Science (086) — AI-generated practice question

(a) The tubular part of the nephron (kidney tubule) is responsible for this massive reduction in volume. After blood is filtered in the Bowman's capsule, the initial filtrate (~180 L/day) passes through the tubule. Here, useful substances such as glucose, amino acids, salts, and a large amount of water are selectively reabsorbed back into the blood. Only waste-rich fluid remains, which becomes urine. This reabsorption reduces the volume from ~180 L to just 1–2 L of urine per day.

(b) The amount of water reabsorbed in the tubule depends on the body's needs. If a person drinks very little water, the body needs to conserve water, so more water is reabsorbed from the tubule back into the blood. This produces a smaller volume of more concentrated urine. Conversely, excess water in the body leads to less reabsorption, producing dilute, larger-volume urine. Similarly, the reabsorption of dissolved wastes is regulated so that harmful substances are retained in the filtrate and excreted. Thus, the tubule adjusts both the composition and volume of the final urine according to the body's requirements.

Source: Chapter 5, Section 5.5.1 (Excretion in Human Beings)

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• (a) Examiners expect you to name the tubule/tubular part of the nephron and explain selective reabsorption of water, glucose, amino acids, and salts. Mentioning Bowman's capsule as the filtration site adds context.
• (b) The key phrase from the textbook is: "The amount of water reabsorbed depends on how much excess water there is in the body." Use this logic to contrast low-water-intake (more reabsorption → concentrated urine) vs. high-water-intake (less reabsorption → dilute urine). Do not go beyond the textbook's explanation — no need to mention ADH or hormones, as the CBSE Class 10 syllabus does not require it.
• Keep answers tied to the source passage; avoid over-detailing the structure of the nephron unless directly asked.