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
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.
Explanation:
Selman Waksman and colleagues isolated streptomycin from Streptomyces griseus in 1943, the first effective treatment for tuberculosis. Fleming discovered penicillin, Pasteur developed vaccines, Koch identified TB bacterium.
Explanation:
Magnesium (Mg²⁺) is the central atom in the porphyrin ring of chlorophyll, essential for absorbing light energy during photosynthesis. Iron is central in heme (hemoglobin, cytochromes). Calcium is a secondary messenger and structural component, zinc is a cofactor. Magnesium deficiency causes chlorosis.
Explanation:
Transpiration occurs mainly through stomata and is a passive process driven by vapor pressure deficit. It creates transpiration pull, aiding water and mineral transport. Guttation is liquid water loss through hydathodes, bleeding is sap oozing from wounds, exudation is a general term for fluid release.
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