3.5.4 - Nutrient Cycles

Question 1

ammonification

Answer 1

• production of ammonia
• from organic nitrogen-containing compounds e.g. urea and proteins (from faeces and remains)
• by saprobiontic microorganisms
• decompose proteins/DNA/RNA/urea
• form ammonium ions in the soil

Question 2

nitrification

Answer 2

• ammonium ions oxidised to nitrite ions
• nitrite ions oxidised to nitrate ions
• by nitrifying bacteria (aerobic)
• requires oxygen (soil with many air spaces → ploughing and good drainage to increase productivity)

Question 3

nitrogen fixation

Answer 3

• nitrogen gas converted into nitrogen-containing compounds
• by free-living nitrogen-fixing bacteria (reduce gaseous nitrogen to ammonia)
• by mutualistic nitrogen-fixing bacteria (live in nodules on plant roots)

Question 4

denitrification

Answer 4

• soil nitrates converted to nitrogen gas
• by denitrifying bacteria (anaerobic)
• in waterlogged soils with a low oxygen concentration
• reduces availability of nitrogen-containing compounds for plants
• bad for productivity

Question 5

phosphorus cycle

Answer 5

phosphates in rocks → erosion and use of fertilisers → dissolved phosphate ions in oceans/lakes/soils (sedimentation into rocks) → absorption → phosphate ions in plants → feeding and digestion → phosphate ions in animals → excretion and decomposition → phosphate ions in waste/remains → deposition

Question 6

mycorrhizae

Answer 6

• associations between some fungi and the roots of most plants
• fungi act like extensions of plant’s root system → increase SA for absorption of water and minerals
• acts like a sponge → holds water/minerals close to roots → plant can better resist drought and take up ions more readily
• mutually beneficial relationship (plant has improved improved water/inorganic ion uptake and fungi gets organic compounds from plant)

Question 7

natural (organic) fertilisers

Answer 7

• consist of dead and decaying remains of plants and animals, as well as animal wastes (e.g. manure/bone meal)

Question 8

artificial (inorganic) fertilisers

Answer 8

• mined from rocks and deposits
• converted into different forms
• blended together to give the appropriate balance of minerals for a certain crop
• nitrogen, phosphorus, potassium

Question 9

how do fertilisers increase productivity?

Answer 9

• minerals (e.g. nitrate ions) required for growth made available
• plants likely to develop earlier
• plants likely to grow taller
• plants likely to have a greater leaf area
• increases rate of photosynthesis
• improves crop productivity

Question 10

environmental issues arising from the use of fertilisers

Answer 10

• reduced species diversity
• leaching
• eutrophication

Question 11

leaching

Answer 11

• process by which nutrients are removed from the soil
• rainwater dissolves soluble nutrients → carries them deep into soil away from roots
• enter and pollute watercourses e.g. streams/rivers/lakes
• contaminate drinking water or cause eutrophication

Question 12

eutrophication

Answer 12

• leaching of nutrients into body of water
• growth/increase of algae/surface plants/algal bloom blocks light
• reduced/no photosynthesis so submerged plants die
• saprobiontic (microorganisms) feed on dead plants and aerobically respire/use oxygen in respiration
• less oxygen for fish to respire → death