Cycles

Question 1

Ammonification

Answer 1

Saprobiontic microorganisms feed on faeces and dead organisms to convert nitrogen containing compounds to ammonia.

Question 2

Nitrification

Answer 2

Nitrifying bacteria convert ammonium ions to nitrate ions, releasing energy for metabolism. Process requires oxygen so must keep soil well aerated.

Question 3

Nitrogen-fixation

Answer 3

Nitrogen gas converted to nitrogen containing compounds from free-living nitrogen-fixing bacteria (convert gaseous nitrogen to ammonia then to amino acids). Mutualistic n fxing bacteria live on nodules of roots of legumes and obtain carbs from plant and supply amino acids to plant.

Question 4

Denitrification

Answer 4

When waterlogged soils have low O2 conc, anaerobic denitrifying bacteria convert soil nitrates to N2.

Question 5

Phosphorous cycle

Answer 5

Phosphate ions in sedimentary rock deposits. Weathering dissolves ions so can be absorbed by plants.
Animals eat plants and then die.
Bacteria can break down corpses to release ions back to soil but phosphate ions in excreta are transported back to lakes and oceans to form rocks again.

Question 6

Mycorrhizae

Answer 6

Association between fungi and roots of plants.
Fungi increase total surface area for absorption of water and minerals.
Better take up ions and resist drought.
Fungus receives organic compounds such as sugars

Question 7

How do saprobiants feed back into the nitrogen cycle

Answer 7

Products of extracellular digestion remain in soil.

Question 8

Eutrophication

Answer 8

Mineral ions from fertiliser leach into waterways causing algae bloom on surface of water. This blocks sunlight for plants below. These plants die and are fed on by aerobic decomposers. No oxygen is brought back into system by photosynthesis and is used by decomposers, lowering O2 conc in water.