Component 1.5 - The Nitogen Cycle

Question 1

Why is nitrogen so important?

Answer 1

• It is found in all amino acids, proteins , DNA, ATP

- It is found in chlorophyll

Question 2

What is the nitrogen cycle?

Answer 2

Flow of organic and inorganic nitrogen within the abiotic and biotic factors of an ecosystem where there is an interchange between certain nitrogenous compounds and atmospheric nitrogen

Question 3

Describe the assimilation of organic nitrogen into plants

Answer 3

Nitrate ions (NO3-) in soil are taken up into the plants by active transport or facilitated diffusion

Question 4

Describe decay, involving ammonification

Answer 4

• Saprotrophs and detritivores have enzymes that decompose producers, consumers and their waste products
• The convert the nitrogen contained in these materials into ammonium (NH4+) ions

Question 5

Describe nitrification

Answer 5

Ammonium ions formed in ammonification are:

1) Converted to nitrites (NO2-) by Nitrosomonas
2) From nitrites to nitrates (NO3-) by Nitrobacter

Question 6

Describe denitrification

Answer 6

• Anaerobic bacteria convert nitrate ions to nitrogen

- This is a reduction reaction (oxygen is lost) so it is a problem in waterlogged soils

Question 7

Describe nitrogen fixing in the root nodules of leguminous plants and how does this help the plant?

Answer 7

Rhizobium reduces nitrogen gas to ammonium ions that the plant can use for protein synthesis and it can grow in low fertility soil.

• mutualistic relationship as Rhizobium gets carbohydrates and organic acids from plant

Question 8

What is the name of another nitrogen fixing bacteria and how is it different?

Answer 8

Azotobacter and it is different because it is a free-living nitrogen-fixing bacteria in the soil

Question 9

How do humans aerate the soil and why do they do this? (Impact on nitrogen cycle)

Answer 9

1) Ploughing fields - Encourage nitrification, prevent denitrification and plant roots respire aerobically so increases active uptake of minerals
2) Draining land - Allows air to enter soil and so it reduces anaerobic conditions so denitrifying bacteria are not favoured and less nitrate is lost

Question 10

What do humans add to soil which have an impact on the nitrogen cycle?

Answer 10

1) Animal waste/slurry - contains nitrogen and other nutrients essential for plant growth.
2) Application of agricultural fertilisers e.g ammonium nitrate adds nitrogen to the soil

Question 11

What can humans plant in soil which has an impact on the nitrogen cycle?

Answer 11

Fields of legumes - this enhances nitrogen fixation and when the crop dies it is ploughed back into the soil and it has a high nitrogen content

Question 12

What are the problems caused by excess nitrate in soils?

Answer 12

Increases use of fertilisers has reduced species diversity on grassland e.g they increase the growth of grasses which can shade out smaller plants

Question 13

Describe the process of what happens when nitrate leached into rivers causes eutrophication (6)

Answer 13

1) Nitrate fertiliser causes algae to grow and may form an algal bloom and so water becomes green and light is unable to penetrate to any depth
2) Plants in deeper regions cannot photosynthesise and they die
3) Decrease in animal diversity as they rely on plants for food and shelter
4) Algae die and are decomposed by saprobiontic fungi - these are aerobic and use a lot of oxygen
5) Water apart from top layer is deoxygenated so fish and other species die
6) Anaerobic bacteria in water reduce nitrate to nitrite, they flourish and release gases

Question 14

How do some farmers prevent eutrophication and what effect has this had?

Answer 14

• The minerals concentrate in drainage ditches which undergo eutrophication
• Water flows slowly in the ditches so they accumulate landfill and this has led to drops in invertebrates
• Biodiversity reduced in adjacent grassland due to waters high nitrate concentration