Wednesday , September 23 2020
7th Class CBSE Science NCERT Book

Water: A Precious Resource – 7 Class CBSE Science Ch 16

Water: A Precious Resource 7th Class NCERT CBSE Science Chapter 16

Question: Suggest one traditional way of storing water from ancient time.

Answer: In ancient times, people used to make Bawris to store water.

Question: What is the source of water in each of the following?

  1. Wells
  2. Ground
  3. Atmosphere

Answer:

  1. The source of water in wells is groundwater.
  2. The source of water on ground is rain.
  3. The source of water in atmosphere is evaporation.

Question: The earth looks blue from space. Explain why?

Answer: The major surface area (71%) of the earth is covered with water. This imparts blue colour to the earth.

Question: Some slogans has been given for the conservation of water. What does the slogan ‘Jal hai to kal hai‘ means?

Answer: This means if you have water, you can think of future, i.e. no life is possible without water.

Question: Reservoir of dam helps us to manage water. How?

Answer: The reservoir of dam or river can release water at our will. We can divert the flow of water at desired places where it is really needed and we can manage water resource effectively.

Question: The excessive use of water leads to a severe problem. Write the problem.

Answer: The excessive use of water leads to water scarcity in an area.

Question: How much of the earth’s surface is covered with water?

Answer: About two-third of the earth’s surface is covered with water.

Question: Mention the year which is celebrated as international year of freshwater?

Answer: The year 2003 was celebrated as International year of freshwater.

Question: State the consequences, if plants do not get enough water.

Answer: The plants will wilt and ultimately dry up in lack of water.

Question: Mention the source of groundwater.

Answer: Rainwater and water from the other sources like rivers, ponds, etc are the source of groundwater.

Question: From where do the workers get water for construction?

Answer: Workers get water from the underground water.

Question: Can we keep on drawing water from under the ground? How will it affect the water table?

Answer: No, we cannot keep on drawing water. It causes the depletion of water table.

Question: State the percentage of actual amount of water available for human use.

Answer: The actual amount of water available for human use is very little, i.e. approx 0.0006 % of all water found on the earth.

Question: If wells dug to get groundwater, then it dry up after sometime, what initiative should be taken to get water from it again?

Answer: In the above condition, the groundwater get recharged through the process of infiltration. It replenishes the groundwater.

Question: Water circulates through the water cycle in the three forms. Name them.

Answer: Water circulates through the water cycle in the three forms, i.e. solid, liquid and gas.

Question: As our population increases, we need more water for drinking, washing and other purposes. Does this affect the water table? Explain.

Answer: Yes, rising population leads to an increase in consumption and at the same time, a decrease in the seepage of water into the . ground leads to the depletion of water table.

Question: The substance W is necessary for the normal growth and development of all types of plants and animals. An acute scarcity of substance W has an ill effect on plants which can hinder the natural process X in plants causing a severe shortage of Y leading to famine. It may also lead the shortage of Z which is essential for breathing and respiration. What could W, X, Y and Z be?

Answer:

  • W- Water
  • X – Photosynthesis
  • Y – Food
  • Z – Oxygen

Question: Explain how the traditional use of groundwater is different from the present use.

Answer: Traditionally in ancient times, people made Bawris to collect rainwater in the old buildings. We still use these structures and are reviving them to harness rainwater.

Question: Planting trees help groundwater conservation. Explain how.

Answer: Plants lose water in the form of water vapour by the process of transpiration. So, forests contribute a lot of water vapors formation which make clouds. Thus, plants help to revive water cycle.

Question: List the reasons for lowering of water table in cities.

Answer: Water drawn from underground water gets replenished by seepage of rainwater. The water table does not get affected as long as we draw the same amount of water as is replenished by natural resources like rain.

However, there are number of factors which cause depletion of water table at a very fast rate which is really a matter of concern for everyone of us. Increase in population, industrial and agricultural activities are some common factors affecting water table. Scanty rainfall, deforestation and decrease in the effective area for seepage of water may also deplete the water table.

Question: Complete the given table.

Form of water Process by which formed Location where found
(a) Liquid
(b) Solid
(c) Gaseous

Answer: The complete table is given below:

Form of water Process by which formed Location where found
(a) Liquid Condensation and melting Water bodies like rivers, lakes etc.
(b) Solid Freezing Cold regions like high mountains, poles, etc.
(c) Gaseous Evaporation Atmosphere

Question: Place the following statements in a proper order to form a meaningful paragraph.

  1. Which in turn decreases the seepage of rainwater into the ground.
  2. This decreases the open areas like parks and playgrounds.
  3. Increasing population create demand for construction of houses, shops, offices, roads and pavements.
  4. This results in depletion of water table and creates scarcity of more water.

Answer: Increasing population create demand for construction of houses, shops, offices, roads and pavements (c). This decreases the open areas like parks and playgrounds (b) which in turn decreases the seepage of rainwater into the ground (a). This results in depletion of water table and creates scarcity of more water (d).

Question: The water bearing layer of the earth called P is made up of two components O and R, in which R water collect under the ground. The top level of layer Pis called S. When too many tubewells are used in an area, the level of S in that area goes down. What are P, Q, R and S?

Answer:

  • P – Aquifer
  • Q – Soil
  • R – Permeable rocks
  • S – Water table

Question: How can you observe the three forms of water

  1. in nature and
  2. at home?

Answer: The three forms of water

  1. in nature are snow (solid), water (liquid) and water vapour (gas).
  2. at home are ice (solid), water (liquid) and steam (gas).

Question: Name some industries familiar to you. Make a list of the products obtained from these and used in our daily life. Discuss how the growing industrial activity is responsible for depletion of water table?

Answer: Following industries and their products pollute the water:

  1. Leather industries, e.g. shoes and other products.
  2. Chemical factories, e.g. fertilizers, different insect repellent sprays etc.
  3. Petrochemical industries, e.g. petroleum and different fuels.
  4. Oil industries.

All the above industries release pollutants such as asbestos, lead, mercury, nitrates, sulphur etc in different rivers, lakes and ponds which are polluting the water and hence is responsible for depletion of water table.

Question: Mention three causes of water scarcity in our country.

Answer: The three causes of water scarcity in our country are

  1. Rapid urbanization.
  2. Increased number of industries.
  3. Population explosion.

Question: Certain pattern of the rainfall in our country leads to scarcity of water. Explain that pattern. Which part of the country gets rainfall twice a year?

Answer: We face shortage of water mainly because water is not evenly distributed by the nature on the earth. Some places such as North East India get so much rains, so that it gets flooded almost every year. On the other hand, Thar desert in Rajasthan may get rains rarely in the monsoon season. This uneven pattern of rains causes water scarcity in India at some places.

Water: A Precious Resource NCERT – Question: A number of problems can be faced due to shortage of water. List some of them.

Answer: The number of problems that can be faced due to shortage of water are as follows

  1. Less amount of pure drinking water will be available.
  2. Lack of equal distribution of water.
  3. Drought.

Water: A Precious Resource NCERT – Question: From where do the following usually get water? In which form is water present in them?

  1. Clouds
  2. Plants
  3. Mountain tops
  4. Aquifer
  5. Animals

Answer:

Source of water Form of water
Clouds Land Liquid form (droplet of water)
Plants Soil Liquid form
Mountain tops Atmosphere Solid form
Aquifer Rain Underground water
Animals Water bodies Liquid

Question: Some definitions are given which can be corrected by changing one word. Correct them.

  1. Aquifer is groundwater stored between layers of hard rock above the water table.
  2. The process of evaporation of water in the ground is called infiltration.
  3. The evaporation of water from oceans and its arrival back into oceans is called vapour cycle.

Answer:

  1. Aquifer is groundwater stored between layers of hard rock below the water table.
  2. The process of seeping of water in the ground is called infiltration.
  3. The evaporation of water from oceans and its arrival back into oceans is called water cycle.

Question: Deforestation can be considered as a reason for depletion of the water table. Comment.

Answer: Large scale deforestation has occurred to accommodate the growing population, to grow food for them and to provide space for industries. Vegetation slows down the flow of rainwater on land and increases the absorption of water by the soil.

Cutting down of trees and destroying vegetation, therefore interferes with the natural process by which seeping takes place and the groundwater is recharged.

It finally results in the depletion of the water table.

Water: A Precious Resource NCERT – Question: Give the main causes of water scarcity in our country.

Answer: The main causes of water scarcity in our country are

  1. Rapid urbanization.
  2. Increased number of industries.
  3. Population explosion.

Question: Sachin lives in an area where on and off water scarcity is there. He gave a thought to the problem and planned to get a solution. He decided to harvest rainwater in his village. He made efforts to convince the people of his area, built some drainage system and water tanks where rainwater could be collected.

  1. Name few structures he might have built.
  2. Name the process of water cycle, Sachin will use for harvesting water.
  3. Write the methods, Sachin will tell the people to use water wisely.

Answer:

  1. Sachin has build up cemented drainage channels in the elevated area and tanks where these channels will collect water.
  2. Sachin is planning to harvest rainwater.
  3. Sachin will educate people to use water judicially in the following way
    (i) Use mug for brushing, shaving and bathing.
    (ii) Water plants with drip irrigation.
    (iii) Use and reuse water in home activities.

Question: Two figures ‘a’ and ‘b’ are given below. Both are revealing two different human activities which are the cause of depletion of water table. Identify the two acts and explain how are these causing the depletion of water resource.

Cause of depletion of water table

Answer:

  1. Large scale construction
  2. Deforestation

Large scale construction It is main cause of water table lowering because it utilizes large amount of water at the time of construction. Most of the time, it is digged water table.

Secondary, when ground surface becomes cemented. It does not allow seepage of rainwater into deeper layers, so rainwater goes waste as run off water and cannot replenish the water table of that particular place.

Deforestation Plants transfer huge amount of water in the form of water vapours. So, when forests are cut down, we interrupt in the process of water cycle of that area. So, no rain occurs at that place and it gradually turns into desert area.

Question: Shishir returned from school and found his mother busy in the kitchen. He noticed that she is making his favorite dosa. Shishir rushed to his mother as he was feeling hungry and found that the tap in the kitchen was leaking. He told his mother to replace it as leaking taps lead to the wastage of water. His mother smiled and ensured him to do the same.

  1. What is water management?
  2. Why should we save water?
  3. What values are shown by Shishir?

Answer:

  1. Minimum wastage of water is called water management.
  2. We should save water to prevent water crisis.
  3. Shishir is sincere, responsible and has capability of applying knowledge practically.

Water: A Precious Resource NCERT – Question: What is groundwater? What are the sources of water which are fed by groundwater?

Answer: The wells, tubewells and handpumps are main sources of water for many people. The water in these sources is the groundwater. It is upper level of underground water which occupies all the spaces in the soil and rocks and form a water table as shown in the figure below:

Groundwater and water table

The upper limit of groundwater is called water table. It represents the depth of water filled area at a given place. The water table rises and falls depending upon the amount of rainwater that seeps into the groundwater and how much groundwater is drawn out for irrigation and industry. The seeping down of rainwater into the groundwater is called infiltration. The groundwater, thus gets recharged by this process.

At some places, the groundwater is stored between layers of hard rock below the water table. This is aquifer which contains the groundwater usable by tubewells and handpumps. These sources however, have limited sources of water and may get exhausted if used excessively.

Water: A Precious Resource NCERT – Question: Water is very precious for all the living beings. What will happen in future, if we do not save water now?

Answer: Water is needed for various life activities. If we continue the misuse of water and do not conserve it, the groundwater level will be depleted. This may result into various consequences like

  1. Lowering of the water table Excessive pumping can lower the groundwater table.
  2. Reduced surface water supply Groundwater and surface water are connected. When groundwater is overused, the lakes, streams and rivers connected to groundwater, can also have little supply.
  3. Loss of plants from land We fully depend on the plants for food directly or indirectly. Plants need water to prepare their food. If there will be scarcity of water on earth, the plants will be unable to prepare their food. This inturn will lead to the end of the life because world without plants means no food, no oxygen, not enough rain and other innumerable problems.
    Therefore, it is true that water is a precious resource.

Question: All the rain that falls over an area is not utilized. Do you agree? Explain.

Answer: Precipitation (rain) is a natural process and is a part of natural water cycle. It replenishes all the natural resources of water like ponds, lakes, river and finally oceans and seas too.

When we say utilization of rainwater, we mean that rain in a particular area.

Yes, it is not properly utilized as most of the water is run off as surface water to the rivers and goes to oceans.
We can harness / harvest this water to local waterbodies like ponds, lakes and groundwater by proper planning as it is being done in some districts of Rajasthan successfully.

Fill in the Blanks: Water: A Precious Resource NCERT

  1. The rainwater and ……………. from other sources such as rivers and ponds seep through the ……………. and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called …………….
  2. Rajasthan is a ……………. and dry place. The challenge of natural ……………. of water was met by a successful experiment. A band of social had transformed a ……………. area into a green place. They have revived five dried-up ……………. by constructing water ……………. structures.
  3. The rainwater can be used to ……………. the groundwater.
  4. The best way to overcome shortage of water is ……………. .
  5. Leaking ……………. is a source of huge water wastage.
  6. The process of ……………. of water into the ground is called infiltration.
  7. The ……………. in the soil indicates the presence of underground water.
  8. Rainwater harvesting ……………. the water table.
  9. Using less water and preventing water from getting polluted is called ……………. of water.
  10. Buildings and roads reduce ……………. of water by the soil.
  11. A tubewell draws underground water contained in an ……………. .
  12. Bawri was the traditional way of collecting …………….

Answer:

  1. water, soil, infiltration
  2. hot, scarcity, workers, dry, rivers, harvesting
  3. recharge
  4. conserve water
  5. pipeline
  6. seepage
  7. moisture
  8. replenish
  9. conservation
  10. absorption
  11. aquifer
  12. rainwater

True / False

  1. Water vapour is the gaseous form of water.
  2. Ice is solid, whereas snow is the semi-solid form of water.
  3. Ocean water cannot be used for domestic purposes.
  4. Rapid growth of industries is one of the cause for water shortage.
  5. The process of seeping of water into ground is called filtration.
  6. 51 % of the earth’s surface is covered with water.
  7. Year 2003 was observed as the International year of freshwater.
  8. Snow and ice both are solid form of water.
  9. Plants wilt and ultimately dry up if they are not watered for few days.
  10. Water found above the water table is called groundwater.

Answer:

  1. True
  2. False, ice and snow both are solid forms of water
  3. True
  4. True
  5. False, the process of seeping of water into ground is called infiltration
  6. False, 71% of the earth’s surface is covered with water
  7. True
  8. True
  9. True
  10. False, the water found below the water table is called groundwater

Water: A Precious Resource NCERT – Question: Match the Column I with Column II.

Column 1 Column II
(a) Solid (i) Water under water table
(b) Liquid (ii) Traditional way for collecting water
(c) Gas (iii) Water between the hard rocks
(d) Groundwater (iv) Ice, snow
(e) Aquifer (v) Water in ponds, rivers, oceans
(f) Bawris (vi) Water vapors

Question: Match the Column I with Column II.

Column I Column II
(a) Groundwater (i) Solid form of water
(b) Bawris (ii) Wastage of water
(c) Snow (iii) Water management
(d) Drip irrigation (iv) Small waterbody
(e) Leaking taps (v) Water table

Answer:

(a) – (v)
(b) – (iv)
(c) – (i)
(d) – (iii)
(e) – (ii)

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