Nutrient Cycles

Question 1

What are Saprobionts and what do they do?

Answer 1

Decomposers that break down complex molecules of the producers and consumers when they die and then release the nutrients in its original form.

Question 2

Why is the role of saprobionts important?

Answer 2

They ensure that nutrients are released for reuse

Question 3

What is Mycorrhizae?

Answer 3

They are associations between certain types of fungi and roots of majority of plants. The fungi increase the total surface area fir the absorption of water and minerals. The mycorrhizae acts as a sponge holding the water and minerals at the roots which enables plant to resist drought and take up inorganic ions more readily.

Question 4

What is the mycorrhizal relationship between plants + fungi referred to as?

Answer 4

Mutualistic

Question 5

Explain the Plants benefit from the mutualistic, mycorrhizal relationship

Answer 5

The plants benefit from the improved water + inorganic ions uptake

Question 6

Explain the Fungi benefit from the mutualistic, mycorrhizal relationship

Answer 6

They receive organic compounds such as sugars and amino acids from plant

Question 7

What is Ammonification?

Answer 7

This is when saprobiotic bacteria and fungi feed on dead and decaying material (urine + faeces) and release ammonia which forms ammonium ions

Question 8

What is nitrification?

Answer 8

This is when nitrifying bacteria convert ammonium ions into nitrites and then into nitrates.

Question 9

What is denitrification?

Answer 9

This is when denitrifying bacteria convert nitrates back into nitrogen gas which occurs in anaerobic conditions

Question 10

What is Nitrogen fixation and what are the 3 examples?

Answer 10

This is combining nitrogen with another molecule which requires energy

• Nitrogen fixing bacteria
• Haber process
• Lightning

Question 11

Explain what happens in Nitrogen fixing bacteria to produce ammonia

Answer 11

Nitrogen and Hydrogen combine to produce ammonia. These bacteria can be in the soil or in leguminous plants

Question 12

Explain what happens in Haber process to produce ammonia

Answer 12

Nitrogen and hydrogen combine to form ammonia which is mostly used for fertilisers

Question 13

Explain what happens in lightning to produce ammonia

Answer 13

Nitrogen and oxygen combine to make various oxides of nitrogen. They wash into the soil and are taken up as nitrates by the plants

Question 14

Explain the Phosphorus cycle

Answer 14

1) Phosphorus ions in rock are released into the soil by weathering
2) The phosphate ions are taken into plants by roots; Mycorrhizae increase rate at which phosphorus is assimilated.
3) The phosphate ions are transferred through food chain as animal eat the plants.
4) The phosphate ions are lost by the animal through waste products
5) When plants + animals die, saprobionts break down the organic compounds, releasing phosphate ions into soil for plants and release ions from urine and faeces
6) Weathering of rocks also releases phosphate ions into seas, lakes & rivers

Question 15

Why is phosphorus needed?

Answer 15

This is for biological molecules such as DNA, ATP, phospholipids etc.

Question 16

Where is phosphorus found?

Answer 16

Rocks or in the ocean in the form of phosphate ions

Question 17

What is weathering?

Answer 17

The breakdown of rocks by mechanical, chemical & biological processes

Question 18

What are 3 advantages of using natural fertilisers?

Answer 18

• Cheap – produced on a farm
• Improves soil quality as it increases humus levels (rotten organic matter) and water retention
• Not easily lost by leaching but can cause eutrophication

Question 19

State 3 disadvantages of natural fertilisers

Answer 19

• Variable nutrient content
• Slow release of nutrients (can be advantageous as its less likely to cause eutrophication
• May contain pathogens

Question 20

State 3 advantages of artificial fertilisers

Answer 20

• Exact composition is known
• Easy to store and handle
• Ions can be immediately used by crops

Question 21

State 3 disadvantages of artificial fertilisers

Answer 21

• Excessive leaching can cause eutrophication
• Expensive
• Could cause osmotic damage as its applied in concentrated farms which means less water enters root cells and could results in water being drawn out of root cells

Question 22

What is the effect of eutrophication?

Answer 22

• Mineral ions (if XS) leached will stimulate a rapid growth of algae in ponds and rivers
• A layer of thick algae which will result in reduction of light for plants = eventually die
• Resulting, in large quantities of decaying organic matter
• Increased No. Of aerobic saprobionts
• Increased BOD
• Fish and other aquatic organisms will die due to lack of dissolved oxygen

Question 23

What does BOD mean?

Answer 23

Biochemical Oxygen Demand: How much O2 used for respiration by saprobionts to decompose organic matter

Question 24

What is leaching?

Answer 24

When water soluble compounds are washed away into bodies of water