Nitrogen Cycle

Question 1

Atmospheric nitrogen into what?

Answer 1

Nitrogen-fixing bacteria in soil
React with nitrogen to form ammonium

Question 2

Nitrogen fixing bacteria?

Answer 2

Ammonium

Question 3

Ammonium?

Answer 3

Nitrification (by nitrifying bacteria) into nitrites and then nitrates

Question 4

Nitrates?

Answer 4

Absorbed into plants by active transport and then assimilated

Question 5

Plants?

Answer 5

Eaten by animals and then ammonification occurs- the conversion of nitrogen containing molecules in dead organisms into ammonia by saprobionts

Question 6

Atmospheric nitrogen into nitrogen fixing bacteria?

Answer 6

Through the root nodules of leguminous plants

Question 7

Nitrates into denitrifying bacteria?

Answer 7

Denitrifying bacteria in soil- convert nitrates back into N2 (gas)

Question 8

2 roles of nitrogen in living organisms?

Answer 8

Building proteins
Building nucleic acids

Question 9

Atmospheric nitrogen into animals?

Answer 9

Nitrogen fixation

Question 10

Definition of saprobiont?

Answer 10

Bacteria/fungi that carry out extracellular digestion

Question 11

Describe the importance to ecosystems of the role played by nitrogen-fixing bacteria in the nitrogen cycle.

Answer 11

They convert nitrogen gas into ammonium
They provide nitrogen in usable forms
To other organisms on all trophic levels
For protein/DNA synthesis

Question 12

Denitrification?

Answer 12

Denitrifying bacteria use nitrates in the soil for respiration
Occurs in anaerobic conditions
Produces nitrogen gas- returns to the atmosphere

Question 13

Nitrification?

Answer 13

Ammonium ions in the soil are converted into nitrates by nitrifying bacteria
Nitrites -> nitrates
Oxi

Question 14

Ammonification?

Answer 14

Nitrogen from living organisms is returned to the soil in the form of ammonia by sapropbionts
Forms ammonium ions in the soil

Question 15

Nitrogen fixation?

Answer 15

N2 gas -> ammonium compounds by nitrogen-fixing bacteria
Bacteria may be free-living in the soil or may live within root nodules of legume plants
Ammonium compounds are converted into nitrates- absorbed by plants and used to build plant proteins

Question 16

Mycorrhizae and their role in the uptake of water and inorganic ions by plants?

Answer 16

Associations between fungi and roots of plants
Form mutualistic relationships with host plants
Fungus receives sugars/ amino acids in return for water and minerals

Question 17

Advantages of natural fertilisers?

Answer 17

Release nutrients slowly over time, nutrients are less likely to be washed away into rivers and lakes after rain
Contain organic matter, so can improve soil structure and water retention

Question 18

Disadvantages of natural fertilisers?

Answer 18

Nutrients are less concentrated- large amounts are needed
Nutrient content is variable and harder to control

Question 19

Advantages of artificial fertiliser?

Answer 19

Nutrients are concentrated and easy to apply
Precise nutrient content allows controlled dosing

Question 20

Disadvantages of artificial fertiliser?

Answer 20

Highly soluble in water- can be leached out of soil into rivers and lakes when it rains
Does not improve soil structure

Question 21

Eutrophication?

Answer 21

1) mineral ions enter water due to leaching, causing rapid growth of algae at the surface- algal bloom
2) algae block sunlight- preventing aquatic plants below the surface from photosynthesising
3) these plants and eventually the algae begin to die and dead organic matter accumulates
4) bacteria decompose the dead matter, respiring aerobically and using up the oxygen dissolved in the water
5) oxygen levels fall and aquatic animals such as fish and insects can no longer survive