The Nitrogen Cycle

What is The Nitrogen Cycle?

Within Biology, which covers cells, the human body, genetics, evolution, plants and ecosystems: the science of living things, this topic explains The Nitrogen Cycle. Biology topics show how living things work, from the cell up to whole ecosystems, with models you can explore step by step.

Check that you can explain The Nitrogen Cycle in your own words and give one example from everyday life. If you can do that, you have understood the core idea.

Understanding The Nitrogen Cycle helps you explain how living things stay alive and respond to their surroundings, which is central to biology exams.

The Nitrogen Cycle in detail

Nitrogen makes up 78% of the air, but most organisms cannot use it directly. Nitrogen-fixing bacteria in the soil and root nodules of legumes convert nitrogen gas into nitrates, and lightning also fixes some. Plants absorb nitrates to make proteins, and animals get nitrogen by eating plants.

Decomposers return nitrogen as ammonia from dead matter and waste, and nitrifying bacteria convert ammonia into nitrates. Denitrifying bacteria convert nitrates back to nitrogen gas in waterlogged soils. Farmers use crop rotation with legumes and fertilisers to maintain soil nitrogen.

How the interactive helps you understand The Nitrogen Cycle

Watch the cycle in the interactive. Use any sliders or buttons it offers to change the values and see how the cycle responds.

Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of The Nitrogen Cycle.

Real-life uses and examples

• Structure a longer answer about The Nitrogen Cycle by moving from definition to example to consequence.
• Explain how The Nitrogen Cycle helps a living thing stay alive, using a plant or animal example.
• Connect The Nitrogen Cycle to health, food and medicine in everyday life.

Common mistakes to avoid

• Listing the steps of a process without saying how one step causes the next.
• Using everyday words, such as “energy” or “bad”, without their scientific meaning.
• Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.