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2024 AQA BIOLOGY A-LEVEL PAPER 2 EXAM WITH CORRECT ANSWERS
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2024 AQA BIOLOGY A-LEVEL PAPER 2 EXAM WITH CORRECT ANSWERS
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2024 AQA BIOLOGY A-LEVELPAPER 2 EXAM WITH CORRECT
ANSWERS
what is autosomal linkage? - CORRECT-ANSWERSwhen 2 or more genes are
carried on the same autosome
describe the formation of glomerular filtrate by ultrafiltration - CORRECT-
ANSWERSblood enters Bowmans capsule. the walls of glomerular capillaries
are made up of epithelial cells. high hydrostatic pressure in glomerulus.
water, glucose and other ions are forced out, forming glomerular filtrate.
leaves behind blood cells and proteins.
how is glucose reabsorbed in the proximal convoluted tubule? - CORRECT-
ANSWERSNa+ actively transported out of cells lining the PCT, into blood
capillaries, which carry them away.
Na+ diffuse down concentration gradient from the PCT into the epithelium by
facilitated diffusion- cotransport.
the molecules in the PCT then diffuse into blood, so they are reabsorbed.
what is the role of the loop of henle? - CORRECT-ANSWERSreabsorbs water
from collecting duct, so it can concentrate urine so that it has a lower water
potential than blood.
how does the loop of henle concentrate urine? - CORRECT-ANSWERS1.
filtrate enters descending limb. water passes out by osmosis and into the
interstitial space as the walls are permeable. Na+ actively transported in.
2. this lowers water potential. lowest water potential is at the bottom of the
hairpin.
3. at the ascending limb, the walls are not permeable to water and so it cant
leave. Na+ is actively transported out into the interstitial space. this creates
a higher water potential.
4. interstitial space between collecting duct and ascending limb has a wp
gradient, from high to low, and so any water left passes out.
explain how the loop of henle acts as a counter current multiplier. -
CORRECT-ANSWERSwater in the loop of henle meets water in the interstitial
space which is of a lower water potential, and so water can pass out by
osmosis for the whole length of the descending tube and collecting duct.
,how does the distil convoluted tubule reabsorb material from the filtrate? -
CORRECT-ANSWERSthe cells lining the DCT have microvilli and mitochondria.
it selects which ions to reabsorb. this controls the pH of the filtrate.
list the steps in osmoregulation - CORRECT-ANSWERS1. Ultrafiltration in
Bowmans capsule
2. reabsorption in the proximal convoluted tubule
3. concentration in the loop of henle distil convoluted tubule
explain the role of hormones in osmoregulation - CORRECT-ANSWERS1.
osmoreceptors in the hypothalamus detect fall in water potential. this causes
water to be lost from osmoreceptors.
2. this makes them produce ADH, which goes to pituitary gland to pass into
blood.
3. ADH goes to kidneys and binds to surface of DCT ad collecting duct,
activating phosphorylase. this causes vesicles to fuse with membrane and
form aquaporins.
4. ADH increases permeability to urea, which passes out and decreases WP
in interstitial space. this causes water to leave by osmosis, so more water is
reabsorbed.
effect of oestrogen on transcription - CORRECT-ANSWERS1. diffuses into
cytoplasm of cell. Binds with complimentary TF.
2. alters tertiary shape of the binding site of TF, so it is activated and can
now bind to genes.
3. TF enters nuclear pore and binds to gene.
4. This stimulates transcription.
describe and explain the steps in the light dependent reaction of
photosynthesis - CORRECT-ANSWERS1. 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-ANSWERS1. 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 glycolysis in respiration. give net formation. - CORRECT-ANSWERS1.
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 links reaction in respiration. give net formation. - CORRECT-
ANSWERS1. pyruvate diffuses into the matrix of mitochondria.
2. pyruvate is oxidised by NAD. CO2 is lost. this forms acetate.
3. acetate and co-enzyme A combine to form acetyl co-enzyme A.
4. NET: CO2, reduced NAD, acetyl co-enzyme A
describe krebs cycle in respiration. give net formation. - CORRECT-
ANSWERS1. 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.
describe oxidative phosphorylation in respiration. - CORRECT-ANSWERS1.
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-ANSWERSthe total mass of organisms in a given
area
what is the 'gross primary production' - CORRECT-ANSWERSthe chemical
energy stored in a plants biomass
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