▶️ Answer/Explanation
Solution
a. Red Blood Cells in Distilled Water: [1]
• Cells will swell and burst (lyse) due to water entering by osmosis ✔
Mechanism: Distilled water is hypotonic → net water movement into cells
b. Stem Cell Treatments: [1]
• Leukemia (hematopoietic system diseases) ✔
• Skin burns (epidermal regeneration) ✔
• Alternative accepted answers: Spinal cord injuries, Parkinson’s disease, diabetes
c. Nerve Impulse Propagation: [3]
1. Depolarization:
- Na+ channels open at threshold potential (-50mV) ✔
- Na+ influx reverses membrane potential (+30mV) ✔
2. Local currents:
- Ions diffuse laterally between depolarized and polarized regions ✔
- Reduces next segment’s resting potential (-70mV → -50mV) ✔
3. Saltatory conduction (in myelinated neurons):
- Impulse jumps between Nodes of Ranvier ✔
- Faster propagation than unmyelinated axons ✔
Sequence: Resting potential → Threshold → Depolarization → Repolarization → Propagation