(ii) Write True or False for the following statements.
(iii) Tick the correct option
(iv) Answer the following questions in brief.
(v) Answer the following questions.
Fill in the blanks
( Exercise )
1. The two main gases present in the air are ___________ and ___________.
2. Animals need ___________ gas for breathing.
3. Plants use ___________ gas to prepare their own food.
4. The process, by which plants prepare their food, is called ___________.
5. ___________ gas, present in the atmosphere, protects us from the harmful rays of sunlight.
6. Air, containing impurities, is called ___________.
Answer
(1) nitrogen, oxygen
(2) oxygen
(3) carbon dioxide
(4) photosynthesis
(5) Ozone
(6) polluted air.
Write True or False for the following statements.
( Exercise )
1. Pure air is colourless, odourless and tasteless.
2. An empty glass bottle contains air.
3. Air gets impure due to the presence of nitrogen gas..
4. Leaves of a plant look greener before rain.
5. Oxygen is required for burning.
Answers
(1) True
(2) True
(3) False
(4) False
(5) True.
Tick the correct option.
( Exercise )
1. The gas, which is present the most in air, is-
2. An air pollutant, which exists in solid form, is-
3. The gas, whose amount varies with weather changes, is-
4. The gas, that gets reduced, through the process of photosynthesis, is-
5. When sulphur dioxide reacts with water and oxygen in air, it results in the production of-
Answer
(i) nitrogen
(ii) smoke
(iii) water vapour
(iv) carbon dioxide
(v) acid rain
Answer the following questions in brief.
( Exercise )
1. Name the main components of air.
Answer: Nitrogen (78%), Oxygen (21%) and other gases (carbon dioxide, water vapour, helium, Ozone, hydrogen, etc.)
2. State the meaning of the term ‘Photosynthesis’.
Answer: The process of making food by green plants in presence of sunlight is called photosynthesis.
3. State two possible harmful effects of ultraviolet rays.
Answer: two possible harmful effects of ultraviolet rays are –
Cause skin and eye diseases in animals.
Affect the growth of plants.
4. Define the term ‘Air pollutant’.
Answer: The impurities present in air are called air pollutants.
…………………………………………………….
5. Name any two of the gaseous pollutants present in air.
Answer: Carbon monoxide and oxides of nitrogen.
…………………………………………………….
6. List any four causes of air pollution.
Answer: four causes of air pollution are-
Dust raised from the ground during dust storm.
Smoke emitted by vehicles.
Smoke raised by burning of coal in power houses.
Burning of wood, cow dung cakes, garbage, etc.
Answer the following questions.
( Exercise )
1. Why is air necessary for animals?
Answer: All animals, including human beings, need air because they take oxygen from air through the process of breathing. The oxygen is used to produce energy from the food that is eaten.
2. How is nitrogen important for plants?
Answer: Nitrogen is important for plant because –
Nitrogen helps in the rapid growth of plants.
It also helps them 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 and 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 because –
It damages crops and reduces the fertility of soil.
It can also damage monuments made up of marble.
5. Why should we feel worried about ‘global warming’?
Answer: We should feel worried about global warming because this can result in an increase in the melting of polar ice caps which can cause widespread damage and destruction.
…………………………………………………….
6. Suggest some ways of reducing air pollution.
Answer: Some ways to reduce air pollution are as follows:
We should plant more and more trees.
Lesser use of vehicles.
Regular checkup of vehicles.
Use of cleaner fuels.
Dumping the garbage in a pit.
…………………………………………………….
7. How does planting of trees help in making air cleaner?
Answer: Planting of trees help in making air cleaner because plants use up carbon dioxide gas present in the air for producing their food using photosynthesis.