WATER

 1. Why is water necessary for us?

Ans: Water is necessary for us , because -

a) for the digestion and absorption of food

b) helps maintain proper muscle tone,

c) supplies oxygen and nutrients to the cells 

d)rids the body of wastes.

e) serves as a national air- conditioning system.

2.How many percent of the Earth's surface is covered by water?

Ans: Nearly 70%.

3. What is water cycle?

Ans: The process by which water continuously changes form and circulates between the oceans, atmosphere and land is known as the water cycle.

4. What is transpiration?

Ans: Transpiration is a process of releasing of water vapour into the atmosphere through the surface of leaves.

5. Why is the ocean water salty?

Ans: As  water flows through rivers, it picks up small amounts of mineral salts from the rocks and soil on the river beds. This slightly salty water flows into the oceans and seas. The water  in the oceans only leaves by evaporating, but the salt remains dissolved in the ocean - it does not evaporate. So the remaining water gets saltier and saltier as time passes.

6. How many percent of water is fresh water?

Ans: Only 3%.

7.Why do water keeps moving?

Or 

Give three reasons for movement of water.

Ans: Water keeps moving due to various reasons which are -

a) Waves 

b) Gravitational pulls of Sun and Moon

c) Variations in temperature.

8. What determines the size of waves?

Ans: The size of a wave depends on:

a) The distance the wind blows over open surface of water.

b) The length of time the wind blows.

c) The speed of the wind.

9.What is the difference between crest and trough?

Ans: The crest is the highest part of the wave.

But the trough is the wave height.

10) Distinguish between spring and neap tide.

Ans: The difference between spring and neap tide is 

Spring Tides: When the Moon is full or new, the gravitational pull of the Moon and Sun are combined because the Sun, the Moon and the Earth are in the same line. At these times, the high tides are very high and the low tides are very low.

Neap Tides: During the Moon's quarter phases, the Sun and Moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides.

11. Why tides are important?

Ans: Tides are important due to following reasons:

a)High tides are helpful as they increase the height of the water near the shores thus enabling big ships to sail off safely. Diamond Harbour in West Bengal makes use of high tides 

b) High tides raise the level of waters in the rivers.That makes sailing from the river ports easier.

c) Tides help in the generation of hydroelectricity which is non- polluting and a renewable source of energy.

d) High tides help in carrying the sediments from the mouth of the river and prevent silting of the harbour.

e) The fishing industry is helped by the rise and fall of the tides. During high tide fish come near the coasts . Low tides enable fishermen to go into the open seas and high tides help them to return to the coast.

12. How are tides useful for ships?

Ans: High tides are helpful as they increase the height of the water near the shores thus enabling big ships to sail off safely.

13. How are tides useful for fishermen?

Ans: The tides are useful for fishermen.During high tide come near the coasts. Low tides are enable fishermen to go into the open seas and high tides help them to return to the coast.

14.How are ocean currents affected by the rotation of the Earth?

Ans: Ocean circulation is driven by energy from the Sun, surface winds and the rotation of the Earth.

15.In which hemisphere of the Earth do currents move in anticlockwise direction.

Ans: In Southern hemisphere of the Earth do currents move in anticlockwise direction.

16.Name the warm current which flows along the east coast of Japan.

And: The name of the warm flows along the east coast of Japan is Kuroshio.

17.Why are most of the deserts located in the western coast of continents?

Ans: As most cold currents flow along the western coast of continents, most of the deserts located in the western coast of continents.

18. What are plankton?

Ans: Plankton are very small organisms, which are food for fish.

19. Choose the correct option.

1. How much of the earth's  surface is covered by water?

i) 70%.      ii) 80%.   iii) 90%.     iv)92%

Ans: i.70%

2. Fresh water is found in 

i) ponds     ii) lakes.     iii) rivers

iv) all of these

Ans: all of these.

3. Plants lose water to the air by the process of 

i) condensation. 

 ii) precipitation 

iii) transportation

iv) run off 

Ans:iii) transpiration 

4. Highest part of the wave is called

i) trough.       ii) crest      iii) tsunami.        iv) tide 

Ans: ii) crest.

5. Which one of the following is a cold current

i) California current

ii) Gulf stream 

iii) Peru current 

iv) Kuroshio Current

Ans: i) California current.

6. Alternate rise and fall of the water due to the gravitational pull of the Sun and Moon is called

i) wave      ii) tide 

iii) ocean current.   iv) none these 

Ans: ii) tide 

7. Atacama Desert is located in 

i) North America      ii) North Africa         iii)South America iv)South Africa.

Ans: South America.

8. Which one of the following is a warm current?

i) Peru current.      ii) California currents.        iii) Kuroshio Current.          iv) none of these 

Ans: iii. Kuroshio Current.

20) Fill in the blanks.

1. Plants lose water to the air by a process called transpiration.

2. Crest is the highest part of the wave.

3. The slower currens are called ocean drift.

4. Warm ocean currents flow from the tropics to higher latitudes.

5. Water flows in clockwise direction in the Northern Hemisphere due to Corriolis effect.