DAV Class 7 Science chapter 16.pdf

DAV CLASS 7 SCIENCE CHAPTER

1. 1.
2.
3.
About ---of water is present in oceans and seas.
Only 0.3 per cent of fresh water available for use is present in
-m-a
nd --a;zt,jfif~.
rivers.l
Ground water is drawn from wells. and ' ' frfi)l]@J ]
4. Use of -fj,J;m&t9• an~
water.
drip
technique
for irrigation reduces wastage of
5.
The network of j-if which carries waste water to water treatment plant is
called CJJfJJZ, 'r~f£{¢§@j

2. 1. About 97 per cent of water on earth is fresh water and is good False ]
for human use.
2. Water occurs in its solid form in glaciers and ice caps. ([ Tr~e
~
3. Farmers rely on ground water for irrigating their crops when ( Tr~e il
there in no rain.
4. Deforestation increases the level of groundwater.
~
False ]
5. More use of ground water causes decrease in water table.
~ ~

3. C. Tick( ✓) the correct option.
1. Ocean water is unfit for drinking as it is-
" 0,ery salty O tasteless
0 too clean =- 0 generally frozen .
2. 'Rain water harvesting• can help us to conserve-
□ sea water D fresh water
.... ~:.,-M, ai; water O pond water

4. is, nearly-
099.7%
03%
097%
[¥<>.3%
4. One of the important factors, that can lead to a scarcity of water, is-
0 excessive rainfall
J Videforestation
S. ·waste water' is also called-
! ·~{sewage
D water table
D afforestation
0 processing of sea water
0 potable wate~
C salty water

5. 1. Name the three forms in which water exists on
the earth.
Answer -Ice, Water and water vapour
2. Give the meaning of the term 'water table'.
Answer -The upper layer of groundwater is
called water table.

6. I
3,.'Name two methods of drawing out ground water.
~--Answer -Two methods of drawing out
ground w_ater -
i) Rehat-~or water wheel
ii) Stepwell / tubewells
4. Name two activities which lead to the formation of
sewage.
Answer -Washin clothes, Bathing etc.

7. s.) State any two precautions that can help to avoid the
/
•choking of drains
Answer ~ two precautions that can avoid choRing
of drains are -
a) Do not throw solids, liRe left over food, eaves,
__ cotton, polythene ags, etc., in the drains.
--
b) Do not throw coo~ing oil, paints, chemicals,
engine oil, in the drains.

8. p
A
R
T
1. How is increase in population responsible for shortage of water?
Answer: Water is considered precious as it supports life on earth. With
increase in population, demand for water has increased whereas its
resources have depleted. This causes a shortage
or scarcity of water.
2. Discuss, in brief, how 'rain water harvesting' can be done.
Answer: Rain water harvesting should be done by collecting rain water in
underground tanks. This stored water can be used for many daily purposes
like irrigation, bathroom flush , vehicle wash etc. This would also help in
replenishing the ground water.
0
0
• i..______ --•

9. 3. Discuss any two causes that lead to a decrease in ground water level.
Answer: Two causes that lead to a decrease in ground water level are:
I. The amount of rainfall in most regions has decreased. This has happened
due to many factors. Some of them are deforestation, increase in
construction activity, etc.
11. As the amount of rainfall decreases, farmers depend more on ground water
for irrigation Hence, level of ground water is constantly decreasing.

10. 4. How can 'better management of water resources' help in conservation of water?
Answer: Better management of water resources can help in conserving water.
The rain water should not be allowed to flow into drains. Use of sprinklers and
drip irrigation technique, for Irrigating the crops, can help in reducing wastage
of
water. Any broken, or leaking, pipe should be immediately repaired or replaced.

11. 5. Write, in brief, about the basic details and the role of the 'sewerage system'.
Answer: Just as a network of pipes brings clean water to our homes, a network
of pipes takes the waste water, or sewage, away. This network of pipes is called
the sewerage system.
Role of the sewerage system
It carries the sewage, from its source, to a waste water treatment plant. The
waste water is cleaned, and purified, by various processes
at these treatment
plants.
The water, thus, treated and cleaned, is then allowed to mix with river or
sea water.