Which one of the following statements about blood elements is correct?
- A.Red blood cells' number is same as that of white blood cells and platelets.
- B.The number of white blood cells is more than red blood cells.
- C.The number of red blood cells is the highest.
- D.The number of red blood cells is lower than platelets.
Correct answer
Explanation
The correct answer is C, The number of red blood cells is the highest. Red blood cells far outnumber both platelets and white blood cells.
A microlitre of healthy adult blood holds about 4.5 to 5.5 million red blood cells, about 1.5 to 4.5 lakh platelets and only about 4,000 to 11,000 white blood cells. So the order by number is RBC, then platelets, then WBC. Red cells are made in the red bone marrow, have no nucleus in mammals, carry oxygen with the help of haemoglobin and live for about 120 days before the spleen removes them. Their sheer number is what gives blood its red colour.
Option A is wrong because the three counts are very different, not equal. Option B is wrong because white blood cells are the fewest of the three, roughly one for every 500 or more red cells. Option D is wrong because platelets, though numerous, are still more than ten times fewer than red cells.
Exam tip: count order RBC > platelets > WBC; RBC lifespan 120 days, the spleen is their graveyard.
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