photosynthesis

V. Arrange the following statements in correct sequence

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.

Answer:

1. Plants take in oxygen and release carbon-di-oxide just as animals.

2. Plants require energy for their growth.

3. Plants take carbon-di-oxide from the atmosphere, use chlorophyll in the presence of sunlight and prepare food.

4. Plants manufacture food by a process called photosynthesis.

5. During this process, oxygen is released by plants.

6. Such oxygen is available to animals and human beings for breathing.

VI. Analogy

1.  Photosynthesis : Carbon-di-oxide :: Respiration : Oxygen

2. 78% of air : Does not support combustion :: 21% of air : Supports combustion

VII. Observe the given figure carefully and answer the questions.

1. What will happen if we remove plants from the aquarium?

If we remove the aquatic plants from the tanks, the fish would not get oxygen. So they will soon die.

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

In the absence of sunlight the green plants will not be able to perform photosynthesis. So they will die in due course.

VIII. Give very short answer

1. What is atmosphere? Name the five layers of atmosphere.

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.

2. How do the roots of land plants get oxygen for breathing?

The roots of land plants have root hair. Using them, plants absorb oxygen from the soil.

3. What should be done if the clothes of a person catch fire accidentally? Why?

We should wrap a thick blanket around his body. We must roll him on the ground. The thick cloth prevents the supply of oxygen to the fire. Naturally, the fire stops burning.

4. What will happen if you breathe through mouth?

Our respiratory track contains hair-like cilia and the sticky mucous membrane. They filter the dust particles and germs from entering the lungs. If we breathe through the mouth these dust particles and germs will reach the lungs unchecked. It will cause infection in our respiratory system.

IX. Give short answer

1. Biscuits kept open on a plate during monsoon days lose its’ crispness. Why?

During monsoon days the humidity in the air is very high. When biscuits and kept exposed in a plate they easily absorb the moisture in the air and lose their crispness.

2. Why do traffic assistants wear a mask on duty?

Traffic constables are forced to inhale large quantities of polluted air impure with vehicle smoke and roadside dust. In order to filter these harmful particles and gases the traffic constables wear masks on duty. These masks help them to prevent the entry of harmful particles into their respiratory tract.

X. Answer in detail

1. How do plants and animals maintain the balance of oxygen and carbon-di-oxide in air?

When animals breathe they give out carbon dioxide. Plants absorb this carbon dioxide during photosynthesis and give out oxygen. This process goes on continuously. Thus plants and animals maintain the balance of oxygen and carbon dioxide in the air.

2. Why is atmosphere essential for life on earth?

The atmosphere has a large quantities of nitrogen and oxygen. Plants and animals take in oxygen during respiration and they get energy from it. The ozone layer in the atmosphere safeguards us from the harmful ultraviolet rays of the sun. The clouds which form in the atmosphere give us rain. So atmosphere is essential for life on earth.

XI. Question based on Higher Order Thinking Skills

1. Can you guess why fire extinguishers throw a stream of carbon-di-oxide while putting - off fire?

Carbon dioxide is heavier than oxygen. It is not a combustible gas and it does not support combustion. Carbon dioxide which comes out from fire extinguishers wrap the fire like a blanket. This prevents the supply of oxygen to the fire. Naturally, the fire stops burning and it is put out immediately.