The Nitrogen Cycle

Question 1

What is the nitrogen cycle an excellent example of?

Answer 1

How interconnected natural processes can make a natural resource that is not very abundant continually satisfy the needs of living organisms by recycling what has been used

Question 2

Why is nitrogen essential?

Answer 2

A component of many essential biological molecules

Question 3

What carries out many of the processes in the nitrogen cycle?

Answer 3

Living organisms, bacteria

Question 4

What are the reservoirs in the nitrogen cycle?

Answer 4

Atmosphere
Biosphere
Lithosphere
Hydrosphere

Question 5

What are the main chemical forms of nitrogen in the atmosphere?

Answer 5

Nitrogen gas
Oxides of nitrogen

Question 6

What are the main forms of nitrogen in the biosphere?

Answer 6

Living organisms- DNA, proteins (enzymes, hormones)
DOM- proteins (releases ammonia when decomposed)

Question 7

What is ionisation? (nitrogen cycle)

Answer 7

Processes such as lightning and meteor trials provide the energy for atmospheric nitrogen and oxygen to react and produce oxides of nitrogen

Question 8

What are the ways that atmospheric nitrogen can be transferred into other forms of nitrogen?

Answer 8

Ionisation
Nitrogen fixation (root nodule)
Nitrogen fixation (nitrifying bacteria)

Question 9

How does dead organic matter turn into ammonium ions?

Answer 9

Ammonification

Question 10

How do Ammonium ions turn into nitrites and nitrates?

Answer 10

Double oxidation
Oxidation by bacteria first to nitrites then nitrates

Question 11

What two things can happen to nitrates?

Answer 11

Absorbed by plant roots
Denitrified bacteria return it to atmosphere

Question 12

What is fixation? (nitrogen cycle)

Answer 12

When some microorganisms chemically reduce nitrogen to ammonia.

Question 13

What are the types of bacteria involved in nitrogen fixation?

Answer 13

Free living bacteria in the soil- Azotobacter
Live symbiotically in root nodules of legumes- Rhizobium

Question 14

How are food chains a part of the nitrogen cycle?

Answer 14

Nitrogen passes between organisms as amino acids and proteins in food

Question 15

What is nitrification?

Answer 15

The oxidation of ammonium ion to nitrites, then nitrates by nitrifying bacteria in the soil

Question 16

What are some examples of the oxidising bacteria in the nitrogen cycle?

Answer 16

Nitrosomonas- nitrites
Nitrobacter- Nitrates

Question 17

What is denitrification?

Answer 17

Chemical reduction of nitrates in the soil to nitrogen and nitrogen oxides by denitrifying bacteria in the soil

Question 18

What is an example of a denitrifying bacteria?

Answer 18

Pseudomonas

Question 19

What is a result of denitrification?

Answer 19

A reduction in soil fertility

Question 20

What conditions does denitrification occur under?

Answer 20

Anaerobic conditions

Question 21

What is leaching?

Answer 21

High solubility of nitrates means they are easily leached up of the soil into water bodies where they act as nutrients for aquatic plants and algae

Question 22

How does root absorption form part of the nitrogen cycle?

Answer 22

Plants absorb nitrogen as soluble ions mainly as nitrates but also ammonium ions

Question 23

How does ammonification form part of the nitrogen cycle?

Answer 23

Amino groups in proteins are released as ammonium ions by the action of bacteria, fungi and detritivores as DOM is decomposed

Question 24

What is the Haber process?

Answer 24

An industrial process for producing ammonia from nitrogen and hydrogen using an iron catalyst with high temp and pressure

Question 25

What is the problem with the Haber process?

Answer 25

Artificial fixation of atmospheric nitrogen to ammonia require a lot of energy

Question 26

What is the main purpose of the Haber process?

Answer 26

Manufacture agricultural fertilisers

Question 27

What is the problem of using nitrate fertiliser in agriculture?

Answer 27

May increase leaching problems such as eutrophication if application by heavy rain are applied near a river

Question 28

How can the nitrogen cycle be affected by field drainage?

Answer 28

Drainage make the field more aerobic Increase number of aerobic nitrifying bacteria Reducing number of anaerobic denitrifying bacteria

Question 29

How can soil disturbances affect the nitrogen cycle?

Answer 29

Ploughing increases the rate of decomposition of DOM which releases more nitrogen oxides into the atmosphere

Question 30

How can leguminous plants affect the nitrogen cycle?

Answer 30

May be grown to increase the levels of nitrogen compounds in the soil which can be absorb by plants

Question 31

What are some examples of legumes?

Answer 31

Peas Beans Clover

Question 32

How can pollution affect the Nitrogen cycle? (Combustion)

Answer 32

Oxides of nitrogen are released into atmosphere form combustion which may increase quantity of nitrates washed into the soil by rain

Question 33

How will control of the combustion processes manage the nitrogen cycle?

Answer 33

Less use of fossil fuel means less NOx released (deliberate choice, depleted supply) Adopting circular economy principle result in low temperature manufacturing process from living organisms instead of fossil fuels

Question 34

How can the Nitrogen cycle be sustainably managed by controlling the release of NOX?

Answer 34

Can be reduced using post combustion processes such as catalytic converters and urea sprays

Question 35

How can the nitrogen cycle be sustainably managed by managing biological waste?

Answer 35

Decomposition of bio waste releases ammonium ions and amino acids Enzymes produced by bacteria remove amino groups which dissolve ammonium ions useful or problem depending on area

Question 36

How does eutrophication occur?

Answer 36

May be washed into water bodies by run off or they may be deliberately dumped there. The ammonium is converted into nitrites and nitrates causing eutrophication

Question 37

How can organic fertilisers be used?

Answer 37

Manure, sewage, food production waste can be used to increase nutrient and humus levels They can be ploughed into the soil or applied to surface May be composted aerobically or digested anaerobically before fertiliser application Reduces bulk

Question 38

What farming practices can be done to increase soil nitrate levels?

Answer 38

Cultivation of legume crops Crop rotation Minimal use of pesticides that harm soil biota Control of nitrate leaching Not applying fertilisers during rain or when rain is likely Use of low solubility fertilisers (Urea) Use of low tillage techniques to reduce soil disturbance Uncultivated ‘buffer strips’ left along rivers Minimal use of nitrate fertiliser where leaching into aquifers is likely