2.7 Nitrogen cycle

Question 1

Why is Nitrogen important?

Answer 1

For production of amino acids
For production of Nucleic acids

Question 2

What are the 4 main stages of the Nitrogen cycle?

Answer 2

Nitrogen fixation
Denitrification
Ammonification (by saprobionts)
Nitrification

Question 3

What do saprobionts do?

Answer 3

• Feed on remains of dead plants/animals including their waste products. (Decomposers)
• They complete extracellular digestion process, where they secrete and digest their food internally, then absorb the nutrients they need. Organic molecules –> inorganic ions.

Question 4

What are mycorrhizae?

Answer 4

When fungi form symbiotic relationships with the roots of plants.

Question 5

How do mycorrhizae fungi form symbiotic relationships with plants?

Answer 5

• They’re made up of long thin strands called hyphae, which connect to the plant roots.
• Hyphae greatly increase SA of the plant’s root system, helping plant to absorb ions from the soil.
• Hyphae also increase the uptake of water by the plant.
• Fungi obtain organic compounds (glucose) from the plant.

Question 6

What happens during Nitrogen fixation stage?

Answer 6

Bacteria (such as Rhizobium) turns Nitrogen into Ammonia, which goes to form ammonia ion in solution that can be used by plants.

• They’re found inside root nodules of leguminous plants (e.g. peas, beans and clover).
• They form a mutualistic relationship with plants (provide plant with Nitrogen compounds, and plant provides them with carbohydrates.

Question 7

What happens during ammonification stage?

Answer 7

• Nitrogen compounds from dead organisms are turned into ammonia by saprobionts, which then go on to form ammonium ions.
• Animal waste also contains nitrogen compounds which are turned into ammonia by saprobionts.

Question 8

What happens during nitrification stage?

Answer 8

• When ammonium ions in the soil are turned into nitrogen compounds that can be used by the plant (nitrates).
• (Nitrosomonas) change ammonium ions into nitrites, then (Nitrobacter) change nitrites into nitrates.

Question 9

What happens during denitrification stage?

Answer 9

• Denitrifying bacteria convert nitrates in the soil to nitrogen gas (they use nitrates in the soil to carry out respiration and produce nitrogen gas). Anaerobic conditions.
• Lightning fixes atmospheric nitrogen into nitrogen oxides.
• Artificial fertilisers produced from atmospheric nitrogen on an industrial scale in the Haber Process.