Nitrogen fixing roots in legumes. Image credit MediaWiki

Nitrogen fixing roots in legumes. Image credit MediaWiki

ZIMSEC O Level Combined Science Notes: The nitrogen cycle

  • Nitrogen makes up 79% of the atmosphere
  • Animals cannot absorb Nitrogen as a gas
  • They absorb it indirectly usually as part of food
  • Recycling of nitrogen is carried out by legumes and by groups of bacteria
  • Examples of legume plants are legumes and acacias
  • Legumes have bacteria that live in their root nodules which convert gaseous nitrogen into proteins in the plant
  • Legumes can as a result of this grow in soils that are low in nitrogen
  • Some types of bacteria also use nitrogen and other organic compounds as sources of food and energy
  • This results in nitrogen being converted from one form to another
  • Lightning energy also combines with gaseous nitrogen and turns into nitrates
  • Human activities such as adding fertilizers containing nitrogen to the soils are also part of the cycle

To access more topics go to the Combined Science Notes page.

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