3.5.4 Nutrient Cycles

nitrogen-containing compounds

amino acids, proteins, DNA, ATP, RNA, urea, chlorphyll

different forms of nitrogen

-nitrogen gas N2

-ammonia NH3

-ammonium ions NH4+

-nitrites NO2-

-nitrates NO3-

the nitrogen cycle 1) ammonification

-protein/amino acids are broken down to ammonia by saprobionts

-ammonia then forms ammonium ions in the soil

the nitrogen cycle 2) nitrification

-first decomposition occurs where saprobionts break down remains of dead material into ammonium ions

-ammonium ions oxidised intro nitrites and nitrites oxidised into nitrates

-occurs by nitrifying bacteria - need aerobic conditions

the nitrogen cycle 3) nitrogen fixation

-converts nitrogen gas into ammonia and is then used to produce amino acids

-occurs by nitrogen fixing bacteria

2 types of nitrogen-fixing bacteria = free-living and mutualistic

the nitrogen cycle 4) denitrification

-converts nitrates into nitrogen gas in the air

-there is an increase in anaerobic denitrifying bacteria when soils become waterlogged and have a low oxygen concentration

saprobionts

decomposers that feed off dead or decaying matter

-secrete digestive enzymes which breaks down cell tissues allowing organism to extract nutrients

the phosphorus cycle

weathering, runoff, assimilation, decomposition, uplift

role of mycorrhizae

-mutualistic relationship between plant and fungi

-fungi increases surface area of plant’s root system

-so plant benefits from increased water and inorganic ion uptake while fungi benefit from receiving sugars and amino acids from plant

benefits of crop rotation

-can grow crops with nitrogen-fixing bacteria

-different crops have different pathogens

-different crops use different minerals

2 types of fertilisers

-natural/organic

-artificial/inorganic

fertilisers increase gross productivity for higher yield

environmental issues with fertilisers

-leaching = nitrates dissolves in rainwater and ‘run off; into water sources

-eutrophication

eutrophication

1) increased fertiliser concentration causes increase in plant growth

2) algal bloom so plants cover surface and block out light so plants under surface die

3) increase in aerobic bacteria/decomposers decreases oxygen levels as they use it for respiration

4) plants also unable to photosynthesise so less oxygen produced so fish die

5) anaerobic organisms reproduce exponentially and produce toxic waste making water putrid