Class 7 Geography Chapter 5 Question Answers - Water

Q1. Define salinity.

Ans: Salinity refers to the concentration of salt in water, specifically the amount of salt in grams found in 1000 grams of water.

Key points about salinity:

• The average salinity of the oceans is 35 parts per thousand (ppt).
• Salinity is commonly expressed in parts per thousand.

For example, the Dead Sea has a salinity of 340 grams per litre, allowing swimmers to float due to the high salt content.

Q2. What is an ocean wave?

Ans: Ocean waves are formed when the surface water of the ocean rises and falls alternately.

Key points about ocean waves:

• Waves are caused by the wind blowing over the water's surface. During storms, strong winds can create large waves that may lead to destruction.
• Natural events like earthquakes or volcanic eruptions can generate massive waves known as tsunamis. 

Q3. What is flood tide and ebb tide?

Ans: The rise of sea level is known as flood tide, while the fall is referred to as ebb tide. These changes are primarily influenced by the gravitational pull of the moon and the sun.

Q4. Why do ocean bodies and seas contain salty water?

Ans: The water in oceans and seas is salty due to the presence of a significant amount of dissolved salts. The majority of this salt is sodium chloride, commonly known as table salt.

• Oceans contain about 35 parts of salt per thousand parts of water.
• Salinity varies in different bodies of water, with some areas being saltier than others.
• Salt is introduced into the oceans through rivers, rainfall, and volcanic activity.

Q5. Name the factors which are responsible for the movement of oceanic water.

Ans: The movement of oceanic water is influenced by several key factors:

• Winds: They drive surface currents across the ocean.
• Temperature: Variations in temperature affect water density and movement.
• Coriolis effect: This causes currents to curve due to the Earth's rotation.
• Gravitational pull: The attraction of the moon and sun affects tides, which in turn influence ocean currents.

Q6. Name the two types of current and their movement on Earth.

Ans: Ocean currents are classified into two main types: warm and cold currents.

• Warm currents originate near the equator and move towards the poles.
• Cold currents carry water from polar or higher latitudes to tropical or lower latitudes.

Examples include:

• The Labrador Current, which is a cold current.
• The Gulf Stream, which is a warm current.

Q7. How tides are formed?

Ans: Tides are the regular rise and fall of ocean water, occurring twice daily. This phenomenon is primarily caused by the gravitational pull of the moon and the sun.

• High tide occurs when water levels rise to their highest point, covering much of the shore.
• Low tide happens when water recedes to its lowest level, exposing more of the shore.

The gravitational forces exerted by the sun and moon lead to:

• Spring tides: These occur during the full moon and new moon when the sun, moon, and Earth align, resulting in the highest tides.
• Neap tides: These happen during the first and last quarters of the moon, causing lower tides due to the opposing gravitational pulls of the sun and moon.

Q8. What is an ocean current?

Ans:

Ocean currents are streams of water that flow continuously on the ocean surface in specific directions.

• They can be classified as warm or cold.
• Warm currents typically start near the equator and move towards the poles.
• Cold currents transport water from polar regions to tropical areas.
• For example, the Labrador Current is cold, while the Gulf Stream is warm.
• Ocean currents significantly affect the temperature of nearby land.
• Areas where warm and cold currents meet are often the best locations for fishing.

Q 9. Why is our earth like a terrarium?

Ans: Our Earth resembles a terrarium because it maintains a closed system of water. The same water that existed centuries ago is still present today. For example: The water used to irrigate fields in Haryana may have once flowed down the Amazon River a hundred years ago.This illustrates the continuity of water on our planet.

The main sources of fresh water include: Rivers, Springs, Ponds, Glaciers.

In contrast, the oceans contain salty water, which is unsuitable for drinking due to the high levels of dissolved salts.

 Long Question Answers:

Q11. Our unique planet Earth is covered by different categories of water. Give the distribution of water in percentage.

Ans:

The distribution of water on Earth is as follows:

• Oceans: 97.3% - The majority of Earth's water is found in oceans, which are large, salty bodies of water.
• Ice Caps: 2.0% - These are frozen reservoirs located in the coldest regions, such as the North and South Poles.
• Groundwater: 0.68% - This hidden resource is stored deep beneath the surface in soil and rock layers.
• Freshwater: 0.01% - This includes the water we drink and use, found in rivers, lakes, and underground reservoirs.
• Inland Seas and Salt Lakes: 0.009% - Smaller, salty bodies of water that create unique ecosystems.
• Atmosphere: 0.0019% - Contains tiny droplets of water vapour, crucial for cloud formation and precipitation.

Despite the abundance of water on Earth, many regions face water scarcity. Most of the water is saline and not suitable for drinking. The limited amount of freshwater highlights the importance of conserving this precious resource.

Q12. Why are tides important to us?

Ans: Tides are significant for several reasons:

• Navigation: High tides raise water levels near the shore, making it easier for ships to enter harbours.
• Fishing: Many fish come closer to the shore during high tides, allowing fishermen to catch more.
• Energy Generation: The rise and fall of tides can be harnessed to produce electricity in certain areas.

Q13. Why the quality of water is deteriorating? 

Ans: The quality of water is deteriorating due to several factors:

• Only about 33,400 kilometres of water are allocated for drinking, agriculture, domestic, and industrial use.
• Widespread water misuse and pollution are significant issues.
• The quality of drinking water is declining because of: Excessive use of pesticides and insecticides. Disposal of hazardous waste and organic decay.
• Industries release chemicals and untreated wastewater into nearby water bodies, greatly contributing to pollution.
• Sewage contamination further worsens water quality.
• The presence of nitrogen in water is associated with reduced lifespans.
• Increased water salinity negatively impacts agricultural fertility.

Q14. Write a short note on the Tsunami.

Ans: Tsunami is a Japanese term meaning "Harbour waves," as these waves can devastate harbours. They are caused by significant disturbances in the ocean, such as:

• Earthquakes
• Volcanic eruptions
• Underwater landslides

These events can displace large volumes of water, creating enormous waves that can reach heights of up to 15 metres. The largest recorded tsunami was an astounding 150 metres high. Tsunamis can travel at speeds exceeding 700 km/h.

The 2004 tsunami caused extensive damage along the coast of India, particularly submerging the Indira Point in the Andaman and Nicobar Islands.

Q15. What are the major movements of ocean water?

Ans: The movements of ocean water can be classified into three main types:

• Waves: Waves are the up and down movements of water on the ocean's surface. They are created when winds blow across the water. Stronger winds produce larger waves.
• Tides:Tides are the regular rise and fall of ocean water, occurring twice a day. High tide: This is when the water level rises and covers more of the shore. Low tide: This is when the water level drops, exposing more of the shore.Tides are caused by the gravitational pull of the sun and the moon on the Earth.
• Ocean Currents:These are continuous streams of water flowing in specific directions on the ocean's surface. Warm currents typically start near the equator and move towards the poles. Cold currents carry water from polar regions to warmer areas.

Examples include the Labrador current (cold) and the Gulf Stream (warm).