3. Nitrogen Cycle

What you need to know...
  • Why is nitrogen important to living things?
  • What is the nitrogen cycle?
  • How are microorganisms important to the nitrogen cycle?

Why is nitrogen important to living things?
Nitrogen is vital to living things because nitrogen is needed to make protein. Proteins are used in living things to make tissues, enzymes, hormones and much more. Without nitrogen, living things cannot survive. 

What is the nitrogen cycle?
There is a limited amount of nitrogen on our planet. If the nitrogen in living things was lost when they die, we would eventually run out of nitrogen and life would cease to exist. Luckily there are a series of processes that recycle nitrogen and make sure there is a constant supply of nitrogen to all living things in our ecosystems. When we look at these processes all together we call it the nitrogen cycle.
The diagram below shows how nitrogen is recycled in an ecosystem. Since this is a cycle you can start to look at the processes from any point in the cycle. We will start by looking at the nitrogen present in plant protein:
  1. Nitrogen in plants is given to animals when plants are eaten.
  2. Nitrogen in animals is given to bacteria when they die. When the bacteria break down dead plants and animals they get energy to survive but they also release useful nitrogen into the soil.
  3. Nitrogen in the soil can be taken up and used by plants.
  4. Nitrogen in the soil can also be released into the atmosphere by special bacteria in the soil.
  5. Nitrogen gas can also be returned to the soil by other special bacteria.
  6. Although it does not happen often, lightning also returns nitrogen gas into the soil.

How are microorganisms important to the nitrogen cycle?
You will see that microorganisms such as fungi and bacteria are vital to the nitrogen cycle. They break down protein in dead animals and plants and even animal waste like faeces. Microorganisms also release nitrogen from the soil and release it into the air. Other microorganisms do exactly the opposite - they take nitrogen gas from the air and return it to the soil.