In some viral infections, number of platelets are reduced quickly. Platelets are essential because :
- 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.
Correct answer
Explanation
The correct answer is D, platelets have a role in blood clotting. Platelets plug a damaged vessel and start the chain that forms a clot.
Platelets, or thrombocytes, are small cell fragments made from large cells called megakaryocytes in the bone marrow. A healthy adult has roughly 1.5 to 4.5 lakh platelets in each microlitre of blood, and each lives for about a week to ten days. When a vessel is cut, they stick to the injury, release clotting factors and help turn fibrinogen into a fibrin mesh. In dengue and some other viral fevers the count can fall sharply, and a very low count brings a risk of bleeding, which is why doctors watch it closely.
Option A is wrong because oxygen is carried by haemoglobin in red blood cells, not by platelets. Option B is wrong because digested food is carried dissolved in plasma. Option C is wrong because carbon dioxide is carried mainly as bicarbonate in plasma and partly by red blood cells.
Exam tip: RBC = oxygen, WBC = defence, platelets = clotting; dengue lowers platelets.
Practice Questions
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