The Water Cycle

This lesson covers the water cycle as required by the Edexcel GCSE Combined Science specification (1SC0). You need to describe the main stages of the water cycle, explain the roles of evaporation, condensation, precipitation and transpiration, and understand how water is recycled through ecosystems.

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Why the Water Cycle Matters

Water is essential for all living organisms:

• It is the solvent for biochemical reactions in cells
• It is needed for photosynthesis (a reactant)
• It transports dissolved substances in the blood and xylem
• It helps maintain body temperature (sweating, transpiration)

There is a finite amount of water on Earth. The water cycle continuously recycles water between the atmosphere, land and oceans so that it is available for living organisms.

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The Water Cycle — Overview

graph TD
    A["Oceans, lakes, rivers"] -->|"Evaporation (heat from the Sun)"| B["Water vapour in atmosphere"]
    B -->|"Condensation (cooling)"| C["Clouds form (tiny water droplets)"]
    C -->|"Precipitation (rain, snow, hail)"| D["Water falls on land"]
    D -->|"Surface run-off"| A
    D -->|"Percolation"| E["Groundwater"]
    E -->|"Groundwater flow"| A
    D -->|"Absorbed by plant roots"| F["Plants"]
    F -->|"Transpiration"| B
    A -->|"Evaporation"| B

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Key Stages of the Water Cycle