Nutrient cycles

Question 1

What are all the stores in the nutrient cycle?

Answer 1

• Nitrates
• Nitrites
• Atmospheric nitrogen
• Nitrogen in plants
• Nitrogen in animals
• Ammonium compounds

Question 2

How is nitrogen transferred from atmospheric nitrogen into ammonium compounds?

Answer 2

Nitrogen fixing bacteria in the soil and roots of legumes reduce N2 gas into ammonium compound in the process of nitrogen fixing

Question 3

How is nitrogen transferred from atmospheric nitrogen into nitrates?

Answer 3

Fixation of N2 gas from the atmosphere to nitrates in soil when lightning strikes

Question 4

How is nitrogen transferred from ammonium compounds into nitrites?

Answer 4

Ammonia is oxidised into nitrites by nitrifying bacteria, in a process called nitrification.

Question 5

How is nitrogen changed from nitrites into nitrates?

Answer 5

Nitrites are oxidised into nitrates by nitrifying bacteria, in a process called nitrification.

Question 6

How is nitrogen changed from nitrates into plant tissues?

Answer 6

Nitrates are absorbed by the plant root hair cell via active transport.

Question 7

How is nitrogen transferred from plant tissues into animal tissues?

Answer 7

Consumers eat plants and digest proteins into amino acids which are absorbed into tissues

Question 8

How is nitrogen changed from plant/animal tissues into ammonium compounds?

Answer 8

Organisms die or excrete nitrogen via urine. Saprobionts digest Nitrogen compounds and release ammonia into the soil in ammonification.

Question 9

How is nitrogen transferred from nitrates into nitrogen gas?

Answer 9

Nitrates are converted into nitrogen gas by denitrifying bacteria in a process called denitrification.

Question 10

What is the main store of the phosphorus cycle?

Answer 10

Sedimentary rock

Question 11

What are the steps of the phosphorous cycle?

Answer 11

1. Main store is sedimentary rocks
2. Rock eroded so phosphate ions dissolved into soil
3. Soil -> plant via absorption
4. Phosphates passed in food chain
5. Organisms die or excrete waste which is broken down and phosphate enters soil
6. Phosphate ions may enter water and be used to form sedimentary rock

Question 12

After harvesting, the remains of crop plants are often ploughed into the soil. Explain how microorganisms in the soil produce a source of nitrates from these remains. (5)

Answer 12

1. Protein/amino acids/DNA into ammonium compounds / ammonia;
2. By saprobionts;
3. Ammonium/ammonia into nitrite;
4. Nitrite into nitrate;
5. By nitrifiying bacteria/microorganisms;

Question 13

Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants. (5)

Answer 13

1 * Named nitrogen compound. (DNA, protein, amino acid) broken down into ammonium compounds
2 * by Saprobionts
3 * Ammonium into nitrite
4 * Nitrite into nitrate
5 * By nitrification/ nitrifying bacteria

Question 14

Describe how the presence of nitrates in a lake may eventually lead to the death of fish. (4)

Answer 14

1. Growth of algae/surface plants/algal bloom blocks light;
2. Reduced/no photosynthesis so (submerged) plants die;
3. Saprobiotic (microorganisms/bacteria);
4. Aerobically respire / use oxygen in respiration;
5. Less oxygen for fish to respire / aerobic organisms die;

Question 15

What is tropism?

Answer 15

The response of a plant to a directional stimulus.
Positive = growth towards stimulus
Negative = growth away from stimulus