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Ecosystem > Nutrient Cycle
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Nutrient Cycles

  • Elements are taken up by producers (plants) / stored as organic matter
  • Passed on across trophic level / consumer digest and absorb food / stored as organic matter
  • Decomposers decay detritus and excretory products / return inorganic ions to environment / taken up by producers
  • Warm temp / higher enzyme activity / faster decomposition

Table 9-14-1: Use of nutrients in plants and animals





Organic substances / lipids /
proteins / ATP / chlorophyll

Organic substances / lipids /
proteins / ATP / chlorophyll


- Amino acid / nucleotide synthesise
- In RNA, DNA, proteins, ATP

- Amino acid / nucleotide synthesise
- In RNA, DNA, proteins, ATP


- In cytochromes / ETC
- Needed for enzymes such as
catalase to work
- Synthesis of chlorophyll

- In cytochromes / ETC
- Needed for enzymes such as
catalase to work
- Part of Hb



Contained in thyroxine (hormone)


Nitrate reductase / reduces nitrates during synthesis of amino acids


Carbon Cycle

  • Producers, consumers, decomposers
    • Add CO2 to the air by respiration
    • Carbon is stored in tissues as organic matter (carbohydrates, lipids, proteins)
    • Carbon is passed along food web by feeding
  • Plants remove CO2 from air by photosynthesis
  • Animals excrete carbon as waste products
  • Decomposers decay detritus and excretory products / add carbon to soil
    • Detrivores digest detritus to small pieces / large surface area
    • Saprophytes digest smaller detritus by
      • Extracellular digestion by secreting enzymes
      • Absorb resulting nutrients across plasma membrane
      • Releases inorganic matter (CO2, H2O, mineral ions) into soil
  • Fossil fuels
    • Combustion releases CO2 into air
    • Fossilisation of carbon atoms in organic compounds in dead remains (plants, animals) and excretory products (animals)
  • Respiring organisms must not die to release stored carbon / differs from other cycles

Respiration, Photosynthesis and CO2

  • Photosynthesis takes up more CO2 than is released by respiration
  • CO2 concentration
    • Higher at night than at daylight; light-dependent reaction cannot take place
    • Peaks at winter time due to high oil consumption; low rate of photosynthesis due to cooler temp, shorter day length, loss of leaves
  • Variation in a graph due to wind mixing CO2 with the surrounding air
    • Graph should show conc over whole area rather over a specific area
  • Rate of photosynthesis and respiration are balanced in a rain forest
    • Forests grow for a long time and have stored lots of carbon in their tissues, other plants have stored carbon as cellulose and lignin

Nitrogen Cycle

  • *processes involved in restoring nitrate conc in soil after cultivation is abandoned

1) Assimilation (→Building up organic molecules)

  • Plants take up NITRATE NO3/AMMONIA NH3 from the soil by active transport
    • Used to synthesis amino acids / synthesise proteins / new cells and tissues
  • Primary consumers feed on plants
    • Proteins are digested into amino acids and absorbed
    • Amino acids synthesise new proteins
  • Nitrogen is passed along the trophic level through the food web

2) Ammonification*

  • Detritus/leaves from plants/excretion from animals/dead animals
  • Broken down by saprotrophs/decomposition
  • Releases ammonia/ammonium ions (from decay)
  • Ammonia dissolves in H2O → NH3 + aq → NH4+

3) Nitrification*

  • Ammonium NH4+ / nitrite NO2-
  • Nitrite / nitrate
  • By aerobic nitrifying bacteria

4) Denitrification

  • Removal of nitrogen from NO2- and NO3- to make N2(g)
  • By anaerobic denitrifying bacteria (NO3- as a RS)

5) Nitrogen Fixation*

  • N2(g) is converted to nitrates by lightning N2(g) + O2 → NO3-
  • By Haber process: N2(g) + H2 → ammonia NH3
    • //used to make fertilisers / added to soil / leakage of ions into river
  • By Nitrogen-fixing bacteria by anaerobic nitrogenase
  • Live free in soil/nodules on the roots of legumes (peas, beans)
  • NH4+ is assimilated by legumes into amino acids
    • //Mutualistic relationship → bacteria get their carbon-containing compounds from the plant while the plant gets nitrates