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How are levels maintained within an ecosystem? - OCR 21st CenturyThe water cycle

Plants compete for light, water, minerals and space. Animals compete for food, mates and territory. Decay is the breakdown of organic matter and is affected by temperature, water and oxygen.

Part of Biology (Single Science)Living together - Food and ecosystems

The water cycle

Water is a key compound for life on Earth. All living organisms need water. Some can survive in a dormant state without it for long periods of time, but all organisms will quickly or eventually die without it.

Water cycle. Precipitation falls on ground, drains into ocean via percolation. Evaporation from ocean and transpiration of surface water create water vapour. Condensation creates clouds.

The is easiest to understand in terms of its processes and what happens to the water in each of these. These are the key processes:

ProcessWhat happens to water
EvaporationWater turns from a liquid to a gas when it evaporates. Energy from the Sun can evaporate water from all places on the Earth's surface such as puddles, ponds, lakes and oceans.
CondensationAfter evaporation water can cool and convert from gas to liquid, often forming clouds.
TransportWater within clouds can be blown many miles by strong winds and so transported to other areas.
PrecipitationPrecipitation occurs when rain, snow, hail and sleet fall from the sky.
Surface run-offMuch water will be absorbed into the ground after precipitation but if a large volume falls or the ground is already wet some water can run along the surface of the ground.
InfiltrationThis occurs when water that has fallen as precipitation is absorbed into the ground. This can then be stored within underground rocks called aquifers.
TranspirationPlants need to maintain a constant stream of water to their leaves for transport and support. So they allow some water to evaporate as water vapour from their leaves to mean that more is continually 'pulled' to their leaves from the soil.
ProcessEvaporation
What happens to waterWater turns from a liquid to a gas when it evaporates. Energy from the Sun can evaporate water from all places on the Earth's surface such as puddles, ponds, lakes and oceans.
ProcessCondensation
What happens to waterAfter evaporation water can cool and convert from gas to liquid, often forming clouds.
ProcessTransport
What happens to waterWater within clouds can be blown many miles by strong winds and so transported to other areas.
ProcessPrecipitation
What happens to waterPrecipitation occurs when rain, snow, hail and sleet fall from the sky.
ProcessSurface run-off
What happens to waterMuch water will be absorbed into the ground after precipitation but if a large volume falls or the ground is already wet some water can run along the surface of the ground.
ProcessInfiltration
What happens to waterThis occurs when water that has fallen as precipitation is absorbed into the ground. This can then be stored within underground rocks called aquifers.
ProcessTranspiration
What happens to waterPlants need to maintain a constant stream of water to their leaves for transport and support. So they allow some water to evaporate as water vapour from their leaves to mean that more is continually 'pulled' to their leaves from the soil.

Learn more about the water cycle with Dr Alex Lathbridge.

Explore the important processes throughout the cycle and what happens to water during each stage.

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