A Level H2 Biology Cells Biomolecules Quiz

A-Level Biology H2 Quiz - Cells Biomolecules (Answer Key)

Topic: Cells Biomolecules
Total Marks: 40
Note: Content generated from LLM-inferred templates (Stage 4/5) using syllabus 9477. Not claimed as past-year derived.

Section A

1. [2 marks]

• Phospholipids: form bilayer barrier, hydrophobic core blocks ions. [1]
• Proteins: transport, enzymes, receptors. [1] (accept glycoproteins/glycolipids/cholesterol with correct role)
  Teaching: Fluid mosaic = proteins floating in phospholipid sea. Mark 1 each component+role.

2. [1 mark] Glycosidic bond.
Teaching: Condensation between glucose monomers releases water forming α-1,4 or α-1,6 glycosidic bonds.

3. [2 marks]

• Bacterial: no membrane-bound organelles; eukaryotic: has mitochondria etc. [1]
• Bacterial: circular DNA, 70S ribosomes; eukaryotic: linear DNA in nucleus, 80S ribosomes. [1]
  Common mistake: stating bacteria have no DNA.

4. [1 mark] Enzyme active site changes shape slightly to better fit substrate upon binding.
Teaching: Contrast with rigid lock-and-key.

5. [2 marks]

• Haemoglobin: primary (aa sequence), secondary (α-helix), tertiary (3D chain), quaternary (4 subunits). [1]
• Myoglobin single chain lacks quaternary structure. [1]

Section B

6. [3 marks]

• Bilayer has hydrophobic fatty acid tails inward. [1]
• Na⁺ is charged/hydrophilic, repelled by non-polar core. [1]
• Requires protein channel/pump to cross. [1]
  Ref Fig 1: ion stuck at outer head.

7. [3 marks]

• Below optimum, higher temp increases KE, more ES collisions. [1]
• At optimum (40°C) max rate. [1]
• Above optimum, denaturation: H-bonds/ionic bonds break, active site lost. [1]

8. [2 marks]

• Facilitated diffusion: no ATP, down gradient via carrier/channel. [1]
• Active transport: ATP needed, against gradient via pump. [1]

9. [3 marks]

• Virus has no cells, no metabolism, no reproduction without host. [1]
• Challenges "all living things are cells" / cell theory. [1]
• Acellular entity with genetic material only. [1]

10. [4 marks]

• Same y-intercept → Vmax unchanged. [1]
• Different x-intercept → Km increased. [1]
• Competitive inhibition: inhibitor binds active site, more substrate overcomes. [1]
• Apparent Km higher as more [S] needed for half Vmax. [1]

11. [2 marks] Competitive inhibition. [1] Apparent Km = substrate concentration at half Vmax in presence of inhibitor. [1]

12. [3 marks]

• A mitochondrion: ATP via respiration. [1]
• B Golgi: modify/sort proteins. [1]
• C rough ER: protein synthesis (ribosomes). [1]

13. [2 marks] Glycogen more branched (α-1,6 every 8–12 residues) vs amylopectin. [1] More ends for rapid glucose release in animals. [1]

14. [3 marks]

• Inter-chain H-bonds stabilise triple helix. [1]
• Glycine small allows tight turns. [1]
• Proline rigidifies chain. [1]

15. [2 marks] Totipotent (zygote → all cell types + extraembryonic). [1] Pluripotent (embryonic stem → all tissues not extraembryonic). [1]

Section C

16. [2 marks] Peptide bonds = n−1 = 5−1 = 4. [2]
Method: condensation removes water between each adjacent pair.

17. [4 marks]
Solution ψ = ψs + ψp = −0.4 + 0.1 = −0.3 MPa. [1]
Cell ψ = −0.5 MPa. [1]
Δψ = cell − soln = −0.5 − (−0.3) = −0.2 MPa. [1]
Water moves into cell (from higher ψ −0.3 to lower −0.5). [1]

18. [3 marks]

• With A, O₂ falls as ETC active. [1]
• After B, plateau: inhibitor blocks ETC, O₂ not used. [1]
• O₂ final electron acceptor at complex IV, forms H₂O. [1]

19. [3 marks] Products: glycerol + 3 fatty acids. [1] Ester bond cleaved. [1] One triglyceride has 3 ester bonds. [1]

20. [3 marks]

• At high T, cholesterol restricts phospholipid movement → less fluid. [1]
• At low T, prevents tight packing of tails → avoids solidify. [1]
• Acts as buffer to membrane fluidity. [1]