Flashcards
Nutrient Cycles
Flashcards do conjunto (21)
- 1Name the general stages in the phosphorus cycle.1. Weathering
2. Runoff
3. Assimilation
4. Decomposition
5. Uplift - 2Why is the phosphorus cycle a slow process?● Phosphorus has no gas phase, so there is no atmospheric cycle.
● Most phosphorus is stored as PO43- inrocks - 3What happens during weathering and runoff?Phosphate compounds from sedimentary
rocks leach into surface water and soil. - 4Explain the significance of phosphorus to living organisms.Plants convert inorganic phosphate into
biological molecules e.g. DNA, ATP, NADP…
Phosphorus is passed to consumers via
feeding - 5What happens during uplift?Sedimentary layers from oceans (formed
by the bodies of aquatic organisms) are
brought up to land over many years. - 6How does mining affect the phosphorus cycle?Speeds up uplift
- 7Name the 4 main stages of the nitrogen cycle.1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification - 8Why can’t organisms use nitrogen directly from the atmosphere?N2
is very stable due to strong covalent
triple bond - 9What happens during atmospheric fixation of nitrogen?1. High energy of lightning breaks N2
into N.
2. N reacts with oxygen to form NO2-
3. NO2-
dissolves in water to form NO3- - 10Outline the role of bacteria in nitrogen fixationMutualistic nitrogen-fixing bacteria in
nodules of legumes & free-living bacteria
in soil.
Use the enzyme nitrogenase to reduce
gaseous nitrogen into ammonia - 11Outline the role of bacteria in ammonification.1. Saprobionts feed on and decompose organic waste containing nitrogen (e.g. urea, proteins, nucleic acids…).
2. NH3 released.
3. NH3 dissolves in water in soil to form
NH4+ - 12Outline the role of bacteria in nitrification2-step process carried out by
saprobionts in aerobic conditions:
2NH4+ + 3O2 → 2NO2- + 2H2O + 4H+
2NO2- + O2 → 2NO3- - 13Outline the role of bacteria in denitrification.Anaerobic denitrifying bacteria convert
soil nitrates back into gaseous nitrogen. - 14Explain the significance of nitrogen to living organisms.Plant roots uptake nitrates via active transport & use them to make biological compounds e.g:
● amino acids
● NAD/ NADP
● nucleic acids - 15Outline the role of mycorrhizae.Mutualistic relationship between plant
and fungus increases surface area of
root system = increases uptake of water
and mineral ions. - 16Give 3 benefits of planting a different crop on the same field each year.● Nitrogen-fixing crops e.g. legumes make soil more fertile by increasing soil nitrate content.
● Different crops have different pathogens.
● Different crops use different proportions of certain ions. - 17Name the 2 categories of fertiliser and state the purpose of using fertiliser● Organic: decaying organic matter & animal waste.
● Inorganic: minerals from rocks, usually containing nitrogen, phosphorus, potassium.
● To increase gross productivity for higher yield. - 18At 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. - 19Outline 2 main environmental issues caused by the use of fertilisers.1. Leaching: nitrates dissolve in rainwater
and ‘runoff’ into water sources.
2. Eutrophication: water source becomes
putrid as a result of algal bloom. - 20What happens during eutrophication?1. Aquatic plants grow exponentially since nitrate level is no longer a limiting factor.
2. Algal bloom on water surface prevents light from reaching the bottom and plants die.
3. Oxygen levels decrease as population of aerobic saprobionts decay dead matter, so aerobic organisms die.
4. Anaerobic organisms reproduce exponentially and produce toxic waste which makes water putrid - 21How can the risk of eutrophication be reduced?● Sewage treatment marshes on farms.
● Pumping nutrient-enriched sediment out of water.
● Using phosphate-free detergent.
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- A level Biology FlashCards sobre Nutrient Cycles, criado por Emily Rose Moorhead em 04-11-2020.
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- Emily Rose Moorhead
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