GSEB Class 7 Science Solutions Chapter 16 પાણી એક અમૂલ્ય સ્ત્રોત

Textbook Exercise Questions And Answers

1. Mark 'T' for true statements and 'F' for false statements:

Question 1. Groundwater is much more abundant than the water in the world's rivers and lakes.
Answer: T

Exam Tip: Remember that groundwater stores a significant portion of the Earth's freshwater, often more than surface water bodies like rivers and lakes.

Question 2. Only rural people are facing the problem of water scarcity.
Answer: F

Exam Tip: Water scarcity is a global issue that affects both urban and rural populations due to various factors, not just geographical location.

Question 3. Rivers are the only source for irrigation in fields.
Answer: F

Exam Tip: Irrigation sources are diverse, including wells, borewells, canals, and reservoirs, not just rivers.

Question 4. Rainfall is the main source of water.
Answer: T

Exam Tip: Rainfall is crucial as it replenishes both surface water bodies and groundwater, making it the primary natural source of freshwater.

Question 2. How is groundwater recharged?
Answer: Rainwater and water from other origins, such as rivers and lakes, enter the ground, filling up empty spots and cracks deep below the surface. This movement of water downwards into the soil is called infiltration. Through this procedure, groundwater gets replenished.
In simple words: When rain or river water soaks into the ground and fills the empty spaces underground, it's called groundwater recharge.

Exam Tip: Understand that infiltration is the key process by which surface water seeps into the ground to become groundwater.

Question 3. There are 10 tubewells in a line of 50 houses. What will be the long-term effect on the water table?
Answer: There are 10 tubewells for 50 houses, meaning that one tubewell meets the water requirements of 5 houses. This might not have a major impact on the water table initially. However, during periods of water shortage, the water table will definitely go down. Moreover, if the 50 houses utilize more water than they need, the water table will fall considerably at this consumption rate.
In simple words: With 10 tubewells for 50 houses, if people use more water than what's naturally refilled, especially in dry times, the underground water level will drop a lot.

Exam Tip: Excessive extraction of groundwater without adequate natural replenishment can lead to a significant decline in the water table, impacting water availability.

Question 4. If you were hired to maintain a garden, how would you minimize water usage?
Answer: In the garden, we would make arrangements to supply water to plants and trees using the drip irrigation method. Plants sown in a line would be given water through a channel. For large trees, we would make a round pit and supply water there. This way, we would ensure minimum water consumption. We would also take care that water does not leak unnecessarily from the pipes used for water movement.
In simple words: To save water, I would use drip irrigation for plants, channels for lined plants, and basins for big trees, making sure pipes don't leak.

Exam Tip: Always suggest efficient irrigation techniques like drip irrigation and creating tree basins to minimize water wastage in gardening.

Question 5. Why is the groundwater table decreasing? Explain.
Answer: The reasons for the decreasing groundwater table are as follows:
1. Increase in population: As the population expands, people's need for water grows. As a result, more borewells need to be drilled, and water has to be pumped out from them, which becomes the reason for the groundwater table to drop.
2. Growing industries: Industries use a large amount of water. This water is mostly acquired through borewells from groundwater. As industries expand, free and barren land diminishes. Consequently, enough water is not soaked up into the ground. As a result, groundwater cannot be recharged. This causes the groundwater table to fall.
3. Agricultural activities: Water is necessary for agriculture. Due to low and erratic rainfall, crops need to be irrigated through wells or borewells. Canal systems are not widespread everywhere. Therefore, water must be extracted from borewells or wells. If six times the water is used, that much water cannot be restored. This causes the groundwater table to go down.
4. Less rainfall: Because of reduced rainfall, water percolation into the ground decreases. If groundwater is used more often and recharge doesn't happen in that quantity, then the groundwater table goes down.
5. Deforestation: Forests are destroyed, and industries and cities are being built. As a result, the effective area for water absorption into the ground is reduced. Water cannot be absorbed into the ground through the paved roads of cities and industries. This causes the groundwater table to go down.
In simple words: The groundwater table decreases due to more people needing water, growing industries using lots of water, farming needing irrigation, less rain, and cutting down forests which stops water from soaking into the ground.

Exam Tip: When explaining environmental issues, remember to link human activities like population growth, industrialization, and agriculture to their specific environmental impacts.

6. Fill In The Blanks With Appropriate Words:

Question 1. _________ and _________ acquire groundwater.
Answer: Wells, borewells

Exam Tip: Recall the common methods people use to access underground water sources.

Question 2. Water is found in _________, _________ and _________ forms.
Answer: Solid, liquid, gas

Exam Tip: Remember the three main states of matter: solid, liquid, and gas, which water can exist in.

Question. The layer that holds groundwater is called _________.
Answer: Water table

Exam Tip: The water table is the upper surface of the zone of saturation, where the pores and fractures in the ground are completely saturated with water.

Question 4. The process of water seeping into the ground is called _________.
Answer: Infiltration

Exam Tip: Recall the term for water moving from the surface down into the soil to replenish groundwater.

Question 7. Which of the following is NOT responsible for water scarcity?
(a) Industrialization area
(b) Population growth
(c) Excessive rainfall
(d) Mismanagement of water resources
Answer: (c) Excessive rainfall
In simple words: Too much rain usually helps with water supply, so it doesn't cause a lack of water.

Exam Tip: Understand the factors that contribute to water scarcity, such as increased demand, pollution, and inefficient use, rather than natural abundance.

Question 8. Choose the correct option: The total amount of water...
(a) remains constant in the world's rivers and lakes.
(b) remains constant in soil layers.
(c) remains constant in seas and oceans.
(d) remains constant in the world.
Answer: (d) remains constant in the world.
In simple words: The total amount of water on Earth always stays the same, even though it changes its form and location.

Exam Tip: Remember the water cycle, which constantly moves water but does not change the overall quantity of water on Earth.

Question 9. Draw and label a diagram showing groundwater and the groundwater table.
Answer:

Exam Tip: Practice drawing and labeling diagrams of key hydrological concepts like the water table and groundwater to reinforce your understanding.

GSEB Class 7 Science Textbook Activities

Textbook Activities Explanation

Activity 1 :

Students should do it themselves.

Activity 2 :

Estimate the relative amount of fresh water available for human use.

Method:

The remaining water in the bucket is saline water present in seas and oceans, and partly as groundwater. This water is not suitable for human use.
The remaining water in the bathing tumbler is in the form of ice, polar ice, and permanent ice on mountains. This water is also not easily available to us.

Observation:
If the total water on Earth is 20 liters, then the total freshwater on Earth is \( \frac{1}{4} \) spoon (or \( \frac{1}{4} \) ml).
Conclusion: Only 0.006% of the world's total available water is potable (drinkable).

Activity 3 :

Students should do it themselves.

Activity 4 :

Obtain information about industries and their products.

Method:
List some industries you are familiar with. Make a list of products used in our daily lives and obtained from them. Discuss this with your teacher and parents.

Information Table:

Activity 5 :

Obtain information by looking at the map of average annual rainfall distribution in our country, India.

The map showing the distribution of average annual rainfall in our country, India, is shown in Figure 16.8 of the textbook.

• Find the area on the map where you reside.
• Does your area receive sufficient rainfall?
• Is sufficient water available in your area throughout the year?

[Note: Each student should find their area and gather information to answer the questions themselves.]