Secondary 4 Pure Biology Preliminary Examination Paper 1

TuitionGoWhere Exam Practice (AI) — Pure Biology Secondary 4

PRELIM Practice Paper Answers — Cells Biomolecules (Version 1 of 5)

Total Marks: 60

Section A Answers (10 marks)

Q1. Root hair cells [1]
Teaching note: Water is absorbed from the soil by root hair cells, which are specialised epidermal cells of the root with long extensions increasing surface area. Common trap: writing "xylem" (xylem transports water, does not absorb from soil) or "epidermis" (too general).

Q2. Nitrogen (or sulphur) [1]
Teaching note: Proteins contain C, H, O, N (and sometimes S). Carbohydrates contain only C, H, O. So N is present in proteins but not carbohydrates.

Q3. Mitochondrion (mitochondria) [1]
Teaching note: Mitochondria are the sites of aerobic respiration where ATP is produced. Avoid "nucleus" (control centre) or "ribosome" (protein synthesis).

Q4. Iodine test [1]
Teaching note: Iodine solution turns blue-black in presence of starch. Benedict's is for reducing sugars, biuret for protein.

Q5. Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. [1]
Teaching note: Must mention "net movement" and concentration gradient. In living organisms this occurs across membranes for gases and small molecules.

Section B Answers (30 marks)

Q6. (a) B [1]
(b) Ribosomes [1]; they are the site of protein synthesis (not labelled here but in a real EM would be small dots; if E is mitochondrion and no ribosome labelled, accept "not shown but ribosome is correct site" – based on figure given, none of A–E is ribosome, so answer: none labelled / ribosome not shown, explain site is ribosome) [1]
Teaching note: Chloroplast (B) is for photosynthesis. Protein synthesis occurs at ribosomes, which are not labelled in this micrograph. Marking: 1 for identifying B, 1 for stating ribosome is site and noting not labelled.

Q7. (a) R [1]
(b) Cell P is in a hypotonic solution (higher water potential outside), so water moves into the cell by osmosis down the water potential gradient, making it turgid. [2]
Teaching note: Osmosis is water moving from high to low water potential. R is plasmolysed → water left. P turgid → water entered.

Q8. [3]

• Long projection (hair) increases surface area for absorption [1]
• Thin wall / short distance for water and ions to diffuse [1]
• Many mitochondria for active transport of ions [1]
  Teaching note: Adaptations link structure to function.

Q9. (a) 40 °C [1]
(b) Above 45 °C the enzyme denatures; tertiary structure breaks, active site loses shape, so substrate cannot bind. [2]
Teaching note: Peak at 40 °C from graph. Denaturation is irreversible change in protein structure.

Q10. [3]

• High glucose lowers water potential of solution [1]
• Water moves out of RBC by osmosis (to lower water potential) [1]
• RBC shrinks / crenates, may be damaged [1]
  Teaching note: Connects Template 3 evidence pattern.

Q11. [3]
Starch: blue-black [1]
Reducing sugar: Benedict's reagent [1]
Protein: Biuret reagent [1]

Q12. (a) Glucose (or maltose) [1]
(b) Amino acids [1]

Q13. [2]

• Amylase active site shape is complementary only to starch (specific) [1]
• Protein shape does not fit amylase active site (lock-and-key) [1]
  Teaching note: Enzyme specificity from lock-and-key model.

Q14. [2]

• Draw line from 18 h to 20 h on timeline [1]
• Label X at 20 h with "formation of cell X" [1]
  Teaching note: Cytokinesis ends at 20 h, daughter cell formed.

Q15. [2]

• Plant cell has cell wall, animal cell does not [1]
• Plant cell has chloroplast, animal cell does not [1]
  (Other: plant has large vacuole, animal has smaller/no vacuole)

Section C Answers (20 marks)

Q16. [4]

• High blood glucose decreases water potential of blood [1]
• Water potential outside RBC now lower than inside? Actually blood lower → water leaves RBC [1]
• Water moves out by osmosis [1]
• RBC loses water, shrinks, crenates, damaged [1]
  Teaching note: Use all three terms as requested.

Q17. [4]

• Independent variable: pH (e.g., 3,5,7,9) [1]
• Dependent: rate of O₂ production / H₂O₂ breakdown [1]
• Controlled: temp, enzyme conc, H₂O₂ conc [1]
• Method: measure gas volume at each pH, compare [1]
  Teaching note: Standard biology experiment design.

Q18. [4]

• Large surface area from finger-like shape [1]
• Thin epithelium short diffusion path [1]
• Capillary network maintains concentration gradient [1]
• Microvilli increase surface area further [1]

Q19. (a) A, C, D [1]
(b) E [1]
(c) C (green) < D (orange) < A (brick red) [2]
Teaching note: Benedict's colour: blue (none) → green (low) → orange (med) → brick red (high).

Q20. [4]

• Ions often at lower conc in soil than root cell [1]
• Active transport moves ions against gradient using energy (ATP) [1]
• Diffusion only moves down gradient, insufficient [1]
• Mitochondria provide ATP for this process [1]