Exam (elaborations)
2024 AQA A LEVEL BIOLOGY 4/5/6 MARK EXAM QUESTIONS WITH ANSWERS
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2024 AQA A LEVEL BIOLOGY 4/5/6 MARK EXAM QUESTIONS WITH ANSWERS
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2024AQA A LEVEL BIOLOGY 4/5/6MARK EXAM QUESTIONS WITH
ANSWERS
Explain how the structure of DNA is related to its functions. (6) - CORRECT-
ANSWERS1. Sugar-phosphate (backbone)/double
stranded/helix so provides strength/stability
/protects bases/protects hydrogen bonds;
2. Long/large molecule so can store lots of
information;
3. Helix/coiled so compact;
4. Base sequence allows information to be
stored/ base sequence codes for amino
acids/protein;
5. Double stranded so replication can occur
semi-conservatively/ strands can act as
templates;
6. Complementary base pairing / A-T and G-C
so accurate replication/identical copies can
be made;
7. (Weak) hydrogen bonds for replication/
unzipping/strand separation;
8. Many hydrogen bonds so stable/strong;
Some substances can cross the cell-surface membrane of a cell by simple
diffusion through the phospholipid bilayer.
Describe other ways by which substances cross this membrane. (5) -
CORRECT-ANSWERSBy osmosis (no mark)
1. From a high water potential to a low water potential/down a water
potential gradient;
2. Through aquaporins/water channels;
By facilitated diffusion (no mark)
3. Channel/carrier protein;
4. Down concentration gradient;
By active transport (no mark)
5. Carrier protein/protein pumps;
6. Against concentration gradient;
7. Using ATP/energy (from respiration);
By phagocytosis/endocytosis (no mark)
8. Engulfing by cell surface membrane to form vesicle/vacuole;
, By exocytosis/role of Golgi vesicles (no mark)
9. Fusion of vesicle with cell surface membrane;
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;
Describe how DNA is replicated. (6) - CORRECT-ANSWERS1. Strands separate
/ H-bonds break;
2. DNA helicase (involved);
3. Both strands/each strand act(s) as (a) template(s);
4. (Free) nucleotides attach;
5. Complementary/specific base pairing / AT and GC;
6. DNA polymerase joins nucleotides (on new strand);
7. H-bonds reform;
8. Semi-conservative replication / new DNA molecules contain one old strand
and one new strand;
Describe how tissue fluid is formed and how it is returned to the circulatory
system. (6) - CORRECT-ANSWERSFormation
1. High blood / hydrostatic pressure /
pressure filtration;
2. Forces water / fluid out;
3. Large proteins remain in capillary;
Return
4. Low water potential in capillary /
blood;
5. Due to (plasma) proteins;
6. Water enters capillary / blood;
7. (By) osmosis;
8. Correct reference to lymph;
Many different substances enter and leave a cell by crossing its cell surface
membrane. Describe how substances can cross a cell surface membrane. (5)
- CORRECT-ANSWERS1 (Simple / facilitated) diffusion from high to low
concentration / down concentration gradient;
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