Major Water Bodies, Class -7, Subject – Social science, solved exercises

A. Choose the correct answer

1. Which of the following does not have freshwater?
Ans: (b) Ocean


2. What is the average salinity of ocean water?
Ans: (b) 35/1000


3. What is the fall of water in a wave called?
Ans: (a) Trough


4. Which of the following tides occurs on a new moon day?
Ans: (c) High tide


5. Which of the following is not a warm ocean current?
Ans: (c) Labrador




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B. Fill in the blanks

1. The Pacific Ocean is connected to the Arctic Ocean through the narrow Bering Strait.


2. Dissolved salt in ocean water is mostly sodium chloride.


3. The horizontal distance between two crests is called wavelength.


4. The combined gravitational pull of the sun and the moon is the greatest on full moon.


5. Ocean currents affect the temperature of coastal areas.




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C. Write T for True and F for False

1. Water cycle is caused by evaporation, condensation and precipitation. — T


2. Oceans form 95% of the total sea bodies. — F


3. Neap tides occur on full moon and new moon days. — F


4. The energy of tides is used to generate electricity. — T


5. Warm ocean currents flow from the poles towards the equator. — F

D. Match the columns

Column A Column B Answer

1. Snow (e) Precipitation 1 – e
2. Freshwater (d) Groundwater 2 – d
3. Earthquake in the ocean (a) Tsunami 3 – a
4. Crest (b) Waves 4 – b
5. Neap tide (c) Half moon 5 – c



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E. Very Short Answer Type Questions (20–30 words)

1. Why is the total amount of water on the Earth’s surface constant?

Because of the water cycle. Water keeps changing its form through evaporation, condensation and precipitation, but the total amount of water on Earth remains the same.

2. What do you understand by freshwater? List the uses of freshwater.

Freshwater is water that has very little salt. It is used for drinking, cooking, washing, farming and many industrial activities.

3. What is saline water?

Saline water contains a high amount of dissolved salts. Ocean water is saline because it has about 3.5% salt.

4. What are tides? How are they caused?

Tides are the rise and fall of sea level. They are caused by the gravitational pull of the moon and the sun on the Earth.

5. What is tidal energy?

Tidal energy is electricity generated by using the movement of tides. The rise and fall of water is used to run turbines.


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F. Short Answer Type Questions (50–60 words)

1. Describe the water cycle with the help of a labelled diagram.

The water cycle is the continuous movement of water on Earth. Water evaporates from oceans and lakes, forms clouds by condensation, and falls as rain or snow (precipitation). This water flows back into rivers, lakes and oceans.


2. Discuss the distribution of water across the surface of the Earth.

About 97% of Earth’s water is in the oceans and is saline. Only 3% is freshwater. Most freshwater is locked in glaciers and ice caps; a small amount is found as groundwater, lakes, rivers and atmospheric moisture.

3. How do ocean currents affect coastal regions?

Warm currents raise the temperature of coastal areas, while cold currents lower it. They affect the climate, rainfall, and weather patterns along the coasts.

4. What are the four major divisions of oceans?

The four major divisions of oceans are the Pacific Ocean, Atlantic Ocean, Indian Ocean and Arctic Ocean. (Some books also include the Southern Ocean.)

5. Write a note on the Pacific Ocean.

The Pacific Ocean is the largest and deepest ocean on Earth. It covers one-third of the Earth’s surface. It has many volcanic islands and is known for the “Ring of Fire.” It also connects to the Arctic through the Bering Strait.


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G. Long Answer Type Questions (80–100 words)

1. Explain saline water in detail.

Saline water contains a large amount of dissolved salts, mainly sodium chloride. Ocean water is saline due to the continuous mixing of minerals from rivers and the seafloor. About 97% of the Earth’s water is saline and cannot be used directly for drinking, farming or industrial needs. The salinity of ocean water varies from place to place due to temperature, evaporation and freshwater inflow. Desalination plants are used in some regions to convert saline water into freshwater.

2. Illustrate the significance of oceans.

Oceans play a vital role in regulating the Earth’s climate. They absorb heat, distribute it through currents and influence weather patterns. Oceans are home to a wide variety of marine life and form an important ecosystem. They also provide resources such as fish, salt, minerals and oil. Oceans are essential for trade and transport as major sea routes pass through them. They also support tourism and recreational activities.

3. Write a detailed note on waves.

Waves are rhythmic movements of ocean water mainly caused by wind. They have two main parts: the crest (top of the wave) and trough (bottom of the wave). Waves transfer energy from the wind to the surface of the water. Strong winds and storms create high waves. When waves approach shallow coastal areas, they become steeper and break on the shore. Waves shape coastlines through erosion and deposition and are used for surfing and recreation.

4. Discuss the importance of tides.

Tides help in navigation by allowing ships to enter and leave ports safely. They help in fishing because many fish follow tidal patterns. Tides also help in removing waste from coastal areas. Tidal energy can be used to generate electricity. Tides influence coastal ecosystems, help in the formation of tidal flats and support mangrove forests. They also play an important role in marine life cycles.

5. Enumerate the importance of ocean currents.

Ocean currents distribute heat across the Earth and regulate climate. Warm currents raise temperatures of coastal areas, while cold currents lower them. They affect rainfall, fog and weather patterns. Currents also help in navigation by affecting speed and direction of ships. They bring nutrients from the deep sea to the surface, supporting marine life. Currents influence the location of fisheries and impact global trade routes.


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H. Higher-Order Thinking Skills

1. In spite of so much precipitation on Earth, the amount of water remains constant. Why is it so?

Because of the water cycle. Water evaporates, condenses to form clouds and falls back as rain or snow. This continuous cycle ensures that water keeps changing forms but its total amount remains constant.

2. Why is freshwater precious?

Freshwater is precious because it forms only about 3% of total water, and most of it is locked in ice caps. Only a very small portion is available for drinking, farming and daily uses. Without freshwater, life cannot exist.