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Page No 210:

Question 1:

Non-renewable resources

(a) can never be replaced once they get used up.
(b) can be replaced but the time of replacement varies from a few hundred to millions of years.
(c) can be replaced in 50-100 years.
(d) can be replaced in 100-200 years.

Answer:

(b) can be replaced but the time of replacement varies from a few hundred to millions of years.

Non-renewable resources, once used up, take millions of years to form.

Page No 210:

Question 2:

Which of these methods does not result in conservation of water?

(a) using drip irrigation
(b) recycling of water
(c) cutting vegetation so that less water is lost by transpiration
(d) planting more trees

Answer:

(c) cutting vegetation so that less water is lost by transpiration
Trees slow down the flow of rainwater on land and increase the absorption by soil. Therefore, if vegetation is cut, the absorption of rainwater by the soil will decrease.



Page No 211:

Question 1:

Why is there a shortage of water even through almost trhee-fourths of the earth is covered with water?

Answer:

There is a shortage of water even though almost three-fourths of the earth is covered with water because 97.5% of water is sea and ocean water. This water cannot be used directly as it has high salt content.

Page No 211:

Question 2:

What are the three states of water? How can water be changed from one state to the other?

Answer:

The three states of water are ice, water and steam. When ice is heated, it melts to form water. When water is boiled, it changes to steam.

Page No 211:

Question 3:

What happens to rainwater once it falls on the earth?

Answer:

When rainwater falls on the earth, some of the water seeps through the soil and replenishes the groundwater.

Page No 211:

Question 4:

What do you mean by water table?

Answer:

The spaces between the soil particles and the gaps between the rocks are filled with groundwater. The level of this groundwater is known as water table.

Page No 211:

Question 3:

Renewable resources need to be conserved because

(a) we should not use them faster than they are replenished by nature.
(b) they are slowly disappearing from the earth
(c) if we overuse them nature will stop replacing them.

Answer:

(a) we should not use them faster than they are replenished by nature.
Renewable resources are exhaustible and we need to conserve them. We should not use them faster than they are replenished by nature.

Page No 211:

Question 4:

How much of the earth's surface is covered with water?

(a) about two-thirds
(b) about three-fourths
(c) exactly three-fourths
(d) about one-fourth

Answer:

(b) about three-fourths
Nearly three-fourth of the earth's surface is covered with water.

Page No 211:

Question 5:

As a natural resource, groundwater is

(a) renewable and exhaustible
(b) renewable and inexhaustible
(c) non-renewable and exhaustible
(d) non-renewable and inexhaustible

Answer:

(a) renewable and exhaustible
Groundwater is a renewable and exhaustible natural resource.

Page No 211:

Question 6:


The water table in an area will go down when

(a) we do not use groundwater.
(b) we use groundwater slowly than it is replenished.
(c) we use groundwater faster than it is replenished.
(d) we plant too many trees causing loss of water by transpiration.

Answer:

(c) we use groundwater faster than it is replenished
If we use groundwater in an area faster than it is replenished, water table will go down.

Page No 211:

Question 7:

The boiling and melting points of water are

(a) 100°C and 0°C
(b) 0°C and 100°C
(c) 100°F and 0°F
(d) 0°F and 100°F

Answer:

(a) 100°C and 0°C
Water starts boiling at 100°C to form steam. Ice melts at 0°C to form water.

Page No 211:

Question 8:

The water table goes down due to

(a) increase in population
(b) increase in agriculture
(c) increase in industrialization
(d) all of these

Answer:

(d) all of these
All these factors - population growth, increased agriculture and increased industrialisation - are responsible for the lowering of the water table.

Page No 211:

Question 1:

Are natural resources living, non-living or both?

Answer:

Natural resources are both living and non-living. Plants and animals are living natural resources, whereas air, soil, water, and minerals are non-living natural resources.

Page No 211:

Question 2:

All renewable resources are inexhaustible. True of false?

Answer:

Given statement is false. All renewable resources are not inexhaustible and some of them like soil, forest, and groundwater are exhaustible.

Page No 211:

Question 3:

Groundwater is a non-renewable resource. True of false?

Answer:

False; groundwater is a renewable resource because it can be renewed by rainwater.

Page No 211:

Question 4:

Population growth is a major reason for water scarcity. True of false?

Answer:

It is a true that population growth is a major reason for water scarcity. As population increases, more water is needed for drinking, cooking, washing, cleaning, construction work etc. Excess consumption of water for these purposes leads to water scarcity.

Page No 211:

Question 5:

Buildings and roads reduce __________ of water by the soil.

Answer:

Buildings and roads reduce seepage of water by the soil.

Page No 211:

Question 6:

Rainwater harvesting lowers the water table. True of false?

Answer:

Given statement is false. Rainwater harvesting raises the water table. Under this process, rainwater is allowed to fall on roofs of the buildings to flow into a deep trench in the ground. This rainwater replenishes the water table instead of flowing down to the drains.

Page No 211:

Question 7:

Using less water and preventing water from getting polluted is called ___________ of water.

Answer:

Using less water and preventing water from getting polluted is called conservation of water.

Page No 211:

Question 8:

What is the name given to the level at which groundwater is found?

Answer:

The level at which groundwater is found is called water table.

Page No 211:

Question 9:

Groundwater is generally free from suspended impurities. True or false?

Answer:

Given statement is true. On passing through the soil, groundwater gets filtered by various layers of sand and rocks, which make it free from suspended impurities.

Page No 211:

Question 10:

Preventing pollution of a natural resource is a part of conservation. True or false?

Answer:

Given statement is true. If we prevent a natural resource from getting polluted, we in turn increase the amount of that clean natural resource. This leads to its conservation for future.



Page No 212:

Question 5:

How are natural springs of water formed?

Answer:

Groundwater flows through the surface of non-porous rocks. At some places, it comes out of the surface and forms natural springs.

Page No 212:

Question 6:

What is drip irrigation?

Answer:

Drip irrigation is a method in which water is supplied to the roots of the plants in drops instead of filling the entire field with water.

Page No 212:

Question 7:

How does planting trees help groundwater conservation?

Answer:

Plants slow down the flow of rainwater on land and facilitates its absorption by soil. Hence, if we plant more trees, soil will absorb more rainwater and groundwater will be conserved.

Page No 212:

Question 1:

Differentiate between renewable and non-renewable resources, giving two examples of each.

Answer:

 

Renewable resources Non-renewable resources
Resources that will either never exhaust or can be recycled through natural processes in some time are called renewable resources. Resources that will exhaust or cannot be recycled after use are called non-renewable resources.
Examples: Water, soil Examples: Coal, petroleum

Page No 212:

Question 2:

If a resource is renewable, it can still get exhausted. Discuss giving two examples.

Answer:

Yes, if a resource is renewable, it can still get exhausted if we use it at a faster rate than it is renewed. It may also get exhausted if we disturb its natural method of renewal. For example, groundwater and trees are the renewable resources which can get exhausted if we use groundwater and cut trees at a faster rate for various purposes.

Page No 212:

Question 3:

What are the reasons for lowering of the water table in cities?

Answer:

The reasons for lowering of the water table in cities are as follows:
i) Rise in population: As population is rising, we need more water to fulfil the needs of people.
ii) Increase in agriculture: We need more food to feed the growing population. This ultimately increases agricultural activities.
iii) Increase in industrialisation: Water is required by almost every industry. As the number of industries increases, the consumption of water also increases.
iv) Deforestation: Trees are being cut to accommodate the growing population. This interferes the natural process by which groundwater is recharged through the seepage of rainwater.
               

Page No 212:

Question 4:

Describe the water cycle in nature.

Answer:

Water cycle:
Water present in water bodies including sea, oceans, rivers and lakes evaporates due to sun's heat. Water is further released in large amounts by the leaves of plants.

The water vapour rises up, cools down and condenses to form tiny droplets of water. These droplets unite to form clouds. This process keeps on repeating and water drops in the clouds fall on earth as rain. Sometimes, if temperature is very low, rainwater falls as hail or snow.
                        

Page No 212:

Question 5:

Conservation of resources means avoiding their wasteful use. Does this definition cover all aspects of conservation? Explain.

Answer:

Yes, conservation of resources means avoiding their wasteful use. However, this definition does not cover all aspects of conservation as reducing the pollution of natural resources such as air, water and soil is also a part of conservation. Besides, conservation also includes non-disturbance of natural processes by which resources are renewed.

Page No 212:

Question 6:

List four methods of conserving water.

Answer:

Four methods of conserving water are:
i) Using better irrigation methods like drip irrigation, which allows water to be supplied to the roots of the plants in drops
ii) Building dams and reservoirs for controlling flood
iii) Planting trees to increase the supply of groundwater
iv) Preventing the pollution of groundwater by using biodegradable fertilisers and pesticides

Page No 212:

Question 7:

Explain one method of groundwater conservation whose importance has been realized recently.

Answer:

One method of groundwater conservation whose importance has been realised recently is the rainwater harvesting. It is a method of storing rainwater for our future use. Rainwater, which falls on the roofs of houses, is allowed to flow into a deep trench in the ground. This process increases the level of groundwater. This process is successful and has given considerable results.

Page No 212:

Question 1:

If a resource can be replaced within ten years by natural processes, would you classify it as renewable of non-renewable? Give reasons.

Answer:

If a resource can be replaced within ten years by natural processes, we would classify it as renewable because it is renewed within a reasonable time period.

Page No 212:

Question 2:

Why do we feel the need for conservation more today than our ancestors did?

Answer:

We need to conserve more today than our ancestors did because of the following reasons:
i) We need more resources to fulfil the demands like, food, clothes and houses etc. due to growing population.
ii) As human progresses, his needs also increase. This has led to an increase in per capita consumption of resources.

Page No 212:

Question 3:

Wells dug to get groundwater often dry up after some time. Why? What can be done to the well to get water from it again?

Answer:

Wells dug to get groundwater often dry after some time because of the decline in the water table. Wells should be dug deeper to get water from it again.

Page No 212:

Question 4:

Water vapour condenses to form drops of water higher up in the atmosphere. Why is the atmosphere cooler higher up?

Answer:

The density of air decreases as we go higher up in the atmosphere. As the air becomes thinner, the temperature decreases. Moreover, the sun heats the surface of the earth due to which the lower atmosphere of the earth is also heated up. As we go up, the temperature decreases.
Hence, the atmosphere higher up is cooler as compared to the lower atmosphere.

Page No 212:

Question 5:

When the humidity is high and the temperature is low, fog often forms. Why?

Answer:

When humidity is high and temperature is low, air cannot hold additional moisture and becomes supersaturated if additional moisture is added. This often leads to the formation of fog.



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