biology - topic 5 - nitrogen and phosphorus cycle

why do organisms need nitrogen?

metabolic processes, constructing organic molecules (nucleic acids), atmosphere = 78% nitrogen but plants and animals can't use it in that form - bacteria needed to convert it to nitrogen containing compounds

nitrogen cycle

shows how nitrogen is converted into a usable form then passed between living organism and non living environment

nitrogen cycle stages

nitrogen fixation, ammonification, nitrification, denitrification

free living nitrogen fixers

bacteria reduce nitrogen to ammonia, used to manufacture amino acids, nitrogen rich compounds released when they die and decay

mutualistic nitrogen fixers

live in root nodules of leguminous plants, nitrogenase converts nitrogen to ammonium ions using H+ and atp, requires anaerobic conditions, plant uses ammonium ions to make amino acids

ammonification

production of ammonia from organic nitrogen containing compounds by saprobionts, saprobionts feed on faeces and dead organisms releasing ammonia which then forms ammonium ions in the soil

nitrification

ammonium ions in soil oxidised to nitrites to be used by plants, nitrites are oxidised to nitrates - carried out by nitrifying bacteria

denitrification

nitrates are reduced in soil to nitrogen gas. denitrifying bacteria carry out anaerobic respiration and produce nitrogen gas

phosphorous cycle

phosphate ions found in plants, which are then consumed and digested by animals. phosphate ions lost from the animal through excretion or decomposition, so that phosphate ions are found in wastes and remains. deposition of waste material forms rocks. erosion of phosphate rich rocks leads to dissolved phosphate ions in oceans, lakes and soils, which are then absorbed by plants

methods of nitrogen fixation

1. Lightning (producing nitrogen oxides), 2. Haber process (producing ammonia), 3. Fixation by microorganisms.