Living Science 2020 2021 Solutions for Class 7 Science Chapter 18 Water A Natural Resource are provided here with simple step-by-step explanations. These solutions for Water A Natural Resource are extremely popular among Class 7 students for Science Water A Natural Resource Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science 2020 2021 Book of Class 7 Science Chapter 18 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science 2020 2021 Solutions. All Living Science 2020 2021 Solutions for class Class 7 Science are prepared by experts and are 100% accurate.
Page No 217:
Question 1:
Is water on the earth a renewable or a non-renewable resource?
Answer:
Water is a renewable resource and is inexhaustible because it can constantly be recycled by water cycle.
Page No 217:
Question 2:
Out of every 1 litre of water on the earth, only 10 mL is available to us as freshwater on the surface of the earth. In what forms is the rest of the water available?
Answer:
Out of the total proportion of water present on the Earth, about 97.4% is constituted by the ocean and sea water. Approximately 2% of the total water is present in the form of polar icecaps. The remaining portion of water is present in the form of fresh water.
Page No 217:
Question 3:
The molecules of water, ice and steam are the same. Do you agree?
Answer:
Yes, steam, ice and water are formed of the same molecules. These three substances represent three physical states of water, but the basic composition of all these substances is same.
Page No 217:
Question 4:
Water evaporates only when it is heated to 100°C. Do you agree? Give reasons.
Answer:
No, water does not evaporate only when it is heated to 100°C. Evaporation is a surface phenomenon and occurs at almost all temperatures. However, an increase in the temperature increases the rate of evaporation. Thus, at 100°C only the rate of evaporation is increased.
Page No 220:
Question 1:
A well was dug in a village up to the deepest level at which water was available. What is the level of groundwater in the village—the depth of the water surface in the well from the surface of the earth, or the depth from the surface of water in the well to the bottom of the well?
Answer:
The level of groundwater in the village is the the depth from the surface of the water in the well to the bottom of the well.
Page No 220:
Question 2:
Deforestation is a reason for depletion of the water table. Do you agree? Give reasons.
Answer:
Yes, deforestation is a major reason for the depletion of water table. The presence of vegetation and forest cover is essential for slowing down the rain water flow. This leads to progressive absorption of rainwater by the soil, which is essential for the maintenance of groundwater level. Due to deforestation, the rainwater is not effectively absorbed by the soil, which results in a decrease in water table.
Page No 220:
Question 3:
What is the term used for 'the wise and careful use' of resources?
Answer:
The term used to describe 'the wise and careful use' of resources is conservation.
Page No 220:
Question 4:
Which method, according to you, is the most promising in raising the water table in a city?
Answer:
The most appropriate method to raise the water table in a city is rainwater harvesting method.
Page No 222:
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 222:
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 222:
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 222:
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 222:
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 222:
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 222:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
Question 5:
Buildings and roads reduce __________ of water by the soil.
Answer:
Buildings and roads reduce seepage of water by the soil.
Page No 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
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 223:
Question 2:
If a resource is renewable, it can still get exhausted. Discuss giving two examples.
Answer:
Page No 223:
Question 3:
What are the reasons for lowering of the water table in cities?
Answer:
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 223:
Question 4:
Describe the water cycle in nature.
Answer:
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 223:
Question 5:
Conservation of resources means avoiding their wasteful use. Does this definition cover all aspects of conservation? Explain.
Answer:
Page No 223:
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 223:
Question 7:
Explain one method of groundwater conservation whose importance has been realized recently.
Answer:
Page No 223:
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 224:
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 224:
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 224:
Question 4:
Water vapour condenses to form drops of water higher up in the atmosphere. Why is the atmosphere cooler higher up?
Answer:
Hence, the atmosphere higher up is cooler as compared to the lower atmosphere.
Page No 224:
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.
Page No 224:
Question 1:
You live near a river. You notice that your neighbours throw all their garbage into the river. They justify their action by saying that the garbage they throw is very little as compared to the dirt thrown into the river by the surrounding factories. Is this thinking correct? Explain.
Answer:
No, this thinking is not correct. The contribution of each and every individual for saving and keeping our environment clean is very important. We should try to fulfill our duties towards the environment and lead others to follow them.
They should stop throwing the garbage in the water body and find alternative ways to dispose it.
If they do so collectively, it can bring about a big change. Also they can lead a campaign against these industries to stop putting their waste into the water body.
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