Std 8 Geography – Chapter 4 Structure of Ocean Floor

Chapter 4 – Structure of Ocean Floor Std 8 Geography

Q1. Choose the Correct Option

(a) Like there are landforms on land, the ocean floor also has submerged landforms because …
(i) There is land under water   (ii) There are volcanoes underwater   (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: Option (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 man?
(i) Continental shelf   (ii) Continental slope   (iii) Abyssal plains   (iv) Marine deeps
Ans: Option (i) – Continental shelf.
(c) Which one of the following options 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: Option (iii) – Volcanic ash, lava, fine particles of soil.

Q2. Diagram-Based Questions

(a) Name the landforms shown in the figure.
Ans:
1Submerged Hill
2Marine Island
3Abyssal Plain
4Marine Trench
5Sea Level
6Continental Shelf
(b) Which of these landforms is useful for deep sea research?
Ans: Submarine plateau and marine trench are the landforms 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: The continental shelf is appropriate to be used for the protection of marine borders and naval base building.

Q3. Give Geographical Reasons

(a) The study of the ocean floor is useful to man.
  1. Various minerals, rocks, and fine soil particles are found on the seafloor.
  2. The remains of marine plants and animals are also found on the ocean floor.
  3. To study marine life, mineral wealth, and the process of volcanic eruption, the study of the ocean floor is useful to man.
(b) The continental shelf is a paradise for fishing activity.
  1. Being the shallowest part of the ocean bed, sunlight reaches up to the continental shelf easily.
  2. As a result, algae, plankton, etc. grow on a large scale on the continental shelf.
  3. Algae, plankton, etc. are food for fish. Therefore, fish are found on a large scale on the continental shelf.
  4. Therefore, the continental shelf is a paradise for fishing activity.
(c) Some marine islands are actually the peaks of sea mountains.
  1. The hundreds of kilometres wide and thousands of kilometres long hills found on the ocean bed are called submerged hills.
  2. The peaks of some of the submerged hills rise above sea level.
  3. These peaks are the visible land areas surrounded on all sides by water. These peaks are called islands.
  4. Thus, some marine islands are actually the peaks of sea mountains.
(d) The continental slope is considered to be the boundary of continents.
  1. The continental slope lies beyond the continental shelf.
  2. The deep abyssal plain begins beyond the continental slope.
  3. Therefore, the 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.
  1. The disposal of waste materials in the oceans by humans increases the pollution of seawater.
  2. These disposed waste materials harm marine animal life and marine plants.
  3. Thus, the disposal of waste materials in the oceans by humans is harmful to the environment.

Q4. Map-Based Questions (Give it a Try – Pg 27)

(a) Madagascar and Sri Lanka are related to which landform of the ocean floor?
Ans: Madagascar and Sri Lanka are related to islands on the ocean floor.
(b) Near which continent are these landforms located?
Ans: Madagascar is located near the continent of Africa, and Sri Lanka is located near the continent of Asia.
(c) Which islands in our country are examples of peaks of submerged mountains?
Ans: The Andaman and Nicobar Islands in our country are an example of peaks of submerged mountains.
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