Class 7 Science Water A Precious Resource Oxford Solution

Water is one of the most valuable natural resources on Earth. It is essential for the survival of all living organisms and plays a vital role in our daily lives. In Class 7 Science Water A Precious Resource Oxford, we learn about the importance of water, its limited availability, and the need to use it wisely.

This chapter also explains the causes of water scarcity, methods of water conservation, and ways to prevent water pollution. Understanding this topic helps us realize why saving water is our responsibility for a better future.

Class 7 Science Water A Precious Resource Oxford

1. Fill in the blanks with the correct words.

Water is used in the industries for ________ (irrigation/generating electricity).
- Water is used in industries for generating electricity. This is primarily through hydroelectric power plants, which use the force of moving water to turn turbines.
________ (Aquifer/Dams) are built on rivers to regulate the flow of water and distribute it more evenly throughout the year.
- Dams are built on rivers to regulate the flow of water and distribute it more evenly throughout the year. Aquifers are underground water reserves.
________ (Punjab/Tamil Nadu) receives over half of its rain from October to November.
- Tamil Nadu receives over half of its rain from October to November. This period corresponds to the northeast monsoon season.
________ (Sea/River) water is not fit for domestic and agricultural use.
- Sea water is not fit for domestic and agricultural use due to its high salt content.
________ (Gangetic/Coastal) plains can get contaminated by saltwater inflow caused by the over-pumping of groundwater.
- Coastal plains can get contaminated by saltwater inflow caused by the over-pumping of groundwater. This process is known as saltwater intrusion.
Rainwater harvesting systems help in ________ (scarcity/conservation) of water.
- Rainwater harvesting systems help in the conservation of water.

2. Choose the correct option.

Q1. Which of the following is responsible for continuous circulation of water on the Earth?
a. Condensation
b. Evaporation
c. Precipitation
d. Transpiration

Answer: Evaporation is the primary process that moves water from the Earth’s surface into the atmosphere, initiating the continuous circulation of water (water cycle).

Q2. At what temperature will water turn into ice?
a. 100°C
b. 0°C
c. 10°C
d. –10°C

Answer: Water freezes and turns into ice at 0°C (32°F) under standard atmospheric pressure.

Q3. Which of the following is the purest form of water?
a. Well water
b. River water
c. Pond water
d. Rainwater

Answer: The purest form of natural water is rainwater (before it mixes with impurities in the atmosphere).

Q4. Which of the following is a rich source of groundwater?
a. Peninsular areas
b. Gangetic plains
c. Hilly regions
d. Mountainous regions

Answer: The Gangetic plains are rich in groundwater because they are made up of thick alluvial deposits that can store large amounts of water.

Q5. Which of the following has led to scarcity of water?
a. Increase in population
b. Deforestation
c. Pollution of freshwater resources
d. All of these

Answer: All the given factors—population growth, deforestation, and pollution—together cause scarcity of water.

Q6. Which of the following methods employ watering the roots of the plants drop by drop?
a. Rainwater harvesting
b. Drip irrigation
c. Root irrigation
d. Recycling water

Answer: Drip irrigation is a highly efficient method of watering plants by delivering water directly to the roots, drop by drop.

Q7. Which of the following forms represents water in liquid state in nature?
a. Dew
b. Glacier
c. Fog
d. Frost

Answer: Fog represents water in liquid state. It consists of tiny water droplets suspended in the air near the ground.

Q8. What is the process by which plants give off water vapour called?
a. Evaporation
b. Condensation
c. Transpiration
d. Precipitation

Answer: Transpiration is the process by which plants give off water vapour through tiny pores in their leaves called stomata.

Q9. Which of the following can be used to conserve water?
a. Deforestation
b. Excessive irrigation
c. Recycling of water
d. Wastage of water

Answer: Recycling of water is an effective method of conservation because it reduces the demand for fresh water.

Q10. What is underground water also known as?
a. Stream
b. Spring
c. Water table
d. Aquifer

Answer: Underground water stored in permeable rock layers is known as an aquifer.

II. Very short answer type questions

Give two examples for the following.

Usage of water in industry
- Water is used for cooling in power plants and factories.
- It is also used as a solvent in manufacturing processes.
Domestic usage of water
- Drinking and cooking.
- Bathing and washing clothes and dishes.
Source of surface water
- Rivers and lakes.
Rivers that originate in the Himalayas
- The Ganges and Yamuna rivers.
Effluents that pollute water
- Industrial waste and sewage.

III. Short answer type questions

1. Differentiate between the terms surface water and groundwater.

Surface water is found in bodies like rivers, lakes, ponds, and wetlands, and is exposed to the atmosphere. It is more susceptible to pollution from human activities and runoff.
Groundwater is located underground in aquifers, in the pores and spaces of rocks and soil. It is generally cleaner than surface water but can still be contaminated by pollutants that seep into the ground.

2. What is a water table? How is a natural spring formed?

The water table is the upper level of the saturated zone of groundwater. Below this level, all the spaces in the soil and rock are filled with water. The depth of the water table can change depending on rainfall and water usage.
A natural spring is formed when the groundwater table meets the surface of the land, causing water to flow out naturally. This often happens where there is an impermeable rock layer that forces the water to the surface.

3. Why are monsoons an important part of our country?

Monsoons are crucial for India because they are the primary source of rainfall, which is vital for agriculture. They also help to recharge groundwater reserves and fill reservoirs, which are essential for drinking water and power generation. Without the monsoons, India would face severe water scarcity.

4. How does deforestation contribute to the scarcity of water?

Trees play a key role in the water cycle. Their roots help the soil absorb rainwater, and they release moisture into the atmosphere through transpiration. When forests are cut down (deforestation), the soil’s ability to retain water is reduced, leading to increased runoff and less groundwater recharge. This results in soil erosion, loss of moisture, and a less stable climate, all of which contribute to water scarcity.

5. How does scarcity of water affect plants?

Water scarcity has a devastating effect on plants. They need water for photosynthesis, to transport nutrients, and to maintain their structure. Without enough water, plants wilt, their growth is stunted, and they may eventually die. Droughts and lack of irrigation can lead to widespread crop failure and desertification.

IV. Long answer type questions

1. Discuss various forms in which the three states of water are found in our natural environment.

Ans: Water exists naturally on Earth in three states: solid, liquid, and gas.

Solid state: Water exists as a solid in the form of ice, snow, glaciers, and ice caps. These are found in polar regions and on high mountains. For example, glaciers on the Himalayas are a massive source of freshwater.
Liquid state: This is the most common form of water we see, found in rivers, lakes, oceans, ponds, and as rain and groundwater. It is essential for all living organisms and is used for a variety of purposes from drinking to agriculture.
Gaseous state: Water exists as a gas in the form of water vapor in the atmosphere. It is an invisible gas that is crucial for the water cycle. It also forms clouds when it condenses.

2. Discuss the various factors that have contributed to the depletion of water table.

Ans: Several factors have led to the depletion of the water table, including:

Increased Population: A growing population requires more water for domestic, agricultural, and industrial use, putting immense pressure on groundwater resources.
Agricultural Demands: Modern agriculture relies heavily on irrigation, often drawing large quantities of water from the ground to water crops, especially in arid and semi-arid regions.
Industrialization: Industries require large volumes of water for manufacturing, cooling, and processing, much of which is drawn from groundwater reserves.
Urbanization: The construction of impervious surfaces like roads, buildings, and pavements prevents rainwater from seeping into the ground, reducing groundwater recharge.
Deforestation: The removal of trees and vegetation reduces the soil’s ability to absorb water, leading to less infiltration and lower water table levels.
Water Pollution: Pollution of surface water bodies and groundwater with industrial chemicals, sewage, and agricultural runoff makes the water unusable, effectively reducing the available freshwater supply.

3. Explain the various practices that can be adopted to conserve water.

Ans: Water conservation is crucial for a sustainable future. Various practices can be adopted:

Rainwater Harvesting: Collecting and storing rainwater in tanks or recharging it into the ground can supplement water supply for domestic or agricultural use. This is particularly effective in areas with high rainfall.
Efficient Irrigation: Using methods like drip irrigation and sprinkler systems instead of flood irrigation can significantly reduce water usage in agriculture.
Household Conservation: Simple changes at home can make a big difference, such as fixing leaks, using a bucket instead of a hose for washing cars, taking shorter showers, and using water-efficient appliances.
Water Recycling: Treating and reusing wastewater for non-potable purposes like flushing toilets, gardening, or industrial processes can reduce the demand on fresh water sources.
Public Awareness: Educating people about the importance of water conservation and encouraging behavioral changes is essential for long-term success.
Afforestation: Planting trees helps to increase groundwater recharge, reduce soil erosion, and improve the overall health of the local water cycle.