O Level Biology Human Physiology Quiz

O-Level Biology Quiz - Human Physiology (Answer Key)

Total Marks: 40
Topic: Human Physiology (syllabus-first, AI-inferred from Stage 4 templates; not claimed as past-year derived)

Section A

1. Pulmonary vein. [1]
Teaching note: The pulmonary vein is unique among veins because it carries oxygenated blood (from lungs to left atrium). Most veins carry deoxygenated blood. Common mistake: naming aorta (that is an artery from heart to body).

2. Absorbs water from undigested food / forms faeces. [1]
Teaching note: The large intestine (colon) reabsorbs water and minerals; this prevents dehydration and solidifies waste.

3. Excretion (or ultrafiltration and reabsorption in nephron). [1]
Teaching note: Urea is a nitrogenous waste from protein breakdown; kidneys filter it from blood. Accept "excretion" as the broad process.

4. Carbon dioxide ($CO_2$). [1]
Teaching note: Body cells respire aerobically producing $CO_2$ which diffuses into blood, to lungs, and is exhaled. Oxygen moves opposite direction.

5. Insulin. [1]
Teaching note: Insulin from pancreas beta-cells lowers blood glucose by promoting glucose uptake and conversion to glycogen.

Section B

6. [4] Mark breakdown: enzyme 1 named + substrate + product [2]; enzyme 2 named + substrate + product [2].
Example: Amylase acts on starch → maltose (in mouth/duodenum) [2]; Protease (e.g. pepsin) acts on protein → peptides (in stomach) [2].
Teaching note: Enzymes are biological catalysts; each has specific substrate. Must state role (speeds digestion) implicitly via substrate→product. Common trap: listing enzyme without substrate/product pair loses marks.

7. [3]

• Biconcave shape → large surface area for oxygen diffusion [1]
• No nucleus → more space for haemoglobin [1]
• Contains haemoglobin → binds oxygen [1]
  Teaching note: Structure-function link is key in O-Level physiology. Red cells trade nucleus for haemoglobin capacity.

8. [4]

• Pulmonary circuit: heart → lungs → heart; deoxygenated blood to lungs, oxygenated back [2]
• Systemic circuit: heart → body → heart; oxygenated to body, deoxygenated back [2]
  Teaching note: Double circulation = two loops; right side pumps to lungs, left side to body. Diagram must show arrows matching this.

9. [3]

1. More protein → more amino acid deamination in liver [1]
2. Produces more urea → higher solute in blood [1]
3. Kidney reabsorbs water by osmosis, urine becomes more concentrated (or volume less) [1]
   Teaching note: Do not confuse volume with concentration. Urea is the osmotic agent pulling water retention.

10. [3]

• Blood glucose rises after meal [1]
• Insulin secreted by pancreas [1]
• Glucose converted to glycogen in liver / stored [1]
  Teaching note: Negative feedback; opposite occurs via glucagon when low.

11. [3]

• Provides oxygen and nutrients to fetus [1]
• Removes $CO_2$ and wastes [1]
• Allows exchange without mixing blood (via umbilical cord) [1]
  Teaching note: Placenta is organ of exchange, not connection of bloodstreams.

12. [4]

• Nervous system increases breathing rate (medulla) [1]
• Sympathetic nerves raise heart rate [1]
• More alveoli ventilated, $O_2$ uptake rises [1]
• Meets higher ATP demand of muscles [1]
  Teaching note: Coordination of systems maintains internal balance (homeostasis) during exercise.

13. [4]

• Stimulus (tap) stretches tendon [1]
• Sensory neuron sends impulse to spinal cord [1]
• Motor neuron triggers quadriceps contraction [1]
• Leg extends; no brain involvement (fast) [1]
  Teaching note: Reflex arc bypasses brain for speed; protects from harm.

14. [3]

• Glucose often lower in lumen than cell [1]
• Must move against gradient [1]
• Active transport uses ATP from respiration [1]
  Teaching note: After meal, co-transport helps, but baseline uptake needs energy.

15. [2]

• Sweating (evaporation cools) [1]
• Vasodilation (blood near surface loses heat) [1]
  Teaching note: Also hair flattening; accept any two valid.

Section C

16. [3]

• Oxygen rises from 60 to 95 units [1]
• Alveoli have high $O_2$, blood low $O_2$ [1]
• Diffusion into blood, binds haemoglobin [1]
  Teaching note: Graph shows pulmonary vein > artery confirming gas exchange efficiency.

17. [3]

• Activity needs more ATP [1]
• Muscles need more $O_2$, produce more $CO_2$ [1]
• Faster heart pumps more blood to supply demand [1]
  Teaching note: Data interpretation: correlation of rate with metabolism.

18. [4]

• Microvilli increase surface area [1]
• Thin epithelium short diffusion path [1]
• Capillaries remove glucose/amino acids quickly [1]
• Lacteal absorbs fats [1]
  Teaching note: Villus structure maximises absorption via area and transport.

19. [3]

• Evaporation needs latent heat from skin → cools [1]
• Water leaves body → loses heat [1]
• Also loses salts / water balance affected [1]
  Teaching note: Thermoregulation via latent heat; secondary effect is dehydration risk.

20. [4]

• Ultrafiltration at glomerulus (pressure forces water/salts/urea out) [2]
• Reabsorption of glucose/water in tubule [2]
  Teaching note: Nephron filters then selectively recovers; urine = waste + excess.