The nitrogen cycle

Question 1

Why is nitrogen important in living organisms

Answer 1

1) synthesis of amino acids/ proteins
2) synthesis of nucleic acids
3) chlorophylls

Question 2

draw the nitrogen cycle

Question 3

What are the four biological processes within the nitrogen cycle

Answer 3

1) Ammonification
2) Nitrification
3) Dentification
4) Nitrogen fixation

Question 4

Describe ammonification

Answer 4

aka purification

• putrifying bacteria and fungi decompose dead organic matter proteins into amino acids
• amino acids are then deaminated to produce NH2 which are used to form ammonium ions

Question 5

Describe Nitrification

Answer 5

in the presence of aerobic conditions

• ammonium ions are converted to nitrites by nitrifying bacteria Nitrosomonas
• nitrites are converted to nitrates by nitrifying bacteria Nitrobacter

Question 6

Describe Denitrification

Answer 6

occurs in anaerobic conditions

- denitrifying bacteria pseudosomomas convert nitrates back to nitrogen gas

Question 7

Describe nitrogen fixation

Answer 7

• free-living bacteria, azotobacter, in the soil, absorb nitrogen gas from the air and convert it to ammonium ions
• these ammonium ions either leach into the soil or are used by the bacteria themselves to synthesis amino acids
• contained bacteria, Rhizobium, in root nodules of legumes convert nitrogen gas into ammonium ions

Question 8

Describe the symbiotic relationship between legumes and Rhizobium bacteria

Answer 8

Bacteria benefits from food and shelter

Plant benefits by having amino acids produced by bacteria

Question 9

Why is nitrogen fixation often an aerobic process

Answer 9

Nitrogen gases diffuse into the legume root nodule and the reduction of N2 to ammonium ions occur using ATP
Nitrogen fixation requires a lot of energy so is often aerobic

Question 10

what human activities affect the nitrogen cycle

Answer 10

1) ploughing fields- improves aeration and nitrogen fixation
2) Drainage of land- reduces anaerobic conditions
3) Haber process- converts nitrogen to fertilisers= increased ammonium ions
4) planting more legumes- enhances nitrogen fixation increasing ammonium ions

Question 10

what human activities affect the nitrogen cycle

Answer 10

1) ploughing fields- improves aeration and nitrogen fixation
2) Drainage of land- reduces anaerobic conditions
3) Haber process- converts nitrogen to fertilisers= increased ammonium ions
4) planting more legumes- enhances nitrogen fixation increasing ammonium ions

Question 11

What are problems that can result from fertilisers being used on habitats

Answer 11

1) leaching of excess nitrates into soils
- reduces species diversity on grassland, fertilisers increase the growth of grasses and plants like nettles which shade out smaller plants

2) Leaching of nitrates in rivers
- eutrophication

Question 12

What is eutrophication

Answer 12

The artificial enrichment of aquatic habitats by excess nutrients, often caused by run off from fertilisers.

Question 13

Describe the process of eutrophication

Answer 13

1) Nitrates are highly soluble so run off with water into large water bodies
2) Nutrients provides by the nitrogen causes an algal bloom
3) The plants in deeper regions cant photosynthesis and die
4) Decrease in animal species that rely on plants for food and shelter
5) Decomposers break down dead organic matter- an aerobic process, oxygen is depleted from the water source
6) Water becomes deoxygenated so aerobic organisms such as fish die
7) anaerobic bacteria reduce nitrate to nitrite

Question 14

How can be avoid problems of high concentrations of nitrates in the water

Answer 14

1) Restrict the volume of fertilizers used
2) only apply fertilizers when actually growing crops
3) create a strip at least 10m wide next to watercourses
4) dig drainage ditches- minerals concentrate in these ditches not water
5) grow more legumes