Biology

7.5 - The Water Cycle

6 min

Intro & recycling

The water cycle

Carbon stores

How carbon moves

note 1 of 1

The water cycle

Water is constantly recycled between the air, the land, and the sea - so the same water is used over and over again.
This constant recycling is why living things always have a supply of fresh water. Without it, the water on land would soon run out, and all living things need water to survive.

Stages of the water cycle

Evaporation - Energy from the sun warms water on the Earth's surface (lakes, oceans, rivers, puddles, and soil), making it evaporate - the liquid water turns into water vapour in the air.
Transpiration - Water also evaporates from the leaves of plants, adding more water vapour to the air.
Rising and condensing - The warm water vapour is carried upwards as the warm air rises. Higher up the air is cooler, so the vapour cools and condenses to form clouds.
Clouds move - The clouds can be blown from one region to another.
Precipitation - At some point the water falls back to the ground as precipitation, usually rain but sometimes snow or hail, providing fresh water for plants and animals on land.
Return to the sea - Once fallen, the water can soak into the soil, be taken up by plants, or flow into rivers. From there it drains into the sea, and the whole cycle begins again.

A coastal landscape with the ocean on the left and green hills on the right, blue arrows running through labels reading ocean, evaporation, transpiration, plants, condensation, clouds move, precipitation and return to sea.

key terms

TermDefinition

TranspirationThe loss of water vapour from a plant, mostly from the leaves through the stomata.

PrecipitationWater falling from clouds to the ground, usually as rain, snow or hail.

end of notes

Key points to remember

The water cycle

Water is constantly recycled between the air, the land, and the sea - so the same water is used over and over again.

This constant recycling is why living things always have a supply of fresh water. Without it, the water on land would soon run out, and all living things need water to survive.

Stages of the water cycle

Evaporation - Energy from the sun warms water on the Earth's surface (lakes, oceans, rivers, puddles, and soil), making it evaporate - the liquid water turns into water vapour in the air.

Transpiration - Water also evaporates from the leaves of plants, adding more water vapour to the air.

Rising and condensing - The warm water vapour is carried upwards as the warm air rises. Higher up the air is cooler, so the vapour cools and condenses to form clouds.

Clouds move - The clouds can be blown from one region to another.

Precipitation - At some point the water falls back to the ground as precipitation, usually rain but sometimes snow or hail, providing fresh water for plants and animals on land.

Return to the sea - Once fallen, the water can soak into the soil, be taken up by plants, or flow into rivers. From there it drains into the sea, and the whole cycle begins again.