nutrient cycles Flashcards
phosphorus cycle
released into soil + water - weathering as phosphate ions
- phosphate compounds from sedimentary rocks leach
phosphate ions taken up by plants - roots or absorbed by water by algae - transferred to consumers by feeding
phosphate ions - waste products and dead organisms - release into soil or water
- saprobiont decomposition
phospholipid+3H2O breaks ester bond - glycerol, fatty acid and a phosphate
nitrogen cycle
nitrogen fixation
- atmospheric nitrogen gas converted nitrogen-containing compounds
- nitrogen-fixing bacteria (nitrogen to ammonia)
forming ammonium ions -> plants
ammonification
- proteins and nucleic acids in dead organic matter converted to ammonium ions by saprobionts
nitrification
- ammonium ions converted (oxidised) into nitrite ions by nitrosomonas
- nitrite ions converted to nitrate ions by nitrobacter
- bacteria are chemo-autotrophs
- bacteria outcompete with plants for ammonium ions - plants only have access to nitrate ions
- faster in aerobic conditions
denitrification
- nitrate ions reduced to nitrogen gas by denitrifying bacteria - faster in anaerobic
name the general stages in the phosphorus cycle
weathering
runoff
assimilation
decomposition
uplift
why is the phosphorus cycle a slow process
phosphorus has no gas phase, so there is no atmospheric cycle
most phosphorus is stored as PO4 3- in rocks
explain the significance of phosphorus to living organisms
plants convert inorganic phosphate into biological molecules eg DNA, ATP, 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 the 4 main stages of the nitrogen cycle
nitrogen fixing
ammonification
nitrification
denitrification
why cant 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 -
NO 2 - 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 nitrogenase to reduce gaseous nitrogen into ammonia
outline the role of bacteria in ammonification
saprobiots feed on and decompose organic waste containing nitrogen (eg proteins, urea)
NH3 released
NH3 dissolves in water in the soil to form NH4+
outline the role of bacteria in nitrification
2-step process carried out by saprobionts in aerobic conditions
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
- amino acids
- NAD / NADP
- 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 containing nitrogen, phosphorus, potassium
used 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 futher
outline 2 main environmental issues caused by the use of fertilisers
leaching - nitrates dissolves in rainwater and runoff into water sources
eutrophication - water source becomes putrid as a result of algal bloom
what happens during eutrophication
• Starts with leaching of N-rich and P-rich chemicals (eg. fertilisers and sewage) into water bodies such as ponds, lakes, rivers and seas. (ie, increased availability to make proteins and nucleic acids).
• Algae grow rapidly (increase in population size of algae). Increased competition for resources, and increased respiration.
• Therefore, concentration of oxygen in water decreases.
• Animals etc die, therefore more decomposition by bacteria and fungi / saprobionts leading to further decrease in oxygen concentration.
• Leading to more death and further depletion of oxygen…
• Eventually leads to everything in the pond dying.
how can the risk of eutrophication be reduced
sewage treatment marshes on farms
pumping nutrient-enriched sediment out of water
using phosphate-free detergent
using less fertiliser in farming land so less is leached by rainfall ect
increasing aeration of water bodies eg cleaning ponds and lakes regularly - less eutrophication in running water than in stagnant water
