nitrogen cycle

Question 1

1. What are mycorrhizae?

Answer 1

An association between certain types of fungi and the roots of plants that increase the surface area of the root system for increased absorption of water/mineral ions.

Question 2

2. How do mycorrhizae benefit the organisms?

Answer 2

They vastly increase the plants root system for absorbing water and minerals. The fungus receives sugars and amino acids from the plant.

Question 3

3. What are saprobionts?

Answer 3

Saprobionts are bacteria and fungi which feed on dead matter/urine and faeces. * They cause the process of decay to occur. * The digest extra cellularly by releasing enzymes onto the organic matter which digests it. They then absorb the soluble products of digestion by diffusion through their surfaces.

Question 4

4. What is ammonification?

Answer 4

Nitrogen containing organic compounds in dead matter/faeces such as amino acids and nucleotides are converted to ammonia. This is performed by saprobionts.

Question 5

5. What is nitrification?

Answer 5

Nitrifying bacteria convert ammonia into nitrites, then nitrate ions. This is an oxidation reaction.

Question 6

6. What is nitrogen fixation?

Answer 6

The process of converting nitrogen gas in the atmosphere into ammonia. Can be performed by free-living nitrogen fixing bacteria in the soil, or bacteria in the root nodules of leguminous plants

Question 7

7. What is denitrification?

Answer 7

When soils are waterlogged, and bacteria are in anaerobic conditions, they convert nitrates into nitrogen gas. Removing it from the soil and making in unavailable to plants

Question 8

8. Explain how microorganisms in the soil produce a source of nitrates from dead organic matter.

Answer 8

Protein, amino acids and DNA are decomposed into ammonium compounds, by saprobionts; Then ammonia is oxidised into nitrites and then nitrates by nitrifying bacteria.

Question 9

9. Explain how eutrophication occurs

Answer 9

Nitrates are leached from fields into rivers or lakes. This causes an algal bloom. The plants/algae at the bottom no longer get sunlight and so die, fall to the bottom and decompose. The saprobionts decompose the dead plants and their population grows. they use up the oxygen in the water and therefore fish and other aerobic organisms die.

Question 10

10. Why are leguminous plants beneficial to farmers?

Answer 10

Nitrogen fixing bacteria live in their root nodules so the soil will contain more nitrates.

Question 11

11. Why do farmers plough in late spring?

Answer 11

To loosen and aerate the soil to ensure there is sufficient oxygen for nitrification to increase productivity and to prevent denitrification which would decrease productivity

Question 12

advantages of artificial fertiliser (ammonia)

Answer 12

-increased growth and productivity providing us with cheaper food
-instant supply of inorganic ions

Question 13

advantages of natural fertiliser (manure)

Answer 13

Increased growth and productivity providing us with cheaper food.
Less expensive than inorganic fertiliser
* Less leaching of nitrates

Question 14

disadvantages of artificial fertiliser (ammonia)

Answer 14

Leaching of fertiliser causing pollution of watercourses
* Eutrophication caused by leaching
* Expensive

Question 15

disadvantages of natural fertiliser (manure)

Answer 15

Some leaching of fertiliser causing pollution of watercourses
* Some eutrophication caused by leaching
* Slower supply of inorganic ions