Nutrient Cycles

Question 1

Nitrogen fixation

Answer 1

Nitrogen to ammonia / ammonium ions
By nitrogen-fixing bacteria in soil or root nodules of legumes

Question 2

Nitrification

Answer 2

Ammonium/ammonia converted into nitrite
Nitrite oxidised into nitrate
By nitrifying bacteria

Question 3

Ammonification

Answer 3

Protein/amino acids/DNA
Converted into ammonium compounds / ammonia.
By saprobiontic bacteria

Question 4

Denitrification

Answer 4

Nitrates
Converted into nitrogen
By denitrifying bacteria

Question 5

Farming practices increase productivity

Answer 5

Fertilisers / minerals added to soil
Mineral absorbed by crops
Increased nitrate to make protein/DNA/ATP
Increased phosphate for ATP/DNA/phospholipids
Ploughing increases aeration of soil allowing nitrification and decreases denitrification
Benefit of crop rotation used to increase soil minerals and reduce pests

Question 6

Eutrophication

Answer 6

Nitrate in water initially limiting factor preventing excess plant growth Fertiliser leached from fields/sewage release
Increased growth of algae blocks light
Reduced / no photosynthesis so submerged plants die
Increased population of saprobiontic microorganisms
Aerobically respire / use oxygen in respiration
Less oxygen for fish to respire / aerobic organisms die
Anaerobic microorganisms population increases
Release toxins into water
Death of aquatic animals

Question 7

Phosphorous cycle

Answer 7

Minerals in rock eroded
Releasing phosphates into soil
Minerals absorbed by plants
Phosphate converted into biological molecules/DNA/ATP/phospholipids
Transfer through trophic levels
Death of organisms
Deposited as sediment
Pressurised to make sedimentary rock