A Level H1 Biology Practice Paper 5

TuitionGoWhere Practice Paper - Biology H1 A-Level (Answers)

Version 5 of 5 — Answer Key & Teaching Notes

Total Marks: 60

Section A (20 marks)

1. [1] One principle: "All living organisms are composed of cells" OR "Cells are the smallest unit of life" OR "All cells come from pre-existing cells".
Teaching note: Cell theory is foundational; any one of the three accepted principles is awarded the mark.

2. [1] Nucleus.
Teaching note: The nucleus houses DNA and the nucleolus; it is membrane-bound in eukaryotes.

3. [2] Phospholipids form a bilayer; hydrophilic heads face outward to aqueous environments, hydrophobic tails face inward away from water. [1+1]
Teaching note: This arrangement creates a selectively permeable barrier.

4. [1] α-glucose has OH on C1 below the ring (same side as CH₂OH in Haworth); β-glucose has OH above the ring.
Teaching note: This difference affects polymer structure (starch vs cellulose).

5. [2] Any two: circular DNA, peptidoglycan cell wall, 70S ribosomes. [1 each]
Teaching note: Bacteria are prokaryotes; no nucleus or mitochondria.

6. [2] Movement of substances down a concentration gradient through a transport protein, no ATP required. [1 for gradient, 1 for protein]
Teaching note: Distinct from active transport which needs energy.

7. [1] Peptide bond.
Teaching note: Formed by condensation between amino and carboxyl groups.

8. [1] Multipotent.
Teaching note: Blood stem cells can form multiple blood cell types but not all tissues.

Section B (20 marks)

9. [4]
(a) C = rough endoplasmic reticulum; function = protein synthesis (with ribosomes). [1+1]
(b) E = ribosome; role = site of translation / polypeptide synthesis. [1+1]
Teaching note: RER is studded with ribosomes; key for secretory proteins.

10. [3] Plateau occurs because transport proteins (carriers/channels) become saturated; all available proteins are occupied at max rate (Vmax-like). [1] Uptake is via facilitated diffusion/active transport with limited proteins. [1] No further increase despite gradient. [1]
Teaching note: Saturation is hallmark of protein-mediated transport.

11. [2] Any two differences: bacteria have circular DNA not linear; bacteria have peptidoglycan wall not cellulose; bacteria lack chloroplasts; bacteria have 70S not 80S ribosomes. [1 each]
Teaching note: Core prokaryote vs eukaryote plant cell contrast.

12. [3]
(a) [1] 40 °C (highest rate).
(b) [2] At 60 °C enzyme denatured; tertiary structure disrupted, active site lost. [1] H-bonds/ionic bonds break. [1]
Teaching note: Beyond optimum, protein unfolding reduces rate.

13. [2] Cholesterol restricts phospholipid movement, reduces fluidity at high temp and prevents solidification at low temp; maintains membrane stability. [1+1]
Teaching note: Shown as III between tails in fluid mosaic.

14. [2] Amylose is unbranched helix; amylopectin is branched. [1] Branching allows rapid hydrolysis for energy release. [1]
Teaching note: Starch function is glucose storage.

Section C (20 marks)

15. [4] Triglyceride = 1 glycerol + 3 fatty acids via ester bonds. [1] Hydrophobic, insoluble in water. [1] High C-H ratio gives high energy per gram. [1] Compact storage without osmotic effect. [1]
Teaching note: Structure directly supports long-term anhydrous energy store.

16. [4] Enzyme active site initially not exact fit. [1] Substrate binds, induces conformational change. [1] Stabilises transition state. [1] Lowers activation energy, speeds reaction. [1]
Teaching note: Induced-fit vs lock-and-key; both reduce Ea.

17. [4] Haemoglobin = 4 polypeptide chains (2α, 2β) = quaternary. [1] Each has haem group binding O₂. [1] Cooperative binding: O₂ uptake eases next. [1] Quaternary allows allosteric regulation. [1]
Teaching note: Structure enables efficient O₂ transport in blood.

18. [4] Mitosis: diploid→diploid, identical cells for growth/repair. [1+1] Meiosis: diploid→haploid, gametes for variation. [1] Stem cells (e.g. embryonic totipotent) use mitosis for development. [1]
Teaching note: H1 expects meiosis significance not stage detail.

19. [4] Pyruvate enters mitochondrial matrix directly for Krebs cycle → CO₂ released. [1+1] Glucose needs glycolysis in cytoplasm first (not in mitochondria). [1] Isolated mitochondria lack cytosolic enzymes. [1]
Teaching note: Location of glycolysis vs Krebs is key.

20. [4] Screening detects trisomy 21 pre-birth. [1] Ethical: informed choice, prevention of suffering. [1] Against: potential discrimination, abortion debate. [1] Stem cells (embryonic totipotent) show development continuity, raising moral status questions. [1]
Teaching note: Link bioethics to stem cell potency and life continuity.