TOPIC 5 - nutrient cycles

Question 1

name + explain the general stages in the phosphorus cycle?

Answer 1

1. weathering + runoff - phosphate compounds from sedimentary rocks leach into soil and into water as phosphate ions
2. phosphate ions taken up by plants through roots, absorbed by algae in water
   transferred into consumers during feeding
3. decomposition - phosphate ions in waste products and dead organisms are decomposed by saprobionts
4. uplift - sedimentary layers from oceans are bought up to land over many years

Question 2

why is the phosphorus cycle a slow process?

Answer 2

• no gas phase so no atmospheric cycle
• most phosphorus stored as po4 3- ions in rocks

Question 3

explain significance of phosphorus in living organisms?

Answer 3

plants convert inorganic phosphate into biological molecules
eg atp dna nadp

phosphorus is passed to consumers via feeding

Question 4

how does mining affect the phosphorus cycle?

Answer 4

speeds up uplift

Question 5

name the 4 main stages of the nitrogen cycle?

Answer 5

1. nitrogen fixation
   2.ammonification
   3.nitrification
2. denitrification

Question 6

what is nitrogen fixation?

Answer 6

• atomospheric nitrogen gas is converted into nitrogen containing compounds
• this is carried out by nitrogen fixing bacteria
  nitrogen gas = ammonium ions
• the nitrogen fixing bacteria is found in root nodules of legumes

Question 7

what is the relationship between the nitrogen fixing bacteria and the plant?

Answer 7

bacteria provides plant with nitrogen containing compounds

plants provide the bacteria with organic compounds such as carbohydrates

Question 8

what is ammonification?

Answer 8

nitrogen compounds in waste products eg faeces and dead organisms are converted to ammonia by saprobionts

this ammonia forms ammonium ions in soil

Question 9

what is nitrification?

Answer 9

ammonium ions converted by nitrifying bacteria into nitrates and nitritres that can be used by plants

Question 10

what is denitrification?

Answer 10

denitrifying bacteria use nitrates in soil during respiration producing nitrogen gas that returns to the atmosphere

this occurs in anaerobic conditions

Question 11

why cant organisms use nitrogen from the atmoshpere?

Answer 11

N2 is very stable due to strong covalent triple bonds

Question 12

explain the significance of nitrogen to living organisms

Answer 12

plant roots uptake nitrates via active transport and use them to make biological compounds

eg nadp/ nad
nucleic acids
amino acids

Question 13

outline the role of mycorrhizae?

Answer 13

mutualistic friendship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions.

Question 14

give 3 benefits of planting a different crop on the same field each year

Answer 14

nitrogen fixing crops eg legumes make soil more fertile by increasing the nitrate content

different crops have different pathogens

different crops use different proportions of certain ions

Question 15

name 2 categories of fertilisers and explain the purpose.

Answer 15

organic/natural - made up of decaying organic matter and animal waste
+ nutrients released over long time periods
- not very concentrated

artificial/inorganic - minerals from rocks eg nitrogen. phosphorus, potassium

+ concentrated so smaller amounts needed
- mineral ions can be transported by water into ponds and lakes (leaching) = causing eutrophication = algal bloom

Question 16

what happens during eutrophication?

Answer 16

• mineral ions from excess fertiliser leach into water ways causing rapid growth of algae at the surface of water
  = algal bloom
• blocks sunlight so plants below the surface die as they can no longer photosynthesise
• increasing numbers of decomposing bacteria respire aerobically, using up all the dissolved oxygen
• aquatic organisms die

Question 17

how can risks of eutrophication be reduced?

Answer 17

• sewage treatment marshes on farm
• pumping nutrient enriched sediment out of water