The Nitrogen Cycle Explained

Question 1

Steps of the Nitrogen Cycle

5 marks

Answer 1

1. Decomposition
2. Nitrification
3. Plant absorption
4. Denitrification
5. Nitrogen fixation

Question 2

1. The Nitrogen Cycle - Decomposition:
   Explained

(7 marks)

Answer 2

In decaying plants + animals;

bacteria/fungi break down protein (found in the corpse) into ammonium compounds -

which are put back into the soil by decomposers.

Urine + faeces sends Nitrogen back into the soil as ammonium compounds (urea contains nitrogen)

Question 3

2. The Nitrogen Cycle - Nitrification:
   Explained

(5 marks)

Answer 3

The plants can’t absorb ammonium compounds requires Nitrifying Bacteria;

Ammonium converted to Nitrites - then to Nitrates - can then be absorbed by + incorporated into plant tissues.

• NB; aerobic (needs O2) - O2 + high temps quickens process.

Question 4

3. The Nitrogen Cycle - Plant absorption:

Explained

Answer 4

Plants absorb Nitrates from soil + use Nitrogen to make proteins.

Animals eat the plants (or other animals) + get the Nitrogen they need from the proteins in Plant/animal.

Question 5

4. The Nitrogen Cycle - Denitrification:
   Explained

(5 marks)

Answer 5

Nitrates also are metabolized by Denitrifying Bacteria (anaerobic) found in poorly aerated soil -
especially active in water-logged anaerobic soils.

action of these bacteria - deplete soil nitrates, taking them out of the soil -
converting them back into Nitrogen gas.

Question 6

5. The Nitrogen Cycle - Nitrogen fixation;
   Explained

(8 marks)

Answer 6

Nitrogen- Fixing Bacteria found free in soil/root nodules of legumes convert Nitrogen gas into nitrates.

O2 is used for this process - process quickened by O2 + higher temps.

In root nodules NFB again carbs from plant - plants gain a source of Nitrates in return.