Secondary 3 Biology Human Physiology Quiz

Secondary 3 Biology Quiz - Human Physiology - ANSWER KEY

Total Marks: 40

Section A: Multiple Choice (5 marks)

Section B: Short Answer (15 marks)

6. State TWO functions of the liver. [2]

Answer: Any two of the following (1 mark each):

• Regulation of blood glucose concentration (converts excess glucose to glycogen / converts glycogen to glucose)
• Breakdown of excess amino acids (deamination) / formation of urea
• Breakdown of alcohol / detoxification
• Production of bile (for fat digestion/emulsification)
• Storage of iron / vitamins
• Breakdown of old red blood cells

7. Explain why the wall of the left ventricle is thicker than the wall of the right ventricle. [2]

Answer:

• The left ventricle pumps blood to the entire body (systemic circulation) [1]
• Therefore, it needs to generate higher pressure to overcome greater resistance / pump blood a longer distance [1]
• (Accept: The right ventricle only pumps blood to the lungs (pulmonary circulation), which is a shorter distance and requires less pressure.)

8. Explain why the pulse rate increased after running. [2]

Answer:

• During running, muscles require more energy / carry out more respiration [1]
• Therefore, the heart beats faster to deliver more oxygen and glucose to muscles / remove carbon dioxide and lactic acid more quickly [1]

9. State ONE structural adaptation of a capillary and explain how this adaptation helps it perform its function. [2]

Answer:

• Adaptation: Capillary walls are one-cell thick / thin walls [1]
• Explanation: This provides a short diffusion distance for efficient exchange of substances (oxygen, carbon dioxide, nutrients, waste) between blood and tissue fluid [1]
• (Accept: Capillaries are narrow / have a small diameter — this slows blood flow, allowing more time for exchange / brings blood close to cells.)

10. Define the term peristalsis and state where it occurs in the digestive system. [2]

Answer:

• Definition: Peristalsis is the rhythmic, wave-like contraction and relaxation of muscles in the wall of the alimentary canal that pushes food along [1]
• Location: It occurs along the oesophagus / stomach / small intestine / large intestine (any correct part of the alimentary canal) [1]

11. Explain why a person with kidney failure may need to undergo dialysis. [2]

Answer:

• In kidney failure, the kidneys cannot effectively filter blood / remove metabolic waste products such as urea [1]
• Dialysis uses a machine with a semi-permeable membrane to remove urea and excess water/salts from the blood, performing the function of the failed kidneys [1]

12. State the equation for aerobic respiration. [1]

Answer:

• C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
• (Accept word equation: glucose + oxygen → carbon dioxide + water + energy)

13. Explain why breathing rate remains elevated for some time after vigorous exercise has stopped. [2]

Answer:

• During vigorous exercise, anaerobic respiration occurs in muscles, producing lactic acid [1]
• After exercise, extra oxygen is needed to break down/oxidise the accumulated lactic acid (repaying the oxygen debt), so breathing rate remains elevated to take in more oxygen [1]

Section C: Structured Response (20 marks)

14. Villus structure and absorption

(a) Identify structure X (the central vessel). [1]

Answer: Lacteal / lymph vessel / lymphatic vessel

(b) Explain how the structure of a villus is adapted for efficient absorption of digested food. [3]

Answer (any three adaptations with explanations, 1 mark each):

• Finger-like projection: increases surface area for absorption
• Thin epithelium / one-cell thick wall: provides a short diffusion distance for absorbed nutrients
• Dense network of blood capillaries: rapidly transports absorbed glucose and amino acids away, maintaining a concentration gradient
• Lacteal present: absorbs and transports fats/fatty acids and glycerol
• Microvilli on epithelial cells: further increase surface area for absorption

(c) Name the process by which glucose is absorbed when its concentration in the small intestine is lower than in the blood. [1]

Answer: Active transport

15. Enzyme activity and temperature

(a) Describe the trend shown in the graph between 10°C and 37°C. [1]

Answer: As temperature increases from 10°C to 37°C, enzyme activity increases.

(b) Explain why enzyme activity increases as temperature rises from 10°C to 37°C. [2]

Answer:

• As temperature increases, the kinetic energy of enzyme and substrate molecules increases [1]
• This leads to more frequent and more energetic collisions between enzyme and substrate molecules, increasing the rate of enzyme-substrate complex formation / increasing the rate of reaction [1]

(c) Explain why enzyme activity decreases sharply above 40°C. [2]

Answer:

• Above 40°C, the high temperature causes the enzyme to denature [1]
• The shape of the active site is altered/changed, so the substrate can no longer fit/bind to the active site (lock-and-key model disrupted) [1]

(d) Predict what would happen to enzyme activity at 70°C. Explain your answer. [2]

Answer:

• Prediction: Enzyme activity would be zero / the enzyme would be completely denatured / no reaction would occur [1]
• Explanation: At 70°C, the enzyme is fully denatured; the active site is permanently destroyed and cannot be restored, so no enzyme-substrate complexes can form [1]

16. Kidney function and urine formation

(a) Explain why protein is present in blood plasma but absent from glomerular filtrate. [2]

Answer:

• During ultrafiltration in the glomerulus, blood is filtered under high pressure through the basement membrane / filtration slits [1]
• Protein molecules are too large to pass through the filtration membrane, so they remain in the blood and are not filtered into the Bowman's capsule [1]

(b) Explain why glucose is present in glomerular filtrate but absent from urine. [2]

Answer:

• Glucose molecules are small enough to pass through the filtration membrane during ultrafiltration, so they enter the glomerular filtrate [1]
• However, all glucose is selectively reabsorbed back into the blood in the proximal convoluted tubule, so no glucose appears in the urine of a healthy person [1]

(c) Explain why the concentration of urea is much higher in urine than in glomerular filtrate. [2]

Answer:

• As filtrate moves through the nephron, most of the water is reabsorbed back into the blood [1]
• Urea is not reabsorbed (or only a small amount is reabsorbed), so it becomes more concentrated as water is removed, resulting in a higher concentration in urine [1]

17. Pathway of blood through the heart [4]

Answer: Blood flows through the heart in the following sequence (1 mark for each correct segment, up to 4 marks):

1. Deoxygenated blood enters the right atrium from the vena cava
2. Blood passes through the tricuspid valve into the right ventricle
3. Right ventricle contracts; blood passes through the semilunar/pulmonary valve into the pulmonary artery → to lungs
4. Oxygenated blood returns from lungs via pulmonary veins into the left atrium
5. Blood passes through the bicuspid/mitral valve into the left ventricle
6. Left ventricle contracts; blood passes through the aortic/semilunar valve into the aorta → to body

(Award marks for correct sequence including: right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → aortic valve → aorta. Accept 4 correct sequential steps for full marks.)

18. Alveolus structure and gas exchange [3]

Answer (any three adaptations with explanations, 1 mark each):

• Thin walls / one-cell thick epithelium: provides a short diffusion distance for oxygen and carbon dioxide
• Large surface area (numerous alveoli): maximises the area available for gas exchange
• Moist inner surface: allows gases to dissolve before diffusing across the membrane
• Dense network of blood capillaries surrounding each alveolus: maintains a steep concentration gradient by rapidly transporting gases to and from the alveoli
• Elastic walls: allow alveoli to expand and recoil during breathing, maintaining airflow

19. Reflex action

(a) Name the type of response described. [1]

Answer: Reflex action / reflex arc / reflex response

(b) Outline the pathway of the nerve impulse in this response, from the receptor to the effector. [3]

Answer:

1. Receptor (in skin) detects the stimulus (heat) and generates a nerve impulse [1]
2. Sensory neurone transmits the impulse to the spinal cord / central nervous system [1]
3. In the spinal cord, the impulse passes across a synapse to a relay neurone, then to a motor neurone
4. Motor neurone transmits the impulse to the effector (muscle in the arm) [1]
5. The effector (biceps muscle) contracts, causing the hand to withdraw

(Award marks for correct sequence: receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector. Accept 3 correct sequential steps.)

20. Blood glucose regulation [4]

Answer:

• When blood glucose concentration is too high (e.g., after a meal):

  • The pancreas detects the increase and releases insulin [1]
  • Insulin stimulates the liver (and muscle cells) to convert excess glucose into glycogen for storage [1]
  • This lowers blood glucose concentration back to normal

• When blood glucose concentration is too low (e.g., during fasting/exercise):

  • The pancreas detects the decrease and releases glucagon [1]
  • Glucagon stimulates the liver to convert stored glycogen back into glucose, which is released into the blood [1]
  • This raises blood glucose concentration back to normal

• This is an example of negative feedback, maintaining blood glucose within a narrow range (homeostasis).

(Award marks for: insulin role [1], glycogen conversion/storage [1], glucagon role [1], glycogen breakdown/glucose release [1]. Accept reference to negative feedback as an additional valid point.)

END OF ANSWER KEY