Nutrient Cycles Unit 4 AQA

NITROGEN CYCLE

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Ammonification

Production of AMMONIA (NH3) from organic ammonium containing compounds, e.g. urea, proteins, nucleic acids, vitamins

By SAPROBIOTIC microorganisms, decomposers e.g. fungi + bacteria                                   - feed on dead organisms ormaterial - release ammonia- form ammonium ions in soil (NH4+)

Nitrogen returns to non-living component of ecosystem.

Nitrification

• Ammonium compounds in soil are changed to nitrogen compounds that can be used by plants
• Plants use light energy to produce organic compounds
• Nitrifying bacteria - e.g. Nitrosomas - need O2 + well areated soils with good draining
• Oxidation reaction + releases energy,E.g. ammonium ions ---> nitrite ions (NO2-) / nitrite ions ---> nitrate ions (NO3-)

Nitrogen Fixation

• N2 gas converted into nitrogen containing compounds - industrially, lightning, microorganisms - able to break down N bond (        )
• Free-living e.g. cyanobacteria (water)
• By mutualistic relationship - SYMBIOTIC bacteria e.g. Rhizobium - found inside root nodules of leguminous plants (e.g. peas, clover, beans)
• Provide the plant with nitrogen compounds (amino acids=proteins) and plant provides carbohydrates to the bacteria.

Denitrification

• Anaerobic process - soils are waterlogged
• Fewer aerobic nitrifying/nitrogen-fixing bacteria
• Increase in denitrifying bacteria - converts soil nitrate into nitrogen gas
• By using nitrates in the soil to carry out respiration and produce N2.

Soils must be kept well-aerated - prevent build up of denitrifying bacteria.

Fertilisers

Used in intensive farming to replenish nutrients

In natural --> removed from soil by plants + returned when plant dies + is decomposed

Increases productivity - plants makes proteins + DNA with nutrients --> required for better growth of plants --> increase SA of leaf --> increases rate of photosyntheis --> increases productivity

OVERUSE of Fertilisers

1) Reduced Species Diversity - favour growth of grasses, nettles ..

2) Leaching - nutrients removed from soil - rain water dissolves soluble nutrients e.g. nitrates + carries them deep into soil  - plant cant reach e.g. organic manure, animal slurry, human sewage, ploughing old grassland, artificial fertilisers

3) Eutrophication --> process by which nutrients build up in bodies of water!!!

EUTROPHICATION

1) Little nitrate in lakes + rivers - limiting factor - keeps in check growth of plants

2) Leaching - nitrate concentration increases

3) Algal growth - algal bloom near surface - water turns green - huge increase of algae

4) Dense layer of algae - block light passing to lower depth so now light is limiting factor

5) Death of plants/algae at lower depths - no photosynthesis

6) Growth of saprobiotic bacteria - increase due to a lot of dead organisms and algae grow exponentially as lack of dead plants - no longer limiting factor

7) Death of fish - saprobiotic bacteria use up O2 - increases demand 4 respiration

8) Lake becomes putrid - Drop in O2 conc - limiting factor - releases N - fish die 

The CARBON CYCLE

Involves 4 processes : photosynthesis, respiration, decomposition and combustion.

Carbon dioxide in the atmosphere and dissolved in oceans...

• CO2 is absorbed by plants - photosynthesis - becomes carbon compounds in plant tissues
• Feeding + Digestion --> Carbon passed on to primary consumers - secondary - tertiary
• All living organisms die and carbon in dead organisms are digested by decomposers e.g. bacteria and fungi - Saprobiontic nutrition
• Carbon is returned to air (and water) when living organisms carry out respiration - produces CO2.
• Dead organic matter that ends up where there are no decomposers e.g. deep oceans - turned into fossil fuels by chemical change (heat + pressure)
• The carbon released by combustion.

Respiration + Photosynthesis cause fluctuations in CO2 concentrations

Photosynthesis - removes CO2 

Respiration - adds CO2

Daily change

• respiration constantly carried out
• photosynthesis - only takes place in daylight
• CO2 conc falls during the day -  being removed by plants
• CO2 conc rises at night 

Yearly change

• most plant life exist in northern hemisphere  - most land is
• most plant growth - summer - more photosynthesis - more energy to grow
• CO2 conc falls during summer  - more being removed by plants
• CO2 conc increases in autumn/winter - fewer plants photosynthesising

Global Warming 

Effects of Global Warming

Effects of Global Warming