P2 Nutrient Cycles

Question 1

Describe the carbon cycle

Answer 1

Carbon fixation:
1. In the atmosphere, carbon is found in the gas, carbon dioxide. Producers (such as trees) take in this carbon dioxide, and use it for photosynthesis.
Producers also release carbon dioxide back into the atmosphere through respiration.
2. During photosynthesis, carbon dioxide is converted into organic, carbon-containing compounds. (Carbon fixation).

3. Consumers eat the producers, and the organic, carbon-containing compound passes along the food chain.
   Consumers also release carbon dioxide back into the atmosphere through respiration.

Decomposition:
4. When producers and consumers die, the carbon containing compounds remain in their waste matter. These compounds are broken down by decomposers, such as bacteria, releasing carbon back into the atmosphere as carbon dioxide.

Fossil fuels:
5. Waste matter that isn’t decomposed will eventually form fossil fuels. When these fossil fuels are burned (combustion) they release carbon dioxide back into the atmosphere.

Question 2

What is nitrogen fixation?

Answer 2

Converting nitrogen gas into ammonia:
- it doesn’t require oxygen (anaerobic)

Question 3

How does nitrogen fixation occur?

Answer 3

1. • Azotobacter (a nitrogen-fixing bacteria freely living in soil) converts nitrogen gas into ammonia.
     - The bacteria then releases this ammonia into the soil, where it dissolves in water, forming ammonium ions.

OR

2. • Rhizobium (a nitrogen-fixing bacteria living in the root nodules of some plants) can also convert nitrogen gas into ammonia.
     - This ammonia is used immediately by the plant.

Question 4

What is nitrification?

Answer 4

• Conversion of ammonium ions to nitrates.
• For plants that do not have nitrogen-fixing bacteria in their nodules, since they do not have access to ammonia.

Question 5

What is the process of nitrification?

Answer 5

1. Nitrosomonas (nitrifying bacteria in the soil) convert ammonium ions to nitrites.
2. Nitrobacter (nitrifying bacteria in the soil) convert nitrites into nitrates.

• This requires oxygen as the nitrifying bacteria need to carry out aerobic respiration, and require oxygen for nitrification.

Question 6

What is the process of ammonification?

Answer 6

1. Nitrogen in plants and animals is returned back to the soil as a result of death and excretion.
2. This waste is fed on by decomposers (eg. bacteria), who break down nitrogen-containing compounds such as DNA into ammonia.
3. Ammonia is released into the soil and dissolves in water, forming ammonium ions.

Question 7

What is ammonification?

Answer 7

• The break down of dead organisms/excretion into ammonia, which dissolves in water to form ammonium ions.
• Ammonification helps replenish the supply of ammonium ions in the soil, meaning that more nitrates can be made, and taken up by new plants.

Question 8

What is the process of denitrification?

Answer 8

When denitrifying bacteria respire anaerobically, they take in nitrates and convert them to nitrogen gas, which returns to the atmosphere.

Question 9

What is the order of processes in the nitrogen cycle?

Answer 9

1. Nitrogen fixation
2. Nitrification
3. Ammonification
4. Denitrification