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Secondary 4 Pure Biology Human Physiology Quiz
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Questions
Secondary 4 Pure Biology Quiz - Human Physiology
Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ________ / 50
Duration: 60 minutes
Total Marks: 50
Instructions
- Answer all questions in the spaces provided.
- The number of marks for each question or part-question is shown in brackets [ ].
- You are advised to spend no more than 60 minutes on this quiz.
- Write your answers clearly and in complete sentences where required.
- Where diagrams are referenced, they are described in the question text.
Section A: Multiple Choice & Short Answer (Questions 1–10)
Questions 1–5: Choose the most accurate answer. Each question carries 2 marks.
1. Which of the following is the primary function of the sinoatrial node (SAN) in the human heart?
A. To regulate blood pressure in the aorta
B. To initiate the electrical impulse that triggers atrial contraction
C. To filter deoxygenated blood entering the right atrium
D. To control the opening and closing of the atrioventricular valves
Answer: _______________ [2]
2. During gas exchange in the alveoli, oxygen moves from the alveolar air space into the blood capillaries by which process?
A. Active transport
B. Osmosis
C. Diffusion down a concentration gradient
D. Facilitated diffusion using carrier proteins
Answer: _______________ [2]
3. A person's blood glucose concentration rises after a meal. Which hormone is primarily responsible for restoring blood glucose to its normal level?
A. Glucagon
B. Adrenaline
C. Insulin
D. Thyroxine
Answer: _______________ [2]
4. Which component of the nephron is responsible for the filtration of blood under high pressure?
A. Loop of Henle
B. Collecting duct
C. Bowman's capsule (glomerulus)
D. Distal convoluted tubule
Answer: _______________ [2]
5. Which of the following correctly describes the role of the medulla oblongata?
A. Coordination of voluntary muscle movement
B. Regulation of body temperature only
C. Control of involuntary actions such as heart rate and breathing
D. Production of growth hormone
Answer: _______________ [2]
Questions 6–10: Short answer questions. Write your answer in the space provided.
6. State two structural features of an alveolus that make it efficient for gas exchange. [2]
(i) _______________________________________________________________
(ii) _______________________________________________________________
7. Define the term homeostasis and give one example of a condition maintained by homeostasis in the human body. [2]
Definition: ___________________________________________________________
Example: ______________________________________________________________
8. Name the blood vessel that carries oxygenated blood from the lungs to the heart. [1]
Answer: ______________________________________________________________
9. State one function of the lymphatic system in human physiology. [1]
Answer: ______________________________________________________________
10. What is the name of the process by which the body loses heat energy through the evaporation of sweat from the skin surface? [1]
Answer: ______________________________________________________________
Section B: Structured Response (Questions 11–17)
Answer all questions. Show your reasoning clearly.
11. Fig. 11 (described below) shows a simplified diagram of the human heart.
Description of Fig. 11: A diagram of the human heart showing four chambers — right atrium (top left), right ventricle (bottom left), left atrium (top right), and left ventricle (bottom right). Blood vessels are labelled: vena cava entering the right atrium, pulmonary artery leaving the right ventricle, pulmonary veins entering the left atrium, and aorta leaving the left ventricle. The left ventricle wall is drawn thicker than the right ventricle wall.
(a) Explain why the wall of the left ventricle is thicker than the wall of the right ventricle. [2]
(b) State the function of the valves located between the atria and ventricles. [1]
(c) A student claims that all arteries carry oxygenated blood. Evaluate this statement using one specific counterexample from the circulatory system. [2]
[Total: 5 marks]
12. An experiment was conducted to investigate the effect of exercise on the breathing rate and heart rate of a student. The results are shown in Table 12.
Table 12:
| Time (min) | Breathing rate (breaths/min) | Heart rate (beats/min) |
|---|---|---|
| 0 (resting) | 15 | 72 |
| 2 | 28 | 130 |
| 4 | 35 | 155 |
| 6 | 38 | 162 |
| 8 (recovery) | 20 | 90 |
| 10 (recovery) | 16 | 75 |
(a) Describe the trend in breathing rate from 0 to 6 minutes. [2]
(b) Explain why the breathing rate increases during exercise. Your answer should refer to cellular respiration. [3]
(c) Suggest why the heart rate at 10 minutes of recovery (75 beats/min) is still slightly higher than the resting heart rate (72 beats/min). [1]
[Total: 6 marks]
13. Fig. 13 (described below) shows a simplified diagram of the human digestive system.
Description of Fig. 13: A diagram showing the oesophagus leading to the stomach, which connects to the small intestine (coiled tube), which leads to the large intestine. The liver and pancreas are also shown, with ducts leading from each into the small intestine.
(a) Name the enzyme produced by the stomach and state its optimum pH. [2]
Enzyme: ______________________________________________________________
Optimum pH: __________________________________________________________
(b) Bile is produced by the liver and stored in the gall bladder. Describe the role of bile in digestion. [2]
(c) Explain how the structure of the small intestine is adapted for the absorption of digested food. State two adaptations. [2]
(i) _______________________________________________________________
(ii) _______________________________________________________________
[Total: 6 marks]
14. The following data was collected from a patient during a medical examination:
| Parameter | Patient's value | Normal range |
|---|---|---|
| Blood glucose (mmol/L) | 9.2 | 4.0–7.0 (fasting) |
| Urine glucose | Present | Absent |
| Urine protein | Absent | Absent |
(a) Suggest a condition the patient may be suffering from. Give one reason for your answer based on the data. [2]
Condition: ____________________________________________________________
Reason: ________________________________________________________________
(b) Explain why glucose appears in the patient's urine. Your answer should refer to the function of the nephron. [3]
(c) State one long-term health consequence if this condition is not managed. [1]
[Total: 6 marks]
15. Fig. 15 (described below) shows a simplified diagram of the human eye.
Description of Fig. 15: A cross-section of the eye showing the cornea at the front, the iris and pupil behind it, the lens suspended by ciliary muscles, the retina at the back, and the optic nerve extending from the retina. The fovea is indicated as a small depression on the retina.
(a) State the function of the ciliary muscles in the eye. [1]
(b) Explain how the eye adjusts when a person moves from a bright environment into a dark room. Include the roles of the iris and pupil in your answer. [3]
(c) State the function of the fovea. [1]
[Total: 5 marks]
16. A student placed their hand in ice-cold water for 30 seconds. They noticed that the skin on their hand became pale.
(a) Explain the physiological response that caused the skin to become pale. Your answer should refer to the role of arterioles. [3]
(b) State the advantage of this response in terms of thermoregulation. [1]
(c) After removing the hand from the ice water, the skin became red and felt warm. Name this process and explain why it occurs. [2]
Process: ______________________________________________________________
Explanation: ___________________________________________________________
[Total: 6 marks]
17. Fig. 17 (described below) shows a simplified diagram of a neurone.
Description of Fig. 17: A motor neurone is shown with a cell body (soma) containing a nucleus, several short branching dendrites extending from the cell body, a long axon extending from the cell body, and axon terminals at the end. The axon is surrounded by a myelin sheath with gaps (nodes of Ranvier) at regular intervals.
(a) Label the direction of impulse transmission on the neurone (from __________ to __________). [1]
(b) Explain the function of the myelin sheath in the transmission of nerve impulses. [2]
(c) A reflex arc involves a sensory neurone, a relay neurone, and a motor neurone. Explain why reflex actions are important for survival. Use one specific example in your answer. [2]
[Total: 5 marks]
Section C: Data Interpretation & Extended Response (Questions 18–20)
Answer all questions in detail.
18. A study was conducted to compare the composition of inspired air and expired air. The results are shown in Table 18.
Table 18:
| Gas | Inspired air (%) | Expired air (%) |
|---|---|---|
| Nitrogen | 78 | 78 |
| Oxygen | 21 | 16 |
| Carbon dioxide | 0.04 | 4 |
| Water vapour | Variable | Saturated |
| Other gases | 0.96 | 0.96 |
(a) Explain why the percentage of oxygen decreases in expired air. [2]
(b) Explain why the percentage of carbon dioxide increases significantly in expired air. [2]
(c) Nitrogen makes up 78% of both inspired and expired air. Explain why the nitrogen content does not change. [1]
(d) Explain why expired air contains more water vapour than inspired air. [1]
(e) A student stated: "We breathe out carbon dioxide, which means the lungs are an excretory organ." Evaluate this statement. [2]
[Total: 8 marks]
19. Fig. 19 (described below) shows the blood glucose concentration of two individuals, P and Q, over a 12-hour period. Both individuals ate identical meals at 0 hours and 6 hours.
Description of Fig. 19: A line graph with time (hours) on the x-axis (0 to 12) and blood glucose concentration (mmol/L) on the y-axis (3 to 12). Individual P shows a normal response: glucose rises to about 7.0 mmol/L after each meal and returns to baseline (~5.0 mmol/L) within 2 hours. Individual Q shows an abnormal response: glucose rises to about 10.5 mmol/L after each meal and remains elevated at approximately 8.5 mmol/L even after 3 hours, not returning to baseline.
(a) Describe the blood glucose pattern for individual P after the first meal (0–3 hours). [2]
(b) Explain the role of insulin in producing the pattern seen in individual P. [3]
(c) Suggest what condition individual Q may have. Explain your reasoning with reference to the data. [3]
(d) State one dietary recommendation that could help individual Q manage their blood glucose levels. [1]
[Total: 9 marks]
20. A patient was admitted to hospital with symptoms including excessive thirst, frequent urination, and unexplained weight loss. Blood tests revealed abnormally high levels of glucagon and low levels of insulin.
(a) Explain how low insulin levels lead to high blood glucose concentration. [3]
(b) Explain why the patient experiences excessive thirst when blood glucose levels are high. Your answer should refer to the effect on the kidney nephron. [3]
(c) Explain why the patient experiences unexplained weight loss. [2]
(d) State the name of the endocrine gland responsible for producing both insulin and glucagon. [1]
[Total: 9 marks]
Answers
Secondary 4 Pure Biology Quiz - Human Physiology
Answer Key
Section A: Multiple Choice & Short Answer (Questions 1–10)
1. B — To initiate the electrical impulse that triggers atrial contraction [2]
Explanation: The sinoatrial node (SAN) is the natural pacemaker of the heart. It generates electrical impulses that spread across the atria, causing atrial contraction. Common mistake: Students may select A (blood pressure regulation), which is controlled by baroreceptors and the medulla oblongata, not the SAN.
2. C — Diffusion down a concentration gradient [2]
Explanation: Oxygen moves from the alveolar air space (high O₂ concentration) into the blood in surrounding capillaries (low O₂ concentration) by simple diffusion. This is a passive process and does not require energy (ruling out A) or carrier proteins (ruling out D). Osmosis (B) refers specifically to the movement of water molecules.
3. C — Insulin [2]
Explanation: After a meal, blood glucose rises. Beta cells in the pancreas secrete insulin, which promotes the uptake of glucose by body cells and the conversion of excess glucose to glycogen in the liver and muscles, thereby lowering blood glucose. Glucagon (A) raises blood glucose and is secreted when levels are low. Adrenaline (B) is involved in the fight-or-flight response. Thyroxine (D) regulates metabolic rate.
4. C — Bowman's capsule (glomerulus) [2]
Explanation: The glomerulus is a network of capillaries within Bowman's capsule where ultrafiltration of blood occurs under high pressure. The Loop of Henle (A) is involved in water reabsorption. The collecting duct (B) concentrates urine. The distal convoluted tubule (D) fine-tunes reabsorption and secretion.
5. C — Control of involuntary actions such as heart rate and breathing [2]
Explanation: The medulla oblongata is part of the brainstem and controls autonomic (involuntary) functions including heart rate, breathing rate, and blood pressure. Coordination of voluntary movement (A) is the role of the cerebellum. Body temperature regulation (B) is controlled by the hypothalamus. Growth hormone (D) is produced by the pituitary gland.
6. Two structural features of an alveolus that make it efficient for gas exchange: [2]
(i) The alveolar wall is one cell thick (or very thin), providing a short diffusion distance for gases.
(ii) The alveoli are surrounded by a dense network of blood capillaries, maintaining a steep concentration gradient for gas exchange.
Other acceptable answers: Large surface area of alveoli (millions of alveoli); moist lining of alveolus allowing gases to dissolve before diffusing.
Marking note: Award 1 mark for each correct feature, up to a maximum of 2 marks.
7. [2]
Definition: Homeostasis is the maintenance of a constant internal environment within the body despite changes in external conditions.
Example: Regulation of body temperature at approximately 37 °C (or regulation of blood glucose concentration / regulation of water balance / regulation of blood pH).
Marking note: 1 mark for a correct definition; 1 mark for a valid example. The definition must convey the idea of maintaining a stable/constant internal environment.
8. Pulmonary vein [1]
Explanation: The pulmonary vein carries oxygenated blood from the lungs to the left atrium of the heart. Common mistake: Students may write "pulmonary artery," which carries deoxygenated blood from the right ventricle to the lungs.
9. One function of the lymphatic system: [1]
Acceptable answers (any one):
- Returns excess tissue fluid (lymph) back to the bloodstream.
- Transports fats absorbed from the small intestine (lacteals).
- Filters pathogens and foreign particles through lymph nodes (immune defence).
- Produces and stores lymphocytes (white blood cells) for immune response.
10. Evaporation [1]
Explanation: When sweat evaporates from the skin surface, it absorbs latent heat energy from the body, thereby cooling the body. This is a key mechanism of thermoregulation.
Section B: Structured Response (Questions 11–17)
11. [Total: 5 marks]
(a) [2] The left ventricle has a thicker muscular wall than the right ventricle because it needs to generate greater pressure to pump oxygenated blood through the aorta to the entire body (systemic circulation). The right ventricle only pumps deoxygenated blood through the pulmonary artery to the lungs (pulmonary circulation), which is a shorter distance and requires less pressure.
Marking note: Award 1 mark for identifying that the left ventricle pumps blood further / to the whole body, and 1 mark for linking the thicker wall to the need to generate higher pressure.
(b) [1] The atrioventricular valves (tricuspid and bicuspid/mitral valves) prevent the backflow of blood from the ventricles into the atria when the ventricles contract.
(c) [2] The student's statement is incorrect. A counterexample is the pulmonary artery, which carries deoxygenated blood from the right ventricle to the lungs. (Alternatively: The umbilical artery in a foetus carries deoxygenated blood.)
Marking note: Award 1 mark for stating the statement is incorrect / providing a valid counterexample, and 1 mark for identifying the specific vessel and the type of blood it carries.
12. [Total: 6 marks]
(a) [2] The breathing rate increases steadily from 15 breaths/min at rest to 38 breaths/min at 6 minutes of exercise. The rate of increase is greatest between 0 and 2 minutes, and the rate of increase slows between 4 and 6 minutes (the breathing rate approaches a maximum).
Marking note: Award 1 mark for describing the overall increase, and 1 mark for describing the change in rate of increase (deceleration / levelling off).
(b) [3] During exercise, muscle cells respire at a faster rate to release more energy (ATP) for muscle contraction. This increased cellular respiration requires more oxygen and produces more carbon dioxide. The increased carbon dioxide concentration in the blood is detected by receptors in the medulla oblongata / carotid bodies, which send signals to increase the breathing rate. This allows more oxygen to be taken in and more carbon dioxide to be removed.
Marking note: Award 1 mark for linking exercise to increased cellular respiration; 1 mark for stating that more CO₂ is produced / more O₂ is needed; 1 mark for explaining the detection of CO₂ and the resulting increase in breathing rate.
(c) [1] The body is still recovering — oxygen is still being used to repay the oxygen debt (or to convert accumulated lactic acid back to pyruvate / glucose), so the heart rate remains slightly elevated to deliver oxygen faster to the muscles.
13. [Total: 6 marks]
(a) [2]
Enzyme: Pepsin
Optimum pH: pH 2 (acidic)
Marking note: 1 mark for pepsin; 1 mark for pH 2 (or "acidic" / "pH 1.5–2").
(b) [2] Bile emulsifies fats — it breaks large fat globules into smaller droplets, increasing the surface area for the enzyme lipase to act on. Bile also neutralises the acidic food coming from the stomach, providing an alkaline pH suitable for enzymes in the small intestine.
Marking note: Award 1 mark for emulsification of fats, and 1 mark for neutralisation of acid / providing alkaline conditions.
(c) [2] Two adaptations of the small intestine for absorption:
(i) It is very long (approximately 5–6 metres), providing a large surface area and sufficient time for absorption.
(ii) The inner wall has finger-like projections called villi (and microvilli on epithelial cells), which greatly increase the surface area for absorption.
Other acceptable answers: The villus wall is one cell thick (short diffusion distance); each villus contains a network of blood capillaries for rapid transport of absorbed nutrients; each villus contains a lacteal for absorption of fats.
Marking note: Award 1 mark for each correct adaptation, up to a maximum of 2 marks.
14. [Total: 6 marks]
(a) [2]
Condition: Diabetes mellitus (Type 1 or Type 2 diabetes).
Reason: The patient's blood glucose level (9.2 mmol/L) is above the normal fasting range (4.0–7.0 mmol/L), and glucose is present in the urine, which should not occur in a healthy individual.
Marking note: 1 mark for identifying diabetes / diabetes mellitus; 1 mark for referencing the elevated blood glucose and/or glucose in urine.
(b) [3] Under normal conditions, glucose is filtered out of the blood in the glomerulus into Bowman's capsule. It is then reabsorbed back into the blood in the proximal convoluted tubule by active transport. In this patient, the blood glucose concentration is so high that the maximum reabsorption capacity (renal threshold / transport maximum) of the kidney tubules is exceeded. As a result, not all glucose can be reabsorbed, and the excess glucose remains in the filtrate and is excreted in the urine.
Marking note: Award 1 mark for stating that glucose is filtered at the glomerulus; 1 mark for stating that glucose is normally reabsorbed in the proximal convoluted tubule; 1 mark for explaining that the renal threshold is exceeded due to high blood glucose concentration.
(c) [1] Acceptable answers (any one): Damage to blood vessels (leading to blindness, kidney failure, or cardiovascular disease); nerve damage (diabetic neuropathy); poor wound healing / increased risk of infection; diabetic ketoacidosis.
15. [Total: 5 marks]
(a) [1] The ciliary muscles change the shape (thickness) of the lens by contracting or relaxing, allowing the eye to focus on objects at different distances (accommodation).
(b) [3] When moving from a bright environment to a dark room, the radial muscles of the iris contract and the circular muscles relax, causing the pupil to dilate (become larger). This allows more light to enter the eye and reach the retina, improving vision in low-light conditions. This is an example of a pupil reflex.
Marking note: Award 1 mark for stating that the pupil dilates / becomes larger; 1 mark for identifying the role of the radial and circular muscles of the iris; 1 mark for explaining that more light enters the eye to improve vision in the dark.
(c) [1] The fovea is the part of the retina with the highest concentration of cone cells, responsible for sharp, detailed, and colour vision (the area of greatest visual acuity).
16. [Total: 6 marks]
(a) [3] When the hand is placed in ice-cold water, the body detects the drop in skin temperature via thermoreceptors. The hypothalamus processes this information and sends impulses via the nervous system to the arterioles in the skin. The smooth muscle in the walls of the arterioles contracts (vasoconstriction), reducing blood flow to the capillaries near the skin surface. With less warm blood flowing near the surface, less heat is lost to the environment, and the skin appears pale.
Marking note: Award 1 mark for detection of cold by thermoreceptors / role of hypothalamus; 1 mark for vasoconstriction of arterioles; 1 mark for reduced blood flow to skin surface causing pale appearance.
(b) [1] This response reduces heat loss from the body (conserves heat), helping to maintain a stable core body temperature.
(c) [2]
Process: Vasodilation (or reactive hyperaemia).
Explanation: When the hand is removed from the ice water, the arterioles in the skin dilate (vasodilation), increasing blood flow to the capillaries near the skin surface. The warm blood from the body's core flows to the skin, restoring heat to the hand and causing the skin to appear red and feel warm.
Marking note: 1 mark for naming vasodilation; 1 mark for explaining increased blood flow bringing warmth to the skin.
17. [Total: 5 marks]
(a) [1] From dendrites (or cell body) to axon terminals.
(b) [2] The myelin sheath is an insulating layer around the axon. It speeds up the transmission of nerve impulses by forcing the electrical signal to jump from one node of Ranvier to the next (saltatory conduction), rather than travelling continuously along the entire length of the axon.
Marking note: Award 1 mark for stating that the myelin sheath is an insulator; 1 mark for explaining saltatory conduction / faster transmission.
(c) [2] Reflex actions are rapid, automatic responses that do not require conscious thought, allowing the body to respond quickly to potentially harmful stimuli and prevent injury. For example, when a person touches a hot object, the reflex arc causes the hand to be withdrawn before the brain consciously perceives the pain, minimising tissue damage.
Marking note: Award 1 mark for explaining that reflexes are rapid/automatic and protect the body from harm; 1 mark for providing a valid example (e.g., touching a hot object, knee-jerk reflex, stepping on a sharp object).
Section C: Data Interpretation & Extended Response (Questions 18–20)
18. [Total: 8 marks]
(a) [2] Oxygen is absorbed from the alveolar air into the blood in the surrounding capillaries during gas exchange. Oxygen diffuses from the alveoli (where its concentration is high) into the blood (where its concentration is low). Therefore, the air that is breathed out contains less oxygen than the air that was breathed in.
Marking note: Award 1 mark for stating that oxygen is absorbed into the blood; 1 mark for explaining diffusion down a concentration gradient.
(b) [2] Carbon dioxide is a waste product of cellular respiration in body cells. It diffuses from the blood (where its concentration is high due to transport from respiring cells) into the alveoli (where its concentration is low) and is then exhaled. This is why expired air contains a much higher percentage of CO₂ than inspired air.
Marking note: Award 1 mark for identifying CO₂ as a product of cellular respiration; 1 mark for explaining diffusion from blood into alveoli.
(c) [1] Nitrogen is an inert gas — it is not used by the body in any metabolic process and is not absorbed into the blood in the lungs. Therefore, the amount of nitrogen breathed in equals the amount breathed out.
(d) [1] The lining of the alveoli is moist, and as air passes through the respiratory tract, it becomes saturated with water vapour. Therefore, expired air contains more water vapour than inspired air.
(e) [2] The statement is partially correct. The lungs do remove carbon dioxide, which is a metabolic waste product, and in this sense they perform an excretory function. However, excretion is formally defined as the removal of metabolic waste products and substances in excess of requirements from the body. While the lungs excrete CO₂, the primary excretory organ for nitrogenous waste (urea) is the kidney. The lungs are more accurately described as organs of gas exchange, with excretion of CO₂ being a secondary function.
Marking note: Award 1 mark for acknowledging that CO₂ is a waste product removed by the lungs; 1 mark for noting that the kidney is the primary excretory organ / that the lungs are primarily gas exchange organs.
19. [Total: 9 marks]
(a) [2] After the first meal at 0 hours, the blood glucose concentration of individual P rises from approximately 5.0 mmol/L to a peak of about 7.0 mmol/L within 1 hour. It then decreases steadily, returning to the baseline level of approximately 5.0 mmol/L by about 2 hours after the meal.
Marking note: Award 1 mark for describing the rise to a peak; 1 mark for describing the return to baseline.
(b) [3] After the meal, blood glucose rises. The beta cells in the pancreas detect this increase and secrete insulin into the bloodstream. Insulin promotes the uptake of glucose by body cells (especially liver and muscle cells), where it is converted to glycogen for storage (glycogenesis). Insulin also promotes the conversion of glucose to fat and increases the rate of glucose usage in cellular respiration. These actions collectively lower the blood glucose concentration back to the normal baseline level.
Marking note: Award 1 mark for stating that insulin is secreted in response to high blood glucose; 1 mark for stating that insulin promotes glucose uptake by cells / conversion to glycogen; 1 mark for explaining that these actions lower blood glucose back to normal.
(c) [3] Individual Q may have diabetes mellitus (Type 2 diabetes). The blood glucose rises to a much higher level (10.5 mmol/L) after each meal compared to individual P (7.0 mmol/L), and it does not return to baseline even after 3 hours, remaining elevated at approximately 8.5 mmol/L. This suggests that either the pancreas is not producing enough insulin, or the body cells are not responding effectively to insulin (insulin resistance). As a result, glucose is not efficiently removed from the blood.
Marking note: Award 1 mark for suggesting diabetes mellitus; 1 mark for referencing the higher peak and failure to return to baseline; 1 mark for suggesting insufficient insulin production or insulin resistance.
(d) [1] Acceptable answers (any one): Reduce intake of simple sugars / refined carbohydrates; eat more complex carbohydrates / foods with a low glycaemic index; eat smaller, more frequent meals; increase dietary fibre intake.
20. [Total: 9 marks]
(a) [3] Insulin is secreted by beta cells of the pancreas when blood glucose is high. Insulin promotes the uptake of glucose by body cells (especially liver and muscle cells) and stimulates the conversion of glucose to glycogen (glycogenesis) for storage. Insulin also promotes the conversion of glucose to fat and increases the rate of glucose usage in respiration. When insulin levels are low, these processes do not occur efficiently, so glucose remains in the blood, leading to high blood glucose concentration.
Marking note: Award 1 mark for stating the role of insulin in promoting glucose uptake by cells; 1 mark for stating that insulin promotes glycogenesis / conversion to glycogen; 1 mark for explaining that without insulin, glucose accumulates in the blood.
(b) [3] High blood glucose concentration exceeds the renal threshold of the nephron. Glucose is filtered at the glomerulus but cannot be fully reabsorbed in the proximal convoluted tubule because the transport proteins are saturated. The excess glucose remaining in the tubular filtrate increases the solute concentration (lowers the water potential) of the fluid in the nephron. This reduces the reabsorption of water by osmosis in the Loop of Henle and collecting duct, resulting in a larger volume of dilute urine (osmotic diuresis). The loss of water from the body leads to dehydration, which is detected by osmoreceptors in the hypothalamus, triggering the sensation of thirst.
Marking note: Award 1 mark for explaining that glucose in the filtrate reduces water reabsorption (osmotic effect); 1 mark for linking this to increased urine output / water loss; 1 mark for linking dehydration to the sensation of thirst.
(c) [2] Because insulin levels are low, body cells cannot take up glucose efficiently for respiration. The body therefore breaks down fats and proteins as alternative energy sources, leading to weight loss. Additionally, the loss of glucose in the urine (glycosuria) means that energy from food is being wasted rather than used by the body.
Marking note: Award 1 mark for stating that cells cannot use glucose and so fats/proteins are broken down; 1 mark for linking this to weight loss / glucose lost in urine.
(d) [1] Pancreas (specifically the islets of Langerhans within the pancreas).