Which of the following statements about the reabsorption process in Henle's loop are correct ? (a) The descending limb of Henle's loop is permeable to water but almost impermeable to electrolytes. (b) Urine gets concentrated in Henle's loop. (c) Reabsorption of Na^+ and water takes place in Henle's loop. (d) Active or passive transport of electrolytes occurs in the ascending limb of Henle's loop. Choose the correct answer from the options given below :
A. (a), (b) and (d) only
Based on the NCERT biology textbook: Statement (a) is correct: The descending limb of the loop of Henle is permeable to water but almost impermeable to electrolytes. This causes the filtrate to become concentrated as it moves down. Statement (b) is correct: The primary role of Henle's loop (along with the vasa recta) is to maintain a high osmolarity in the medullary interstitial fluid, which is essential for the concentration of urine. Statement (d) is correct: The ascending limb of Henle's loop is impermeable to water but allows the transport of electrolytes (like NaCl) either actively or passively. Statement (c) is a generalized statement, but since the descending limb is impermeable to electrolytes and the ascending limb is impermeable to water, they do not occur simultaneously in the same segment. Based on the given options, the most appropriate choice containing the exact correct statements (a) and (d) is option (1). Answer: (a), (b) and (d) only
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