Secondary 3 Biology Human Physiology Quiz

Secondary 3 Biology Quiz - Human Physiology: Answer Key

Total Marks: 40
Duration: 50 minutes

Section A: Multiple Choice

1. A — Liver [1]
Teaching note: The liver produces bile, which emulsifies fats. The gall bladder only stores bile; the pancreas makes digestive enzymes, not bile. Common mistake: choosing gall bladder because it is associated with bile storage.

2. B — contracts; increases [1]
Teaching note: During inhalation, the diaphragm contracts and flattens, increasing thoracic volume and decreasing pressure so air enters. Relaxation occurs during exhalation.

3. B — alveoli [1]
Teaching note: Alveoli are the small air sacs surrounded by capillaries where O₂ and CO₂ exchange. Bronchi and bronchioles are airways; ventricles are heart chambers.

4. C — Pulmonary vein [1]
Teaching note: The pulmonary vein is unusual—it carries oxygenated blood from lungs to left atrium. The pulmonary artery carries deoxygenated blood away from heart to lungs.

5. B — Bowman's capsule [1]
Teaching note: Filtration of blood under pressure occurs at the glomerulus inside Bowman's capsule. The loop of Henle and collecting duct are for reabsorption.

Section B: Structured Questions

6. [2]

• Enzyme: amylase (salivary amylase) [1]
• Product: maltose (or reducing sugars) [1]
  Teaching note: Salivary glands secrete amylase which hydrolyses starch to maltose. Mark for named enzyme and correct product.

7. [2]

• Villi increase surface area for absorption [1]
• This allows more nutrients to be absorbed efficiently into blood [1]
  Teaching note: Folded wall → larger SA → faster diffusion/absorption. Common mistake: saying "to digest food" (digestion is earlier, in lumen).

8. [1]

• Alveolus (or alveoli cluster) labelled at end of bronchioles
  Teaching note: Based on Q8-fig1, the gas exchange site is the alveolus. Image must show alveoli as small sacs at bronchiole ends.

9. [2]
(i) Thin wall (one cell thick) → short diffusion distance [1]
(ii) Large surface area / many capillaries / moist surface [1]
Teaching note: Any two correct features. Mark each clearly.

10. [2]

• Carries blood from intestine to liver [1]
• Transports absorbed nutrients (e.g., glucose, amino acids) for processing [1]
  Teaching note: Hepatic portal vein is a portal vein (between two capillary beds). Not the same as hepatic vein.

11. [2]
Working:
Increase = 128 − 72 = 56 beats/min
Percentage = (56 ÷ 72) × 100 = 77.8% ≈ 78% [2 for correct working and answer]
Teaching note: Show subtraction then divide by original (rest) value × 100. Common error: dividing by 128.

12. [2]

• Aorta (or artery / systemic artery) [1]
• Thick muscular wall / elastic tissue to withstand high pressure [1]
  Teaching note: Aorta carries oxygenated blood to body. Adaptation links to high pressure from ventricle.

13. [2]

• Process: ultrafiltration (or filtration) [1]
• Substance retained: blood cells / proteins (e.g., red blood cells, plasma proteins) [1]
  Teaching note: Based on Q13-fig1, Bowman's capsule receives filtrate; large molecules stay in blood.

14. [3]

• Biconcave shape → increased surface area for O₂ loading [1]
• No nucleus → more space for haemoglobin [1]
• Contains haemoglobin which binds O₂ [1]
  Teaching note: Each adaptation linked to function = 1 mark. Common omission: not stating haemoglobin's role.

15. [2]

• Function: produces digestive enzymes (or bicarbonate) into duodenum [1]
• Enzyme: amylase / protease / lipase [1]
  Teaching note: Pancreas is exocrine (enzymes) and endocrine (insulin). Here focus on digestion.

16. [2]

• Left ventricle [1]
• Pumps blood to whole body (systemic circulation) at high pressure, needs thick wall [1]
  Teaching note: From Q16-fig1, left ventricle wall thicker. Right ventricle pumps only to lungs.

17. [2]

• Circular muscles contract behind food bolus [1]
• Wave of contraction pushes food downwards [1]
  Teaching note: Peristalsis is involuntary wave-like muscle action, not gravity-dependent.

Section C: Extended Response

18. [4]
Mark descriptors:

• Mouth: salivary amylase breaks starch → maltose [1]
• Oesophagus: peristalsis moves to stomach [1]
• Stomach: protease (pepsin) begins protein digestion; no carbohydrate enzyme [1]
• Small intestine: pancreatic amylase continues starch breakdown; maltase → glucose; protease → peptides/amino acids; lipase → fats [1]
  Teaching note: Must name enzymes and actions. Bread = starch + some protein; reward sequence and enzyme specificity.

19. [4]
Mark descriptors:

• Ventilation brings fresh air with high O₂ to alveoli [1]
• Blood flow removes O₂-poor blood and brings CO₂-rich blood away [1]
• Alveolar air O₂ > venous blood O₂, maintaining gradient [1]
• Thin alveolus wall + capillaries keep diffusion fast [1]
  Teaching note: Steep gradient maintained by constant replacement of air and blood (double perfusion/ventilation).

20. [4]
Mark descriptors:

• Filtration at Bowman's capsule: water and small solutes forced into nephron [1]
• Reabsorption: most water reabsorbed in proximal tubule and loop of Henle [1]
• Collecting duct: final adjustment of water reabsorption controlled by ADH [1]
• Explains balance: more ADH → more water retained, less urine [1]
  Teaching note: Nephron filters then selectively reabsorbs. Collecting duct crucial for osmoregulation.