Secondary 4 Combined Science Biology Human Physiology Quiz

Secondary 4 Combined Science Biology Quiz - Human Physiology

Answer Key

Section A: Multiple Choice & Short Answer (Questions 1–10)

1. D — Left ventricle [1]
Explanation: The left ventricle has the thickest muscular wall because it must generate enough pressure to pump oxygenated blood throughout the entire body (systemic circulation), whereas the right ventricle only pumps blood to the lungs (pulmonary circulation), which is a shorter distance and requires less pressure.

2. C — Clot blood at wound sites [1]
Explanation: Platelets (thrombocytes) are cell fragments that release thromboplastin at wound sites, initiating the clotting cascade. Red blood cells transport oxygen, and white blood cells fight infection.

3. C — Bowman's capsule [1]
Explanation: Blood is forced under high pressure into the glomerulus (a network of capillaries) inside Bowman's capsule. The high pressure forces small molecules (water, glucose, urea, ions) out of the blood and into the Bowman's capsule, forming the glomerular filtrate. Large molecules like proteins and blood cells are too large to pass through.

4. B — The body requires more oxygen and needs to remove more carbon dioxide [1]
Explanation: During exercise, muscle cells carry out aerobic respiration at a faster rate, consuming more oxygen and producing more carbon dioxide. The increased breathing rate ensures a greater supply of oxygen to the blood and faster removal of carbon dioxide from the body.

5. C — Insulin [1]
Explanation: When blood glucose rises (e.g., after a meal), beta cells in the islets of Langerhans in the pancreas detect the increase and secrete insulin. Insulin stimulates cells (especially liver and muscle cells) to take up glucose from the blood and convert it to glycogen for storage, thereby lowering blood glucose concentration back to normal.

6. Two structural features of an artery compared to a vein: [2]
(i) Arteries have thicker, more muscular and elastic walls than veins. [1]
(ii) Arteries have no valves (except the semi-leart valves at the base of the aorta and pulmonary artery), whereas veins have valves to prevent backflow of blood. [1]
Alternative acceptable answer: Arteries have a smaller lumen (internal diameter) compared to veins.
Marking note: Award 1 mark for each correct feature. Do not accept "arteries carry oxygenated blood" as this is a functional, not structural, feature (and the pulmonary artery is an exception).

7. The left ventricle has a thicker muscular wall than the right ventricle because it needs to pump blood all around the body (systemic circulation), which requires much greater pressure. [1] The right ventricle only pumps blood to the lungs (pulmonary circulation), which is a much shorter distance and requires less pressure. [1]
Marking note: Award 1 mark for identifying the greater distance/systemic circulation and 1 mark for linking the thicker wall to the need for greater pressure.

8. In distilled water, the red blood cells would swell up and eventually burst (haemolyse). [1] This is because distilled water is a hypotonic solution — it has a higher water potential (lower solute concentration) than the cytoplasm of the red blood cells. Water molecules move into the cells by osmosis, from a region of higher water potential (outside the cell) to a region of lower water potential (inside the cell). [1]
Marking note: Award 1 mark for the observation (swell/burst/haemolyse) and 1 mark for the explanation involving osmosis and water potential. "Osmosis" must be mentioned for the explanation mark.

9. Definition: Homeostasis is the maintenance of a constant internal environment within the body. [1]
Example: Body temperature is maintained at approximately 37°C. [1]
Alternative acceptable examples: Blood glucose concentration maintained at approximately 90 mg/100 cm³; water content of the blood; blood pH; concentration of carbon dioxide in the blood.
Marking note: The definition must include the idea of maintaining a constant/ stable internal environment. Award 1 mark for a correct example.

10. (a) X: Trachea [0.5] Y: Bronchus (plural: bronchi) [0.5]
(b) Any one of the following: [1]

• Alveoli have a large surface area for gas exchange.
• Alveoli have thin walls (one cell thick / squamous epithelium) for rapid diffusion.
• Alveoli are surrounded by a dense network of blood capillaries to maintain a steep concentration gradient.
• Alveoli have a moist surface for gases to dissolve before diffusing.
  Marking note: Award 1 mark for any one correct feature.

Section B: Structured Response (Questions 11–17)

11. (a) Glucose is present in the glomerular filtrate because it is a small molecule that is filtered out of the blood at the Bowman's capsule. [1] It is absent from urine because it is selectively reabsorbed back into the blood in the proximal convoluted tubule by active transport. [1]
(b) Protein molecules are too large to pass through the filtration membrane (the walls of the capillaries and the Bowman's capsule) during ultrafiltration. [1]
(c) Water is reabsorbed from the filtrate back into the blood along the nephron (especially in the Loop of Henle and collecting duct), but urea is not reabsorbed. This means the same amount of urea is present in a smaller volume of fluid, so its concentration increases. [1]
Marking note for (c): Accept answers that mention water reabsorption concentrating the urea, or that the kidneys remove water but retain urea.

12. [4 marks — 1 mark for each of the following key points, up to 4]
Deoxygenated blood from the body enters the right atrium through the vena cava. [1]
It passes through the tricuspid (right atrioventricular) valve into the right ventricle. [1]
The right ventricle pumps the blood through the pulmonary (semi-lunar) valve into the pulmonary artery, which carries it to the lungs for gas exchange. [1]
Oxygenated blood returns from the lungs via the pulmonary vein into the left atrium. [1]
It passes through the bicuspid (left atrioventricular/mitral) valve into the left ventricle. [1]
The left ventricle pumps the blood through the aortic (semi-lunar) valve into the aorta, which distributes it to the rest of the body. [1]
Marking note: Award up to 4 marks. The answer must include all four chambers (right atrium, right ventricle, left atrium, left ventricle) and at least two named blood vessels and two named valves for full marks. Award 1 mark for each correct component mentioned, up to a maximum of 4.

13. [4 marks]
After a carbohydrate-rich meal, blood glucose concentration rises above the normal level. [1]
The beta cells in the islets of Langerhans in the pancreas detect this increase and secrete the hormone insulin into the bloodstream. [1]
Insulin stimulates liver cells and muscle cells to take up excess glucose from the blood and convert it into glycogen for storage (glycogenesis). [1]
Insulin also increases the rate of glucose uptake and usage by body cells for respiration. [1]
As a result, blood glucose concentration falls back to the normal range (approximately 90 mg/100 cm³). [1]
Marking note: Award up to 4 marks. Key points: detection by pancreas, insulin named, target organs (liver/muscle), conversion to glycogen, blood glucose returns to normal. Award 1 mark per valid point up to 4.

14. (a) Resting heart rate = 70 beats per minute. [1]
(b) During exercise, the muscle cells need more energy, so they carry out aerobic respiration at a faster rate. [1] This requires more oxygen to be delivered to the muscles and more carbon dioxide to be removed. The heart rate increases to pump blood faster, delivering more oxygen and glucose to the muscles and removing carbon dioxide more quickly. [1]
(c) After exercise, the heart rate remains elevated because the body needs to repay the oxygen debt — extra oxygen is needed to break down the lactic acid that accumulated in the muscles during anaerobic respiration, and to restore the oxygen levels in the blood and muscles. [1]
Alternative for (c): The body is still removing excess carbon dioxide produced during exercise.
Marking note for (b): Award 1 mark for linking exercise to increased respiration and 1 mark for explaining the need for faster oxygen delivery/CO₂ removal.

15. [3 marks — 1 mark for each correct adaptation, up to 3]

• Capillaries have very thin walls (only one cell thick / made of a single layer of endothelial cells), which provides a short diffusion distance for substances to pass between the blood and the tissues.
• Capillaries have a very narrow diameter (lumen), which means red blood cells pass through in single file, slowing down blood flow and allowing more time for exchange of substances.
• Capillaries are present in an extensive, dense network throughout all body tissues, providing a very large total surface area for exchange.
• The walls of capillaries are partially permeable, allowing small molecules (glucose, oxygen, amino acids, water) to pass through while retaining larger molecules like proteins in the blood.
  Marking note: Award 1 mark for each correct structural adaptation linked to its function, up to 3 marks.

16. (a) Type 1 diabetes (insulin-dependent diabetes mellitus). [1]
(b) Two symptoms with explanations: [2]
Symptom 1: High blood glucose concentration (hyperglycaemia) — because without insulin, glucose cannot be taken up by liver and muscle cells and converted to glycogen, so it accumulates in the blood. [1]
Symptom 2: Glucose in the urine (glucosuria) — because the blood glucose level exceeds the renal threshold, and the kidneys cannot reabsorb all the filtered glucose, so it passes into the urine. [1]
Alternative acceptable symptoms: Excessive thirst (because high blood glucose increases the water potential of blood, causing water to be drawn from tissues); weight loss (because the body starts breaking down fats and proteins for energy instead of glucose); frequent urination (because glucose in the urine draws water out by osmosis).
Marking note: Award 1 mark for each symptom with a correct explanation, up to 2 marks.

17. [3 marks]

Marking note: Award 0.5 marks for each correctly filled cell, up to 3 marks. The word equation for aerobic respiration is: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP). For anaerobic respiration in muscles: Glucose → Lactic acid + Energy (ATP).

Section C: Data Interpretation & Application (Questions 18–20)

18. (a) Working: (28 + 30 + 32) ÷ 3 = 90 ÷ 3 = 30 [1]
Answer: 30 breaths/min

(b) The breathing rate approximately doubles after exercise (from 15 breaths/min at rest to 30 breaths/min after exercise). [1]
Marking note: Accept any correct description of the trend (e.g., "breathing rate increases significantly after exercise").

(c) During exercise, muscle cells respire at a faster rate, using up more oxygen and producing more carbon dioxide. [1] The increased breathing rate brings more air (and therefore more oxygen) into the lungs, increasing the rate of gas exchange so that more oxygen enters the blood and more carbon dioxide is removed. [1]
Marking note: Award 1 mark for linking exercise to increased respiration and 1 mark for explaining the need for more oxygen/removal of CO₂.

(d) Taking three trials and calculating an average increases the reliability of the results / reduces the effect of random errors / allows anomalous results to be identified. [1]
Marking note: Award 1 mark for any valid reason related to reliability, accuracy, or identifying anomalies.

19. (a) [3 marks — 1 mark each]
A: Sweat gland
B: Blood vessel (arteriole / capillary)
C: Temperature receptor (thermoreceptor)
Marking note: Accept "capillary network" or "arteriole" for B. Accept "thermoreceptor" or "heat receptor" for C.

(b) When blood vessels in the skin dilate (vasodilation), more blood flows near the surface of the skin. [1] This increases heat loss from the blood to the surroundings by radiation (and conduction/convection), which helps to lower the body temperature back to 37°C. [1]
Marking note: Award 1 mark for describing vasodilation/increased blood flow to the skin surface and 1 mark for explaining heat loss by radiation.

(c) When body temperature rises, sweat glands produce sweat, which is mostly water. [1] The sweat evaporates from the skin surface, and this process of evaporation requires heat energy (latent heat of vaporisation), which is taken from the body, thereby cooling the skin and lowering body temperature. [1]
Marking note: Award 1 mark for sweat production and 1 mark for evaporation causing cooling. The term "evaporation" must be mentioned for the second mark.

20. (a) Any two of the following: [2 — 1 mark each]
(i) Heart beats faster and more forcefully
(ii) Breathing rate increases
(iii) Blood glucose levels rise (glycogen converted to glucose in the liver)
(iv) Blood is redirected away from the digestive system and towards skeletal muscles

(b) Blood glucose levels rise so that more glucose is available in the blood for muscle cells to use as a respiratory substrate. [1] During a "fight or flight" response, the muscles need to work harder and faster, which requires more energy. Increasing the glucose supply ensures that muscle cells can carry out aerobic (and anaerobic) respiration at a higher rate to produce the ATP needed for rapid muscle contraction. [1]
Marking note: Award 1 mark for linking glucose to energy/respiration and 1 mark for explaining the increased demand during fight or flight.

(c) Blood is redirected away from the digestive system so that more blood (carrying oxygen and glucose) can be sent to the skeletal muscles, which need more energy for movement during the "fight or flight" response. [1]
Alternative acceptable answer: Digestion is not a priority during an emergency, so blood is diverted to where it is most needed (the muscles).
Marking note: Award 1 mark for explaining the redirection of blood to muscles for energy/movement.

End of Answer Key