Assertion (A): The plasma membrane is selectively permeable. Reason (R): It allows some substances to pass through while blocking others. MCQ with Answer and Explanation
Assertion (A): The plasma membrane is selectively permeable.
Reason (R): It allows some substances to pass through while blocking others.
A. A true, R false.
B. Both A and R are true, and R is the correct explanation.
C. Both A and R are true, but R is not the correct explanation.
D. A false, R true.
Answer: Option B
Solution (By JKExamLibrary)
Selective permeability means the membrane controls entry and exit of substances based on size, charge, and solubility. R defines this property and explains A.
Consider statements about human circulation: 1. Arteries carry oxygenated blood. 2. Veins have valves to prevent backflow. 3. Capillaries have thick walls. Which are correct?
Explanation:
While most arteries carry oxygenated blood, the pulmonary artery carries deoxygenated blood from the heart to the lungs. Veins possess valves along their length to ensure unidirectional blood flow back to the heart against gravity. Capillaries are composed of a single layer of endothelial cells (thin walls) to facilitate the exchange of gases and nutrients. Only statement 2 is universally correct.
The hormone aldosterone, which acts on the distal convoluted tubule and collecting duct to increase sodium reabsorption and potassium excretion, is secreted by the:
Explanation:
Aldosterone is a mineralocorticoid hormone secreted by the zona glomerulosa, the outermost layer of the adrenal cortex. Its primary function is to regulate electrolyte balance by promoting the active reabsorption of sodium (Na+) and the excretion of potassium (K+) and hydrogen ions (H+) in the distal tubules and collecting ducts of the kidneys. The zona fasciculata secretes glucocorticoids (cortisol).
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