What is the Water Cycle?

• The water cycle recycles water between the land, sea, and atmosphere.
• It provides fresh water for plants and animals on land.
• Water is constantly evaporating, condensing, and falling as precipitation.

Key Processes in the Water Cycle

1. Evaporation:

• Energy from the Sun heats water in rivers, lakes, and oceans.
  The water evaporates, changing from a liquid to water vapour in the air.

2. Condensation:

• Water vapour cools as it rises and condenses into clouds (tiny water droplets).

3. Precipitation:

• Water droplets in clouds grow and fall as rain, snow or hail, returning water to the ground.

4. Transpiration:

• Plants take up water from the soil through their roots via osmosis.
  Water moves up through the plant in the xylem vessels and evaporates from the leaves, mainly via the stomata.
  This loss of water vapour is called transpiration.

5. Run-off and infiltration:

• Water runs off the surface of the land - for example, soil, hills, fields, and hard surfaces like roads.
  Run-off water flows into rivers, streams, and lakes.
  Some water soaks into the ground (this is called infiltration) and becomes groundwater, which plants can use or which can feed into rivers later.

Why Is the Water Cycle Important?

• It makes sure fresh water is always available for plants, animals, and humans.
• It helps plants grow by pulling water up the xylem vessels from roots to leaves.
• It links to other cycles like the carbon cycle, as plants need water for photosynthesis as well as carbon dioxide.

Practice Question