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Secondary 4 Pure Biology Human Physiology Quiz
Free Sec 4 Pure Biology Human Physiology quiz, Qwen3.6 Exam version, with questions, answers, and O Level-style practice for Singapore students.
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Secondary 4 Pure Biology Quiz - Human Physiology (Answer Key)
Total Marks: 40
Section A: Multiple Choice Answers
1. A
Marks: [1]
Reasoning: Arteries carry blood away from the heart, veins to the heart, and capillaries are the site of exchange.
2. A
Marks: [1]
Reasoning: Coronary arteries supply the heart muscle itself. Blockage leads to ischemia (lack of oxygen) in the heart muscle.
3. B
Marks: [1]
Reasoning: Diaphragm contraction increases thoracic volume, decreasing pressure (Boyle's Law). Lowest pressure corresponds to maximum inhalation effort.
4. C
Marks: [1]
Reasoning: Human anaerobic respiration produces lactic acid and a small amount of ATP. No CO2 is produced in human muscle anaerobic respiration.
5. B
Marks: [1]
Reasoning: Glucose is selectively reabsorbed in the proximal convoluted tubule via active transport.
Section B: Structured Answers
6.
(a) Bicuspid valve (or Mitral valve). [1]
(b) The left ventricle pumps blood to the whole body (systemic circulation), which requires high pressure to overcome resistance in distant vessels. The right ventricle only pumps to the lungs (pulmonary circulation), which is a shorter distance with lower resistance. [2]
7.
(a) Protein molecules are too large to pass through the pores of the glomerular capillaries / Bowman’s capsule filter. [2]
(b) Water is reabsorbed from the filtrate back into the blood (in the Loop of Henle and collecting duct), but urea is not reabsorbed (or only partially). This concentrates the urea in the remaining fluid (urine). [2]
8.
(a) As temperature increases, kinetic energy of enzyme and substrate molecules increases. This leads to more frequent successful collisions between the enzyme active site and substrate, increasing the rate of reaction. [2]
(b) At 60°C, the high heat energy breaks the bonds holding the enzyme's tertiary structure. The enzyme denatures, changing the shape of the active site. The substrate can no longer fit into the active site, so no reaction occurs. [2]
9.
(a) Any two of:
- Wall is one cell thick (short diffusion distance).
- Large surface area (due to finger-like projection/microvilli).
- Rich blood supply (capillary network) maintains concentration gradient. [2]
(b) Hepatic portal vein. [1]
10.
(a) Working: Volume per breath = Total Volume / Breathing Rate
Answer: 2.0 dm³ [2]
(b) During exercise, muscles respire more aerobically to produce energy (ATP). This requires more oxygen and produces more carbon dioxide. The increased breathing rate and volume allow for greater gas exchange to meet these demands. [2]
11.
(a) Pancreas. [1]
(b) Insulin causes glucose to be converted into glycogen in the liver and muscle cells. It also increases the uptake of glucose by body cells for respiration. This lowers blood glucose concentration. [2]
12.
(a) Arm muscle (or biceps). [1]
(b) Reflex actions are involuntary and bypass the brain (processed in spinal cord), resulting in a much faster response time. This minimizes tissue damage from harmful stimuli. [2]
13.
(a) Carbon monoxide binds to haemoglobin with a higher affinity than oxygen, forming carboxyhaemoglobin. This reduces the amount of haemoglobin available to carry oxygen. [2]
(b) Tar contains carcinogens (cancer-causing chemicals) that damage the DNA of lung cells, leading to uncontrolled cell division (tumors). [1]
14.
(a) Excretion is the removal of toxic metabolic waste products (such as urea and carbon dioxide) from the body. [1]
(b) To prevent the loss of useful substances from the blood by diffusion. If the concentration in the dialysis fluid were lower, glucose/salts would diffuse out of the blood. If higher, they would diffuse into the blood. Equilibrium ensures no net movement. [2]
15.
(a) Iris. [1]
(b) Circular muscles of the iris contract. Radial muscles of the iris relax. This causes the pupil to constrict (become smaller), reducing the amount of light entering the eye to prevent damage to the retina. [2]
Section C: Free Response Answers
16.
Structure: Arteries have thick, elastic walls and a small lumen. Veins have thinner walls, a larger lumen, and contain valves.
Function: Arteries carry blood away from the heart under high pressure; elasticity helps withstand pressure surges. Veins carry blood to the heart under low pressure; valves prevent backflow of blood.
[4 marks: 2 for structure comparison, 2 for function link]
17.
- Large Surface Area: Millions of alveoli provide a vast surface area for gas exchange.
- Thin Walls: Alveolar walls and capillary walls are one cell thick, providing a short diffusion distance for oxygen and carbon dioxide.
- Moist Surface: The lining is moist, allowing gases to dissolve before diffusing.
- Rich Blood Supply: Dense capillary network maintains a steep concentration gradient for efficient diffusion.
[4 marks: 1 mark per point explained]
18.
- Blood enters the glomerulus under high pressure (due to wider afferent arteriole than efferent arteriole).
- This high pressure forces small molecules (water, glucose, urea, salts) out of the blood.
- These molecules pass through the porous capillary walls and the basement membrane into the Bowman’s capsule.
- Large molecules like blood cells and plasma proteins remain in the blood as they are too large to pass through the filter.
[4 marks: 1 mark per step]
19.
- After 24 hours, blood glucose levels drop below normal.
- The pancreas detects this low level and secretes glucagon.
- Glucagon travels to the liver via the blood.
- It stimulates the conversion of stored glycogen into glucose (glycogenolysis).
- Glucose is released into the bloodstream, raising blood glucose levels back to normal.
[4 marks: Logical sequence of homeostatic mechanism]
20.
Nervous Coordination:
- Signals are electrical impulses along neurones.
- Transmission is very fast.
- Response is short-lived.
- Effectors are muscles or glands.
- Localized response.
Hormonal Coordination:
- Signals are chemicals (hormones) transported in blood.
- Transmission is slower.
- Response is long-lasting.
- Effectors are specific target organs.
- Widespread response.
[4 marks: 2 distinct differences clearly explained]