Topic 7: Nitrogen Cycle

Question 1

Nitrogen

Answer 1

It is essential for living organisms in biological molecules
It isnt very abundant so it is recycles

Question 2

4 main nitrogen reservoirs

Answer 2

Atmosphere
Lithosphere
Hydrosphere
Biosphere

Question 3

Stores of nitrogen in the atmosphere

Answer 3

Nitrogen gas
Oxides of nitrogen

Question 4

Stores of nitrogen in the hydrosphere

Answer 4

Dissolved nitrates and ammonium ions

Question 5

Lithosphere stores of nitrogen

Answer 5

Soil-ammonium compounds,nitrites,nitrates
Rock-minerals containing nitrogen

Question 6

Stores of nitrogen in the biosphere

Answer 6

Living organisms-DNA,proteins (e.g cell membranes,hormones,enzymes)
Dead organic matter-proteins that release dead organic matter as they decompose

Question 7

Main processes of the nitrogen cycle

Answer 7

Ionisation
Fixation
Food chains
Nitrification
Root absorption
Denitrification
Ammonification
Leaching

Question 8

Ionisation as a process in the nitrogen cycle

Answer 8

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

Question 9

Fixation as a process in the nitrogen cycle

Answer 9

Some micro-organisms chemically reduce nitrogen to ammonia
This cold be by free-living bacteria in the soil or symbiotically in the root nodules of legumes

Question 10

Food chains as a process of the nitrogen cycle

Answer 10

Nitrogen passes between organisms as amino acids or proteins in food

Question 11

Nitrification as a process in the nitrogen cycle

Answer 11

Involves the oxidation of ammonium ions to nitrites
Then to nitrates by nitrifying bacteria in the soil

Question 12

Root absorption as a process in the nitrogen cycle

Answer 12

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

Question 13

Denitrification as a process in the nitrogen cycle

Answer 13

Chemical reduction of nitrates in the soil to nitrogen and nitrogen oxide gases by denitrifying bacteria in the soil
This reduces soil fertility and normally occurs under anaerobic conditions

Question 14

Ammonification as a process in the nitrogen cycle

Answer 14

The amino group in proteins are released as ammonium ions by the actions of bacteria,fungi and detrivores because they decompose organic matter

Question 15

Leaching as a process of the nitrogen cycle

Answer 15

The high solubility of nitrates means they are easily leached out of soil and into water bodies were they act as nutrients for aquatic plants like algae

Question 16

3 ways that humans impact the nitrogen cycle

Answer 16

Pollution
Haber process
Agriculture

Question 17

Pollution

Answer 17

Oxides of nitrogen are released into the atmosphere by combustion processes and may subsequently increase the quantity of nitrates washed into the soil by rain

Question 18

Haber process

Answer 18

An industrial plant process to produce ammonia from nitrogen and hydrogen using an iron catalyst at high temps/pressure
Artificial fixation of atmospheric nitrogen to ammonia requires lost of energy

Question 19

Impacts of agriculture on the nitrogen cycle

Answer 19

Use of nitrate fertilisers-eutrophication
Drainage of fields- less anaerobic denitrifying bacteria, more aerobic nitrifying bacteria
Ploughing-increases rate of decomposition so more nitrogen e=oxides released into the atmosphere

Question 20

5 ways the nitrogen cycle can be sustainably managed

Answer 20

Control of combustion processes
Control of NOx releases
Management of biological wastes
Eutrophication
Organic fertilisers

Question 21

Control of combustion processes

Answer 21

Reduce use of fossil fuels reduces nitrogen oxides

Question 22

Control of NOx releases

Answer 22

Can be reduced by using post combustion processes e.g. catalytic converters and urea sprays

Question 23

Organic fertilisers

Answer 23

Wastes like sewage and manure can be used as fertiliser to increase nitrogen or humus levels