Nutrient cycles

Question 1

What is nitrogen fixation?

Answer 1

The process of nitrogen fixation is carried out by nitrogen fixing bacteria.

These take nitrogen gas (N2) from the air and produce ammonia. The ammonia then dissolves as ammonium ions.

Some of these bacteria live free in the soil, but most live in the root nodules of leguminous plants.

This is a mutualistic symbiotic relationship. The bacteria receive sugars from the plant , the plant receives ammonia/ nitrate from the bacteria.

Question 2

What are examples of a leguminous plant?

Answer 2

Peas
beans
clover

Question 3

What is the process of ammonification?

Answer 3

This is the decay of dead and waste material forming ammonia. This is carried out by saprobiotic organisms- these digest extracellularly.

Saprobionts are bacteria and fungi.

Question 4

What is the process of nitrification?

Answer 4

Nitrifying bacteria in the soil convert ammonia ions to nitrite and then to nitrate.

Question 5

What is the process of denitrification?

Answer 5

Denitrifying bacteria convert nitrate into nitrogen gas. These are anaerobic bacteria commonly found in waterlogged soils.

Question 6

What is the process of eutrophication?

Answer 6

1. Excess nitrates get into water courses (rivers/lakes)
2. This causes an algal bloom, which prevents light getting to aquatic plants.
3. They can’t photosynthesise and die.
4. Saprobionts decay occurs increasing the biological demand for oxygen.
5. The oxygen levels are depleted, killing fish and other aquatic animals.
6. Only anaerobic bacteria can survive, the water becomes stagnant.

Question 7

What are Mycorrhizae?

Answer 7

They are mutualistic fungi that grow on plant roots. They increase the surface area of the roots for absorption of nutrients in water, and in return receive sugars from the plant.