A Level H2 Biology Human Physiology Quiz

A-Level Biology H2 Quiz - Human Physiology (Answer Key)

Topic: Human Physiology
Total Marks: 40

Section A: Short Structured Questions

1. [1 mark]
Answer: Capillaries have a single-cell-thick endothelium (or are very thin-walled / have pores/fenestrations).
Teaching note: The thin wall (one cell thick) provides a short diffusion distance for substances to exchange with tissues.
Common mistake: Stating “large surface area” alone without the structural feature.

2. [1 mark]
Answer: Left atrium.
Teaching note: Oxygenated blood from lungs returns via pulmonary veins into the left atrium.

3. [2 marks]
Answer: Insulin; promotes uptake of glucose by liver (and muscle/adipose) and conversion to glycogen (or inhibits glycogenolysis). [1 for hormone, 1 for effect]
Alternative: Glucagon; stimulates glycogenolysis and gluconeogenesis in liver.
Teaching note: Blood glucose is regulated by pancreatic hormones; insulin lowers, glucagon raises.

4. [2 marks]
Answer: The SA node is the natural pacemaker; it generates electrical impulses (action potentials) that spread across the atria causing atrial contraction. [2]
Marking: 1 for “pacemaker/ generates impulses”, 1 for “causes atrial contraction / sets rhythm”.

5. [1 mark]
Answer: 13.0 – 5.3 = 7.7 kPa.
Teaching note: Diffusion is driven by partial pressure gradient; subtract venous from alveolar value.

6. [1 mark]
Answer: Efferent arteriole.
Teaching note: Blood leaves glomerulus via efferent arteriole (note: not vein).

7. [1 mark]
Answer: Osmosis.
Teaching note: ADH increases aquaporins; water moves by osmosis from filtrate to hypertonic medulla.

8. [2 marks]
Answer: Left ventricle pumps blood to the whole body (systemic circulation) at higher pressure; right ventricle pumps only to lungs (pulmonary, lower resistance). [2]
Marking: 1 for systemic vs pulmonary, 1 for pressure/resistance difference.

Section B: Data and Diagram Interpretation

9. [2 marks]
Answer: Aortic valve open during ventricular systole (~0.2–0.4 s) when left ventricular pressure exceeds aortic pressure. [1 for phase, 1 for explanation]
Teaching note: From graph, ventricle pressure rises above aorta (~16 > 12 kPa), pushing valve open.

10. [2 marks]
Working: Increase = (132 – 68) / 68 × 100 = 64 / 68 × 100 = 94.1%
Answer: 94% (or 94.1%).
Marking: 1 for correct subtraction, 1 for percentage calculation.

11. [3 marks]
Answer: Wall is one cell thick (type I pneumocyte + endothelium) → short diffusion distance [1]; dense capillary network maintains gradient [1]; large surface area of alveolus [1].
Teaching note: Structure minimises distance and maximises area for Fick’s law.

12. [2 marks]
Answer: Proteins are too large to pass through filtration slits / basement membrane of glomerulus [1]; only small molecules filtered [1].
Marking: 1 size, 1 membrane barrier.

13. [2 marks]
Answer: Tidal volume = 0.5 L [1]; Assumption: no gas exchange occurs in spirometer / person breathes normally without leak [1].
Teaching note: Tidal volume is volume per normal breath from trace amplitude.

14. [2 marks]
Working: Cardiac output = stroke volume × heart rate
20.0 L min⁻¹ = 0.100 L × HR → HR = 20.0 / 0.100 = 200 beats min⁻¹
Answer: 200 beats per min.
Marking: 1 for conversion (100 mL = 0.1 L) and formula, 1 for answer.

Section C: Applied and Extended Response

15. [4 marks]
Answer:

• SA node in right atrium spontaneously depolarises due to leaky Na⁺ channels / funny current. [1]
• Impulse spreads via gap junctions across atrial walls → atrial systole. [1]
• Reaches AV node, delayed, then via Bundle of His and Purkinje fibres. [1]
• Ventricular myocardium depolarises from apex up → ventricular contraction. [1]
  Teaching note: Electrical sequence ensures atrial then ventricular contraction.

16. [4 marks]
Answer:

• Ascending limb actively transports Na⁺, Cl⁻ out (impermeable to water) → medullary interstitium hypertonic. [1]
• Descending limb permeable to water, not solutes → water leaves by osmosis. [1]
• Flow opposite directions (countercurrent) multiplies gradient. [1]
• Collecting duct under ADH reabsorbs water into hypertonic medulla → concentrated urine. [1]

17. [4 marks]
Answer:

• Likely respiratory acidosis due to hypoventilation / COPD retaining CO₂. [1]
• CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻; high pCO₂ shifts right → more H⁺ → lower pH. [1]
• Normal regulation: chemoreceptors detect pH/CO₂, increase ventilation to blow off CO₂. [1]
• Kidney can also excrete H⁺ and reabsorb HCO₃⁻ (slower). [1]

18. [4 marks]
Answer:

• Abnormality: dropped P wave / irregular beat at 1.6 s suggesting AV block or ectopic focus. [1]
• ECG P = atrial depolarisation, QRS = ventricular depolarisation, T = repolarisation. [2]
• Missing P indicates impulse did not originate in SA node or blocked at AV. [1]

19. [4 marks]
Answer:

• O₂: bound to haemoglobin in RBC (98%), small dissolved; loaded in lungs high pO₂. [2]
• CO₂: mostly as HCO₃⁻ in plasma, some carbamino-haemoglobin, dissolved; unloaded in lungs. [2]
• Contrast: O₂ mainly protein-bound, CO₂ chemically converted / buffered.

20. [4 marks]
Answer:

• Na⁺/K⁺ ATPase maintains low intracellular Na⁺. [1]
• Glucose reabsorption uses SGLT (Na⁺-glucose cotransport) driven by Na⁺ gradient. [1]
• Inhibiting pump collapses gradient → less glucose reabsorption (glycosuria). [1]
• Water follows solutes osmotically → less water reabsorption. [1]