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5.4 nutrient cycles - Coggle Diagram
5.4 nutrient cycles
lesson 2: nitrogen cycle (detailed)
1) inert nitrogen gas in the atmosphere
2) nitrogen fixation by nitrogen fixing bacteria in the soil or in root nodules
3) proteins in nitrogen fixing bacteria
4) ammonification/ release of ammonia by nitrogen fixing bacteria
5) ammonium ions in the soil
6) nitrification by nitrifying bacteria - oxidation of ammonium to nitrite ions and then the oxidation of nitrite ions to nitrate ions
7) nitrate ions are absorbed and assimilated into proteins in plants
8) consumers eat the plants - proteins in animals
9) egestion and excretion (face and urine) and death :
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lightning causes reaction between oxygen and nitrogen in the air resulting in nitrate ions
3) proteins in plants (legumes)
4) death
5) proteins in dead organic materials/urea in urine
6) decomposition and ammonification by saprobints
nitrogen fixation
nitrogen gas converted to nitrogen containing compounds
occurs through nitrogen fixing bacteria or when lightning causes reaction between oxygen and nitrogen
ammonia only released to the soil when bacteria die and decompose
free-living nitrogen fixing bacteria
convert gaseous nitrogen to ammonia which they then use to make amino acids
found in the soil - nitrogen rich compounds released when they die
mutualistic nitrogen fixing bacteria
live in the nodules on the roots of plants
obtain carbohydrates from the plant and plant requires amino acids from the bacteria
decomposition and ammonification
ammonification = production of ammonia from organic nitrogen-containing compounds e.g. proteins/nucleic acids
saprobiontic microorganisms feed on faeces and dead organisms materials, releasing ammonia which forms ammonium ions in the soil - nitrogen returns to the non-living components of the ecosystem
nitrification
conversion of ammonium ions to nitrate ions
oxidation reaction (releases energy)
carried out by nitrifying bacteria in two stages: 1) oxidation of ammonium to nitrite ions, 2) oxidation of nitrite ions to nitrate ions
oxygen is required (exist in a well aerated environment)
denitrification
conversion/reduction of soil nitrates into gaseous nitrogen
caused by anaerobic denitrifying bacteria
reduces the availability of nitrogen-containing compounds In plants
lesson 1: nitrogen cycle (intro)
role of saprobionts (decomposers)
e.g. fungi and bacteria
feed on dead or organic material
carry out extracellular digestion
returns nutrients back to the soil
nitrogen
component of
ATP
nucleic acids (DNA and RNA)
proteins/amino acids
but nitrogen in the atmosphere is chemically inert and not able to be used by most organisms
plants
plants must secure their nitrogen in 'fixed' form i.e. incorporated in components such as: nitrate ions, ammonia
basic pattern of nutrient cycling
nutrient taken up by producers
assimilated into complex organic molecule
passes into consumers through food chains and along/up trophic levels
released during breakdown of dead organic matter and saprobiontic microorganisms
simple form of nutrient returned to non-living state
lesson 3: fungi and fertilisers
mycorrhizae
mycorrhizae are associations between plant roots and fungi
mutualistic relationship - of mutual benefit, plant gets water and mineral ions from fungi and fungi gets carbohydrates from plant
why are mycorrhizae beneficial to the plant
the fungi act like extensions of the plants root system so vastly increase the total surface area for the absorption of water and mineral ions
act like a sponge so holds water and mineral ions in the region of the roots - this enables the plant to better resist draught and take up inorganic ions more readily
why are mychorrizae beneficial to the fungi
fungi receives organic compounds such as sugars and amino acids from the plant
farming issues:
when crops and livestock are removed from fields the amount of nitrogen in the ecosystem is reduced
plants
less nitrogen stored in proteins/legumes
less dead organic matter to be broken down by saprobiants
less ammonia released to soil via ammonification - less ammonia absorbed by plants
animals
less nitrogen stored in proteins
less excretion and egestion (faeces and urine)
less dead organic matter - less decomposition and ammonifcation - less ammonia released to the soil
ways farmers can deal with this:
organic fertilisers (e.g. faeces)
inorganic fertilisers (add mineral ions to the soil)
compost - add mineral ions back to the soil once they decompose
rotate crop with nitrogen fixing crop (e.g. legumes -peas) which can be ploughed into the soil after growing to decompose
lesson 4: fertiliser issues
why does crop rotation increase the yield
ammonium ions oxidised by nitrifying bacteria to nitrate ions; nitrite ions oxidised to nitrate ions
more nitrates in the soil, more nitrates absorbed by plants and used to make proteins/amino acids/ DNA for growth
environmental consequences of nitrogen containing fertilisers
1) reduces species diversity
nitrogen rich soil favour the growth of grasses, nettles and rapidly growing species
these outcompete other species - leads to low diversity
wildflower meadows only occur where N levels are low enough to allow other species to compete
2) leaching
rain water dissolves soluble nutrients e.g. nitrate ions and carries them away - removes them from the soil
this causes them to be carried into streams/rivers and fresh water lakes which results in eutrophication
eutrophication
1) leaching causes mineral ions such as nitrates to enter stream/river
2) this causes rapid growth of algae at the surface of the water - algal bloom
3) the algae blocks sunlight which prevents plants from below the surface from photosynthesising - causing them to die
4) dead organic material from plants builds up
5) saprobiants feed off dead organic material (decomposition and ammonification) population of saprobiants increases - saprobiants use oxygen
6) larger organisms such as fish die as plants are not photosynthesising - not enough oxygen produced - organisms unable to aerobically respire
field/greenhouse crop experiments
crops grown in controlled conditions to test the effect of fertiliser/mycorrhizae/soil pH
soil may be sterilised before the experiment to remove saprobiants/mycorrhizae/nitrogen fixing bacteria
evaluating field experiments
may only use one species of plant
may be done in controlled conditions but actual crops will be in different conditions
may be done in the field where soil cannot be sterilised (unable to control extraneous variables)
lesson 5: phosphorus cycle
plants and animals require phosphorus for the production of:
phospholipids
ATP
nucleic acids
phosphorus is necessary for growth and repair
no phosphorus is found in the atmosphere: mainly found in phosphate ions in sedimentary rocks
cycle
phosphorus in rocks is released into the soil and into water sources in the form of phosphate ions via erosion/weathering
Phosphate ions are taken up from the soil by plants, or absorbed from water by algae
Phosphate ions are transferred to consumers during feeding
Phosphate ions in waste products are released into the soil or water via excretion
phosphate ions from waste and remain including bones guano and shells are released into soil and water via decomposition and erosion
phosphate ions in the soil and water may become trapped in rocks again due to sedimentation