O Level Biology Human Physiology Quiz

Answer Key - Human Physiology Quiz

1. Excretion: The removal of metabolic waste products from the body. [1]

2. Equation: Glucose $\rightarrow$ Lactic acid + Energy (or $\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_3\text{H}_6\text{O}_3 + \text{Energy}$). [1]

3. Hormone: Insulin. [1]

4. Vessel: Pulmonary vein. [1]

5. Structure: Iris. [1]

6. Function: Transports absorbed nutrients (e.g., glucose, amino acids) from the small intestine to the liver. [1]

7. Component: Platelets. [1]

8. Brain part: Midbrain (or Brain stem). [1]

9. (a) Arteries have thicker muscular walls and no valves; veins have thinner walls and contain valves to prevent backflow. [2] (b) The left ventricle must pump blood to the entire body (systemic circulation), requiring higher pressure than the right ventricle, which only pumps to the lungs. [2]

10. High pressure in the glomerulus forces small molecules (water, glucose, salts, urea) out of the blood into the Bowman's capsule, while large proteins and blood cells remain in the capillaries. [3]

11. (1) Large surface area for maximum gas exchange; (2) One-cell thick wall (short diffusion distance); (3) Rich supply of capillaries to maintain a steep concentration gradient. [3]

12. High protein intake $\rightarrow$ increased deamination of excess amino acids in the liver $\rightarrow$ increased production of urea $\rightarrow$ higher concentration of urea in urine. [3]

13. Diaphragm contracts and flattens; external intercostal muscles contract, pulling the ribcage upwards and outwards. This increases thoracic volume, decreasing pressure and drawing air into the lungs. [3]

14. (a) Insulin stimulates the liver to convert glucose to glycogen; glucagon stimulates the liver to convert glycogen back to glucose. [2] (b) Cells become resistant to insulin (insulin resistance), meaning glucose is not efficiently taken up by cells, leading to hyperglycemia. [2]

15. Cilia are hair-like projections that sweep mucus (trapping dust and pathogens) upwards and away from the lungs toward the throat. [2]

16. During vigorous exercise, oxygen supply is insufficient, leading to anaerobic respiration and lactic acid buildup (oxygen debt). After exercise, increased breathing rate provides extra oxygen to oxidize lactic acid into $\text{CO}_2$ and water. [3]

17. Double Circulation:

    • Right atrium receives deoxygenated blood from the body $\rightarrow$ Right ventricle pumps it to lungs via pulmonary artery. [2]
    • Blood is oxygenated in lungs $\rightarrow$ returns to left atrium via pulmonary vein. [2]
    • Left ventricle pumps oxygenated blood to the rest of the body via the aorta. [2]

18. Reflex Arc:

    • Receptor in skin detects heat stimulus. [1]
    • Impulse travels along sensory neurone to the spinal cord. [1]
    • Relay neurone in spinal cord transmits impulse to motor neurone. [1]
    • Neurotransmitters cross the synapse to trigger the motor neurone. [1]
    • Motor neurone carries impulse to the effector (biceps muscle). [1]
    • Muscle contracts, pulling the hand away. [1]

19. Menstrual Cycle:

    • FSH stimulates follicle growth and secretion of oestrogen. [1]
    • Oestrogen repairs/thickens the uterine lining. [1]
    • LH surge triggers ovulation (release of egg). [1]
    • Corpus luteum secretes progesterone to maintain the uterine lining for implantation. [1]
    • If no fertilisation, progesterone drops, causing the lining to shed (menstruation). [2]

20. Temperature Regulation (Cold):

    • Thermoreceptors in skin detect cold $\rightarrow$ signal sent to hypothalamus. [1]
    • Vasoconstriction: blood vessels narrow to reduce heat loss from skin. [2]
    • Shivering: rapid contraction of skeletal muscles to generate metabolic heat. [2]
    • Piloerection: hairs stand up to trap a layer of insulating air. [1]