Recycling within ecosystems

Carbon cycle

  • carbon in form CO2 from air and water is absorbed by plants when they carry out photosynthesis

    • form glucose

    • used to produce other carbon containing macromolecules

  • primary feeders feed on the producers

    • take up carbon containing compounds to make their own biomass

    • carbon containing biomass is then passed up the food chain

  • Decomposers (saprophytes) feed on dead and decaying organic matter

    • assimilate carbon into their biomass

  • all living organisms return carbon to the air or water as carbon dioxide

    • waste product of cellular respiration

  • If DOM ends up in places where there are no decomposers fossil fuels may form

    • the carbon in fossil fuels is released by combustion

  • Marine animal shells may be turned into rock

    • limestone and chalk formed from calcium carbonate in shells

  • the carbon in rock can also be returned to the atmosphere

    • volcanic eruptions

    • physical and chemical weathering

CO2 fluctuations

  • daily fluctuations

    • photosynthesis removes CO2 from the air only during the day

    • respiration occurs all the time

      • so atmospheric CO2 levels are lower during the day

  • seasonal fluctuations

    • photosynthesis rates are higher during the warmer and lighter summer months

      • so CO2 levels are lower on a summer’s day

carbon cycle

Nitrogen cycle

  • 78% of atmosphere

  • inert

  • has to be converted into a form that is useable by living organisms

  • bacterial processes

    • nitrogen fixation

    • nitrification

    • dentrification

    • ammonification

Nitrogen fixation

  • converting atmospheric nitrogen into ammonia

    • nitrogen fixing bacteria

    • contain nitrogenase enzyme

      • azotobacter (free living soil bacteria)

      • rhizobium (root nodules of legumes)

        • symbiotic and mutualistic

  • nitrogen fixation

Nitrification

  • ammonia is converted into nitrogen containing molecules

    • oxidation reaction so only occurs in well aerated soil

    • nitrifying bacteria

      • nitrosomonas converts ammonia to nitrites (NO2-)

      • nitrobacter converts nitrite to nitrates (NO3-)

    • nitrate ions are soluble and easily taken up by plant roots

Denitrification

  • in the absence of oxygen denitrifying bacteria converts nitrates back into nitrogen gas

    • released back into the atmosphere

    • only under anaerobic conditions

      • eg waterlogged soil

    • Pseudomonas denitrificans

      • bacteria use the nitrates as an energy source for respiration

Ammonification

  • decomposers convert nitrogen containing molecules in dead organisms, urine, and faeces into ammonia

    • nitrifying bacteria will then use the ammonia as an energy source producing nitrites and nitrates