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

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