9th Std Social Science Term 2 Solution | Lesson.5 Hydrosphere

Lesson.5 Hydrosphere

9th Standard Social Science Book Term 2 - Hydrosphere

Lesson.5 Hydrosphere

I. Choose the correct answer

1. The Sunda Trench lies in the …………… Ocean.

  1. Atlantic
  2. Pacific
  3. Indian
  4. Antarctic

Ans : c) Indian

2. The temperature of the ocean waters generally …………… at greater depth.

  1. Increases
  2. Decreases
  3. Remains constant
  4. None of the above

Ans : d) None of the above

3. Ocean currents are produced due to ……………

  1. Due to rotation of Earth
  2. Due to variation in temperature
  3. Due to Earth’s movement
  4. All the above

Ans : b) Due to variation in temperature

4. Consider the following statements.

1. Most of the fishing grounds occur in areas where the continental shelf is wide

2. Fishing is well developed in warm tropical waters.

3. Mixing of warm and cold currents facilitates plant nutrients for fish.

4. Inland fishing became significant in India.

  1. 1 and 2 are correct
  2. 1 and 3 are correct.
  3. 2,3 and 4 are correct.
  4. 1,2 and 3 are correct

Ans : d) 1,2 and 3 are correct

5. The oceanic ridge comes into existence due to ……………

  1. Convergence of tectonic plates
  2. Divergence of tectonic plates
  3. Lateral movements of plates
  4. Stearing of plates

Ans : b) Divergence of tectonic plates

6. Which of the following indicates the correct sequence of the topography beneath the surface of the sea?

  1. Continental shelf-Continental slope-Sea plain-Sea trench.
  2. Continental slope-Continental shelf-Sea plain-Sea trench.
  3. Sea plain-Continental slope-Continental shelf-Sea trench.
  4. Continental slope-Sea plain-Continental shelf-Sea trench.

Ans : a) Continental shelf-Continental slope-Sea plain-Sea trench.

7. Which of the following is not correctly matched?

  1. Gulf Stream – Pacific Ocean
  2. Labrador current – North Atlantic Ocean
  3. Canary current – Mediterranean sea.
  4. Mozambique current – Indian Ocean

Ans : b) Labrador current – North Atlantic Ocean

8. The amount of planktons to be found in the ocean is determined by

1. Depth of the water.

2. Ocean currents.

3. Temperature and Salinity.

4. Length of day and night.

  1. 1 and 2 are correct
  2. 1, 2 and 3 are correct
  3. 1, 3 and 4 are correct
  4. All are correct.

Ans: b) 1, 2 and 3 are correct

II. Questions 9 to 13 are of Assertion (A), Reason (R) type.

  1. both A and R are correct and R explains A.
  2. both A and R are correct but R does not explain A.
  3. A is correct but R is false.
  4. A is false but R is correct.

9. Assertion (A) : Oceans are always shown in blue in maps.

Reason (R) : It indicates the natural colour of the oceans.

Ans : c) A is correct but R is false.

10. Assertion (A) : Flat topped seamounts are known as Guyots.

Reason (R) : All guyot features are of volcanic origin.

Ans: b) both A and R are correct but R does not explain A.

11. Assertion (A) : Submarine canyons are deep gorges on the ocean floor.

Reason (R) : They are mainly restricted to continental shelf, slope and rise.

Ans : b) both A and R are correct but R does not explain A.

12. Assertion (A) : Atolls are more common in the Atlantic Ocean.

Reason (R) : The marine population at the depth is less.

Ans : b) both A and R are correct but R does not explain A.

13. Assertion (A) : Salinity is higher in closed ocean basins.

Reason (R) : They are mainly restricted to continental shelf, slope and rise.

Ans : c) A is correct but R is false.

II. Match the following

1. Mariana trenchDecreases salinity in the oceans
2. Great Barrier ReefAlong the coast of Japan
3. Sargasso seaDeepest point in the Pacifc
4. Spring tidesAustralia
5. Heavy rainsSecond order landform
6. Kuroshio currentNorth Atlantic Ocean
7. Continental slopeOn full and new moon days
 Ans: 1 – C, 2 – D, 3 – F, 4 – G, 5 – A, 6 – B, 7 – E

III. Answer the following in brief:

1. What do you mean by the term Hydrosphere?

  • The hydrosphere is the watery part of the Earth.
  • Earth is called the Blue Planet because it holds water in abundance.
  • Hydrosphere consists of water in various forms found on the Earth.

2. What is hydrological cycle?

  • The Earth’s water is not static. It is always in motion.
  • This continuous movement of water on, above and below the Earth’s surface is called the Hydrological cycle.

3. Mention the various relief features of ocean floor.

  • Continental shelf
  • Continental slope
  • Continental rise
  • Deep sea plain or Abyssal plain
  • Oceanic deep
  • Oceanic ridge

4. What are the factors that generate the ocean currents?

The factors that generate ocean currents are:

  • Earth’s rotation
  • Prevailing winds and
  • Differences in temperature and salinity of ocean water.

5. Write a brief note on sea waves.

  • Sea waves are ripples on water causes when winds blow over the sea.
  • Of all the movements of the oceans, sea waves are considered the strongest.
  • The height of the waves depends on the speed of wind, its duration and the direction.
  • The waves that are caused by tremors on the ocean are called Tsunami.

IV. Distinguish the following:

1. Spring tide and Neap tide.

Spring tideNeap tide
1. This tide occurs when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides.When the Sun and the Moon are at right angles, their gravitational forces work against each other causes Neap tide
2. Spring tide is also known High tideNeap tide is also called as Low tide.
3. It always occurs on full moon and new moon days.It occurs twice in a month – the first and last quarter moon appears

2. Abyssal plains and Ocean deeps.

Abyssal plainsOcean deeps
1. Abyssal plains are the deep sea plains Found on the deep ocean floor.These oceanographic features are the deepest parts of the ocean floor.
2. These plains are usually covered by the thick layer of sediments.It is sediment free zones.
3. The gradient of the slope is very gentleThe trenches are V shaped with steep slides.

3. Tidal power and Hydel power.

Tidal powerHydel power
The power generated from the waves of sea water is known as tidal power.Hydel power’ is the short form of hydroelectric power.
2. We can get tidal power throughout the year.It depends on monsoon. We cannot depend on this power.
3. This power plants are installed at Vizhinjam in Kerala coast and Andaman & Nicobar islands of India.Nagarjuna Sagar Dam, Guntur and Sardar Sarovar Dam, Gujarat are the best examples.

V. Give reasons for the following: 

1. The Northern hemisphere and the Southern hemisphere are called land and Water hemispheres respectively.

  • Northern hemisphere holds 61% of land. So, it is called as Land hemisphere.
  • Southern hemisphere holds 81% of water. So, it is called as Water hemisphere.

2. The ocean waters are saline in nature.

  • Ocean water contains lots of different mineral salts such as sodium, chloride, sulphate, calcium, potassium, bicarbonate, etc.
  • These salts enter the ocean through rivers.
  • When the sea water evaporates, it doesn’t take the salt with it.
  • So with less water and the same amount of salt, the sea water becomes pretty salty.

3. Continental shelf provides good fishing ground.

  • A shallow and genteelly sloping platform enables sunlight to penetrate through the water.
  • This encourages abundant growth of grass, see weeds and plankton.
  • Hence, this zone provides good fishing ground in the world.

4. Salinity of Bay of Bengal is greater than the Arabian sea.

Salinity of Arabian Sea is much higher than in the Bay of Bengal because-

  • Evaporation over the Arabian Sea is much greater and
  • It receives relatively less river runoff.

VI. Answer in a paragraph 

1. Write a paragraph on the origin of oceans.

  • The ocean is a continuous body of salt water that forms the major part of hydrosphere.
  • Geoscientists believe that the oceans were formed on Earth nearly three billion years ago.
  • It is difficult to believe that in the beginning there was no water on our planet.
  • In due course of time, when the Earth started cooling, steam escaped from the interior and entered the atmosphere to form clouds.
  • At first, the clouds brought incessant rains. The rain water filled the depressions for tens of thousands of years and eventually a super ocean was formed.

2. Write a note on continental shelf and continental slope.

Continental shelf :

  • A shallow and gently sloping platform extending out from the adjoining continental land mass into the sea is called Continental Shelf.
  • It enables sunlight to penetrate through the water which in turn encourages abundant growth of grass, sea weeds and plankton.
  • Hence these zones become the richest fishing grounds in the world. Eg. The Grand Banks of New Foundland.

Continental Slope :

  • A steep slope which descends from the edge of the continental shelf to the deep ocean-bed is called continental slope.
  • It forms a boundary between the Continental Crust and the Oceanic crust.
  • This zone is free from deposits as they are steep.
  • Due to the low penetration of sunlight, the slope has nearly freezing temperature. Hence aquatic life has very slow rate of metabolism

3. What do you mean by ocean currents? Explain its types.

The movement of oceanic water on the surface and at the depths in a definite direction is called ocean current. Ocean currents are in clockwise motion in the northern hemisphere and in the anti-clockwise motion in the southern hemisphere.

Warm Current:

The movement of ocean currents from the low latitudes (tropical zones) towards high latitudes (temperate and polar zones) is called warm current.

Eg. Gulf Stream in Atlantic Ocean.

Cold Current:

The movement of ocean currents from high latitudes (temperate and polar regions) to low latitudes (tropical regions) is called cold currents.

Eg. Labrador Current in Atlantic Ocean.

4. Explain the influences of the marine resources on mankind.

  • The biotic and abiotic resources found in the oceanic water and at the bottoms are called marine resources. The ocean’s resources play a vital role in sustaining the needs of society.
  • Oceans are the life blood of planet earth and mankind. The humankind depends on the marine resources for its survival. They are also essential for the economic prosperity, social well-being and quality of life.
  • A diverse array of marine organisms is used for food, medicine, cosmetics, and a wealth of industrial applications.
  • The world’s demand for energy, minerals and water has become increasingly dependent on non-living marine resources.
  • Oceans have extensive deposits of oil reserves. Besides a major fishing ground, it helps in generating non-conventional energy, development of many ports and harbours for trade activities. Coastal tourism also attracts people around the world, thereby contributing to the economy of many countries.


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