5.4 NUTRIENT CYCLES

Question 1

What is the nitrogen cycle?

Answer 1

The process by nitrogen is recycled within a natural ecosystem.

Question 2

What are the stages of the nitrogen cycle?

Answer 2

1. Nitrogen fixing
2. Nitrification
3. Absorption/feeding
4. Death & Ammonification
5. Denitrification

Question 3

What is nitrogen fixing?

Answer 3

Microorganisms in root nodules fix the nitrogen gas from the atmosphere into the soil as ammonium ions.

Question 4

What is nitrification?

Answer 4

Microorganisms oxidise the ammonium ions to nitrites and the oxidise them again to nitrate ions in the soil.

Question 5

What is absorption?

Answer 5

Plants take up the nitrate ions in the soil.

Question 6

What is feeding?

Answer 6

When consumers feed on plants and then get passed the nitrate ions - are absorbed by the plants.

Question 7

What is ammonification?

Answer 7

When organisms die, saprobionts break them down into ammonium ions by the process of ammonification. These can later be oxidised into nitrates during nitrification.

Question 8

What is denitrification?

Answer 8

Denitrifying bacteria convert nitrate ions back into nitrogen gas and release it into the atmosphere.

Question 9

Outline the phosphorus cycle.

Answer 9

1. Phosphorus ions found in oceans from the erosion of rocks.
2. Ions are absorbed by plants and passed on to animals who feed on them.
3. Excess phosphorus ions are released as excretion. (ie guano - seagulls)
4. Saprobionts break down waste back into the phosphorus ions.
5. Some leftover phosphorus ions are put in sedimentary rocks to link the cycle back.

Question 10

What are mycorrhizae fungi?

Answer 10

Fungi that facilitate the uptake of water and ions for plants via a symbiotic relationship.

Question 11

What is a symbiotic relationship?

Answer 11

Where both entities are successful. The plant gets more water and ions, and the fungi can get sugar/amino acids/biological molecules from the plant.

Question 12

How do mycorrhizae fungi work?

Answer 12

They increase the SA of plant roots to take up and even store more water and ions.

Question 13

Why do we need fertilisers?

Answer 13

• Supply minerals that have been lost through harvesting. (ie nitrates)
• Add supplements to the soil for a better yield.

Question 14

What are natural fertilisers?

Answer 14

Those made from organic matter (ie waste/dead remains)

Question 15

What are artificial fertilisers?

Answer 15

Mined from rocks and converted into ions in compounds, so specific ions can be provided.

Question 16

What are the environmental issues with the use of fertilisers? (2)

Answer 16

1. Leaching

2. Eutrophication

Question 17

What is leaching?

Answer 17

Water washes excess fertilisers into bodies of water.

Question 18

What are the negative implication of leaching?

Answer 18

• Harmful to drinking water and aquatic life.

- Leads to eutrophication.

Question 19

Outline eutrophication?

Answer 19

1. Nitrates cause excess algal bloom on the water’s surface.
2. Block the sunlight so producers lower down cannot photosynthesise, and then die.
3. Saprobionts break these dead remains down and use up oxygen for aerobic respiration.
4. Oxygen debt means fish cannot respire and therefore die.