The Water Cycle (Edexcel GCSE Combined Science) : Revision Note

Lára Marie McIvor

Last updated

The Water Cycle

  • Water molecules move between various locations – such as rivers, oceans and the atmosphere – by specific processes

  • This is possible because water changes state at a relatively low temperature

The-water-cycle, IGCSE & GCSE Biology revision notes

The water cycle

  • Water enters the atmosphere as water vapour in one of two processes

    • Energy from the Sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes

    • Transpiration from plants releases water vapour into the air

  • The warmer air of the lower atmosphere rises, taking the water vapour with it

    • The moist air cools down as it rises

    • Water vapour condenses back into liquid water, forming clouds

  • Water returns to earth in the form of precipitation

    • As the water droplets in the cloud get bigger and heavier, they begin to fall as rain, snow and sleet

    • This is called precipitation

The importance of the water cycle

  • All life on earth depends upon water for a variety of reasons, this includes photosynthesis

  • The water cycle, therefore, is a fundamental process for all living things as it distributes fresh water globally providing us with clean water for drinking

Dealing with drought

  • In some areas, drought may become an issue as it means that populations living in those areas would not have access to the potable water they require

  • One way to manage this is through desalination of salty water such as sea water

    • Desalination means removing the excess mineral ions (salts) from the water to make it drinkable

    • There are several ways of removing these salts

      • Distillation - saline water is boiled, the water vapour is funnelled through a tube before it is condensed and the pure water is collected

      • Reverse osmosis - saline water is forced at high pressure through a partially permeable membrane which filters out all the mineral ions leaving pure water

Diagram of reverse osmosis filtering saline water into potable water using applied pressure and a partially permeable membrane.
Reverse osmosis can be used for desalination of sea water
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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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