Q. With reference to the circulatory system in a healthy human, which one of the following statements is correct?

[A] Veins are significantly fewer in number and hold a smaller volume of blood compared to arteries.

[B] Formed elements (blood cells) constitute approximately 70% of the total blood volume.

[C] White Blood Cells (WBCs) are produced exclusively within the lymph nodes.

[D] In a normal blood count, the number of platelets is significantly higher than the number of White Blood Cells.

Answer: D
Notes:

Explanation:

(a)   is incorrect: Veins are more numerous and act as blood reservoirs, holding about 65% of the body’s blood.

(b)   is incorrect: Blood cells constitute about 45%; Plasma is 55%.

(c)    is incorrect: WBCs are produced in the bone marrow and matured in various lymphoid organs.

(d)   is correct: A normal adult has 1.5–4.5 lakh platelets per microliter, whereas WBC count is only 4,000–11,000.

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