SSC Selection Post 2025 PYQ — Question 4

Correct Answer

Solar energy

Explanation

The primary source of energy that drives the water cycle (hydrological cycle) on Earth is Solar energy. The heat from the Sun warms the water in oceans, rivers, lakes, and other water bodies, causing it to change from a liquid into a gas through the process of evaporation. Solar radiation also powers transpiration, where plants release water vapor into the atmosphere.

Once the water vapor rises into the atmosphere, it cools and undergoes condensation to form clouds. Eventually, gravity brings this water back to Earth's surface through precipitation (rain, snow, sleet, etc.), completing and restarting the continuous loop.

Key Points

The entire water cycle relies on the combination of solar energy (which moves water upward against gravity via evaporation) and gravity (which pulls water back downward via precipitation and surface runoff).

Evaporation, transpiration, condensation, and precipitation are the core hydrological processes regulated by solar heating dynamics.

Wind energy assists in distributing water vapor and shifting cloud formations across continents, but the initial thermal engine remains the Sun.

Important Questions and Answers

Question: What is the biological process called when water is absorbed by plant roots and then released as vapor through small pores in their leaves into the atmosphere?

Answer: Transpiration.

Question: Besides solar energy, which fundamental physical force is responsible for pulling precipitation down to Earth and pulling surface runoff toward the oceans?

Answer: Gravitational force (Gravity).