Something to Know
A. Fill in the blanks.
1. The two main gases present in the air are nitrogen and oxygen.
2. Animals need oxygen gas for breathing.
3. Plants use carbon dioxide gas to prepare their own food.
4. The process, by which plants prepare their food, is called photosynthesis.
5. Ozone gas, present in the atmosphere, protects us from the harmful rays of sunlight.
6. Air, containing impurities, is called polluted air.
B. Write True or False for the following statements.
1. Pure air is colourless, odourless and tasteless. True
2. An empty glass bottle contains air. True
3. Air gets impure due to the presence of nitrogen gas. False
4. Leaves of a plant look greener before rain. False
5. Oxygen is required for burning. True
C. Tick (✔) the correct option.
1. The gas, which is present the most in air, is-
(a) oxygen
(b) nitrogen (✔)
(c) carbon dioxide
(d) water vapour
Answer – (b) nitrogen (✔)
2. An air pollutant, which exists in solid form, is-
(a) sulphur
(b) nitrogen
(c) smoke (✔)
(d) ozone
Answer – (c) smoke (✔)
3. The gas, whose amount varies with weather changes, is-
(a) nitrogen
(b) helium
(c) water vapour (✔)
(d) oxygen
Answer – (c) water vapour (✔)
4. The gas, that gets reduced, through the process of photosynthesis, is-
(a) sulphur oxide
(b) nitrogen oxide
(c) ozone
(d) carbon dioxide (✔)
Answer – (d) carbon dioxide (✔)
5. When sulphur dioxide reacts with water and oxygen in air, it results in the production of-
(a) snow
(b) acid rain (✔)
(c) nitrogen oxide
(d) carbon dioxide
Answer – (b) acid rain (✔)
D. Answer the following questions in brief.
1. Name the main components of air.
Answer – The main components of air nitrogen, oxygen and other gases like carbon dioxide and water vapour.
2. State the meaning of the term ‘Photosynthesis’.
Answer – The process by which green plants prepare their own food is called photosynthesis.
3. State two possible harmful effects of ultraviolet rays.
Answer – Two possible harmful effects of ultraviolet rays are:
(I)It can cause skin and eye diseases in animals.
(ii) It affects the growth of the plants.
4. Define the term ‘Air pollutant’.
Answer – Impurities present in air which causes air pollution are called air pollutants.
5. Name any two of the gaseous pollutants present in air.
Answer – Any two gaseous pollutants present in air are carbon monoxide, ozone.
6. List any four causes of air pollution.
Answer – Main causes of air pollution are:
Dust raised from the ground during the dust storms.
Smoke emitted by vehicles.
Smoke raised by burning of coal in powerhouses.
Burning of wood, cow dung cakes, garbage, etc. in households and in open places.
E. Answer the following questions.
1. Why is air necessary for animals?
Answer – All animals need oxygen to live. They take in this oxygen present in air and use it to produce energy from the food that is eaten.
2. How is nitrogen important for plants?
Answer – Nitrogen is essential for plants as:
It helps in the growth of plants.
It helps to develop their fruits and seeds.
It also increases the size and quality of their leaves.
3. How is the balance of oxygen and carbon dioxide in air, maintained in nature?
Answer – Animals and human beings use oxygen present in the air and give out carbon dioxide gas. Plants on the other hand consume carbon dioxide during photosynthesis in day time. They then give out oxygen. In this way a balance of carbon dioxide and oxygen is maintained in the air.
4. Why is ‘acid rain’ harmful?
Answer – Acid rain is harmful as:
It damages crops and reduces the fertility of soil.
It can also damage monuments made of marble.
5. Why should we feel ‘worried’ about ‘global warming’?
Answer – We should be worried about global warming because it can result in an increase in the melting of polar ice caps which can cause wide-spread damage and destruction.
6. Suggest some ways of reducing air pollution.
Answer – Ways of reducing air pollution are:
We should plant more trees.
We should use less personal vehicles and should prefer public transport instead.
We should regularly check-up our vehicles for their pollution level.
We should use cleaner fuels like LPG or biogas or CNG.
7. How does planting of trees help in making air cleaner?
Answer – Plants use up carbon dioxide gas present in air. It also helps to reduce the greenhouse effect and maintain the earth’s temperature at a desirable rate.
Value Based Question
Reema and her neighbour Neha study in the same school. Their parents used to drop them to the school, separately, in their own cars. One day Reema suggested to her father that she and Neha could share, or ‘pool’ the car. Her father appreciated the suggestion and agreed to talk to Neha’s father.
Neha’s father also liked the idea. From the next day they started going to school together.
1. Do you agree with Reema and why?
Answer – Yes, I agree with Reema because it will not only help in reducing air pollution but also saves fuel and also money.
2. Would this practice of commuting to school help nature?
Answer – This practice of commuting to school will help nature as it will help in reducing air pollution.
Something to Do
1. Make a poster on ‘Go Green-to breathe clean’ using magazine pictures.
Answer –
2. Try to find out the answer to the following questions:
(a) Why do plants look greener after rain?
Answer – plants look greener after rain because after rain all the dust particles removed and water is pulling nitrogen along with it into the plants.
(b) Why are LPG and biogas called ‘cleaner fuels’?
Answer – LPG and biogas called ‘cleaner fuels’ because it burns cleanly in stoves with very few emissions.
3. With the help of block diagram, explain the role of nitrogen, in the growth of plants.
Answer –
4. Power stations, which burn fossil fuels to produce electricity, are one of the main causes of increasing the amount of carbon dioxide in the air. One way, to reduce the air pollution caused by power stations, is to use less electricity. Suggest how you can try to make an effort to reduce the electricity consumption in your home.
Answer – Effort to reduce the electricity consumption in our home are
Switch off all unnecessary lights.
Turn off fans when they aren’t needed.
Make use of natural light whenever possible.
Make the best use of solar radiation.
Unplug any unused electronics.
By Sunaina Karmakar