Nutrient Cycles

  • Created by: Rachelezy
  • Created on: 03-02-20 10:53

Nitrogen Cycle

Nitogen Fixation:

  • Atmospheric nitrogen gas converted into N-containing compounds
  • Can be through N2 -> NH3 or NH4+    N2 -lightening--> NO3- (nitrate) and industrial use (Haber Process)


  • Breaks down organic nitrogen into ammonia or ammonium compounds. e.g. nucleic acids/amino acids
  • Broken down by saprobiotic organisms (decomposers)


  • Carried out by nitrifying bacteria (needs aerated conditions)
  • Oxidation reaction


  • Nitrates in soil are converted into nitrogen gas by denitrifying bacteria - occurs under anaerobic conditions (e.g. waterlogged soil)
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Phosphorous Cycle

  • Phosphate ions are released from rock on land (by chemical weathering) and washed into soils
  • They are absorbed by plant roots by active transport
  • Used to produce ATP and nucleic acid to plant cells

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Saprobionts + Mycorrhizae


  • Known as true decomposers
  • Secret a range of enzymes and can hydrolyse multiple different biological molecules

Organisms which secrete digestive enzymes onto the dead remains of other organisms:

  • They then digest te biological molecules in these dead remains
  • They then absorb some of the products of this digestion (ammonium, phosphate ions etc.)


  • Receive sugars and amino acids (increases water uptake)
  • Absorbs water and more minerals
  • Fungi made up of long strands called hyphae that connect to plant roots (fungi obtain organic compounds, such as glucose, from the plant)
  • All increases the total surface area for absorption of water and minerals
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Environmental Challenges


  • 1 - Nitrates are leached from fertilised fields that stimulates the growth of algae in rivers and ponds
  • 2 - Algae blocks light from reaching the plants below
  • 3 - Plants die due to insufficient photosynthesis able to take place
  • 4 - Bacteria feed on dead plant matter 
  • 5 - Increased bacteria reduces the oxygen concentration in the water
  • 6 - fish ie due to insufficient levels of dissolved oxygen

higher nitrae concentration results in an increased growth of algae due to an increase in DNA and cell division

Leaching - Water soluble compounds in soil washed away and often washed into nearby rivers and ponds. If nitrogen fertiliser is leached into water ways it can cause eutrophication

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Advantages - *Cheap *Improves soil structure *Can contain valuable macronutrients *Less soluble, inorganic ions released more slowely (prevents leaching)

Disadvantages - *Less concentrated (more is needed) *Smelly *Can contain unwanted substances such as weeds, seeds and fungal spores


Advantages - *Concentrated source of macronutrients can be appled in small amounts *Lacks strong smell *Easier to evenly spread

Disadvantages - *Lacks micro-nutrients *Expensive *Leads to eutrophication as nitrate and ammonium ions are very soluble so can leach out

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