Nutrient Cycles

Question 1

What are saprobionts?

Answer 1

Microorganisms that feed on decaying or dead organic matter

Question 2

Why is nutrient recycling important?

Answer 2

• Allows nutrients to be continuously reused

Question 3

What is extracellular digestion?

Answer 3

When saprobionts secrete enzymes onto dead organic matter

Question 4

What happens during extracellular digestion?

Answer 4

• The enzymes break down the large organic matter into smaller soluble molecules
• The small molecules are then absorbed by the saprobionts
• To be used during respiration or be stored

Question 5

What happens during nitrogen fixation?

Answer 5

• Atmospheric nitrogen is converted to ammonia by nitrogen fixing bacteria
• Bacteria(Rhizobium) found in the root nodules form a mutualistic relationship with leguminous plants
• The bacteria provide ammonia while the plant provides the sugars

Question 6

What is a mutualistic relationship?

Answer 6

• A relationship where both species benefit

Question 7

What happens during ammonification?

Answer 7

• When an organism dies or produces waste, it is decomposed by saprobionts
• Producing ammonia which will later form ammonium ions in the soil

Question 8

What happens during nitrification?

Answer 8

• Ammonium ions released in ammonification are converted into nitrites by one nitrifying bacteria before being converted to nitrates via another nitrifying bacteria

Question 9

What happens during denitrification?

Answer 9

• Denitrifying bacteria converts nitrates back into atmospheric nitrogen
• In an anaerobic conditions

Question 10

What are hyphae?

Answer 10

• Long strands that extend the cell body of mycorrhizae

Question 11

What is the function hyphae?

Answer 11

• To increase the SA of the plant root system

- This increases the volume of water and ions the plant can take up in a give time

Question 12

How are phosphate ions take up by the plant?

Answer 12

They are assimilated due to the symbiotic relationship

Question 13

How is phosphorus recycled through the ecosystem?

Answer 13

• PO₄³⁻ ions in rocks are released via weathering
• PO₄³⁻ ions become assimilated with plant, rate increased by mycorrhizae
• PO₄³⁻ ions are transferred through the food chain through feeding and then lost via excretion
• Saprobionts decompose dead organic matter, faeces and urine to release PO₄³⁻ ions into the soil

Question 14

Why is guano used as a natural fertiiser?

Answer 14

• It contains a high proportion of PO₄³⁻ ions so can return a significant amount to the soil

Question 15

How does agriculture impact soil?

Answer 15

• It leads to depleted levels of nutrients in the soil as crops are removed so nutrients are not recycled
• Also the removal of livestock as the nutrients are not replaced by decomposition

Question 16

What are the benefits of using fertiliser?

Answer 16

• They replace the lost nutrients

- It enables farmers to continue without negative impacts

Question 17

What are artificial fertilisers?

Answer 17

• They contain inorganic matter

- Produced specifically to replace nutrients

Question 18

What are natural fertilisers?

Answer 18

• They contain organic matter

- Taken from organic matter and used to replace nutrients

Question 19

What is leaching?

Answer 19

• The process where water-soluble compounds in the soil are washed away

Question 20

What is the process of eutrophication?

Answer 20

• Fertilisers that are sprayed onto fields leach through the soil and end up in waterways
• Causing a build up of nutrients in the water
• Algae grows rapidly on the surface, so light cannot reach plants underneath
• Causing plant death as they are unable to photosynthesise
• Bacteria number increases as more matter needs to be decomposed
• Oxygen conc decreases so fish and other organisms die