3.5.4 - NUTRIENT CYCLES Flashcards
freshwater marsh soils are normally waterlogged. this creates anaerobic conditions.
use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions. (2)
- less nitrification OR less nitrifying bacteria OR nitrifying bacteria require aerobic conditions
- less oxidation of ammonium to nitrite to nitrate
suggest one way in which an increase in the uptake of phosphate could increase plant growth (1)
used to produce DNA/ATP/phospholipids in cells
arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate.
suggest one way in which AMF may benefit from their association with plants (1)
- amino acids
- carbohydrates
- vitamins
upwelling is a process where water moves from deeper parts of the sea to the surface. this water contains a lot of nutrients from the remains of dead organisms.
describe the role of microorganisms in producing nitrates from the remains of dead organisms (3)
- saprobiotic microorganisms/bacteria/saprobionts breakdown remains into ammonia/ammonium
- ammonium ions converted into nitrite then into nitrate
- by nitrifying bacteria/nitrification
upwelling is a process where water moves from deeper parts of the sea to the surface. this water contains a lot of nutrients from the remains of dead organisms.
upwelling often results in high primary production in coastal waters.
explain why some of the mostly productive fishing areas are found in coastal waters (2)
- nitrate/phosphate absorbed by algae/plants/producers
- more producers/food so more fish move to area/reproduce
nitrate from fertiliser applied to crops may enter ponds and lakes.
explain how nitrate may cause the death of fish in fresh water (5)
- growth of algae creates algal bloom which blocks light
- reduced photosynthesis so submerged plants die
- saprobiotic microorganisms/bacteria
- aerobically respire
- so less oxygen for fish to respire
nitrates and phosphates provide a source of nitrogen and phosphorus for cells.
give a biological molecule that contains: (2)
- nitrogen
- phosphorous
- amino acid/protein/enzyme/DNA/RNA/ATP/NAD
- DNA/RNA/ATP
describe the role of microorganisms in producing nitrates from the remains of dead organisms (3)
- saprobiotic bacteria break down remains into ammonia
- ammonia converted into nitrite then into nitrate
- by nitrifying bacteria
describe the role of saprobionts in the nitrogen cycle (2)
- they decompose proteins/DNA/RNA/urea
- producing/releasing ammonia/ammonium ions
denitrification requires anaerobic conditions. ploughing aerates the soil. explain how ploughing would affect the fertility of the soil (2)
- fertility increased as) more nitrate formed / less nitrate removed/broken down
- less/no denitrification/denitrifying bacteria
one farming practice used to maintain high crop yields is crop rotation. this involves growing a different crop each year in the same field.
suggest two ways in which crop rotation may lead to high crop yields. (2)
- grow crops with nitrogen-fixing (bacteria);
- different crops use different minerals / salts / nutrients / ions
- different crops have different pests / pathogens / diseases.
leguminous crop plants have nitrogen-fixing bacteria in nodules on their roots. on soils with a low concentration of nitrate ions, leguminous crops often grow better than other types of crop.
explain why. (2)
- they convert nitrogen to ammonia
- produce protein/amino acids/DNA/RNA
applying very high concentrations of fertiliser to the soil can reduce plant growth.
use your knowledge of water potential to explain why. (2)
- soil has lower water potential
- osmosis from plant
after harvesting, the remains of crop plants are often ploughed into the soil.
explain how microorganisms in the soil produce a source of nitrates from these remains (5)
- protein/amino acids/DNA into ammonium compounds
- by saprobionts
- ammonium/ammonia into nitrite
- nitrite into nitrate
- by nitrifying bacteria
describe how the action of microorganisms in the soil produces a source of nitrates for crop plants (5)
- protein/amino acids/DNA into ammonium compounds
- by saprobionts
- ammonium/ammonia into nitrite
- nitrite into nitrate
- by nitrifying bacteria
- nitrogen to ammonia
name the process by which some bacteria oxidise ammonia to nitrate (1)
nitrification
reeds have hollow, air-filled tissue in their stems which supplies oxygen to their roots.
explain how this enables the roots to take up nitrogen-containing substances (2)
- uptake by roots involves active transport
- requires ATP/aerobic respiration
an increase in nitrate concentration in the water entering the lake could affect algae and fish in the lake.
explain how (3)
- increase in algae blocks light
- decomposers/saprobionts break down dead plant material
- saprobionts use up oxygen in respiration causing fish to die
the over-application of fertiliser increases the rate of leaching.
explain the consequences of leaching of fertiliser into ponds and lakes (3)
- increases algae/algal bloom causes light to be blocked out
- plants cannot photosynthesise so they die
- saprobionts breakdown dead organisms, using up oxygen
nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. the reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced.
nitrogen gas is the usual substrate for this enzyme.
name the product (1)
ammonia/ammonium
describe the role of bacteria in making the nitrogen in dead leaves available to growing plants (5)
- saprobionts
- break down DNA/proteins
- ammonia produced
- ammonia converted to nitrite to nitrate
- nitrifying bacteria
- oxidation
describe how nitrogen-containing substances get into a lake (1)
dissolve/leaching
nitrifying bacteria are one kind of bacteria that are important in the nitrogen cycle, nitrogen-fixing bacteria are another kind.
describe the part played by nitrogen-fixing bacteria in the nitrogen cycle (2)
- convert nitrogen (gas) into ammonia
- they add usable nitrogen to an ecosystem
name the type of bacteria which convert nitrogen in the air into ammonium compounds (1)
nitrogen-fixing bacteria
name the type of bacteria which convert nitrites into nitrates (1)
nitrifying bacteria
purification ponds can be used in warm climates to break down sewage. the ponds are around 1m deep and contain bacteria and green algae.
explain the advantage of having both algae and bacteria in a purification pond (4)
- breakdown of organic matter by enzymes from bacteria
- nitrates/ammonia used by algae to make amino acids/proteins
- algae photosynthesise
- bacterial respiration uses O2
- respiration allows for reproduction of bacteria
purification ponds can be used in warm climates to break down sewage. the ponds are around 1m deep and contain bacteria and green algae.
purification ponds only work efficiently when they are shallow and warm.
explain why (4)
- sufficient light penetration for photosynthesis of algae
- warm leads to faster enzyme activity
- faster bacterial respiration
- faster photosynthesis
- increased reproduction of bacteria
explain how a high nitrate concentration increases the growth of algae (2)
- more proteins/amino acids/DNA
- increased cell division/no of cells formed
suggest how increased growth of algae could lead to death of the submerged plants (2)
- reduced light/shading
- less photosynthesis
explain how the decay of dead plants results in reduced oxygen concentration and increased nitrate production (6)
- saprobionts feed on dead matter
- respiration uses up oxygen
- converts proteins to amino acids
- then to ammonium compounds
- nitrifying bacteria convert ammonium compounds
- via nitrates
describe how the reduced oxygen concentration of the water will change the composition of the communities in the river (2)
- lower species diversity/number of species
- species requiring high oxygen die out
