NCERT Class-9 Science Solutions: Chapter 14-Natural Resources Part 5

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Question 29:

What happens when rain falls on soil without vegetation cover?

  1. Rain water percolates in soil efficiently

  2. Rain water causes loss of surface soil

  3. Rain water leads to fertility of the soil

  4. Rain water does not cause any change in soil

Answer: B

Image rain water causes loss surface soil

Image Rain Water Causes Loss Surface Soil

Image rain water causes loss surface soil

Question 30:

Oxygen is harmful for

  1. Ferns

  2. Nitrogen fixing bacteria

  3. Chara

  4. Mango tree

Answer: B

Image the Nitrogen fixing bacteria

Image the Nitrogen Fixing Bacteria

Image the Nitrogen fixing bacteria

Short Answer Questions

Question 31:

Rivers from land, add minerals to sea water. Discuss how?

Answer:

Water is capable of dissolving a large number of substances. As water flows over the rocks containing soluble minerals, some of them get dissolved in the water. Thus, rivers carry many nutrients from land to the sea.

Image rivers land, add minerals sea water

Image Rivers Land, Add Minerals Sea Water

Image rivers land, add minerals sea water

Question 32:

How can we prevent the loss of top soil?

Answer:

Loss of top soil can be prevented by

  1. Increasing the vegetation cover

  2. Checking the falling of trees

  3. By preventing excessive grazing by animals

Image Loss of top soil prevented

Image Loss of Top Soil Prevented

Image Loss of top soil prevented

Question 33:

How is the life of organisms living in water affected when water gets polluted?

Answer:

Addition of undesirable chemicals like pesticides, fertilizers, industrial waste and domestic wastes not only kill the organisms, they also cause diseases to the aquatic organisms. Besides, the requirement of oxygen by aquatic organisms is also increased. There is a reduction in the dissolved oxygen in water which adversely affects the aquatic organisms.

Image water affected when water gets polluted

Image Water Affected when Water Gets Polluted

Image water affected when water gets polluted

Question 34:

During summer, if you go near the lake, you feel relief from the heat, why?

Answer:

During summer, we feel relief from the heat when visit near the lake. The lake breeze forms during daylight in summer months because water does not warm as quickly as the surrounding land surfaces. Air cooled by contact with the cold lake water is denser than that surrounding the lake and thus forms a zone relatively high pressure over the lake. When the sun heats land, the air above it warms becoming less dense. With high pressure over the lake and low pressure over land, the regional pressure gradient pushes cool winds towards the land. This is the lake breeze flow because of which we feel better during summer near the lake.

Question 35:

In coastal area, wind current moves from the sea towards the land during day; but during night it moves from land to the sea. Discuss the reason.

Answer:

In coastal areas, during daytime, there is a regular flow of cool air from the sea towards the land. At night, there is a reverse flow of air from land to sea. This happens because during the daytime, land gets heated faster than water and radiated heat from land, heats the air above it. The hot air rises and creates an area of low pressure. Sea water does not get heated so rapidly, so air above the sea is comparatively cool A high pressure area forms above sea water as compared to air over land. Therefore, cooler air over the sea, flows towards the land (region of low pressure) area. The movement of air from one region to the other creates winds.

Image cool and Warm air During Dayand night

Image Cool and Warm Air During Dayand Night

Image cool and Warm air During Dayand night

Movement of wind from sea to land during day and from land to sea during night During the night, reverse flow of air occurs. Land cools down rapidly and the air above the land becomes cooler. Sea water cools down slowly so, the air above the sea is hotter and has a lower air pressure as compared to air pressure above the land. Therefore, cooler air present over land flows towards sea.