Consider statements about human blood: 1. Red blood cells lack a nucleus at maturity. 2. Platelets are essential for blood clotting. 3. Plasma constitutes about 45% of blood volume. Which are correct? MCQ with Answer and Explanation

Question

Consider statements about human blood: 1. Red blood cells lack a nucleus at maturity. 2. Platelets are essential for blood clotting. 3. Plasma constitutes about 45% of blood volume. Which are correct?

A. 2 and 3 only

B. 1 and 2 only

C. 1 and 3 only

D. 1, 2 and 3

Answer: Option B

Solution (By JKSSB Mock Tests)

Mature mammalian red blood cells (erythrocytes) are enucleated to maximize space for hemoglobin. Platelets (thrombocytes) are cell fragments crucial for the blood coagulation cascade. Blood plasma, the liquid component, constitutes about 55% of total blood volume, while the formed elements (RBCs, WBCs, platelets) make up the remaining 45%. Thus, statements 1 and 2 are correct.

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The blood vessel that has valves to prevent backflow is:

A. Capillary

B. Artery

C. Vein

D. Arteriole

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Correct Answer: Option C

Explanation:
Veins, especially in limbs, have one-way valves that prevent the backflow of blood as it returns to the heart against gravity. Arteries have thick walls to withstand pressure and lack valves. Capillaries have no valves.

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Question #2

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The enzyme that catalyzes the conversion of pyruvate to acetyl-CoA is:

A. Pyruvate kinase

B. Lactate dehydrogenase

C. Citrate synthase

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Correct Answer: Option D

Explanation:
Pyruvate dehydrogenase complex (PDC) oxidatively decarboxylates pyruvate, producing acetyl-CoA, NADH, and CO₂ in the mitochondrial matrix, linking glycolysis to the Krebs cycle. Pyruvate kinase is in glycolysis, lactate dehydrogenase converts pyruvate to lactate, citrate synthase starts the Krebs cycle.

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