CAPF AC 2023 Q24: Science & Technology – Health & Diseases
- (a) they along with red blood cells carry oxygen.
- (b) platelets are important to carry food to cells through blood.
- (c) platelets remove carbon dioxide from blood.
- (d) platelets have a role in blood clotting.
Answer: (d) platelets have a role in blood clotting.
Explanation
Why platelets matter
How to think: blood has three kinds of cells, each with one main job.
Platelets stop bleeding.
They gather at a wound, plug it and start clotting.
| Blood component | Main job |
|---|---|
| Red blood cells | Carry oxygen (haemoglobin) |
| White blood cells | Fight infection |
| Platelets (thrombocytes) | Blood clotting |
| Plasma | Carries food, carbon dioxide, hormones and wastes |
The link with viral fever: in dengue the platelet count can fall sharply.
The normal count is 1.5 to 4 lakh per cubic millimetre.
A very low count brings the danger of internal bleeding.
Answer: (d).
Why each option is right or wrong
- (a) Incorrect. Only red blood cells carry oxygen.
- (b) Incorrect. Food is carried dissolved in the plasma.
- (c) Incorrect. Carbon dioxide is carried mainly by the plasma.
- (d) CORRECT. Platelets are needed for blood clotting.
Key point
Platelets (thrombocytes): made in bone marrow from megakaryocytes, life about 7 to 10 days, normal 1.5 to 4 lakh per cubic mm; clotting also needs fibrinogen, calcium and vitamin K. Dengue (Aedes mosquito) lowers the platelet count.
Remember
Platelets = clotting. Dengue lowers platelets.
Common mistakes
- Mixing up the jobs of platelets and red blood cells.
- Thinking platelets fight the virus, which is the work of white blood cells.
- Forgetting that vitamin K and calcium are also needed for clotting.
Exam tip
Educated guess: the news about dengue always warns of bleeding when platelets fall. Bleeding and clotting go together.
Sources
- NCERT Class X Science — Life Processes (transportation: maintenance by platelets)
- NCERT Class XI Biology — Body Fluids and Circulation (formed elements; coagulation of blood)