IB DP Biology- C3.2 Defense against disease - IB Style Questions For SL Paper 1A -FA 2025
▶️ Answer/Explanation
✅ Answer: (A) Phagocytes
▶️ Answer/Explanation
Answer: (B) They block metabolic pathways in prokaryotes.
Explanation:
Antibiotics are effective because they selectively target metabolic pathways or cell structures that exist in prokaryotic cells (bacteria) but not in human cells. Examples include:
• Inhibiting bacterial cell wall synthesis
• Blocking bacterial ribosomes to stop protein synthesis
These differences allow antibiotics to kill or stop bacteria without harming human cells.
Option Evaluation:
A. Incorrect — Antibody production is done by the immune system, not antibiotics.
B. Correct — Antibiotics target pathways unique to bacteria.
C. Incorrect — Viruses lack their own metabolic pathways, so antibiotics cannot affect them.
D. Incorrect — Antibiotics do not inhibit mitosis in eukaryotes; that would damage human cells.
✅ Answer: (B)
▶️ Answer/Explanation
Answer: (D) Thrombin
Explanation:
The diagram represents the blood clotting cascade, in which several clotting factors activate one another in sequence, leading to the formation of a fibrin clot.
Key steps:
• Tissue damage releases clotting factors from platelets and damaged cells.
• These activate an enzymatic cascade involving multiple clotting factors.
• Upstream factors (often labelled W and X) help convert prothrombin into thrombin.
• Factor Y is thrombin, the active enzyme that converts fibrinogen (Factor Z) into fibrin, forming the clot mesh.
Matching each option:
| Option | Substance | Role | Label |
|---|---|---|---|
| A | Fibrin | Forms clot mesh | Factor Z |
| B | Prothrombin | Inactive precursor of thrombin | Precursor to Y |
| C | Fibrinogen | Converted into fibrin | Not Y |
| D | Thrombin | Converts fibrinogen to fibrin | Factor Y |
✅ Answer: (D) Thrombin