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Water and Life - The Water Cycle

Grade 6CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Water is essential for all living organisms and covers approximately 71%71\% of the Earth's surface.

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The chemical formula for water is H2OH_2O, representing two atoms of Hydrogen and one atom of Oxygen.

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Water exists in three states on Earth: Solid (ice), Liquid (water), and Gas (water vapor).

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Evaporation: The process where liquid water turns into water vapor due to the heat from the Sun.

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Transpiration: The process by which plants release water vapor into the atmosphere through tiny pores in their leaves called stomata.

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Condensation: The process where water vapor cools down and changes back into tiny droplets of liquid water, which aggregate to form clouds.

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Precipitation: When water droplets in clouds become too heavy, they fall to the Earth as rain, snow, or hail.

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Water Cycle: The continuous movement of water from the Earth's surface to the atmosphere and back again, maintaining the total amount of water on Earth constant.

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Rainwater Harvesting: A technique used to collect and store rainwater for future use, helping to conserve water and recharge groundwater levels.

📐Formulae

H2OH_2O

Total Water on Earth≈71% of surface area\text{Total Water on Earth} \approx 71\% \text{ of surface area}

Available Fresh Water<1% of total water\text{Available Fresh Water} < 1\% \text{ of total water}

Liquid Water→HeatWater Vapor (Evaporation)\text{Liquid Water} \xrightarrow{\text{Heat}} \text{Water Vapor (Evaporation)}

Water Vapor→CoolingLiquid Water (Condensation)\text{Water Vapor} \xrightarrow{\text{Cooling}} \text{Liquid Water (Condensation)}

💡Examples

Problem 1:

Explain why a glass of ice-cold water shows water droplets on its outer surface after a few minutes.

Solution:

This happens due to the process of Condensation.

Explanation:

The air surrounding the glass contains water vapor (gaseous H2OH_2O). When this vapor comes in contact with the cold surface of the glass, it loses heat and changes its state from gas to liquid, forming droplets.

Problem 2:

What is the primary difference between evaporation and transpiration in the context of the water cycle?

Solution:

Evaporation occurs from open water bodies, while transpiration occurs from living plants.

Explanation:

Evaporation is the conversion of water from oceans, lakes, and rivers into vapor due to solar energy. Transpiration is a biological process where plants lose water through their leaves. Both contribute to the total moisture in the atmosphere.

Problem 3:

If the total surface area of Earth is AA, and the area covered by land is LL, write the approximate relation for the area covered by water WW.

Solution:

W≈0.71×AW \approx 0.71 \times A

Explanation:

Since approximately 71%71\% of the Earth's surface is covered by water, the area WW can be represented as 71/10071/100 or 0.710.71 times the total surface area AA.