AQA BIOLOGY A-LEVEL PAPER 2 QUESTION PAPER AND
WELL DEFINED MARKING SCHEME 2025 (7402/2)NEWEST
EXAM 2025
describe oxidative phosphorylation in respiration. - CORRECT ANSWERS-1. reduced coenzyme
passes its H to a carrier protein in the ETC. this splits into a proton and electron.
2. the protons pass through the space between inner and outer mitochondrial membrane.
3. electrons pass through proteins on ETC.
4. protons return back via ATP synthase in the membrane, producing ATP.
5. the protons and electrons recombine to form H, which combines with O to form water.
6. oxygen is the last electron acceptor in the ETC.
define biomass - CORRECT ANSWERS-the total mass of organisms in a given area
what is the 'gross primary production' - CORRECT ANSWERS-the chemical energy stored in a
plants biomass
what is the 'net primary production' - CORRECT ANSWERS-the chemical energy stores in a
plants biomass after respiratory losses have been considered. this energy is available to consumers.
how can you calculate the net primary production? - CORRECT ANSWERS-NPP = GPP - R
why is converting sunlight energy into biomass in producers inefficient? - CORRECT
ANSWERS-some light isn't the correct wavelength to be absorbed
some light doesnt hit chloroplast
some light is converted into heat energy
some light energy is reflected
describe the nitrogen cycle. - CORRECT ANSWERS-fixation:
atmospheric nitrogen can be fixed by rhizbium bacteria.
,if struck by lightning, it becomes reactive and combines with oxygen to form NO.
ammonification:
saprobionts feed on organic matter and release ammonia, which then forms ammonium ions in the soil.
nitrification:
nitrifying bacteria convert ammonium ions into nitrite ions and then to nirate ions.
denitrification:
anaerobic denitrifying bacteria convert soil nitrates into gaseous nitrogen.
homeostasis - CORRECT ANSWERS-the maintenance of an internal environment within
restricted limits in organisms. all cells are in an environment that meets their requirements and allows
them to function normally despite external changes.
why is homeostasis important? - CORRECT ANSWERS-1. the enzymes that control biochemical
reactions in cells are sensitive to change e.g. in pH or temperature, which can cause them to denature.
homeostasis allows enzyme controlled reactions to take place at a suitable rate.
2. homeostasis allows a constant blood glucose concentration to ensure a constant water potential, so
cells don't shrink or burst.
3. homeostasis allows organisms to be more independent of external changes.
list the parts of control mechanisms in homeostasis. - CORRECT ANSWERS-1. optimum
temperature
2. receptor- detects any deviation from the optimum temperature
3. coordinator- info from receptor to effector
4. effector- often a muscle/gland, brings about change to return the system to optimum level
5. feedback mechanism
, why does using nitrogen containing fertilisers result in reduced species diversity? - CORRECT
ANSWERS-nitrogen rich soils favour the growth of grasses etc., which can outcompete other
species, which die as a result.
what is "leaching"? - CORRECT ANSWERS-the process by which nutrients are removed from
the soil. rainwater will dissolve soluble nutrients and carry them deep into the soil, away from plant
roots. the leached ions can reach rivers that drain into lakes.
what is "eutrophication"? - CORRECT ANSWERS-the process by which nutrient concentrations
increase in bodies of water, often as a result of leaching. may result in algael bloom, which blocks
sunlight from reaching plants underneath, causing them to die.
define population. - CORRECT ANSWERS-a group of individuals of one species that occupy the
same habitat at the same time and are potentially able to interbreed.
define community. - CORRECT ANSWERS-all the populations of different species living and
interacting in a particular place at the same time.
define niche. - CORRECT ANSWERS-the role and position a species has in its environment;
how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche
includes all of its interactions with the biotic and abiotic factors of its environment.
codominance - CORRECT ANSWERS-occurs where heterozygote has a phenotype that is
different from both homozygotes.
neither allele is dominant over the other; they both contribute equally to the phenotype.
sex linkage - CORRECT ANSWERS-alleles carried on the X chromosome.
why are sex linked diseases more common in males than females? - CORRECT ANSWERS-
because males only have one X chromosome, and so if there is a recessive allele there, then there will be
no dominant allele on Y chromosome to "hide" it.
WELL DEFINED MARKING SCHEME 2025 (7402/2)NEWEST
EXAM 2025
describe oxidative phosphorylation in respiration. - CORRECT ANSWERS-1. reduced coenzyme
passes its H to a carrier protein in the ETC. this splits into a proton and electron.
2. the protons pass through the space between inner and outer mitochondrial membrane.
3. electrons pass through proteins on ETC.
4. protons return back via ATP synthase in the membrane, producing ATP.
5. the protons and electrons recombine to form H, which combines with O to form water.
6. oxygen is the last electron acceptor in the ETC.
define biomass - CORRECT ANSWERS-the total mass of organisms in a given area
what is the 'gross primary production' - CORRECT ANSWERS-the chemical energy stored in a
plants biomass
what is the 'net primary production' - CORRECT ANSWERS-the chemical energy stores in a
plants biomass after respiratory losses have been considered. this energy is available to consumers.
how can you calculate the net primary production? - CORRECT ANSWERS-NPP = GPP - R
why is converting sunlight energy into biomass in producers inefficient? - CORRECT
ANSWERS-some light isn't the correct wavelength to be absorbed
some light doesnt hit chloroplast
some light is converted into heat energy
some light energy is reflected
describe the nitrogen cycle. - CORRECT ANSWERS-fixation:
atmospheric nitrogen can be fixed by rhizbium bacteria.
,if struck by lightning, it becomes reactive and combines with oxygen to form NO.
ammonification:
saprobionts feed on organic matter and release ammonia, which then forms ammonium ions in the soil.
nitrification:
nitrifying bacteria convert ammonium ions into nitrite ions and then to nirate ions.
denitrification:
anaerobic denitrifying bacteria convert soil nitrates into gaseous nitrogen.
homeostasis - CORRECT ANSWERS-the maintenance of an internal environment within
restricted limits in organisms. all cells are in an environment that meets their requirements and allows
them to function normally despite external changes.
why is homeostasis important? - CORRECT ANSWERS-1. the enzymes that control biochemical
reactions in cells are sensitive to change e.g. in pH or temperature, which can cause them to denature.
homeostasis allows enzyme controlled reactions to take place at a suitable rate.
2. homeostasis allows a constant blood glucose concentration to ensure a constant water potential, so
cells don't shrink or burst.
3. homeostasis allows organisms to be more independent of external changes.
list the parts of control mechanisms in homeostasis. - CORRECT ANSWERS-1. optimum
temperature
2. receptor- detects any deviation from the optimum temperature
3. coordinator- info from receptor to effector
4. effector- often a muscle/gland, brings about change to return the system to optimum level
5. feedback mechanism
, why does using nitrogen containing fertilisers result in reduced species diversity? - CORRECT
ANSWERS-nitrogen rich soils favour the growth of grasses etc., which can outcompete other
species, which die as a result.
what is "leaching"? - CORRECT ANSWERS-the process by which nutrients are removed from
the soil. rainwater will dissolve soluble nutrients and carry them deep into the soil, away from plant
roots. the leached ions can reach rivers that drain into lakes.
what is "eutrophication"? - CORRECT ANSWERS-the process by which nutrient concentrations
increase in bodies of water, often as a result of leaching. may result in algael bloom, which blocks
sunlight from reaching plants underneath, causing them to die.
define population. - CORRECT ANSWERS-a group of individuals of one species that occupy the
same habitat at the same time and are potentially able to interbreed.
define community. - CORRECT ANSWERS-all the populations of different species living and
interacting in a particular place at the same time.
define niche. - CORRECT ANSWERS-the role and position a species has in its environment;
how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche
includes all of its interactions with the biotic and abiotic factors of its environment.
codominance - CORRECT ANSWERS-occurs where heterozygote has a phenotype that is
different from both homozygotes.
neither allele is dominant over the other; they both contribute equally to the phenotype.
sex linkage - CORRECT ANSWERS-alleles carried on the X chromosome.
why are sex linked diseases more common in males than females? - CORRECT ANSWERS-
because males only have one X chromosome, and so if there is a recessive allele there, then there will be
no dominant allele on Y chromosome to "hide" it.
