AQA biology a-level paper 2
actual exam questions with
solved answers.
acetylation of DNA - CORRECT ANSWER✅✅acetyl groups added to histones, so DNA
is less tightly wound round it, making it easier for RNA polymerase and transcriptional
factors to bind, so transcription can occur.
allopatric speciation - CORRECT ANSWER✅✅When populations of a species become
geographically isolated. Gene flow between them ceases (reproductive isolation). the
new environment will trigger a change in the gene pool due to natural selection imposed
on them.
If the populations are relatively small, they may experience a founder effect.
Selection and genetic drift will act differently on these two different genetic
backgrounds, creating genetic differences between the two new species.
codominance - CORRECT ANSWER✅✅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.
define biomass - CORRECT ANSWER✅✅the total mass of organisms in a given area
define community. - CORRECT ANSWER✅✅all the populations of different species
living and interacting in a particular place at the same time.
define niche. - CORRECT ANSWER✅✅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.
define population. - CORRECT ANSWER✅✅a group of individuals of one species that
occupy the same habitat at the same time and are potentially able to interbreed.
describe and explain the role of hormones in osmoregulation. - CORRECT
ANSWER✅✅1.osmoreceptors in hypothalamus detect fall in water potential as they
begin to shrink, causing hypothalamus to produce ADH.
2. ADH goes to posterior pituitary gland, where it is secreted into capillaries.
3. ADH goes from blood to kidneys, where it binds to receptors on the cells of of distil
convoluted tubule and collecting duct.
4. this activates phosphorylase enzyme.
5. this causes vesicles, which contain water channel proteins, to fuse with cell surface
membrane. hence, making it more permeable to water.
, 6. also increases permeability of collecting duct to urea so it passes out and lowers
water potential, so more water can pass out by osmosis.
describe and explain the steps in the light dependent reaction of photosynthesis -
CORRECT ANSWER✅✅1. photoionisation: light reaches chlorophyll in PSII, which is
absorbed by an electron, which becomes excited and moves to a higher energy level.
2. the electron passes to a carrier protein in the thylakoid membrane, and is passed
down a series of carrier molecules called an electron transfer chain.
3. as the electron moves down, energy is lost from the electron and is released as ATP.
4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which
also produces hydrogen and oxygen.
5. the lost electron reaches PSI, which absorbs light energy and boosts another electron
to a higher energy level (excitation).
6. this electron also goes down an electron transport chain.
7. this reaches the final electron acceptor which is a proton. they combine to form H and
reduce NADP to NADPH.
describe and explain the steps in the light independent reaction pf photosynthesis. -
CORRECT ANSWER✅✅1. CO2 diffuses into stroma and combines with ribulose
bisphosphate (RuBP) using the enzyme rubisco.
2. this forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules,
glyercate-3-phosphate (G3P) .
3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for
energy.
4. TP can be converted into useful organic substances.
5. TP can also be reformed into RuBP using ATP.
describe fast twitch fibres - CORRECT ANSWER✅✅contract more rapidly and more
powerful but over a shorter period of time.
adapted for intense exercise
have thicker and more numerous myosin filament, have more glycogen, have more
enzymes to carry out anaerobic respiration, has phosphocreatine.
describe glycolysis in respiration. give net formation. - CORRECT ANSWER✅✅1.
glucose is converted into phosphorylated glucose by 2ATP. this makes it very reactive,
so it splits into 2 triose phosphate (TP).
2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate.
3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+
describe krebs cycle in respiration. give net formation. - CORRECT ANSWER✅✅1.
acetyl co-enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon
citric acid.
2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce. this
forms 5 carbon compound.
3. it is oxidised by 2NADH and FAD, and is decarboxylated.
4. this forms 4 carbon molecule again.
actual exam questions with
solved answers.
acetylation of DNA - CORRECT ANSWER✅✅acetyl groups added to histones, so DNA
is less tightly wound round it, making it easier for RNA polymerase and transcriptional
factors to bind, so transcription can occur.
allopatric speciation - CORRECT ANSWER✅✅When populations of a species become
geographically isolated. Gene flow between them ceases (reproductive isolation). the
new environment will trigger a change in the gene pool due to natural selection imposed
on them.
If the populations are relatively small, they may experience a founder effect.
Selection and genetic drift will act differently on these two different genetic
backgrounds, creating genetic differences between the two new species.
codominance - CORRECT ANSWER✅✅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.
define biomass - CORRECT ANSWER✅✅the total mass of organisms in a given area
define community. - CORRECT ANSWER✅✅all the populations of different species
living and interacting in a particular place at the same time.
define niche. - CORRECT ANSWER✅✅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.
define population. - CORRECT ANSWER✅✅a group of individuals of one species that
occupy the same habitat at the same time and are potentially able to interbreed.
describe and explain the role of hormones in osmoregulation. - CORRECT
ANSWER✅✅1.osmoreceptors in hypothalamus detect fall in water potential as they
begin to shrink, causing hypothalamus to produce ADH.
2. ADH goes to posterior pituitary gland, where it is secreted into capillaries.
3. ADH goes from blood to kidneys, where it binds to receptors on the cells of of distil
convoluted tubule and collecting duct.
4. this activates phosphorylase enzyme.
5. this causes vesicles, which contain water channel proteins, to fuse with cell surface
membrane. hence, making it more permeable to water.
, 6. also increases permeability of collecting duct to urea so it passes out and lowers
water potential, so more water can pass out by osmosis.
describe and explain the steps in the light dependent reaction of photosynthesis -
CORRECT ANSWER✅✅1. photoionisation: light reaches chlorophyll in PSII, which is
absorbed by an electron, which becomes excited and moves to a higher energy level.
2. the electron passes to a carrier protein in the thylakoid membrane, and is passed
down a series of carrier molecules called an electron transfer chain.
3. as the electron moves down, energy is lost from the electron and is released as ATP.
4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which
also produces hydrogen and oxygen.
5. the lost electron reaches PSI, which absorbs light energy and boosts another electron
to a higher energy level (excitation).
6. this electron also goes down an electron transport chain.
7. this reaches the final electron acceptor which is a proton. they combine to form H and
reduce NADP to NADPH.
describe and explain the steps in the light independent reaction pf photosynthesis. -
CORRECT ANSWER✅✅1. CO2 diffuses into stroma and combines with ribulose
bisphosphate (RuBP) using the enzyme rubisco.
2. this forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules,
glyercate-3-phosphate (G3P) .
3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for
energy.
4. TP can be converted into useful organic substances.
5. TP can also be reformed into RuBP using ATP.
describe fast twitch fibres - CORRECT ANSWER✅✅contract more rapidly and more
powerful but over a shorter period of time.
adapted for intense exercise
have thicker and more numerous myosin filament, have more glycogen, have more
enzymes to carry out anaerobic respiration, has phosphocreatine.
describe glycolysis in respiration. give net formation. - CORRECT ANSWER✅✅1.
glucose is converted into phosphorylated glucose by 2ATP. this makes it very reactive,
so it splits into 2 triose phosphate (TP).
2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate.
3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+
describe krebs cycle in respiration. give net formation. - CORRECT ANSWER✅✅1.
acetyl co-enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon
citric acid.
2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce. this
forms 5 carbon compound.
3. it is oxidised by 2NADH and FAD, and is decarboxylated.
4. this forms 4 carbon molecule again.
