SEBA Class 9 Science: Natural Resources

INTEXT QUESTOIN

1. How is our atmosphere different from the atmospheres on Venus and Mars?

Answer: Our atmosphere is a mixture of gases like nitrogen, oxygen, carbon dioxide and water vapour. On Venus and Mars, no life exists and their atmospheres contain mainly carbon dioxide, up to 95–97%. In contrast, Earth has very little carbon dioxide and enough oxygen to support life.

2. How does the atmosphere act as a blanket?

Answer: The atmosphere acts like a blanket around the Earth. Air is a bad conductor of heat, so it keeps the average temperature of the Earth steady. It prevents a sudden rise in temperature during the day and slows down the escape of heat at night. Without the atmosphere, like on the Moon, the temperature would vary from –190°C to 110°C

3. What causes winds?

Answer: Winds are caused by the uneven heating of air. When air is heated it rises, creating a low-pressure area, and cooler air moves in to take its place. This movement of air from one region to another sets up winds.

4. How are clouds formed?

Answer: Clouds are formed when water bodies are heated and a large amount of water evaporates into the air. The warm air carrying water vapour rises, expands and cools. This cooling makes the vapour condense into tiny droplets, which join together to form clouds.

5. List any three human activities that you think would lead to air pollution.

Answer: Three human activities that lead to air pollution are:

1. Burning of fossil fuels like coal and petroleum.

2. Emissions from vehicles.

3. Smoke and gases released from industries.

INTEXT QUESTION

1. Why do organisms need water?

Answer: Organisms need water because all cellular processes occur in a water medium. All body reactions happen between substances dissolved in water, and transport of materials in the body also takes place in dissolved form. Without water, life cannot be sustained.

2. What is the major source of fresh water in the city/town/village where you live?

Answer: The major sources of fresh water in my town are tube-wells, ponds and the nearby river. Most people depend on tube-wells and hand-pumps for drinking water.

3. Do you know of any activity that may be polluting this water source?

Answer: Yes, activities like washing clothes and utensils in ponds, throwing garbage, and the use of chemical fertilisers in fields pollute our water sources. These wastes mix with the water and reduce its quality.

INTEXT QUESTION

1. How is soil formed?

Answer: Soil is formed from rocks over a long time by physical, chemical and biological processes. Heat from the Sun, action of water and wind, and the growth of lichens and plant roots slowly break rocks into fine particles that become soil.

2. What is soil erosion?

Answer: Soil erosion is the process in which the fertile top layer of soil is removed by strong winds or flowing water. If this topsoil gets washed away and the rocks underneath are exposed, the land becomes less fertile, and very little can grow on it.

3. What are the methods of preventing or reducing soil erosion?

Answer: Soil erosion can be prevented or reduced by keeping the land covered with vegetation. The roots of plants hold the soil tightly and stop it from being carried away by water or wind. Avoiding deforestation, especially in hilly and mountainous areas, also helps in reducing soil erosion.

INTEXT QUESTION

1. What are the different states in which water is found during the water cycle?

Answer: In the water cycle, water exists in three states:

1. Solid – in the form of ice and snow on mountains and at the poles.

2. Liquid – in rivers, lakes, ponds, oceans and underground water.

3. Gas – as water vapour present in the atmosphere.

2. Name two biologically important compounds that contain both oxygen and nitrogen.

Answer: Two biologically important compounds that contain both oxygen and nitrogen are proteins and nucleic acids (DNA and RNA). Plants also make amino acids, which contain nitrogen and oxygen, and these are later used to form proteins

3. List any three human activities which would lead to an increase in the carbon dioxide content of air.

Answer: Three human activities that increase the carbon dioxide content of air are:

1. Burning of fossil fuels like coal and petroleum for energy and transport.

2. Industrial processes where fuels are burnt for heating or production.

3. Deforestation, which reduces the number of trees that absorb carbon dioxide.

4. What is the greenhouse effect?

Answer: Written in the above.

5. What are the two forms of oxygen found in the atmosphere?

Answer: The two forms of oxygen found in the atmosphere are dioxygen (O₂) and ozone (O₃).

EXERCISE QUESTIONS

1. Why is the atmosphere essential for life?

Answer: The atmosphere is essential for life because it provides gases like oxygen for respiration and carbon dioxide for photosynthesis. It also acts like a blanket and keeps the Earth’s temperature steady by preventing sudden rise during the day and slowing down heat loss at night.

2. Why is water essential for life?

Answer: Water is essential for life because all cellular processes take place in a water medium. The reactions inside our body and cells occur between substances dissolved in water. Transport of materials in the body also happens in dissolved form. Terrestrial organisms need fresh water since their bodies cannot tolerate high amounts of salts in saline water.

3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?

Answer: Living organisms are closely dependent on soil because it supplies minerals, nutrients and water needed by plants to grow. Since plants are the producers in all food chains, animals and humans also depend on soil indirectly for their food. Soil also has humus and microorganisms which help recycle nutrients and keep the soil fertile.

Aquatic organisms are also not totally independent of soil as a resource. The particles of soil carried by rivers contain nutrients and minerals that finally reach seas and oceans. These dissolved substances are then used by aquatic plants and animals for their growth and survival.

4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?

Answer: We are able to predict the weather with the help of scientific instruments and observations. Satellites and weather stations collect information about temperature, air pressure, humidity, wind patterns and cloud movements. By studying these data, scientists can understand the changes taking place in the atmosphere and make predictions about rainfall, storms, or temperature in advance.

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: No, isolating polluting activities to specific and limited areas will not help much in reducing pollution. This is because both air and water move from one place to another and spread the pollutants far beyond that area. For example, smoke released from factories does not remain in one place but mixes with the air and spreads to nearby towns and villages. In the same way, dirty water released into a river will flow downstream and pollute places far away.

6. Write a note on how forests influence the quality of our air, soil and water resources.

Answer: Forests play a very important role in maintaining the quality of air, soil and water. Trees take in carbon dioxide and release oxygen during photosynthesis, which keeps the air clean and suitable for life. Forests also prevent soil erosion as the roots of trees hold the soil firmly and stop it from being washed away by rain or wind. They help in maintaining the fertility of soil by adding humus from decayed leaves and plant parts. Forests also influence the availability of water because they allow rainwater to seep into the ground and recharge groundwater, while reducing surface runoff and floods. Thus, forests are essential for balancing and protecting our natural resources.