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NCERT Class 7 Science Chapter 16 Water: A Precious Resource
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Water: A Precious Resource
Chapter: 16
NCERT TEXT BOOK EXERCISES
Q. 1. Mark “T” if the statement is true and “F” if it is false:
(a) The fresh water stored in the ground is much more than that present in the rivers and lakes of the world. (TIF)
Ans: True.
(b) Water shortage is a problem faced only by people living in rural areas. (T/F)
Ans: False.
(c) Water from rivers is the only source for irrigation in the fields. (TIF)
Ans: False.
(d) Rain is the ultimate source of water. (T/F)
Ans: True.
Q. 2. Explain, how groundwater is recharged.
Ans: The ground water get recharged through the process of infiltration. Infiltration means seeping in water from rivers and lakes into the empty spaces and crack deep below the ground.
Q. 3. There are ten tube wells in a lane of fifty houses. What could be the long-term impact on the water table?
Ans: The effect on the water table depends on the replenishment of the underground water. As only five families will share a tube well, the water used for daily domestic purpose will not effect the water table as such. But if there is acute shortage of rains the water used by the families will not replenished and water table will fall down.
Q. 4. You have been asked to maintain a garden. How will you minimise the use of water?
Ans: To minimize the wastage of water, we will use the drip irrigation which throws the water at the base of plants. We will check the leakage in the water pipes and arrange small pits for rain water harvesting. The collected rainwater will be used later.
Q. 5. Explain the factors responsible for the depletion of water table.
Ans: Various factors are responsible for the depletion of water table:
(i) Increased Population: Increase in the human population has increased the demand for water. As the number of humans will keep on increasing, the consumption of water will also increase. Sources of water remain limited but consumption keeps on increasing causing great fall in water table.
(ii) Increasing industries: All industries need water. In increase in human population, the number of industries has also increased; so this has increased the consumption of water mainly from ground. This has caused depletion of ground water.
(iii) Agricultural activities: India is a country whose economy depends on the agriculture. With time the land used for cultivation has increased. Therefore, the consumption of water for agricultural purpose has increased. Rains are the main source of water for irrigation. But irregular rainfall has increased the dependence of farmers on the ground water. This has increased the depletion of ground water.
(iv) Lack of water conservation techniques: Main source of water on earth and for the underground water is the rain. The water of the rain, if conserved can increase the water level. But this is not done due to the lack of rain water harvesting techniques and other water conservation techniques.
Q. 6. Fill in the blanks with the appropriate answers:
(a) People obtain groundwater through _________ and _________.
Ans: Wells and hand pumps.
(b) Three forms of water are _________ , __________ and __________.
Ans: Solid, liquid and vapor.
(c) The water bearing layer of the earth is __________.
Ans: Aquifer.
(d) The process of water seepage into the ground is called ___________.
Ans: Infiltration.
Q. 7. Which one of the following is not responsible for water shortage?
(i) Rapid growth of industries.
(ii) Increasing population.
(iii) Heavy rainfall.
(iv) Mismanagement of water resources.
Ans: (iii) Heavy rainfall.
Q. 8. Choose the correct option. The total water:
(i) in the lakes and rivers of the world remains constant
(ii) under the ground remains constant.
(iii) in the seas and oceans of the world remains constant.
(iv) of the world remains constant.
Ans: (iii). In the seas and oceans of the world remains constant.
Q. 9. Make a sketch showing ground- water and water table. Label it.
Ans:
Fig. 16.10. Groundwater and water table.
ADDITIONAL IMPORTANT QUESTIONS
Very Short Answer Questions
Q.1. When do we celebrate water day?
Ans: We celebrate Water Day on 22nd March every year.
Q.2. Name: (a) Solid form of water.
Ans: Ice (or Snow).
(b) gaseous form of water.
Ans: Water vapor.
Q. 3. Name the technique of watering plants which minimizes the wastage of water.
Ans: Drip irrigation.
Q.4. What Is the water-bearing layer of the earth known as?
Ans: Aquifer.
Q.5. What natural process continuously converts some of the saline sea water into fresh water?
Ans: Water cycle.
Q.6. There are ten tube-wells in a lane of fifty houses, What could be the long term impact on the water table in the area?
Ans: Water table will fall drastically.
Q.7. Name the process which maintains the amount of water on earth.
Ans: Water cycle.
Q.8. What will happen if a plant is not watered for few days?
Ans: The plant will wilt and ultimately dry up.
Q.9. What is the source of the ground Water?
Ans: The rain water and water from other sources such as rivers and ponds are the sources of the ground water.
Q.10. What is the name of the process in which rain-water falling on earth is stopped from flowing and made to percolate into the ground?
Ans: Rain water harvesting.
Q.11. What is the main purpose of rain- water harvesting?
Ans: The main purpose of rain-water harvesting is to make rain water percolate under the soil so as to recharge ground water.
Q.12. What is the minimum amount of water per person per day recommended by the United Nations for drinking, washing, cooking and maintaining proper hygiene.
Ans: 50 Liters.
Q.13. Why do certain regions on the earth become desert?
Ans: Certain regions on the earth become desert because they get very little rain.
Q.14. Name the process by which ground water gets recharged.
Ans: Infiltration.
Q. 15. What is the percentage of water on earth available for use by human?
Ans: 0.006 %.
Short Questions Answer
Q. 1. The water-bearing layer of the earth called P is made up of two components Q and R in which water collects under the ground. The top level of layer P is called S. When too many tube-wells are used in an area, the level of S in that area goes down. What are P, Q, R and S?
Ans: P: Aquifer.
Q: Soil.
R: Permeable rocks.
S: Water table.
Q. 2. What is surface water? What are its source?
Ans: The water present on the surface of the earth is called the surface water. It can be obtained from rainwater, water from rivers and lakes and sea water contains maximum surface water.
Q. 3. Give two advantages of rain water harvesting.
Ans: (i) Rain water harvesting in rural areas increases agricultural production and hence the income of farmers.
(ii) Rain water harvesting makes less severe the effect of droughts on agricultural production.
Q. 4. Name the factors that affect water table.
Ans: Water table is affected by the following factors:
(i) Average rainfall in that area.
(ii) Use (pumping out) of the ground water.
Q. 5. How does ground water help plants/trees?
Ans: (i) Ground water provides soil moisture for plant growth.
(ii) Plants get nutrients from the soil with the help of water. Ground water helps plants to prepare their food by photosynthesis, when there is no external source of water.
Q. 6. Why is water management necessary?
Ans: Usable water is a common necessity. Therefore, water management is necessary to ensure that the water and other natural resources are used judiciously so that they fulfil the needs of present generation and also last for the generation to come.
Q. 7. Write two ill effects of water scarcity on plants.
Ans: (i) Plants wilt and ultimately dry up if they are not watered for a few days.
(ii) Seeds do not germinate and there is less production.
Q. 8. Why is ground water clean and safe to drink?
Ans: The ground water is clean and safe to drink because it passes through several layers of soil which acts as a natural filter. The water stored in ground is protected from contamination by human and animal wastes.
Q. 9. Find out the source of water in your region/locality. Is water from this source available to all people living in that area?
Ans: In our locality, the water is supplied by Municipal board through taps. This water is mainly obtained from rivers or from tube wells. The water supply is not sufficient to cater the needs of general people. Some rich and resource- ful people get more water supply as compared to poor people. Some village people get their water supply from wells.
Q. 10. What is the importance of ground water? How does it get replenished?
Ans: Ground water is a significant resource both for irrigation and supply of water for our use. Big trees draw water from ground water table. Wells both dug wells and tube wells supply ground water. Ground water is mainly replenished from rainfall.
Short Questions Answer
Q. 1. What is meant by water table? Name one factor which raises water table.
Ans: The upper level of water under the ground which occupies all the spaces in the sail and rocks, is called water table. In other words, the upper level of ground water below the surface of the earth is called water table.
The water rises depending upon the amount of rainwater which seeps into the ground.
Q. 2. Water circulates in three forms, solid, liquid and gas, during the water cycle in nature. Where is water present naturally:
(a) in solid form?
Ans: As snow (or ice) on snow-covered mountains, glaciers and polar ice caps.
(b) in liquid form?
Ans: As water in seas and oceans, rivers, lakes, ponds and ground water.
(c) in gaseous form?
Ans: As water vapour in the atmosphere.
Q. 3. The distribution of water over the globe is not even. Give reasons.
Ans: The distribution of water over the globe is not even due to a number of factors. Some places have good amount of rain and are water rich. On the other hand, there are deserts which have scanty rainfall.
India is a vast country and the rainfall is not same every where. Some regions have excessive rain while some others have very little rainfall. Excessive rains cause the floods whereas the absence of rains results in droughts.
Therefore, some regions in our country may have floods while others may suffer from droughts at the same time.
Q. 4. What are the causes of failure to sustain water availability underground?
Ans: The causes of failure to sustain water availability underground are as follows:
(i) Loss of vegetation cover.
(ii) Diversion for high water demanding crops.
(iii) Pollution from industrial effluents and urban wastes.
Q. 5. Write three effects of water scarcity on the life of the people.
Ans: (i) People have to walk long distances to fetch water. They have to pay high price for buying water.
(ii) There is uncertainty over availability of water for agriculture. The water scarce areas remain backward and neglected.
(iii) There are more incidences of diseases due to poor sanitary conditions. Life becomes hard and miserable.
Long Answer Questions
Q. 1. Give five advantages of water harvesting.
Ans: (i) It helps to recharge the ground water beneath.
(ii) The stored water does not evaporate, but spreads to recharge wells and provides moisture for vegetation over a wide area.
(iii) It does not provide breeding grounds for mosquitoes like stagnant water collected in ponds or artificial lakes.
(iv) It helps in protecting ground water from contamination by human and animal waste.
(v) It solves the problems of water scarcity.
Q. 2. Explain why, despite good rains, we are not able to meet the demand for water of all the people in our country.
Ans: Despite good rains, we are not able to meet the demand for water of all the people because:
(i) Our population is increasing rapidly.
(ii) Due to lack of sufficient vegetation cover on ground, only a little rain water seeps into the ground and gets stored as a ground water.
(iii) The high yielding varieties of crops require much more water for irrigation.
(iv) Discharge of untreated sewage and industrial wastes into rivers and lakes reduces the availability of usable water.
(v) The changing life style of people, especially in urban areas, is consuming more water.
Q. 3. What are the various advantages of water stored in the ground?
Ans: (i) The water stored in ground does not evaporate.
(ii) The water stored in ground spreads out to recharge wells and provides moisturizer for crops over a wide area.
(iii) The water stored in ground does not promote breeding of mosquitoes (unlike stagnant water collected in ponds or artificial lakes).
(iv) The water stored in ground is protected from contamination by human and animal wastes.
(v) The water stored in ground is utilized for the benefit of the local population.
Q.4. What role you can play to minimize wastage of water?
Ans: The various ways to minimize the wastage of water at home are given below:
(i) Get the leaking taps repaired immediately. Leaking taps waste a lot of water. Turn off the tap immediately after use. Do not keep the tap running all the time while brushing the teeth.
(ii) Take bath by filling water in a bucket and not directly under the flowing tap. Wash the utensils filling water in a basin and not under the running tap.
(iii) Use the water from washing rice, vegetables or fruits for watering the plants at home.
(iv) Do not use a full flush from the cistern in the toilet when a half flush is sufficient.
(v) Mob the floor instead of washing it daily.
Q. 5. Write any five methods to prevent water scarcity.
Ans: (i) Control of population by adopting small family norms.
(ii) Prevent water pollution. Prevent misuse and wastage of water.
(iii) Building dams, bunds and tanks to store rain water.
(iv) Recharging underground water.
(v) Efficient use of water in agriculture. Following drip irrigation or low water sprinklers for agriculture.
HOTS QUESTIONS
Q.1. The substance Wis necessary for the normal growth and development of all type 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 to the shortage of Z which is essential for breathing and respiration. What could W, X, Y and Z be?
Ans: W = Water
X = Photosynthesis
Y = Food
Z = Oxygen.
Q. 2. The water bearing layer of the earth called P is made up of two component Q and R in which water collects under the ground. The top level of layer P is called S. When too many tube-wells are used in an area, the level of S in that area goes down. What are P, Q, Ranil S?
Ans: P: Aquifer.
Q: Soil.
R: Permeable rocks.
S: Water table.
Q.3. List two advantages associated with water harvesting at the community level.
Ans: (i) Recharging of wells etc., increases the ground water level.
(ii) It ensures water availability in non-rainy seasons.
Q. 4. What is the use of capturing water falling on the land?
Ans. The use of capturing water falling on the land is that it raises the ground water levels and brings rivers back to life.
Q. 5. The area A in India gets an average annual rainfall of 19 cm whereas another area B receives an average annual rainfall of 280 cm. Which area could be:
(a) Assam.
Ans: Area B is Assam.
(b) Rajasthan?
Ans: Area A is Rajasthan.
SKILL BASED QUESTIONS
Q.1. Observe the following figure and identify it. What is the importance of this process?
Fig. 16. 11.
Ans: This figure shows drip irrigation in a field. Drip irrigation is a technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant. This process is used to save water.
Q. 2. Draw some posters to show importance of water and write the message of these posters.
Ans:
Fig. 16. 12.
All these posters provide the same message that is. ‘Jal Hi Jeevan Hai’ or ‘Jal Hai to Kal Hai’.
FORMATIVE ASSESSMENT
1. Fill in the following blanks with suitable words:
(i) About _________ per cent of the earth’s surface is covered with water.
Ans: 71.
(ii) The water found below the water table is called _________.
Ans: Ground water.
(iii) A tube-well draws underground water contained in an _________.
Ans: Aquifer.
(iv) Bawri was the traditional way of collecting _________.
Ans: Water.
(v) If a person is living in an area having sufficient rainfall and yet there is shortage of water, it is due to the _________ of water resources.
Ans: Mis-management.
(vi) Water cycle helps regulating the _________ of the earth.
Ans: Temperature.
(vii) Ground water can be recharged by _________.
Ans: Infiltration.
(viii) The huge reservoir of water stored between the layers of hard rocks is called _________.
Ans: Aquifer.
(ix) The best way to recharge ground water is _________.
Ans: Rain water harvesting.
(x) Leaking _________ and _________ waste a lot of _________.
Ans: Taps, pipes, water.
2. State whether the following statements are true or false:
(i) Water table is constant at every place on the earth.
Ans: False.
(ii) The water-bearing layer of the earth is called water table.
Ans: False.
(iii) In nature, water exists as only liquid water.
Ans: False.
(iv) All animals and plants contain large amounts of water.
Ans: True.
(v) Excessive use of ground water raises the water cycle at that place.
Ans: False.
(vi) Sea water cannot be used for drinking and cooking because it contains large quantity of salts.
Ans: True.
(vii) You can save water by taking a shower in place of bath with a mug.
Ans: False.
(viii) In drip irrigation, water is sprinkled over the plants.
Ans: False.
(ix) Underground water is generally free from suspended impurities.
Ans: True.
(x) The three states of water are interchangeable.
Ans: True.
3. Matching Type Questions:
| Column – A | Column – B |
| 1. World Water Day | (a) year 2003 |
| 2. International year of fresh water | (b) March 22 |
| 3. Top most level of underground water | (c) Ground water |
| 4. Water present inside the earth | (d) Surface water |
| 5. Water present on the surface of the earth | (e) Water table |
Ans:
| Column – A | Column – B |
| 1. World Water Day | (b) March 22 |
| 2. International year of fresh water | (a) year 2003 |
| 3. Top most level of underground water | (e) Water table |
| 4. Water present inside the earth | (c) Ground water |
| 5. Water present on the surface of the earth | (d) Surface water |
4. Write one word for the following:
(i) Global shortage of usable water.
Ans: Water crises.
(ii) Continuous cycling of water in nature.
Ans: Water cycle.
(iii) The minimum depth in the soil where all the pore spaces are filled with water.
Ans: Water table.
(iv) Huge reservoirs of water inside the earth.
Ans: Aquifer.
(v) Recharging of ground water by making the rainwater to percolate into the soil.
Ans: Rain water harvesting.
(vi) Water which is present on the surface of the earth.
Ans: Surface water.
(vii) The method of watering the roots of plants drop by drop.
Ans: Drip irrigation.
(viii) Wise and judicious use of water.
Ans: Water conservation.
(ix) Seeping of rain water through different layers of soil till they join ground water.
Ans: Infiltration.
(x) The decrease in the water table due to over use of ground water.
Ans: Depletion.
5. Multiple Choice Questions:
(i) Which of the following is not an effect of acute scarcity of water in plants?
(a) shortage of food
(b) shortage of oxygen
(c) shortage of carbon dioxide
(d) shortage of rainfall
Ans: (c) Shortage of carbon dioxide.
(ii) The minimum amount of water recommended by United Nations per person per day is:
(a) 25 L
(b) 50 L
(c) 75 L
(d) 40 L
Ans: (b) 50 L.
(iii) The water bearing layer of the earth is called:
(a) conifer
(b) hydrosphere
(c) aquifer
(d) water table
Ans: (c) Aquifer.
(iv) Ground water will not be depleted due to:
(a) afforestation
(b) thermal power plants
(c) loss of forest and decreased rainfall
(d) cropping of high water demanding crops
Ans: (a) Afforestation.
(v) The main source of water in India is:
(a) rain water
(b) ground water
(c) surface water
(d) sea water
Ans: (a) Rain water.
(vi) Water which falls from the clouds as rain or snow is called:
(a) condensation
(b) precipitation
(c) infiltration
(d) transpiration
Ans: (b) Precipitation.
(vii) Sea/ocean water cannot be used for domestic use because it contains:
(a) soluble salts
(b) dust
(c) insoluble salts
(d) acids
Ans: (a) Soluble salts.
(viii) Which of the following increases the rate of percolation of rain water into the soil?
(a) constructing check dams
(b) vegetation and trees
(c) over grazing
(d) construction of roads
Ans: (a) Constructing check dams.
(ix) Water exists in its gaseous form as water vapor above:
(a) 50°C
(b) 0°C
(c) 100°C
(d) 4°C
Ans: (c) 100°C.
(x) Rain water harvesting is one of the ways to conserve:
(a) fresh water
(b) sea water
(c) potable water
(d) rain water
Ans: (d) Rain water.
