9th Social Science Guide – Geography 4 Hydrosphere

9th Social Science Geography Solutions Chapter 4 Hydrosphere – English Medium 

9th Standard Social Science Geography Unit 4 Hydrosphere Book Back Answers History Lesson 4 Geography Hydrosphere Book Back Answers English Medium. 9 all Subject Book Answers. Class 9 Social Science All Unit Book in Answers TM & EM.

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9th Social Science Guide – Geography 4 Hydrosphere

I. Choose the correct answer.

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

(a) Atlantic

(b) Pacific

(c) Indian

(d) Antarctic

Answer:(c) Indian

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

(a) increases

(b) decreases

(c) remains constant

(d) none of the above

Answer:(b) decreases

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

(a) due to rotation of earth

(b) due to variation in temperature

(c) due to earth’s movement

(d) all the above

Answer:(d) all the above

 

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.

(a) 1 and 2 are correct

(b) 1 and 3 are correct

(c) 2, 3 and 4 are correct

(d) 1, 2 and 3 are correct

Answer:(b) 1 and 3 are correct

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

(a) convergence of tectonic plates

(b) divergence of tectonic plates

(c) lateral movements of plates

(d) stearing of plates

Answer:(b) divergence of tectonic plates

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

(a) Continental shelf-Continental slope-Sea plain-Sea trench.

(b) Continental slope-Continental shelf-Sea plain-Sea trench.

(c) Sea plain-Continental slope-Continental shelf-Sea trench.

(d) Continental slope-Sea plain-Continental shelf-Sea trench.

Answer:(a) Continental shelf-Continental slope-Sea plain-Sea trench.

7. Which of the following is not correctly matched?

(a) Gulf Stream—Pacific Ocean

(b) Labrador current—North Atlantic Ocean

(c) Canary current—Mediterranean sea

(d) Mozambique current—Indian Ocehn.

Answer:(a) Gulf Stream—Pacific Ocean; (c) Canary current—Mediterranean sea

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

(a) 1 and 2 are correct

(b) 1, 2 and 3 are correct

(c) 1, 3 and 4 are correct

(d) All are correct

Answer:(b) 1, 2 and 3 are correct

Questions 9 to 12 are of Assertion (A), Reason (R) type.

(A) both A and R are correct and R explains A.

(B) both A and R are correct but R does not explain A.

(C) A is correct but R is false.

(D) A is false but R is correct

Samacheer Kalvi 9th Social Question 9.

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

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

Answer:(A) both A and R are correct and R explains A.

Samacheer Kalvi 9th Social Science Geography Chapter 1 Question 10.

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

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

Answer:(C) A is correct but R is false.

Question 11.

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

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

Answer:(B) both A and R are correct but R does not explain A.

Question 12.

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

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

Answer:(A) both A and R are correct and R explains A.

9th Social Science Guide – Geography 4 Hydrosphere

II. Match the following:

I

1. Mariana trench – (i) Decreases salinity in the oceans
2. Great Barrier Reef – (ii) Along the coast of Japan
3. Sargasso Sea – (iii) Deepest point in the Pacific
4. Spring tides – (iv) Australia
5. Heavy rains – (v) Second order landform
6. Kuroshio current – (vi) North Atlantic Ocean
7. Continental slope – (vii) On full and new moon days

Answer:

1. – (iii)
2. – (iv)
3. – (vi)
4. – (vii)
5. – (i)
6. – (ii)
7. – (v)

III. Answer the following in brief:

1. What do you mean by the term Hydrosphere?

Answer:

• Hydrosphere, the third sphere of Earth is a collection of all forms of water on the earth.

 

2. What is the hydrological cycle?

Answer:

• The 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.

Answer:

The ocean basins are characterised by the following major relief features:

• 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?

Answer:

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.

Answer:

Sea waves are ripples on water caused when winds blow over the sea. The height of these waves depends on the speed of wind, its duration and the direction from which they blow.

 

IV. Distinguish the following:

1. Spring tide and Neap tide.

Answer:

S.No.	Spring tide	Neap tide
(i)	When the Sun, Moon and Earth aligned in the same line, the collective gravitation pull of the Sun and Moon on earth’s water strengthens to form a high tide known as spring tide.	When the Sun and Moon are at right angles their gravitational forces work against each other causing a low tide called Neap tide.
(ii)	These tides always occur on Full moon and New moon days.	A Neap tide occurs between two spring tides, i.e., twice a month when the first and last quarter moon appears.

 

2. Abyssal plains and Ocean deeps.

Answer:

S. No.	Abyssal plain	Ocean deeps
(i)	Abyssal plains are under water plains found on the deep ocean floor.	These are the deepest part of the oceans.
(ii)	These plains extend from continental rise to the mid-oceanic ridges.	Trenches are the deepest part of the oceans. They occupy about 7% of the total relief of the ocean flour.
(iii)	Abyssal plains are usually covered by the thick layer of sediments composed of clay, silt and sand.	These are sediment free. So most trenches are V-shaped with steep sides.
(iv)	Abyssal hills, sea mounts, guyots, coral atoll, etc., are the characteristic features.	Epicentre of the great earthquakes is all found in the trenches.

 

3. Tidal power and Hydel power.

Answer:

S.No.	Tidal power	Hydel power
(i)	Tidal power (or) tidal energy is a form of Hydro power that converts the energy obtained from tides into useful forms of power mainly electricity.	Hydel power (or) water power is derived from the energy of falling water (or) fast running water which may be harnessed for useful purposes.
(ii)	Tidal energy has potential for future electricity generation. Tides are more predictable than the wind and the sun.	This is a renewable energy source because the water cycle is constantly renewed by the sun. Hydro power was used for mechanical milling such as grinding grains.

 

V. Give reasons for the following.

Question 1.

The northern hemisphere and the southern hemisphere are called land and water hemispheres respectively.

Answer:

The continents and oceans are however, not evenly distributed in the northern and the southern hemispheres. The northern hemisphere holds 61% of land whereas the southern hemisphere holds 81% of water. It is because of this pattern of land and water distribution, the northern hemisphere is called as the land hemisphere and the southern hemisphere is called the water . hemisphere.

Question 2.

Continental shelf provides good fishing ground.

Answer:

They are shallower, thus enables sunlight to penetrate through the water. This encourages abundant growth of grass, sea weeds and plankton. Hence these zones become the richest fishing grounds in the world, e.g. The Grand Banks of Newfoundland.

 

VI. Answer in a paragraph:

Question 1.

Write a paragraph on the origin of oceans.

Answer:

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

Question 2.

Write a note on continental shelf and continental slope.

Answer:

Continental Shelf:

1. A shallow and gently sloping platform extending out from the adjoining continental land mass into the sea is called Continental Shelf.
2. It is almost a uniform zone of sea bed with a gentle gradient.
3. They are shallower, thus enables sunlight to penetrate through the water. This encourages abundant growth of grass, sea weeds and plankton. Hence these zones become the richest . fishing grounds in the world, e.g. The Grand Banks of Newfoundland.
4. The continental shelves have extensive deposits of minerals and mineral fuels. Hence, this zone becomes accessible for oil drilling and mining activities: e.g. Mumbai High in Arabian Sea.

Continental Slope:

1. A steep slope which descends from the edge of the continental shelf to the deep ocean- bed is called continental slope.
2. It forms a boundary between the Continental Crust and the oceanic crust.
3. This zone is free from deposits as they are steep. The most important characteristic of . continental slope is the presence of deep canyons and trenches.
4. Due to the low penetration of sunlight, the slope has nearly freezing temperature.

Hence aquatic life has very slow rate of metabolism. .

Question 3.

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

Answer:

Oceans Currents: 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.

The factors that generate ocean currents are:

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

On the basis of temperature, ocean currents are classified as warm currents and cold currents. The movement of ocean currents from the low latitudes (tropical zones) towards high latitudes (temperate and polar zones) is called warm current, e.g. Gulf Stream in Atlantic Ocean, North Equatorial Current in Pacific Ocean.

The movement of ocean currents from high latitudes (temperate and polar regions) to low latitudes (tropical regions) is called cold currents, e.g. Labrador Current in Atlantic Ocean and Peruvian Current in Pacific Ocean.

Question 4.

Explain the influences of the marine resources on mankind.

Answer:

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.

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 have become increasingly dependent on non-living marine resources.

 

Hydrosphere Additional Questions

I. Choose the correct answer.

Question 1.

The ……………. is called the Blue Planet.

(a) Earth

(b) Jupiter

(c) Mars

(d) Mercury

Answer:(a) Earth

Question 2.

The …………… is the watery part of the earth.

(a) Lithosphere

(b) Atmosphere

(c) Hydrosphere

(d) Biosphere

Answer:(c) Hydrosphere

Question 3.

The land of thousand lakes is ……………

(a) Norway

(b) Finland

(c) Britain

(d) Swedwen

Answer:(b) Finland

Question 4.

The purest form of water is …………….

(a) rain water

(b) well water

(c) river water

(d) sea water

Answer:(a) rain water

Question 5.

Extensive deposits of Minerals and Mineral fuels are found in ……………

(a) Continental slope

(b) Continental shelf

(c) Continental rise

(d) Deep Sea Plains

Answer:(b) Continental shelf

Question 6.

Consider the following statements.

(i) Submarine Fans which are similar to the alluvial fans found in water.

(ii) Aquatic life has very slow rate of metabolism.

(iii) Dragon Hole is the deepest known under water sink hole in the world.

(iv) Abyssal plains are usually covered by the thick layer of sediments. ,

(a) (i) and (ii) are correct

(b) (ii) and (iii) are correct

(c) (iii) and (iv) are correct

(d) (ii), (iii) and (iv) are correct

Answer:(d) (ii), (iii) and (iv) are correct

Question 7.

The humankind depends on the Marine resources for its …………….

(a) Agricultural purposes

(b) Survival

(c) Industrial purposes

(d) None of the above

Answer:(b) Survival

Question 8.

Which of the following correctly matched?

(a) Pacific ocean and Green land

(b) Atlantic ocean and Mariana Trench

(c) Arctic ocean and Trinity Islands

(d) Indian ocean and Andaman Nicobar Islands

Answer:(d) Indian ocean and Andaman Nicobar Islands

Questions 9 to 12 are Assertion (A) Reason (R) type.

(A) Both A and R are correct and R explains A.

(B) Both A and R are correct but R does not explain A.

(C) A is correct but R is false.

Question 9.

Assertion (A): Continental slope is free from deposits as they are steep.

Reason (R): Abyssal plains appear as a uniform flat and featureless plain.

Answer:(B) Both A and R are correct but R does not explain A.

Question 10.

Assertion (A): Continental shelf is almost a uniform zone of sea bed with gentle gradient.

Reason (R): This enables sunlight to penetrate through the water.

Answer:(A) Both A and R are correct and R explains A.

Question 11.

Assertion (A): Ocean currents are in clockwise motion in the Northern Hemisphere and in the anti-clockwise motion in the Southern hemisphere.

Reason (R): The movement of ocean currents from high latitudes to low latitudes is called warm currents.

Answer:(C) A is correct but R is false.

Question 12.

Assertion (A): The ocean/sea water does not contains calcium in great quantities.

Reason (R): Many of the aquatic animals with shells use the dissolved calcium in the sea water to build their protective shells.

Answer:(A) Both A and R are correct and R explains A.

9th Social Science Guide – Geography 4 Hydrosphere

II. Match the following.

1. Finland – (i) Atlantic Ocean
2. Land Hemisphere – (ii) Fishing grounds
3. Green land – (iii) Equal depths
4. New foundland – (iv) Kerala
5. Iso bath – (v) Goa
6. Vizhinjam – (vi) Land of Thousand Lakes
7. NIO – (vii) Northern Hemisphere

Answer:

1. – (vi)
2. – (vii)
3. – (i)
4. – (ii)
5. – (iii)
6. – (iv)
7. – (v)

III. Answer the following in brief.

9th Social Science Guide – Geography 4 Hydrosphere

1. Mention the three major processes involved in the Hydrological cycle.

Answer:

The three major processes involved in the water cycle are evaporation, condensation and precipitation.

2. Why do we consider the oceans and seas as resource bowl of the earth?

Answer:

Oceans and seas are considered as resource bowl of the earth because of the immense availability of food, minerals, etc.

3. What Is Hypsometric curve?

Answer:

A Hypsometric Curve is a graphic representation which shows the height of a certain place • found on land and the height of ocean features at sea. ‘Hypso’ means height in Greek.

4. What do you know about Water Table?

Answer:

Water table is a level below the ground, where water is found collected beneath the Earth’s surface,

5. What is Dragon Hole?

Answer:

Dragon Hole is the deepest known underwater sink hole in the world. The local fishermen call it the‘eye’of the South China Sea.

6. Write a short note on the movement of the ocean water.

Answer:

The ocean water is dynamic. Temperature, salinity, density, external forces of the sun, moon and the winds keep the ocean waters in movement, both horizontally and vertically. . Waves and currents are in horizontal motion while tides have vertical motion.

7. What is called continental rise?

Answer:

At the base of the continental slope is a gently sloping layer of sediments which merge into the deep-sea floor. This underwater feature found between continental slope and abyssal plains is called the continental rise.

8. How is the energy of the falling wave water used?

Answer:

The energy of the falling wave water is used to turn hydro turbines to generate power. Wave energy power plants have been installed at Vizhinjam in Kerala coast and Andaman and Nicobar islands of India.

9. When was the National Institute oceanography established? What do they do?

Answer:

NIO (National Institute of Oceanography) was established in 1st January 1966. The headquarters of NIO is located at Dona Paula, Goa. It Conducts research and observations to understand oceanic features, Ocean engineering, marine Archaeology etc.

10. What is Sea Mount?

Answer:

Sea mount is an underwater mountain that rise from the sea floor due to undersea volcanic

9th Social Science Guide – Geography 4 Hydrosphere

IV. Distinguish the following.

Question 1.

Warm current and Cold current.

Answer:

Warm current	Cold current
The movement of ocean currents from the low latitudes (tropical zones) towards high latitudes (temperate and polar zones) is called warm current, e.g. Gulf Stream in Atlantic Ocean, North Equatorial Current in Pacific Ocean.	The movement of ocean currents from high latitudes (temperate and polar regions) to low latitudes (tropical regions) is called cold currents, e.g. Labrador Current in Atlantic Ocean and Peruvian Current in Pacific Ocean.

Question 2.

Water table and Aquifers.

Answer:

Water table	Aquifers
Water table is a level below the ground, where water is found collected beneath the Earth’s surface.	Aquifers are porous rock strata filled with water, found below the earth’s surface.

Question 3.

Isobath and Isohaline.

Answer:

Isobath	Isohaline
An imaginary line on a map joining the points of equal depths.	An imaginary line on a map joining the points of equal salinity in oceans.

V. Give reasons for the following.

Question 1.

The earth is called the Blue Planet.

Answer:

The Earth is also called the Blue planet, as it holds water in abundance and thus stands unique among all other planets.

Question 2.

Oceans are the lifelines of Earth and Mankind.

Answer:

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 wellbeing and quality of life.

Question 3.

Most of the Creek area get submerged.

Answer:

Most of the Creek area gets submerged due to high tide and at times of low tide, the creek emerges out along with poisonous creatures like snakes, scorpions.

Question 4.

Continental shelf provides good fishing ground.

Answer:

They are shallower, thus enables sunlight to penetrate through the water. This encourages abundant growth of grass, sea weeds and plankton. Hence these zones become the richest fishing grounds in the world, e.g. The Grand Banks of Newfoundland.

VI. Answer in a paragraph.

Question 1.

The Great Barrier Reef. Explain.

Answer:

The Great Barrier Reef: The Great Barrier reef is the world’s largest coral reef system composed of 2,900 individual reefs and 900 islands stretching for about 2,000 kilometres. It covers an area of about 3,50,000 km. The reef is located in the Coral sea, off the coast of Queensland, Australia. The Great Barrier Reef can be seen from the outer space. This sprawling coral reef system is one of the most biologically diverse places on the planet. .Coral reefs are built by billions of tiny organisms, known as Coral polyps.CNN labelled it as one of the seven natural wonders of the world.

In-text HOTs Questions

Question 1.

“71% of the earth is covered by water but very little can be used by humans. Why?

Answer:

“A little amount of fresh water which is suitable for human consumption is present on the earth. Rest of the water we find in oceans. Sea water is saline and not suitable for consumption.

Question 2.

The oceans are salty. Why?

Answer:

1. As the rain erodes the rock acids in the rain water break down the rock.
2. Ions (or) electrically charged atomic particles are created.
3. These ions are carried away in runoff to streams and rivers and ultimately to the ocean.
4. Many of the dissolved ions are used by organisms in the ocean are removed from the water.
5. Others are left for long periods time where their concentrations increased overtime.
6. Sodium and chloride are the most prevalent ions in Sea water, (about 90%) making sea water salty as it is salty.

Question 3.

Why is the salinity at the equator less even though it experiences high temperature.

Answer:

The salinity at the equator is less even though it experiences high temperature, because of heavy rainfall and high relative humidity as precipitation adds good amount of fresh water to ocean water.

Question 4.

“Though Caspian Sea is enclosed its salinity is just 14 to 17 parts per thousand. Why is it so?

Answer:

1. The Caspian Sea is a fresh water lake in its Northern portions due to the current inflow of fresh water, and is most saline on the Iranian shore where the catchment basin centributes little flow.
2. Currently the mean salinity of the Caspian sea is one third that of Earth’s oceans.

Question 5.

What will happen if the seas and oceans contain only fresh water?

Answer:

1. Marine organisms would die as they are capable of surviving only in sea water (salt water).
2. Coral formation could not take place as they are made up of calcareous minerals.
3. Salt is quite important in daily usage.
4. We would have to rely on artificial production without natural salt, which would incur a lot of monetary and infrastructural expenses.
5. Salt water can hold heat better.
6. Sea life is adapted to salt water.
7. Ocean currents would be completely disrupted.

9th Social Science Guide – Geography 4 Hydrosphere

VIII. Enrichment Activity.

Question 1.

1. A) Study the map of ocean currents and then complete the table given below:

Major Ocean currents
Oceans	Northern Hemisphere	Southern Hemisphere
Pacific Ocean	Kurashio Current (Warm) Oyashio/Kurile Current (Cold) Alaska Current (Warm) California Current (Cold)	Peruvian/Humboldt Current (Cold)
Atlantic Ocean	Canaries (Cold) Gulf Stream (Warm) North Atlantic Drift (Warm) Labrador (Cold)	Benguela (Cold)
Indian Ocean	North East Monsoon Current (Warm) South West Monsoon Current (Warm)	West Australian Current (Cold)

1. B) Map Work:

Mark the cold currents in blue and the warm currents in red in a World outline map.

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