Nutrient cycles

• Name the general stages in phosphorus cycle

  ~Weathering

  ~Runoff

  ~Assimilation

  ~Decomposition

  ~Uplift
• Why is the phosphorus cycle a slow process

  ~Phosphorus has no gas phase, so there is no atmospheric cycle

  ~Most phosphorus is stored as phosphate ions in rocks
• What happens during weathering and runoff

  Phosphate compounds from sedimentary rocks leach into surface water and soil
• Explain the significance of phosphorus to living organisms

  ~Plants convert inorganic phosphate ion into biological molecules

  ~Phosphorus is passed to consumers via feeding
• What happens during uplift

  Sedimentary layers from oceans are brought up to land over many years
• How does mining affect the phosphorus cycle

  Speeds up uplift
• Name the four stages of the nitrogen cycle

  ~Nitrogen fixation

  ~Ammonification

  ~Nitrification

  ~Dentrification
• Why can't organisms use nitrogen directly from the atmosphere

  N2 is very stable due to strong covalent triple bond
• What happens during atmospheric fixation of nitrogen

  ~High energy of lighting breaks N2 into N

  ~N reacts with oxygen to form No2-

  ~No2- dissolves in water to form NO3-
• Outline the role of bacteria in nitrogen fixation

  ~Mutualistic nitrogen - fixing bacteria in nodules of legumes and free living bacteria in soil

  ~Use the enzyme nitrogenase to reduce gaseous nitrogen into ammonia
• Outline the role of bacteria in ammonification

  ~Saprobionts feed on and decompose organic waste containing nitrogen

  ~NH3 released

  ~NH3 dissolves in water in soil to form NH4+
• Outline the role of bacteria in nitrification

  Two step process carried out by saprobionts in aerobic conditions
• Outline the role of bacteria in denitrification

  Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen
• Explain the significance of nitrogen to living organisms

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

  ~amino acids

  ~NAD/NADP

  ~nucleic acids
• Outline the role of mycorrhizae

  Mutualistic relationship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions
• Give three benefits of planting a different crop on the same field each year

  ~Nitrogen fixing crops

  ~Different crops have different pathogens

  ~Different crops use different proportions of certain ions
• Name the two categories of fertiliser and state the purpose of using fertiliser

  ~Organic = decaying organic matter and animal waste

  ~Inorganic = minerals from rocks, usually containing nitrogen, phosphorus, potassium

  ~To increase gross productivity for higher yield
• At a certain point, using more fertiliser no longer increases crop yield, why

  A factor unrelated to the concentration of mineral ions limits the rate of photosynthesis, so rate of growth cannot increase any further
• Outline two main environmental issues caused by the use of fertilisers

  ~Leaching = nitrates dissolve in rainwater and runoff into water sources

  ~Eutrophication = water source becomes putrid as a result of algal bloom
• What happens during eutrophication

  ~Aquatic plants grown exponentially since nitrate level is no longer a limiting factor

  ~Algal bloom on water surface prevents light from reaching the bottom and plants die

  ~Oxygen levels decreases as population of aerobic saprobionts increases to decay dead matter, so fish die

  ~Anaerobic organisms reproduce exponentially and produce toxic waste which makes water putrid
• How can the risk of eutrophication be reduced

  ~Sewage treatment marshes on farms

  ~Pumping nutrient enriched sediment out of water

  ~Using phosphate free detergent