CAPF AC 2020 Q18: Science & Technology – Biology
Which one of the following is the major function of platelets?
- (a) Clotting of blood
- (b) O2 transport
- (c) Immunity
- (d) Phagocytosis
Answer: (a) Clotting of blood
Explanation
Function of platelets
How to think: blood has three kinds of cells.
Give each cell its own job, and the options sort themselves out.
| Blood component | Main job | Option it matches |
|---|---|---|
| Red blood cells | Carry oxygen using haemoglobin | (b) O2 transport |
| White blood cells | Immunity; some swallow germs by phagocytosis | (c) and (d) |
| Platelets | Clotting of blood | (a) |
| Plasma | Carries food, carbon dioxide and wastes | Not in the options |
How clotting helps:
| Point | Detail |
|---|---|
| When | A blood vessel is cut |
| What platelets do | Gather at the cut and help form a clot |
| Result | Bleeding stops and pressure in the vessels is kept |
Platelets are also called thrombocytes.
In dengue, the platelet count falls and bleeding can occur.
Answer: (a) Clotting of blood.
Why each option is right or wrong
- (a) CORRECT. Platelets gather at an injury and help the blood to clot.
- (b) Incorrect. Oxygen transport is done by the haemoglobin of red blood cells.
- (c) Incorrect. Immunity is the work of white blood cells.
- (d) Incorrect. Phagocytosis is done by certain white blood cells, which swallow germs.
Key point
Red blood cells: oxygen. White blood cells: immunity and phagocytosis. Platelets (thrombocytes): clotting. Plasma: transport of food and wastes.
Remember
Platelets = clotting of blood.
Common mistakes
- Mixing up platelets with white blood cells and choosing immunity.
- Forgetting that a low platelet count in dengue leads to bleeding.
- Thinking platelets are full cells; they are cell fragments.
Exam tip
One job per cell: red carries, white fights, platelets plug.
Sources
- NCERT Class X Science — Life Processes (transportation in human beings)
- NCERT Class XI Biology — Body Fluids and Circulation