Natural Cycles

There are three types of natural cycles: 

  1. The carbon cycle

  2. The nitrogen cycle

  3. The water cycle


The carbon cycle:


Carbon is an essential element of life on earth, every living organism has carbon in its cells.

Ways that carbon enters the atmosphere:

  • Respiration

  • Combustion

  • Burning of fossil fuels

  • Volcanoes erupting 

Ways that carbon is taken out of the atmosphere:

  • Photosynthesis


The nitrogen cycle:


The nitrogen cycle is a bit more difficult to understand. Nitrogen makes up around 78% of the earth's atmosphere and it is very unreactive which means that plants cannot directly use it to make protein.

Stages of the nitrogen cycle:

  • Nitrogen gas from the air is converted to nitrate compounds by nitrogen-fixing bacteria in the soil or root nodules. Lightning can also convert nitrogen gas to nitrate compounds.

  • Nitrifying bacteria in the soil convert ammonia to nitrates.

  • Plants can now use the nitrogen nitrates and build them into protein. The plant's biomass is used to make animal proteins if it is eaten.

  • Decomposers then break down the dead animals, faeces or urine which results in the nitrogen being returned to the soil in the form of ammonia. Nitrifying bacteria convert the ammonia to nitrates.

  • De-nitrifying bacteria can then break down the nitrates down in the soil back into nitrogen gas. This usually happens in waterlogged soil.


The water cycle:


The water cycle has several stages to it:

  • Water evaporates from into the air from the ocean, puddles, lakes, the ground etc.

  • Water vapour rises into the air and cools down to make tiny droplets of water, forming clouds.

  • When the clouds get too heavy, water falls back down to earth as rain or snow.

  • The water makes its way back to the ocean.


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