Secondary 3 Biology Human Physiology Quiz

Secondary 3 Biology Quiz - Human Physiology (Answer Key)

Section A: Multiple Choice Questions

1. B
Reasoning: The hepatic portal vein carries nutrient-rich blood from the small intestine to the liver for processing (e.g., deamination, storage) before it enters general circulation.

2. B
Reasoning: Thickened walls increase the diffusion distance, slowing down the rate of gas exchange according to Fick's Law.

3. C
Reasoning: Arteries carry blood away from the heart under high pressure generated by ventricular systole. Thick muscular and elastic walls withstand this pressure and help maintain flow.

4. B
Reasoning: Glucose molecules are small enough to pass through the semi-permeable dialysis tubing via diffusion. Starch molecules are too large to pass through the pores.

5. B
Reasoning: The proximal convoluted tubule is the site where 100% of glucose and amino acids, along with most water and ions, are selectively reabsorbed back into the blood.

Section B: Structured Questions

6. (a) Structure B: Lacteal [1]; Structure C: Blood Capillary / Capillary Network [1] (b) The outer layer (epithelium) is one cell thick [1]. This provides a short diffusion distance for nutrients to pass into the blood/lacteal [1]. (c) Fatty acids and Glycerol (or Fats/Lipids) [1]

7. (a) (i) Maltose [1] (ii) Protease (or Pepsin/Trypsin) [1] (iii) Glycerol [1] (b) Enzymes have a specific active site shape [1]. Only substrates with a complementary shape can fit into the active site to form an enzyme-substrate complex (Lock and Key) [1].

8. (a) The diaphragm contracts and flattens/moves downwards [1]. The external intercostal muscles contract, pulling the rib cage upwards and outwards [1]. (b) These movements increase the volume of the thoracic cavity [1]. This causes the pressure inside the thorax to drop below atmospheric pressure, causing air to rush in [1].

9. (a) The left ventricle pumps blood to the entire body (systemic circulation) which requires higher pressure [1]. The right ventricle only pumps blood to the lungs (pulmonary circulation) which is a shorter distance/lower resistance [1]. (b) Bicuspid valve (or Mitral valve) [1] (c) To ensure efficient circulation and prevent mixing of oxygenated and deoxygenated blood / to maintain pressure gradients [1].

10. (a) The maintenance of a constant internal environment within narrow limits despite changes in the external environment [1]. (b) Any two of: Shivering (muscle contraction generates heat) [1]; Vasoconstriction of skin arterioles (reduces heat loss) [1]; Hair erector muscles contract (traps insulating air layer) [1].

11. (a) Glycogenesis [1] (b) The liver detoxifies alcohol [1]. Excessive alcohol consumption causes liver cells to die and be replaced by scar tissue (cirrhosis), reducing liver function [1].

12. (a) Ultrafiltration [1] (b) Glucose is small enough to be filtered into the Bowman's capsule [1]. However, it is actively reabsorbed (or selectively reabsorbed) in the proximal convoluted tubule back into the blood [1].

13. (a) Coronary arteries [1] (b) Saturated fats can lead to high cholesterol levels in the blood [1]. Cholesterol deposits form plaques in the coronary arteries, narrowing the lumen and restricting blood flow to the heart muscle [1].

14. (a) Glucose → Lactic Acid (+ Energy) [1] (b) Oxygen debt is the amount of oxygen required to oxidize the lactic acid accumulated in muscles during anaerobic respiration [1]. This oxygen is used to convert lactic acid back to glucose/pyruvate in the liver [1].

15. (a) Sweat glands secrete sweat onto the skin surface [1]. As sweat evaporates, it absorbs latent heat from the body, cooling the blood/skin [1]. (b) Arterioles near the skin surface dilate (widen) [1]. This increases blood flow to the skin surface, allowing more heat to be lost to the environment via radiation/convection [1].

Section C: Free Response Questions

16.

• Ingestion/Digestion: Protein is mechanically broken down in the mouth/stomach. In the stomach, pepsin breaks protein into peptides. In the small intestine, trypsin/peptidases break peptides into amino acids [1].
• Absorption: Amino acids are absorbed into the blood capillaries of the villi via active transport [1].
• Transport: Blood carries amino acids via the hepatic portal vein to the liver [1].
• Assimilation: The liver regulates amino acid levels. Excess amino acids may be deaminated. Remaining amino acids enter general circulation and are taken up by muscle cells to build new proteins (growth/repair) [1].

17.

• Surface Area: Alveoli are numerous and spherical, providing a very large total surface area for gas exchange [1].
• Diffusion Distance: Alveolar walls and capillary walls are both one cell thick, creating a very short diffusion distance for oxygen and carbon dioxide [1].
• Concentration Gradient: Continuous blood flow in capillaries and ventilation in alveoli maintain a steep concentration gradient (high O2 in alveoli, low in blood; high CO2 in blood, low in alveoli) [1].
• Moisture: Alveoli are lined with moisture, allowing gases to dissolve before diffusing [1].

18.

• Arteries: Thick muscular/elastic walls to withstand high pressure; narrow lumen; no valves (except semi-lunar); carry blood away from heart [1].
• Veins: Thinner walls with less muscle/elastic tissue; wide lumen; contain valves to prevent backflow; carry blood to heart under low pressure [1].
• Capillaries: Walls are one cell thick; very narrow lumen (RBCs pass single file); no valves; site of exchange of materials between blood and tissues [1].
• Comparison: Arteries have the thickest walls, capillaries the thinnest. Veins have valves, arteries (mostly) do not [1].

19.

• Detection: After a meal, blood glucose levels rise. Beta cells in the Islets of Langerhans (pancreas) detect this increase [1].
• Secretion: The pancreas secretes the hormone insulin into the bloodstream [1].
• Action: Insulin travels to the liver (and muscle cells). It stimulates the liver to convert glucose into glycogen (glycogenesis) [1].
• Result: Blood glucose levels decrease back to normal. If levels drop too low, glucagon would be secreted to convert glycogen back to glucose [1].

20.

• Principle: Dialysis uses the principles of diffusion and ultrafiltration across a semi-permeable membrane [1].
• Process: Patient's blood is pumped through tubes made of semi-permeable membrane, surrounded by dialysis fluid [1].
• Diffusion: Waste products like urea and excess salts diffuse from the blood (high concentration) into the dialysis fluid (low/zero concentration) down the concentration gradient [1].
• Selectivity: Glucose and essential proteins are too large to pass through the membrane or are balanced in the dialysis fluid, so they remain in the blood. The cleaned blood is returned to the patient [1].