nitrogen cycle

Question 1

what are the 4 main stages of the nitrogen cycle

Answer 1

Ammonification
Nitrification
Nitrogen Fixation
Denitrification

Question 2

what is Ammonification

Answer 2

Production of Ammonia from organic nitrogen containing compounds. For example the break down of Urea (from the breakdown of excess amino acids), proteins, nucleic acids and vitamins (found in faeces and dead organisms). Carried out by Saprobionts, e.g. fungi and bacteria. They release Ammonia which turns to Ammonium ions in the soil.

Question 3

Nitrification

Answer 3

Conversion of Ammonium ions to Nitrate ions by Nitrifying Bacteria. This is an oxidation reaction carried out by bacteria. It therefore releases energy for the bacteria to use and requires Oxygen, so requires a soil with air spaces. This is why farmers keep their soil well aerated by ploughing and good drainage. These bacteria are free living in the soil. The conversion occurs in two stages, first oxidation of ammonium ions to nitrite ions, and then a further oxidation to nitrate ions.

Question 4

Nitrogen fixation

Answer 4

Nitrogen Gas is converted into Nitrogen containing compounds. It occurs naturally when lightening passes through the atmosphere, but also by two different types of bacteria. firstly free living nitrogen fixing bacteria. they reduce the nitrogen gas to ammonia, which they use to manufacture amino acids for themselves. When they die and decay nitrogen containing compounds are therefore released into the ground. There are also mutualistic nitrogen fixing bacteria which live in the root nodules of leguminous plants. They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

Question 5

Denitrification

Answer 5

Conversion of soil nitrates into gaseous nitrogen by denitrifying bacteria. They are abundant in anerobic conditions, i.e. waterlogged soil with low oxygen concentrations.