A Level H1 Biology Practice Paper 5

TuitionGoWhere Exam Practice (AI) – Biology H1 A-Level

Practice Paper: Cells & Biomolecules (Version 5 of 5) – Answer Key

Section A (20 marks)

1. [1] One feature: Cells are the smallest unit of life (or: all cells come from pre-existing cells / living organisms are composed of cells).
Teaching note: Cell theory has three tenets; any one accepted.

2. [2] Structure X = Golgi body (Golgi apparatus). Function: modifies, sorts, and packages proteins (e.g. enzymes, hormones) into vesicles for secretion.
Marking: 1 for name, 1 for function linked to secretory role.

3. [2] Phospholipids form a bilayer; hydrophilic heads face outward to aqueous environments, hydrophobic tails face inward away from water.
Marking: 1 bilayer, 1 orientation of heads/tails.

4. [2] Oxygen moves by simple diffusion directly through the lipid bilayer down its concentration gradient; no protein needed as it is small and non-polar.
Marking: mechanism + through lipid core.

5. [1] Glycosidic bond (α-1,4 or α-1,6 in starch).

6. [1] Zygotic (totipotent) stem cell (or totipotent stem cell).

7. [2] Y = peptidoglycan cell wall; differs from plant wall as it is made of peptidoglycan not cellulose.
Marking: 1 name, 1 difference.

8. [2] Induced-fit: enzyme active site changes shape slightly to fit substrate, forming enzyme–substrate complex, lowering activation energy.
Marking: change shape + complex/energy.

9. [1] Cholesterol reduces membrane fluidity at high temp and prevents crystallisation at low temp (stabilises membrane).

10. [2] Example: maltose = glucose + glucose (or sucrose = glucose + fructose; lactose = glucose + galactose).
Marking: 1 example, 1 monomers.

Section B (25 marks)

11. [4 total]
(a) [1] Facilitated diffusion (or carrier-mediated diffusion).
(b) [2] Graph plateaus → saturation of carriers; shows protein carriers limited, not simple diffusion.
(c) [1] Channel or carrier protein in membrane.

12. [4 total]
(a) [1] e.g. mitochondrion (or nucleus, Golgi, ER).
(b) [1] ATP production / aerobic respiration.
(c) [2] Bacterium has 70S ribosomes and circular DNA; can transcribe/translate proteins without membrane-bound organelles.

13. [4 total]
(a) [1] NH2 circled, COOH boxed.
(b) [2] Condensation: –OH from carboxyl of one + –H from amino of next removed as H2O; peptide bond forms.
(c) [1] Condensation (dehydration).

14. [6 total]
(a) [2] Optimum = 40 °C (peak rate).
(b) [2] Above 40 °C, enzyme denatures: H-bonds/ionic bonds break, active site lost.
(c) [2] % decrease = (38–8)/38 ×100 = 78.9%. Working: 30/38×100.

15. [3] Golgi receives proteins from rough ER, modifies (e.g. adds carbs), packages antibodies into vesicles for exocytosis.
Marking: receive 1, modify 1, package/secret 1.

16. [3] Cellulose = β-glucose polymers with β-1,4 glycosidic bonds; straight chains cross-linked by H-bonds → microfibrils; provides tensile strength.
Marking: monomer 1, bond/structure 1, strength link 1.

17. [3 total]
(a) [1] 0.25 M (isotonic, no net change).
(b) [2] At 0.4 M, solution hypertonic → water leaves by osmosis → mass decreases.

Section C (15 marks)

18. [7]
Structure: glycerol + 2 fatty acids + phosphate group (polar head, 2 non-polar tails). [2]
Fluid mosaic: bilayer with proteins embedded; hydrophobic tails give fluid core, heads face water; cholesterol restricts/permits movement. [3]
Properties: amphipathic nature lets self-assemble; fluidity allows fusion, transport. [2]

19. [8]
Primary: sequence of amino acids (2×α+2×β chains). [2]
Secondary: α-helix/β-sheet via H-bonds. [1]
Tertiary: folding, H/ionic/disulfide bonds. [2]
Quaternary: 4 subunits + haem group; Fe²⁺ binds O₂ reversibly. [3]
Marking descriptors: each level described + link to O₂ transport.