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2024 AQA A-LEVEL BIOLOGY EXAM WITH CORRECT ANSWERS
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2024 AQA A-LEVEL BIOLOGY EXAM WITH CORRECT ANSWERS
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2024 AQA A-LEVEL BIOLOGY EXAMWITH CORRECT ANSWERS
Glucose is absorbed from the lumen of the small intestine into epithelial
cells. Explain how the transport of sodium ions is involved in the absorption
of glucose by epithelial cells. (5 marks) [Unit 1, June 16] - CORRECT-
ANSWERS1. Na+ ions leave epithelial cell and enter blood;
2. (Transport out is by) active transport / pump / via carrier protein using
ATP;
3. So, Na+ conc. in cell is lower than in lumen (of gut);
4. Sodium/Na+ ions enter by FACILITATED diffusion;
5. Glucose absorbed with Na+ ions against their concentration/diffusion
gradient / glucose absorbed down an electrochemical gradient;
Explain how water enters a plant root from the soil and travels through to the
endodermis. (5) - CORRECT-ANSWERS1. Water enters root hair cells;
2. By osmosis;
3. Because active uptake of mineral ions has crated a water potential
gradient;
4. Water moves through cortex;
5. Down water potential gradient;
6. Through cell vacuoles and cytoplasms (symplastic pathway);
7. And through apoplastic pathway (cell walls);
Root pressure is a force that is partly responsible for the movement of water
through xylem in stems. Explain how the active transport of mineral ions into
the xylem vessels in the roots results in water entering these vessels and
then being moved up the xylem tissue. (5) - CORRECT-ANSWERS1. Entry of
ions leads to a reduced water potential;
2. Water potential established between xylem and surrounding cells;
3. Plasma membranes of surrounding cells are partially permeable;
4. Water enters xylem by osmosis;
5. Volume of water in xylem increases;
6. Cannot move back due to gradient;
7. Pressure in xylem increases and forces water upwards.
The presence of an air bubble in a xylem vessel in the stem blocks the
movement through that vessel. Use the cohesion-tension theory to explain
why. (4) - CORRECT-ANSWERS1.Evaporation from leaves (transpiration);
2. Water in xylem under tension (pulled up);
,3. Because water molecules cohere (stick together) (because of hydrogen
bonds);
4. So water travels in a single column;
5. A water bubble would break the column;
Describe two features you would expect in the leaves of a tree adapted to a
dry environment. Explain how each feature helps the tree's survival. (6) -
CORRECT-ANSWERSSunken stomata;
water evaporation into pit creates local humidity;
increased humidity reduces gradient for water evaporation;
close arrangement of stomata;
diffusion shells of individual stomata overlap;
interferes with water diffusion and slows evaporation;
restriction of stomata to lower side of leaf;
rate of air movement below leaf less/ heating effect of sun less;
gradient for water evaporation reduced/ water molecules have less kinetic
energy;
thick cuticle/wax/suberin (on upper surface);(wax/suberin )waterproof;
water unable to diffuse onto surface to evaporate,presence of trichomes/
hairs;
surface traps water close to leaf surface;
increased humidity reduces gradient for water evaporation;
reduced leaves/spines/small surface area to volume;
less surface area for evaporation;
more distance across leaf for water to diffuse
;rolled leaves;
stomata enclosed in localised humidity;
increased humidity reduces gradient for water evaporation;
Xylem transports water through a plant. Describe and explain how the cells
of xylem are adapted for this function. (5) - CORRECT-ANSWERSThick cell
walls;
Withstand tension / negative pressure;
Lignin in cell walls;
Walls waterproof / withstand tension / negative pressure;
Xylem cells have no end walls / tubular (not hollow);
So a continuous column of water;
Xylem vessels are stacked on top of each other;
So a continuous column of water;
Have no cytoplasm / hollow;
Reduces resistance to flow of water / so a continuous column of water;
Xylem cells have pores / pits (in side walls);
Enable sideways flow / by-pass blockages / allows entry or exit of water;
Narrow tubes;
,Allows capillarity / increased surface area for adhesion;(Molecules in) cell
walls;
Allows adhesion
Describe the mass flow hypothesis for the mechanism of translocation in
plants. (4) - CORRECT-ANSWERS1. In the leaf sugars are actively transported
into phloem;
2. By companion cells;
3. Lowers water potential of sieve tubes and water enters by osmosis;
4. Increase in pressure causes mass movement (towards roots);
5. Sugars used (converted) in root for respiration/for storage;
Explain how oxygen is loaded, transported and unloaded in the blood (6) -
CORRECT-ANSWERS1. Haemoglobin carries oxygen / has a high affinity for
oxygen / oxyhaemoglobin;
2. In red blood cells;
3. Loading / uptake/association in lungs;at high p.O2;
4. Unloads / dissociates / releases to respiring cells / tissues;
5. at low p.O2;
6. Unloading linked to higher carbon dioxide (concentration);
What is atheroma and how may it cause myocardial infarction? (5) -
CORRECT-ANSWERS1. Cholesterol/ plaque / lipoprotein / LDL / fatty material /
cells;
2. In artery wall / under lining / endothelium of artery / blood vessel;
3. Atheroma linked with blood clotting / thrombosis;
4. (Blocks) coronary artery / artery supporting heart muscle / tissue / cells;
5. Reduces oxygen / glucose supply (to heart muscle / tissues / cells);
6. (Heart muscle / tissue / cells) unable to respire / dies;
The diet of a person can increase the risk of coronary heart disease. Explain
how. (5) - CORRECT-ANSWERS1. Too much saturated fat / cholesterol in diet;
2. Increase in LDL / cholesterol in blood;
3. Atheroma / fatty deposits / plaques in artery walls;
4. Reduces diameter of / blocks coronary arteries;
5. Less oxygen / glucose to heart muscles / tissues / cells;
6. Increase in blood pressure;
7. (Increased risk of) clot / thrombosis / embolism / aneurysm.
Describe the processes involved in the transport of sugars in plant stems. (5)
- CORRECT-ANSWERS1. (At source) sucrose is actively (transported) into the
phloem/sieve element/tube;
2. By companion/transfer cells;
3. Lowers water potential in phloem/sieve element/tube and water enters by
osmosis;
4. (Produces) high (hydrostatic) pressure;
, 5. Mass flow/transport towards sink/roots/storage tissue;
6. At sink/roots sugars are removed/unloaded;
Glucose is absorbed from the lumen of the small intestine into epithelial
cells. Explain how the transport of sodium ions is involved in the absorption
of glucose by epithelial cells. (5) - CORRECT-ANSWERS1. Na+ ions leave
epithelial cell and enter blood;
2. (Transport out is by) active transport / pump / via carrier protein using
ATP;
3. So, Na+ conc. in cell is lower than in lumen (of gut)
;4. Sodium/Na+ ions enter by facilitated diffusion;
5. Glucose absorbed with Na+ ions against their concentration/diffusion
gradient / glucose absorbed down an electrochemical gradient;
Describe the role of the enzymes of the digestive system in the complete
breakdown of starch. (5) - CORRECT-ANSWERSAmylase;
(Starch) to maltose:Maltase;
Maltose to glucose;
Hydrolysis;
(Of) glycosidic bond
Describe the processes involved in the absorption of the products of starch
digestion. (5) - CORRECT-ANSWERSGlucose moves in with sodium (into
epithelial cell);
Via (carrier / channel) protein / symport;
Sodium removed (from epithelial cell) by active transport / sodium-
potassium pump;
Into blood;
Maintaining low concentration of sodium (in epithelial cell) / maintaining
sodiumconcentration gradient (between lumen and epithelial cell);
Glucose moves into blood;
By (facilitated) diffusion;
Atheroma formation increases a person's risk of dying. Explain how. (5) -
CORRECT-ANSWERS1. Atheroma is fatty material/cholesterol/foam
cells/plaque/calcium deposits/LDL;
2. In wall of artery;
3. (Higher risk of) aneurysm/described;
4. (Higher risk of) thrombus formation/blood clot;
5. Blocks coronary artery;
6. Less oxygen/glucose to heart muscle/cells/tissue;
7. Reduces/prevents respiration;
8. Causing myocardial infarction/heart attack;
9. Blocks artery to brain;
10. Causes stroke/stroke described;
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