NCERT In Text Solution
Question 1. How is our atmosphere different from the atmospheres on Venus and Mars?
Answer: Atmospheres of Venus and Mars do not prevent the surface of these planets from being too hot during day and too cold during night. Earth’s atmosphere prevents the earth from becoming too hot or too cold. Thus, our atmosphere makes the earth a conducive place for life.
Question 2. How does the atmosphere act as a blanket?
Answer: Atmosphere is a bad conductor of temperature. Thus, it prevents the earth from becoming too hot during the day. Atmosphere also prevents solar radiation from escaping the earth’s surface. Thus, it prevents the earth from becoming too cold during the night. Thus, atmosphere acts like a blanket.
Question 3. What causes winds?
Answer: Uneven heating of the earth’s surface causes convection currents in the air. This causes movement of air, i.e. winds.
Question 4. How are clouds formed?
Answer: Evaporation of water from oceans and other water bodies causes water vapours to rise in air. Water vapour condenses to become clouds.
Question 5. List any three human activities that you think would lead to air pollution.
Answer: Following human activities would lead to air pollution:
- Burning of fuels in automobiles.
- Burning of fuels in factories.
- Dust from mining activities.
Question 6. Why do organisms need water?
Answer: All metabolic functions take place in presence of water. Hence, organisms need water.
Question 7. What is the major source of fresh water in the city/town/village where you live?
Question 8. Do you know of any activity which may be polluting this water source?
Answer: Sewage water is discharged in nearby fields. The contaminated water seeps down the ground to pollute groundwater.
Question 9. How is soil formed?
Answer: Soil if formed by weathering of rocks by various agents of weathering. The process takes place over thousands of years.
Question 10. What is soil erosion?
Answer: Removal of topsoil by agents of weathering is called soil erosion.
Question 11. What are the methods of preventing or reducing soil erosion?
Answer: Following methods help in preventing soil erosion:
- Shelter belt planting
- Terrace farming in hilly areas
Question 12. What are the different states in which water is found during the water cycle?
Answer: Solid, Liquid and Gas
Question 13. Name two biologically important compounds that contain both oxygen and nitrogen.
Answer: Protein and Amino acids
Question 14. List any three human activities which would lead to an increase in the carbon dioxide content of air.
Answer: Following human activities would lead to an increase in the carbon dioxide in air:
- Burning of fossil fuels in automobiles.
- Burning of fossil fuels in thermal power plants.
- Burning of firewood in kitchens.
Question 15. What is the greenhouse effect?
Answer: Some gases trap solar radiation in atmosphere. This is called greenhouse effect.
Question 16. What are the two forms of oxygen found in the atmosphere?
Answer: Oxygen and Ozone
NCERT Exercise Solution
Question 1. Why is the atmosphere essential for life?
Answer: Atmosphere helps in maintaining ambient temperature on earth. It is a source of important raw materials for living beings, e.g. oxygen, carbon dioxide, nitrogen, etc. Atmosphere is an important conduit in the water cycle. Thus, atmosphere is essential for life.
Question 2. Why is water essential for life?
Answer: Living beings need water to carry out various metabolic activities. Hence, water is essential for life.
Question 3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer: Soil provides the base on which plants can grow. Soil is the source of water and minerals for plants. We know that all other living beings depend on plants for food. Even aquatic animals take food from plants. Thus, aquatic animals are not independent of soil as a resource.
Question 4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Answer: Data on various parameters are collected by satellites. The data is then analysed by computer to predict the weather.
Question 5. We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
Answer: Air keeps on moving from one place to another. Similarly, water is also in constant motion through water cycle. So, pollution can easily travel through movement of air and water; anywhere in the world. This means that isolating human activities to a limited area is not going to help in reducing pollution.
Question 6. Write a note on how forests influence the quality of our air, soil and water resources.
Answer: Forests influence the quality of air, soil and water resources in many ways. Trees take carbon dioxide and give oxygen during photosynthesis. Thus, trees help in maintaining the balance of carbon dioxide and oxygen in air. Roots of trees make the soil porous and thus help in recharge of groundwater. Trees also help in precipitation by adding water vapour by means of transpiration. Trees hold the topsoil in place with their roots. Discarded parts of a tree get decomposed and contribute to humus in soil.