AQA biology a-level paper 2 QUESTIONS
AND VERIFED CRRECT ANSWERS
GRADED A+ LATEST 2026-2027 100%
GUARANTEED PASS
what is negative feedback? - CORRECT ANSWER-this is when the change produced by the
system leads to a change in the stimulus detected by the receptor, turning the system off.
what is positive feedback? - CORRECT ANSWER-this is when a deviation from the optimum
causes changes that result in an even greater deviation from the norm
e.g. in neurones, a stimulus leads to an influx of Na+, which increases the membrane
permeability to allow further NA+ to enter.
describe the second messenger model. - CORRECT ANSWER-1. Adrenaline binds to
transmembrane protein receptor in the cell surface membrane of a liver cell.
2. the binding of adrenaline causes the protein to change shape on the inside of the membrane.
3. the change in tertiary structure activates adenyl cyclase, which converts ATP to cAMP.
4. cAMP binds to kinase, changes structure and activates it.
5. this catalyses the conversion of glycogen to glucose, which moves out of the liver cell and into
the blood by facilitated diffusion.
glycogenesis - CORRECT ANSWER-conversion of glucose to glycogen. this is when glucose levels
are abnormally high.
,glycogenolysis - CORRECT ANSWER-breakdown of glycogen to glucose. this is when glucose
levels are abnormally low.
gluconeogenesis - CORRECT ANSWER-production of glucose from sources other than
carbohydrates, such as glycerol or fatty acids. occurs when there's insufficient glycogen.
how does insulin and beta cells in the pancreas affect glucose levels? - CORRECT ANSWER-1. the
beta cells in the pancreas detect a rise in the blood glucose concentration and respond by
secreting insulin into blood.
2. insulin binds to glycoprotein receptors on cells.
3. this causes a change in the tertiary structure of the glucose transport proteins, making them
more permeable to glucose and so allowing more in by facilitated diffusion.
4. activates the enzymes that convert glucose to glycogen and fat.
how does glucagon and alpha cells in the pancreas affect glucose levels? - CORRECT ANSWER-1.
alpha cells detect a fall in blood glucose levels and so secrete glucagon.
2. glucagon attaches to receptors on cell surface membrane of liver cells.
3. this activates enzymes which convert glycogen to glucose.
4. also activates enzymes that convert amino acids to glucose.
does insulin increase or decrease glucose levels? - CORRECT ANSWER-decrease
does glucagon increase or decrease glucose levels? - CORRECT ANSWER-increase
does adrenaline increase or decrease glucose levels? - CORRECT ANSWER-increase
, 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 what is happening to a neurone at resting potential. - CORRECT ANSWER-1. neurone is
polarised
2. Na+ actively transported out of axon
3. K+ actively transported in to axon
4. 3 sodium move out for every 2 potassium in
hence, the outward movement of Na+ is greater than the inward movement of K+. this creates
an electrochemical gradient as the outside is more negative than inside.
5. K+ begins to diffuse back out while Na+ diffuses back in, although most Na+ gates are closed.
describe the processes that occur when an action potential is formed. - CORRECT ANSWER-1.
the energy of a stimulus causes some sodium voltage-gated channels in the axon membrane to
open and so Na+ diffuses into axon, down electrochemical gradient.
2. this triggers a reversal in potential difference across the membrane because Na+ is positively
charged.
3. as more Na+ goes in, more channels open and so even more Na+ goes in.
4. when action potential is +40mV the Na+ channels close and the K+ channels open.
5. K+ diffuses out of axon.
AND VERIFED CRRECT ANSWERS
GRADED A+ LATEST 2026-2027 100%
GUARANTEED PASS
what is negative feedback? - CORRECT ANSWER-this is when the change produced by the
system leads to a change in the stimulus detected by the receptor, turning the system off.
what is positive feedback? - CORRECT ANSWER-this is when a deviation from the optimum
causes changes that result in an even greater deviation from the norm
e.g. in neurones, a stimulus leads to an influx of Na+, which increases the membrane
permeability to allow further NA+ to enter.
describe the second messenger model. - CORRECT ANSWER-1. Adrenaline binds to
transmembrane protein receptor in the cell surface membrane of a liver cell.
2. the binding of adrenaline causes the protein to change shape on the inside of the membrane.
3. the change in tertiary structure activates adenyl cyclase, which converts ATP to cAMP.
4. cAMP binds to kinase, changes structure and activates it.
5. this catalyses the conversion of glycogen to glucose, which moves out of the liver cell and into
the blood by facilitated diffusion.
glycogenesis - CORRECT ANSWER-conversion of glucose to glycogen. this is when glucose levels
are abnormally high.
,glycogenolysis - CORRECT ANSWER-breakdown of glycogen to glucose. this is when glucose
levels are abnormally low.
gluconeogenesis - CORRECT ANSWER-production of glucose from sources other than
carbohydrates, such as glycerol or fatty acids. occurs when there's insufficient glycogen.
how does insulin and beta cells in the pancreas affect glucose levels? - CORRECT ANSWER-1. the
beta cells in the pancreas detect a rise in the blood glucose concentration and respond by
secreting insulin into blood.
2. insulin binds to glycoprotein receptors on cells.
3. this causes a change in the tertiary structure of the glucose transport proteins, making them
more permeable to glucose and so allowing more in by facilitated diffusion.
4. activates the enzymes that convert glucose to glycogen and fat.
how does glucagon and alpha cells in the pancreas affect glucose levels? - CORRECT ANSWER-1.
alpha cells detect a fall in blood glucose levels and so secrete glucagon.
2. glucagon attaches to receptors on cell surface membrane of liver cells.
3. this activates enzymes which convert glycogen to glucose.
4. also activates enzymes that convert amino acids to glucose.
does insulin increase or decrease glucose levels? - CORRECT ANSWER-decrease
does glucagon increase or decrease glucose levels? - CORRECT ANSWER-increase
does adrenaline increase or decrease glucose levels? - CORRECT ANSWER-increase
, 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 what is happening to a neurone at resting potential. - CORRECT ANSWER-1. neurone is
polarised
2. Na+ actively transported out of axon
3. K+ actively transported in to axon
4. 3 sodium move out for every 2 potassium in
hence, the outward movement of Na+ is greater than the inward movement of K+. this creates
an electrochemical gradient as the outside is more negative than inside.
5. K+ begins to diffuse back out while Na+ diffuses back in, although most Na+ gates are closed.
describe the processes that occur when an action potential is formed. - CORRECT ANSWER-1.
the energy of a stimulus causes some sodium voltage-gated channels in the axon membrane to
open and so Na+ diffuses into axon, down electrochemical gradient.
2. this triggers a reversal in potential difference across the membrane because Na+ is positively
charged.
3. as more Na+ goes in, more channels open and so even more Na+ goes in.
4. when action potential is +40mV the Na+ channels close and the K+ channels open.
5. K+ diffuses out of axon.
