Nutrient Cycles

Question 1

Give 2 examples of nutrient cycles

Answer 1

Nitrogen and phosphorus

Question 2

Describe fixation in the nitrogen cycle

Answer 2

• nitrogen in the atmosphere converted to ammonia/ammonium compounds by bacteria
• bacteria found in the nodules of leguminous plants and free-living bacteria found in the soil

Question 3

Describe nitrification

Answer 3

• nitrifying bacteria convert ammonia into nitrites and then to nitrates
• aerobic process, O2 required

Question 4

Describe denitrification

Answer 4

• nitrates get converged back into nitrogen in the atmosphere by denitrifying bacteria
• anaerobic process

Question 5

Describe ammonification

Answer 5

• dead organic matter decayed by decomposers (saprophytic bacteria + fungi)
• is converted back into ammonia

Question 6

Role of mycorrhizae fungi

Answer 6

• increase surface area of plant roots
• facilitate/increase uptake of water and inorganic ions by plants

Question 7

Advantages of organic fertilisers

Answer 7

• provide a steady supply of nutrients to plants, + contains both macro and micro nutrients
• provides structure to the soil
• provides a useful means of disposing of farm waste
• nutrients not readily leached from the soil

Question 8

Disadvantages of organic fertilisers (3)

Answer 8

• offensive smells
• may be difficult to spread
• slow mineral release

Question 9

Advantages of inorganic fertilisers (4)

Answer 9

• nutrients in concentrated form. Can be applied in smaller amounts (more cost effective)
• nutrients released rapidly from the soil
• easy to apply to fields
• clean chemicals, lack the odour of organic manure

Question 10

Disadvantages of inorganic fertilisers (4)

Answer 10

• readily leached from the soil (mineral ions not taken up by plants transported by rainwater or water from irrigation systems to ponds, Lakes or streams and rivers-waterways)
• increased risk of eutrophication
• expensive to manufacture/buy
• risk of fertiliser spray spreading to other areas

Question 11

Describe the process of eutrophication

Answer 11

• high levels of inorganic ions (nitrates, phosphates and potassium ions) from fertiliser- leaches
• algae grows rapidly, making water green and cloudy—> light restricted, algae and other plants die
• impacts on biodiversity
• algae + other biological waste decomposed by aerobic bacteria
• these bacteria (saprobionts) remove O2 from the water due to their aerobic activity. Decreasing oxygen levels in the water
• other aquatic life die
• anaerobic bacteria convert nitrates into toxic nitrites- water poisoned. Aquatic ecosystem undermined, food web collapses