Secondary 4 Pure Biology Human Physiology Quiz

Answer Key - Secondary 4 Pure Biology Quiz (Human Physiology)

1. Hepatic Portal Vein

• Transports absorbed nutrients (glucose, amino acids) from the small intestine/villi directly to the liver for processing/regulation. [1]

2. Villus Adaptation

• One-cell thick epithelium/wall: reduces diffusion distance for faster absorption. [1]
• Rich network of blood capillaries: maintains a steep concentration gradient by transporting absorbed nutrients away. [1]
• Large surface area (due to many villi/microvilli): increases the rate of absorption. [1]

3. Liver and Blood Glucose (Post-meal)

• Pancreas detects high blood glucose and secretes insulin. [1]
• Insulin stimulates the liver to convert excess glucose into glycogen. [1]
• Glycogen is stored in the liver, lowering blood glucose levels back to normal. [1]

4. Artery vs. Vein

• Arteries: Thick, muscular, and elastic walls to withstand and maintain high blood pressure from the heart. [2]
• Veins: Thinner walls and contain valves to prevent the backflow of blood under low pressure. [2]

5. Blood Transfusion (Group A vs B)

• Blood group A has anti-B antibodies in the plasma. [1]
• If group B blood is transfused, the anti-B antibodies will attack the B-antigens on the donor's red blood cells. [1]
• This leads to agglutination (clumping) of red blood cells, which can be fatal. [1]

6. Ventricular Systole

• Ventricles contract, increasing pressure within the chambers. [1]
• Atrioventricular (AV) valves close to prevent backflow into the atria. [1]
• Semi-lunar valves (aortic/pulmonary) are forced open. [1]
• Blood is pumped out of the heart into the aorta and pulmonary artery. [1]

7. Left Ventricle Thickness

• The left ventricle must pump blood to the entire body (systemic circulation). [1]
• This requires much higher pressure than the right ventricle, which only pumps blood to the lungs (pulmonary circulation). [1]

8. Oxygen Debt

• Definition: The amount of oxygen required to break down lactic acid that accumulated during anaerobic respiration. [1]
• Repayment: After exercise, breathing remains rapid to provide extra oxygen. [1]
• This oxygen is used by the liver/muscles to oxidize lactic acid back into pyruvate or glucose. [1]

9. Aerobic Respiration Equation

• Glucose + Oxygen $\rightarrow$ Carbon Dioxide + Water + Energy (ATP). [1]

10. Alveoli Adaptation

• One-cell thick walls: short diffusion distance for gases. [1]
• Large total surface area: maximizes the volume of gas exchanged. [1]
• Moist lining: allows gases to dissolve before diffusing. [1]
• Rich capillary network: maintains a steep concentration gradient. [1]

11. Breathing vs. Cellular Respiration

• Breathing: Physical process of inhaling $\text{O}_2$ and exhaling $\text{CO}_2$ (ventilation). [1]
• Cellular Respiration: Chemical process in cells to release energy from glucose. [1]

12. Ultrafiltration

• High blood pressure in the glomerulus forces small molecules (water, glucose, urea, salts) out of the blood. [1]
• These molecules pass through the basement membrane/podocytes into the Bowman's capsule. [1]
• Large molecules (proteins) and blood cells remain in the blood as they are too large to pass. [1]

13. Dialysis and Diffusion

• Blood is passed through a semi-permeable membrane. [1]
• The dialysis fluid has a lower concentration of urea than the blood (or zero urea). [1]
• Urea moves down its concentration gradient from the blood into the dialysis fluid by diffusion. [1]
• This removes metabolic waste from the blood, mimicking the kidney's excretory function. [1]

14. Homeostasis and Negative Feedback

• Homeostasis: Maintenance of a constant internal environment despite external changes. [1]
• Negative Feedback: A mechanism where a change in a variable triggers a response that counteracts the initial change. [1]
• This brings the variable back to its set point/normal level. [1]

15. Response to Cold

• Vasoconstriction: Blood vessels near the skin surface constrict to reduce heat loss to the environment. [1]
• Shivering: Rapid muscle contractions generate metabolic heat. [1]
• Piloerection: Hairs stand up to trap a layer of insulating air. [1]
• Hypothalamus coordinates these responses. [1]

16. ADH and Water Potential

• When blood water potential is low (dehydration), the pituitary gland releases more ADH. [1]
• ADH increases the permeability of the collecting ducts in the nephron to water. [1]
• More water is reabsorbed back into the blood by osmosis. [1]
• This increases blood water potential and produces more concentrated urine. [1]

17. Nervous vs. Endocrine

• Nervous: Rapid response, short-lived effect. [1]
• Endocrine: Slower response (travels via blood), longer-lasting effect. [1]

18. Reflex Arc

• Stimulus (Heat) $\rightarrow$ Receptor (Thermoreceptors in skin). [1]
• Sensory neurone transmits impulse to the spinal cord (CNS). [1]
• Relay neurone processes the signal in the spinal cord. [1]
• Motor neurone transmits impulse to the effector. [1]
• Effector (Biceps muscle) contracts, pulling the hand away. [1]

19. Pupil Response to Light

• Circular muscles of the iris contract. [1]
• Radial muscles of the iris relax. [1]
• The pupil constricts (becomes smaller) to protect the retina from excessive light. [1]

20. Type 1 vs Type 2 Diabetes

• Type 1: Pancreas fails to produce sufficient insulin (autoimmune/genetic). [1]
• Type 2: Body cells become resistant to insulin or pancreas produces insufficient insulin (lifestyle/genetic). [1]
• In both cases, blood glucose levels remain high (hyperglycemia). [1]
• Type 1 requires insulin injections; Type 2 is managed by diet, exercise, and medication. [1]