4. Structure of Ocean Floor / Class 8 Geography/ Exercise/ Questions and answers/

Class 8 Geography

4. Structure of Ocean Floor

EXERCISE (Page no. 28)

 Q. 1 Choose the correct option.

 (a) Like there are landforms on land, ocean 

floor also has submerged landforms because ……

 (i) There is land under water 

 (ii) There are volcanoes under water 

 (iii) Land is continuous and there is 

 water in deeper parts. 

 (iv) Though land is continuous, its level 

 is not the same everywhere like 

 that of water .

Ans: (iv) Though land is continuous, its level 

 is not the same everywhere like 

 that of water.

 (b) Which part of the ocean floor is most useful to the man ?

 (i) Continental shelf 

 (ii) Continental slope 

 (iii) Abyssal plains 

 (iv) Marine deeps 

Ans: (i) Continental shelf 

 (c) Which one of the following option is 

related to marine deposits? 

 (i) Rivers, glaciers, remains of plants 

 and animals 

 (ii) Volcanic ash, continental shelf, 

 remains of plants and animals

 (iii) Volcanic ash, lava, fine particles 

 of soil

 (iv) Volcanic ash, remains of plants 

 and animals, abyssal plains 

Ans: (iii) Volcanic ash, lava, fine particles 

 of soil

Q 2. (a) Name the landforms shown in the 

figure.

Ans:

1. Marine deep

2.Island

3. Submarine plateau 

4. Mariana strench

5. Sea level

6. Continental shelf

(b) Which of these landforms is useful for 

deep sea research?

Ans: Submarine platue and marina strench are useful for deep sea research. 

 (c) Which of these are appropriate to be 

used for the protection of marine borders and naval-base building?

Ans: Continental self is appropriate to be used for the protection of marine borders and naval-base building. 

Q 3. Give geographical reasons: 

 (a) The study of ocean floor is useful to 

man. 

Ans: The study of ocean floor is usful to man because of following reasons:

1. Various minerals, rocks, fine I soil particles are found on the sea floor.
2. Remains of marine plants and animals are also found on the ocean floor.
3. To study the marine life, mineral wealth as well as the process of volcanic eruption, the study of ocean floor is useful to man. ‘

 (b) The continental shelf is a paradise for 

fishing activity. 

Ans:

✔The continental shelf is very important 

from the point of view of humans. 

✔Extensive fishing grounds are found in the continental shelf.

✔ As this part is shallow, the sunlight 

reaches its bed. 

✔Algae, plankton, etc. grow 

here. This is food for fish. Hence fish found here in large scale.

 (c) Some marine islands are actually the 

peaks of sea mountains. 

Ans:

✔The hills and mountains found on the ocean-bed are called submerged hills 

and mountains.

✔ These hills are hundreds of kilometers wide and thousands of kilometers long. 

✔Peaks of some of the submerged hills 

come above the sea level.

 ✔They are visible to us as marine islands.

 (d) The continental slope is considered to be the boundary of continents. 

Ans:

✔After the extent of continental shelf is over, the slope of the sea bed becomes steeper. ✔This is called continental slope. 

✔The depth of the slope is from 200 m to 3600 metres.

✔ In some places, it is more. The continental slope is narrow. 

✔The lower boundary of continental slope is considered to be the boundary of continents.

 (e) The disposal of waste materials in the 

oceans by man is harmful to the

environment. 

Ans:

 ✔Some human-induced material is also found here. 

✔This includes sewage, solid waste, radio-active material, waste chemicals, 

plastics, etc.

 ✔These wastes prove hazardous to the hydrosphere.

 ✔These materials are extremely harmful to the marine life and its environment. 

Q 4. Observe the map on Pg 27 in 'Give it a try' and answer the following questions:

 (a) Madagascar and Sri Lanka are related 

to which landform of the ocean floor? 

Ans: Madagascar and Sri Lanka are related Island of the ocean floor.

 (b) Near which continent are these land 

forms located? 

Ans: Madagascar is located near African Continent and Sri lanka is located near Asia Continent.

 (c) Which islands in our country are examples of peaks of submerged 

mountains? 

Ans: Andaman and Nicobar islands are the examples of peaks of submerged mountains. 

ACTIVITY :

Prepare a model of the ocean floor.