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Secondary 4 Pure Biology Human Physiology Quiz
Free Sec 4 Pure Biology Human Physiology quiz, DeepSeek 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: Short Answer & Identification
1. Pulmonary artery. [1]
2. Platelets are involved in blood clotting / help to clot blood at wound sites. [1]
3. Bowman's capsule / glomerulus. [1]
4. Glucagon. [1]
5. It transports absorbed nutrients (e.g., glucose, amino acids) from the small intestine directly to the liver for processing / before they enter general circulation. [1]
Section B: Structured Response
6. (a) Vessel A is the artery. Reason: It has a thicker muscular wall / narrower lumen compared to vessel B. [2]
(b) Arteries have thick, muscular, and elastic walls to withstand and maintain the high pressure of blood pumped from the heart. The elastic fibres allow the artery wall to stretch and recoil, helping to push blood along and maintain blood pressure between heartbeats. [2]
7. (a) As time after exercise increases, the heart rate decreases / heart rate falls from 140 bpm to 85 bpm over 10 minutes. [1]
(b) After exercise, the body needs to continue delivering extra oxygen to muscles to repay the oxygen debt (remove lactic acid produced during anaerobic respiration). The elevated heart rate maintains increased blood flow to remove waste products and restore normal conditions. [2]
(c) Decrease = 140 – 85 = 55 bpm. Percentage decrease = (55 ÷ 140) × 100 = 39.3% (accept 39.3% or 39%). [2] Marking: 1 mark for correct working, 1 mark for correct answer with units.
8. (a) In the healthy person, blood glucose rises to a lower peak (~7 mmol/L) and returns to resting level within 3 hours. In the diabetic person, blood glucose rises to a higher peak (~12 mmol/L), takes longer to peak, and does not return to resting level within 3 hours / remains elevated. [2]
(b) When blood glucose rises after a meal, the pancreas releases insulin. Insulin stimulates the liver and muscle cells to take up glucose and convert it to glycogen for storage, thereby lowering blood glucose back to normal. [2]
(c) The diabetic person's body cells are resistant to insulin / the pancreas does not produce enough insulin, so glucose uptake by cells is reduced. [1]
9. Peristalsis is the rhythmic, wave-like contraction and relaxation of circular and longitudinal muscles in the wall of the alimentary canal. It pushes food along the digestive tract from the oesophagus to the anus. It is important because it ensures food is mixed with digestive enzymes and moved through the gut for digestion and absorption. [3] Marking: 1 mark for describing muscle contraction/relaxation, 1 mark for movement of food, 1 mark for importance in digestion/absorption.
10. (a) The dialysis fluid contains no urea so that a concentration gradient for urea exists between the patient's blood (high urea) and the dialysis fluid (no urea), allowing urea to diffuse out of the blood. [1]
(b) The patient's blood flows on one side of a partially permeable membrane, and dialysis fluid flows on the other side. Urea diffuses from the blood (high concentration) across the membrane into the dialysis fluid (low concentration) down the concentration gradient. The dialysis fluid is continually replaced to maintain the gradient. [2]
11. (a) Structure C is the lacteal. Its function is to absorb fats / fatty acids and glycerol / lipids into the lymphatic system. [2]
(b) Two adaptations:
- The epithelium is one cell thick, providing a short diffusion distance for absorbed nutrients to reach the blood capillaries.
- The villus has a dense network of blood capillaries to rapidly transport absorbed glucose and amino acids away, maintaining a steep concentration gradient. (Accept: large surface area due to finger-like shape; presence of microvilli on epithelial cells.) [2]
12. During sprinting, muscles carry out anaerobic respiration due to insufficient oxygen supply, producing lactic acid. This creates an oxygen debt. After the race, heavy breathing continues to supply extra oxygen to the muscles to oxidise / break down the accumulated lactic acid into carbon dioxide and water (or convert it back to glucose in the liver). The increased breathing rate also helps remove excess carbon dioxide produced during respiration. [3] Marking: 1 mark for anaerobic respiration/lactic acid, 1 mark for oxygen debt, 1 mark for removal/breakdown of lactic acid.
Section C: Data Interpretation & Analysis
13. (a) Oxygen is absorbed from the alveoli into the blood and used by body cells for aerobic respiration, so less oxygen remains in expired air. [1]
(b) Carbon dioxide is a waste product of aerobic respiration in body cells. It diffuses from the blood into the alveoli and is exhaled, increasing its concentration in expired air. [1]
(c) Nitrogen is an inert gas that is not used or produced by the body, so its concentration remains unchanged. [1]
14. (a) The relay neurone connects the sensory neurone to the motor neurone within the spinal cord / central nervous system. [1]
(b) Reflex actions are rapid, automatic responses that occur without conscious thought. They protect the body by quickly withdrawing from harmful stimuli (e.g., heat, sharp objects) before serious tissue damage occurs. The speed of the response minimises injury. [2]
(c) A reflex action involves fewer synapses / a shorter neural pathway (only through the spinal cord, not the brain), reducing the time taken for impulse transmission. [1]
15. (a) As temperature increases from 10°C to 40°C, the rate of respiration increases / more CO₂ is produced. [1]
(b) Above 40°C, the enzymes involved in respiration begin to denature. The active site of the enzymes changes shape, so the substrate can no longer bind, and the rate of respiration decreases. At 60°C, the enzymes are completely denatured and respiration stops. [2]
(c) Glucose + Oxygen → Carbon dioxide + Water (+ Energy released). [1] Accept: correct chemical equation.
16. (a) Structure R (bladder) stores urine temporarily before it is expelled from the body. [1]
(b) The kidney filters blood, removing urea (a toxic nitrogenous waste produced from the breakdown of excess amino acids) and excess water and salts. It forms urine, which is then passed to the bladder for excretion. This process maintains the correct water and solute balance in the blood. [2]
(c) Urea is toxic. If it accumulates in the blood, it can damage cells and organs, leading to serious illness or death. [1]
17. (a) Sensory neurone. [1]
(b) The reflex arc involves the impulse travelling from the receptor to the spinal cord and directly to the motor neurone, causing immediate muscle contraction. The impulse for pain travels separately to the brain for conscious sensation, which takes longer. The withdrawal occurs before the brain processes the pain signal. [2]
18. (a) A person with blood group O has no antigens on their red blood cells, so their blood will not trigger an immune response in a recipient with blood group AB (who has both A and B antigens). However, a person with blood group AB has both A and B antigens, which would be recognised as foreign by a person with blood group O (who has anti-A and anti-B antibodies), causing agglutination / clumping of red blood cells. [2]
(b) If incompatible blood groups are mixed, the recipient's antibodies will attack the donor's red blood cells, causing agglutination, which can block blood vessels and be fatal. [1]
19. (a) R (pulmonary vein). [1]
(b) Chamber Z is the left ventricle, which pumps blood to the entire body (systemic circulation). This requires high pressure to overcome the resistance of the long systemic circuit. Chamber X is the right ventricle, which pumps blood only to the nearby lungs (pulmonary circulation), requiring lower pressure. The thicker muscular wall of the left ventricle generates the greater force needed. [2]
(c) Valves prevent the backflow of blood, ensuring that blood flows in one direction through the heart. [1]
20. On a hot day:
- Thermoreceptors in the skin and hypothalamus detect the rise in blood temperature.
- The hypothalamus sends signals to effectors.
- Sweat glands increase sweat production; evaporation of sweat from the skin surface removes heat, cooling the body.
- Arterioles in the skin dilate (vasodilation), allowing more blood to flow near the skin surface, increasing heat loss by radiation and convection.
- Hair erector muscles relax, so hairs lie flat, reducing insulation and allowing more heat to escape.
- Metabolic rate may decrease to reduce internal heat production. [4] Marking: 1 mark for detection (thermoreceptors/hypothalamus), 1 mark for sweating/evaporation, 1 mark for vasodilation, 1 mark for hair/other mechanism. Accept any four valid points.
END OF ANSWER KEY