1. The Nitrogen Cycle
A2 OCR Biology

2. By the end of this session I will:
be able to describe the importance of nitrogen in living systems.
outline the role of micro-organisms in the cycling of nitrogen
Describe the nitrogen cycle using the appropriate AS/A2 scientific language.

3. Nitrogen the basics – needed for
Nitrogen (N) is an element like carbon. All creatures need nitrogen to survive.
Nitrogen is needed for the synthesis of proteins e.g. enzymes.
Nitrogen is also an important component of nucleic acids

4. Nitrogen the basics – chemistry of
There are huge amounts of nitrogen gas in the atmosphere, but most animals and plants have no way of using it as it is very unreactive due to the triple covalent bond.
It needs to be fixed (put into a biologically useful compound). After it is fixed, it can then start to move through the cycles and organisms in an ecosystem.

5. Nitrogen the basics – sources of
Let's start with the main sources of nitrogen. Nitrogen gas is the most abundant element in our atmosphere.
The other main source of nitrogen is in the nitrates of soil. The nitrogen in the atmosphere cannot be used while the nitrates in the soil can be used by plants. Nitrogen can be converted into useful nitrate compounds by bacteria, algae, and even lightning. Once in the soil, the nitrogen becomes biologically accessible.

6. Importance of bacteria in the nitrogen cycle
Nitrogen fixing bacteria
Nitrifying bacteria
Denitrifying bacteria

7. Nitrogen fixing bacteria
Function…….
…… converts nitrogen into nitrogen containing compounds
E.g. ….
…… Rhizobium
Found in ….
….. Roots nodules of leguminous plants and soil

8. Mutualism

9. Nitrifying bacteria Function….
….. Convert ammonia in nitrite ions and then into nitrite ions.
E.g. …..
…..Nitrosomonas and Nitrobacter.
Found in….
….well aerated soils.

10. Denitrifying bacteria
Function….
…. Convert nitrate into nitrogen gas
Found in….
…. Sewage works, compost and wet soils

12. Other ways in which nitrogen can be fixed
Lightning
Haber process

13. Lightning
The electrical energy of lightning causes nitrogen gas (N2) to react with oxygen (O2) in the atmosphere to produce nitrate ions (NO3-) which reach the soil dissolved in precipitation.
Recent research suggests the amount of nitrates produced by lightning may be as high as 50%.

14. Haber process

15. Basic summary of the nitrogen cycle