nutrient cycles Flashcards
name the general stages in the phosphorus cycle
- weathering
- runoff
- assimilation
- decomposition
- uplift
why is the phosphorous cycle a slow process?
- phosphorous has no gas phase, so there is no atmospheric cycle
- most phosphorous is stored as PO4 3- in rocks
what happens during weathering and runoff
phosphate compounds from sedimentary rocks leach into surface of water and soil
explain the significance of phosphorus to living organisms
- plants convert inorganic phosphate into biological molecules like DNA, ATP and NADP
- phosphorus is passed to consumers via feeding
what happens during uplift
sedimentary layers from oceans (formed by the bodies of aquatic organisms) are brought up to land over many years
how does mining affect the phosphorus cycle
speeds up uplift
name 4 main stages of the nitrogen cycle
- nitrogen fixation
- ammonification
- nitrification
- denitrification
why can’t organisms use nitrogen directly from the atmosphere
N2 is very stable due to strong covalent triple bond
what happens during atmospheric fixation of nitrogen
- high energy of lightning breaks N2 into N
- N reacts with oxygen to form NO2 -
- NO2 - dissolves in water to form NO3 -
outline the role of bacteria in nitrogen fixation
- mutualistic nitrogen-fixing bacteria in nodules of legumes and free living bacteria in soil
- use the enzyme nitrogenous to reduce gaseous nitrogen into ammonia
outline the role of bacteria ammonification
- saprobionts feed on and decompose organic waste containing nitrogen
- NH3 released
- NH3 dissolves in water in soil to form NH4+
outline the role of bacteria in nitrification
- 2 step process carried out by saprobionts in aerobic conditions:2NH4+ + 3O2 → 2NO2- + 2H2O + 4H+2NO2- + O2 → 2NO3-
outline the role of bacteria in denitrification
anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen
explain the significance of nitrogen to living organisms
plant roots uptake nitrates via active transport and use them to make biological compounds like amino acids, NAD and nucleic acids
outline the role of mycorrhizae
mutualistic relationship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions
give 3 benefits of planting a different crop on the same field each year
- nitrogen fixing crops eg legumes make soil more fertile by increasing soil nitrate content
- different crops have different pathogens
- different crops use different proportions of certain ions
name the 2 categories of fertiliser and state the purpose of using fertiliser
- organic: decaying organic matter and animal waste
- inorganic: minerals from rocks, usually contain nitrogen, phosphorous and potassium
- to increase gross productivity for higher yield
at a certain point, using more fertiliser no longer increases crop yield why
a factor unrelated to the concentration of mineral ions limits the rate of photosynthesis so rate of growth cannot increase any further
outline 2 main environmental issues caused by the use of fertilisers
- leaching: nitrates dissolve in rainwater and runoff into water sources
- eutrophication: water source becomes putrid as a result of algal bloom
outline what happens during eutrophication
- aquatic plants grow exponentially since nitrate level is no longer a limiting factor
- algal bloom on water surface prevents light from reaching the bottom and plants die
- oxygen levels decrease as population of aerobic saporbionts increase to decay the dead matter, so fish die
- anaerobic organisms reproduce exponentially and produce toxic waste which makes water putrid
how can the risk of eutrophication be reduced
- sewage treatment marshes on farms
- pumping nutrient enriched sediment out of water
- using phosphate free detergent
