Excretory Organs and Their Functions — NEET Biology
📚 Practice ConceptProtonephridia, nephridia, malpighian tubules, green glands and the kidneys are the common excretory organs in animals. They not only eliminate nitrogenous wastes but also help in the maintenance of ionic and acid-base balance of body fluids.
Which of the above statements are correct regarding tubular secretion? S1: Tubular cells in different segments of the nephron actively secrete substances such as H+, K+, and ammonia into the filtrate. S2: The selective secretion of H+ and K+ ions by the collecting duct is important for regulating the pH and ionic balance of blood. S3: Reabsorption of all essential nutrients like glucose and amino acids occurs exclusively through active secretion by tubular cells. S4: Urea is primarily reabsorbed by the collecting duct into the medullary interstitium via active transport to maintain osmolarity. S5: Tubular secretion is an important step in urine formation as it helps in the maintenance of ionic and acid-base balance of body fluids.
View solution & NCERT explanation
Correct answer: D — S1, S2 and S5
The question asks for the correct statements concerning tubular secretion. S1: "During urine formation, the tubular cells secrete substances like H+, K+ and ammonia into the filtrate." This process is often active. So, S1 is correct. S2: "(Collecting Duct) It also plays a role in the maintenance of pH and ionic balance of blood by the selective secretion of H+ and K+ ions." So, S2 is correct. S3: Glucose and amino acids are actively reabsorbed, not secreted, and not exclusively through secretion. So, S3 is incorrect. S4: "This segment (collecting duct) allows passage of small amounts of urea into the medullary interstitium to keep up the osmolarity." This passage is passive, not active reabsorption. So, S4 is incorrect. S5: "Tubular secretion is also an important step in urine formation as it helps in the maintenance of ionic and acid base balance of body fluids." So, S5 is correct. Therefore, statements S1, S2, and S5 are correct. Final Answer: The final answer is D.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
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