• 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

• 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

   

• Nutrients such as carbon and nitrogen are not endless resources
• There is a finite amount of each element on the planet and as such, they need to be?recycled?in order to allow new organisms to be made and grow
• Carbon?is taken out of the atmosphere in the form of?carbon dioxide?by plants to be used for photosynthesis
• It is passed on to animals (and microorganisms) by?feeding
• It is returned to the atmosphere in the form of?carbon dioxide?by plants, animals and microorganisms as a result of respiration
• If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies can be converted, over millions of years and significant pressure, into?fossil fuels
• When fossil fuels are burned (the process is known as?combustion), the carbon combines with oxygen and?carbon dioxide is released?into the atmosphere
• Increased use of fossil fuels?is contributing to an increase in the carbon dioxide content of the atmosphere
• In addition,?mass deforestation?is?reducing the amount of producers?available to take carbon dioxide out of the atmosphere by photosynthesis
• This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they are?burnt down, releasing yet more carbon dioxide into the atmosphere

The carbon cycle