Secondary 4 Combined Science Biology Practice Paper 2

TuitionGoWhere Practice Paper — Answer Key (Version 2)

Subject: Combined Science Biology
Level: Secondary 4
Topic: Cells & Biomolecules
Total Marks: 40

Section A (12 marks)

1. [1 mark] Diffusion.
Teaching note: Oxygen moves from high concentration in alveoli to low concentration in muscle tissue fluid by diffusion, a passive process needing no energy.

2. [1 mark] Mitochondrion (or mitochondria).
Teaching note: Mitochondria are the sites of aerobic respiration where ATP is produced.

3. [1 mark] Any one correct difference, e.g., "Plant cell has a cell wall; animal cell does not." / "Plant cell has chloroplasts; animal cell does not."
Marking: Accept other valid structural differences (large vacuole, shape).

4. [1 mark] Animal cell.
Teaching note: Presence of nucleus and mitochondria but no cell wall indicates an animal cell (could be generic animal cell, not red blood cell due to nucleus).

5. [1 mark] Osmosis.
Teaching note: Osmosis is the net movement of water across a partially permeable membrane down a water potential gradient.

6. [1 mark] Cellulose.
Teaching note: Plant cell walls are made mainly of cellulose, a polysaccharide providing rigidity.

Section B (16 marks)

7. [2 marks]

• Skeletal muscle cells require large amounts of ATP for contraction. [1]
• They therefore have more mitochondria to carry out aerobic respiration and produce energy. [1]
  Teaching note: Link structure (many mitochondria) to function (high energy need).

8. [2 marks]

• Red blood cells have no mitochondria so they do not use the oxygen they carry for their own respiration. [1]
• This allows them to transport maximum oxygen to tissues. [1]
  Common mistake: Saying they "do not need energy" – they do, but produce ATP by glycolysis only.

9. [4 marks]

• Process: Facilitated diffusion (or active transport if context implies low glucose in intestine – but standard is facilitated diffusion down gradient after digestion). [1] Glucose moves through carrier proteins in the membrane.
• Factor 1: Concentration gradient – steeper gradient increases rate. [1]
• Factor 2: Number of carrier proteins / temperature (higher temp = faster molecular motion). [1]
• (Additional clarity) No energy needed for facilitated diffusion; if active, energy from ATP. [1]
  Teaching note: Intestinal epithelial cells absorb glucose via co-transport (active) but simplified facilitated diffusion acceptable at this level if stated as down gradient.

10. [2 marks]

• Cell wall [1]
• Chloroplast [1] (or large vacuole acceptable if diagram shows; but question asks two organelles only in plant)
  Based on placeholder: Diagram must show cell wall and chloroplasts in plant cell only.

11. [3 marks]

• Long thin extension (root hair) increases surface area for absorption. [1]
• Thin cell wall and membrane allow easy passage of water/minerals. [1]
• Many mitochondria provide energy for active transport of minerals. [1]

12. [2 marks]

• The cell will shrink (lose water by osmosis). [1]
• Water moves out to the region of lower water potential (higher solute concentration). [1]

13. [1 mark]
Increase = 28 mm – 12 mm = 16 mm.
Working: $28 - 12 = 16$.

14. [2 marks]

• Higher temperature gives particles more kinetic energy. [1]
• Molecules move faster, so diffusion distance is greater in same time. [1]

Section C (12 marks)

15. [6 marks]

1. Oxygen inhaled into alveoli of lung. [1]
2. Diffuses across alveolar epithelium and capillary wall into blood plasma. [1]
3. Enters red blood cell, binds to haemoglobin. [1]
4. Transported via pulmonary vein → left atrium → left ventricle → aorta → coronary artery. [1]
5. Diffuses from capillary into heart muscle tissue fluid. [1]
6. Diffuses across cell membrane into mitochondrion for respiration. [1]
   Teaching note: Must name structures and processes; omission of any step loses mark.

16. [3 marks]

• Active transport requires energy (ATP); diffusion does not. [1]
• Active transport moves substances against concentration gradient; diffusion is down gradient. [1]
• Both are membrane transport processes. [1] (or other valid comparison point)

17. [2 marks]

• Pancreatic cells secrete enzymes which are proteins. [1]
• Ribosomes are the site of protein synthesis, so many ribosomes are needed. [1]

18. [2 marks]

• Contractile vacuole activity decreases (or cell shrinks). [1]
• In salty water (lower water potential), water leaves amoeba by osmosis, less excess water to pump out. [1]

19. [2 marks]

• Phospholipid bilayer blocks large/polar molecules. [1]
• Channel/carrier proteins allow specific molecules through. [1]

20. [2 marks]

• Incorrect. [1]
• Proteins are synthesised at ribosomes using instructions from DNA in nucleus; ribosomes are the site of assembly. [1]

Total: 40 marks. Paper internally timed for 1h with review buffer.