Excretory Products and Elimination: the nephron, segment by segment

Free questions

30 solved MCQs, answer marked and reasoning written out

Every question below is free to read — no sign-up, no email. 2 of them are real questions from past NEET papers. The other 203 questions in this chapter are in the book and in practice access.

1. Q1 Multi-statement analysis

   Reabsorption: (i) a comparison of the filtrate formed per day (180 litres) with the urine released (1.5 litres) shows nearly 99 per cent of the filtrate is reabsorbed (ii) glucose, amino acids and Na+ are reabsorbed actively (iii) nitrogenous wastes are absorbed by passive transport (iv) water reabsorption is active in the initial segments. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; water reabsorption occurs PASSIVELY in the initial segments, so (iv) is wrong.

   What this is testing: the numbers and mechanisms behind tubular reabsorption.

   (i) is correct — 180 litres of filtrate against 1.5 litres of urine means about 99 per cent is reabsorbed. (ii) is correct: glucose, amino acids and Na+ move back by active transport. (iii) is correct — nitrogenous wastes are reabsorbed passively. (iv) is the trap: water reabsorption in the initial segments is PASSIVE, following the osmotic pull created by solute movement, not active.

   So three are correct. Only solutes like glucose, amino acids and Na+ are actively pumped; water always follows passively.

   180 litres in, 1.5 litres out - 99 per cent reclaimed. The kidney filters everything and then takes almost all of it back.

   NCERT Class 11 Biology, page 209

2. Q2 Multi-statement analysis

   Glomerular filtration rate: (i) is the amount of filtrate formed by the kidneys per minute (ii) is approximately 125 mL per minute in a healthy individual (iii) amounts to 180 litres per day (iv) is approximately 1200 mL per minute. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; 1100-1200 mL/min is the volume of BLOOD FILTERED, not the GFR, so (iv) is wrong.

   What this is testing: telling the glomerular filtration rate apart from the volume of blood filtered per minute.

   (i) is correct — GFR is the amount of filtrate formed by the kidneys per minute. (ii) and (iii) are correct: it is about 125 mL per minute in a healthy person, which adds up to 180 litres a day. (iv) is the trap: 1100-1200 mL per minute is the volume of BLOOD filtered, a separate and much larger figure than the GFR itself.

   So three are correct. Blood filtered and filtrate formed are two different numbers on the same page, and mixing them up is the trap.

   125 mL a minute of filtrate; 1100-1200 mL a minute of blood. Two rates, two units, and the question relies on confusing them.

   NCERT Class 11 Biology, page 209

3. Q3 Multi-statement analysis

   The kidneys: (i) are reddish brown, bean shaped structures (ii) lie between the levels of the last thoracic and third lumbar vertebra (iii) lie close to the dorsal inner wall of the abdominal cavity (iv) lie in the thoracic cavity. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; the kidneys lie in the ABDOMINAL cavity, so (iv) is wrong.

   What this is testing: the basic location and appearance of the human kidneys.

   (i) is correct — the kidneys are reddish brown and bean shaped. (ii) and (iii) are correct: they lie between the last thoracic and third lumbar vertebra, close to the dorsal inner wall of the abdominal cavity. (iv) is the trap: the kidneys lie in the ABDOMINAL cavity, not the thoracic cavity, which houses the heart and lungs instead.

   So three are correct. The vertebral levels in (ii) already place the kidneys in the abdomen, which (iv) then wrongly contradicts.

   Abdominal cavity, behind the peritoneum, between the last thoracic and third lumbar vertebra. Retroperitoneal is the word for that position.

   NCERT Class 11 Biology, page 206

4. Q4 Multi-statement analysis

   Regarding kidney structure: (i) the hilum is a notch towards the centre of the inner concave surface (ii) the ureter, blood vessels and nerves enter through the hilum (iii) inner to the hilum is a broad funnel shaped space called the renal pelvis (iv) the renal pelvis bears projections called nephrons. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; the projections of the renal pelvis are the CALYCES, so (iv) is wrong.

   What this is testing: what actually projects from the renal pelvis.

   (i) is correct — the hilum is a notch towards the centre of the kidney's concave inner surface. (ii) is correct: the ureter, blood vessels and nerves all enter through the hilum. (iii) is correct — just inside the hilum lies the broad, funnel-shaped renal pelvis. (iv) is the trap: the projections of the renal pelvis are the CALYCES, not nephrons, which are microscopic tubules found throughout the kidney tissue.

   So three are correct. Calyces are visible, funnel-shaped extensions of the pelvis; nephrons are a completely different, microscopic structure.

   Hilum, pelvis, calyces, then the ureter. Everything enters and leaves the kidney through that one notch.

   NCERT Class 11 Biology, page 206

5. Q5 Multi-statement analysis

   The juxta glomerular apparatus (JGA): (i) is a special sensitive region (ii) is formed by cellular modifications in the distal convoluted tubule and the afferent arteriole (iii) lies at the location of their contact (iv) a fall in GFR activates the JG cells to release renin. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.Three
   4. 4.FourCorrect answer

   Why option 4 is the answer

   The trap: All four are correct.

   What this is testing: the identity and trigger point of the juxtaglomerular apparatus (JGA).

   All four are correct. The JGA is a special sensitive region formed by cellular modifications where the distal convoluted tubule contacts the afferent arteriole; a fall in the glomerular filtration rate activates its JG cells to release renin.

   Nothing here is false — the question checks whether you can connect the JGA's location to the specific event, a falling GFR, that switches it on.

   NCERT Class 11 Biology, page 209

6. Q6 Multi-statement analysis

   The collecting duct: (i) extends from the cortex of the kidney to the inner parts of the medulla (ii) large amounts of water can be reabsorbed here to produce a concentrated urine (iii) it allows the passage of small amounts of urea into the medullary interstitium (iv) it plays no role in pH balance. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; the collecting duct DOES maintain pH and ionic balance by secreting H+ and K+, so (iv) is wrong.

   What this is testing: the collecting duct's roles beyond simple water reabsorption.

   (i) is correct — the collecting duct runs from the cortex down into the inner medulla. (ii) is correct: large amounts of water can be reabsorbed here to concentrate the urine. (iii) is correct — it also lets small amounts of urea pass into the medullary interstitium. (iv) is the trap: the collecting duct DOES help maintain pH and ionic balance, by secreting H+ and K+, so it is wrong to say it plays no role.

   So three are correct. The duct is not just a passive water-reabsorbing pipe; it is also actively involved in acid-base regulation.

   The collecting duct makes the final decision on water. ADH acts here, which is why one hormone controls urine concentration.

   NCERT Class 11 Biology, page 210

7. Q7 Multi-statement analysis

   Glomerular filtration: (i) on an average 1100-1200 mL of blood is filtered by the kidneys per minute (ii) this is roughly one-fifth of the blood pumped out by each ventricle in a minute (iii) filtration is driven by the glomerular capillary blood pressure (iv) filtration occurs through two layers. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; blood is filtered through THREE layers, so (iv) is wrong.

   What this is testing: two renal figures alongside the number of filtration layers.

   (i) is correct — about 1100-1200 mL of blood is filtered by the kidneys each minute. (ii) is correct: that is roughly a fifth of the blood each ventricle pumps out in a minute. (iii) is correct — filtration is driven by the glomerular capillary blood pressure. (iv) is the trap: filtration occurs through THREE layers, the endothelium, the basement membrane and Bowman's epithelium, not two.

   So three are correct. The volume and pressure facts are separate from the layer count, and it is the layer count that is misstated here.

   A fifth of the cardiac output goes through the kidneys every minute. They filter far more blood than their size suggests.

   NCERT Class 11 Biology, page 208

8. Q8 Multi-statement analysis

   The peritubular capillaries: (i) are formed by the efferent arteriole emerging from the glomerulus (ii) form a fine capillary network around the renal tubule (iii) a minute vessel of this network runs parallel to Henle's loop as the vasa recta (iv) the vasa recta is U-shaped. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.Three
   4. 4.FourCorrect answer

   Why option 4 is the answer

   The trap: All four are correct.

   What this is testing: how the peritubular capillary network, including the vasa recta, is formed and shaped.

   All four are correct. The efferent arteriole leaving the glomerulus forms a fine capillary network around the renal tubule; one branch of this network runs parallel to Henle's loop as the U-shaped vasa recta.

   Nothing is false here — the question checks whether you can trace the peritubular capillaries back to the efferent arteriole, and recognise the vasa recta as simply one specialised, U-shaped part of that same network.

   NCERT Class 11 Biology, page 208

9. Q9 Assertion and Reason

   AssertionKidney transplantation is the ultimate method in the correction of acute renal failure.

   ReasonA functioning kidney is taken from a donor, preferably a close relative, to minimise the chances of rejection.

   1. 1.Both A and R are true and R is the correct explanation of A
   2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
   3. 3.A is true but R is false
   4. 4.A is false but R is true

   Why option 2 is the answer

   The trap: Both are true of transplantation; the choice of a related donor is a parallel precaution and does not explain why transplantation is the ultimate remedy.

   What this is testing: whether choosing a related donor explains why transplantation is the ultimate treatment for renal failure.

   A says kidney transplantation is the ultimate method for correcting acute renal failure — true. R says a functioning kidney is taken from a donor, preferably a close relative, to reduce rejection — also true, but this describes how a donor is chosen, not why transplantation itself ranks as the ultimate remedy.

   So both are true but R is not the explanation, giving option (2).

   The trap: R is a genuine precaution taken during transplantation, but it explains donor selection, not the status of transplantation as the last resort.

   NCERT Class 11 Biology, page 214

10. Q10 Assertion and Reason

    AssertionAnticoagulant heparin is added to the blood drained for haemodialysis.

    ReasonAnti-heparin is added to the cleared blood before it is pumped back into the body.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true steps of dialysis running in parallel; the later addition of anti-heparin does not explain the initial use of heparin.

    What this is testing: whether returning anti-heparin explains why heparin was added in the first place.

    A says the anticoagulant heparin is added to the blood drained for haemodialysis — true. R says anti-heparin is added to the cleared blood before it is pumped back into the body — also true, but this is a later, separate step and does not explain why heparin was needed at the start.

    So both are true but R is not the explanation, giving option (2).

    The trap: heparin going in and anti-heparin coming out are two ends of the same procedure, not cause and effect.

    NCERT Class 11 Biology, page 214

11. Q11 Assertion and Reason

    AssertionThe juxta glomerular apparatus is formed by cellular modifications in the proximal convoluted tubule and the efferent arteriole.

    ReasonThe JGA is formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of A
    3. 3.A is true but R is false
    4. 4.A is false but R is trueCorrect answer

    Why option 4 is the answer

    The trap: A is false — the JGA arises from the DCT and the afferent arteriole; R is true.

    What this is testing: which two structures actually form the juxtaglomerular apparatus.

    A says the JGA is formed by cellular modifications in the proximal convoluted tubule and the efferent arteriole — false: it actually forms from the DISTAL convoluted tubule and the AFFERENT arteriole, as R correctly states. R is true.

    So A is false but R is true, giving option (4).

    The trap: A swaps both PCT-for-DCT and efferent-for-afferent at once, so a small slip on either term alone would still make A wrong.

    NCERT Class 11 Biology, page 209

12. Q12 Assertion and Reason

    AssertionSweat helps in the removal of some wastes.

    ReasonThe primary function of sweat is to facilitate a cooling effect on the body surface.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of sweat; its cooling role is a parallel and indeed primary function and does not explain its excretory contribution.

    What this is testing: whether sweat's cooling role explains its excretory role.

    A says sweat helps in the removal of some wastes — true. R says the primary function of sweat is to cool the body surface — also true, and it is indeed sweat's main job, but that cooling function does not explain why sweat also happens to carry away wastes like NaCl and urea.

    So both are true but R is not the explanation, giving option (2).

    The trap: R correctly names sweat's PRIMARY function, but a primary function does not automatically explain a secondary one it merely accompanies.

    NCERT Class 11 Biology, page 213

13. Q13 Assertion and Reason

    AssertionThe cortex extends between the medullary pyramids as the columns of Bertini.

    ReasonThe outer layer of the kidney is a tough capsule and the two internal zones are the cortex and the medulla.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of kidney structure; the general zonation is a parallel fact and does not explain the formation of the cortical columns.

    What this is testing: whether general kidney zonation explains the specific formation of the columns of Bertini.

    A says the cortex extends between the medullary pyramids as the columns of Bertini — true. R says the kidney has a tough outer capsule and two internal zones, the cortex and medulla — also true, but this is the broad zonation fact and does not by itself explain why the cortex specifically forms those cortical columns.

    So both are true but R is not the explanation, giving option (2).

    The trap: R is real background anatomy, but background is not the same as a direct explanation of the named structure.

    NCERT Class 11 Biology, page 207

14. Q14 Assertion and Reason

    AssertionHuman kidneys can produce urine nearly four times concentrated than the initial filtrate.

    ReasonThe flow of filtrate in the two limbs of Henle's loop is in opposite directions and forms a counter current.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of the concentrating mechanism; the counter current flow is a parallel structural fact and is not itself the statement of the osmotic gradient that permits the fourfold concentration.

    What this is testing: whether the counter current flow itself explains the fourfold concentration of urine.

    A says human kidneys can produce urine nearly four times as concentrated as the initial filtrate — true. R says the flow of filtrate in the two limbs of Henle's loop runs in opposite directions, forming a counter current — also true, but this describes the structural arrangement, a fact that runs alongside the fourfold figure rather than stating the osmotic-gradient reasoning that produces it.

    So both are true but R is not the explanation, giving option (2).

    The trap: the counter current arrangement is a real and necessary fact, but by itself it is only the setup, not the stated explanation for the specific fourfold number.

    NCERT Class 11 Biology, page 212

15. Q15 Assertion and Reason

    AssertionAmmonia is the least toxic nitrogenous waste.

    ReasonUric acid, being the least toxic, can be removed with a minimum loss of water.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of A
    3. 3.A is true but R is false
    4. 4.A is false but R is trueCorrect answer

    Why option 4 is the answer

    The trap: A is false — ammonia is the MOST toxic; R is true.

    What this is testing: which nitrogenous waste is actually the least toxic.

    A says ammonia is the least toxic nitrogenous waste — false: ammonia is the MOST toxic; uric acid holds the least-toxic spot instead. R says uric acid, being the least toxic, can be removed with a minimum loss of water — true, and correctly gives uric acid the title A wrongly gave to ammonia.

    So A is false but R is true, giving option (4).

    The trap: A takes the correct fact from R and attaches it to the wrong substance — always check which end of the toxicity scale a statement is describing.

    NCERT Class 11 Biology, page 205

16. Q16 Assertion and Reason

    AssertionThe proximal convoluted tubule is the major site of reabsorption.

    ReasonThe PCT also helps to maintain the pH and ionic balance of the body fluids by the selective secretion of hydrogen ions and ammonia.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of the PCT; its secretory role in pH balance is a parallel function and does not explain its absorptive primacy.

    What this is testing: whether the PCT's secretory role explains its status as the main site of reabsorption.

    A says the proximal convoluted tubule is the major site of reabsorption — true. R says the PCT also maintains pH and ionic balance by selectively secreting hydrogen ions and ammonia — also true, but this describes a separate secretory job, not the reason the PCT reabsorbs the bulk of the filtrate.

    So both are true but R is not the explanation, giving option (2).

    The trap: the PCT does both reabsorption and secretion, and R names the wrong one of the two as if it explained the other.

    NCERT Class 11 Biology, page 209

17. Q17 Assertion and Reason

    AssertionProtonephridia are primarily concerned with osmoregulation.

    ReasonProtonephridia or flame cells are the excretory structures of Platyhelminthes, rotifers, some annelids and Amphioxus.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of protonephridia; the list of animals possessing them is a parallel fact and does not explain their osmoregulatory role.

    What this is testing: whether the list of animals possessing protonephridia explains their osmoregulatory role.

    A says protonephridia are primarily concerned with osmoregulation — true. R says protonephridia, or flame cells, are the excretory structures of Platyhelminthes, rotifers, some annelids and Amphioxus — also true, but this simply lists which animals have them, without explaining what job they actually do.

    So both are true but R is not the explanation, giving option (2).

    The trap: naming the owners of a structure is not the same as stating its function, which is what A is really about.

    NCERT Class 11 Biology, page 206

18. Q18 Statement I and Statement II

    Statement IThe JGA is formed by cellular modifications in the DCT and the afferent arteriole.

    Statement IIA fall in GFR activates the JG cells to release renin.

    1. 1.Both Statement I and Statement II are correctCorrect answer
    2. 2.Both Statement I and Statement II are incorrect
    3. 3.Statement I is correct but Statement II is incorrect
    4. 4.Statement I is incorrect but Statement II is correct

    Why option 1 is the answer

    The trap: Both statements are correct.

    What this is testing: the JGA's location and the trigger that activates it.

    Statement I: the JGA is formed by cellular modifications in the DCT and the afferent arteriole. Correct.
    Statement II: a fall in GFR activates the JG cells to release renin. Correct.

    Both are correct, so the answer is (1).

    Between them, these two statements cover both where the JGA sits and what switches it into action, and NCERT confirms both.

    NCERT Class 11 Biology, page 209

19. Q19 Statement I and Statement II

    Statement INearly 99 per cent of the filtrate is reabsorbed by the renal tubules.

    Statement IIGlucose and amino acids are reabsorbed by passive transport.

    1. 1.Both Statement I and Statement II are correct
    2. 2.Both Statement I and Statement II are incorrect
    3. 3.Statement I is correct but Statement II is incorrectCorrect answer
    4. 4.Statement I is incorrect but Statement II is correct

    Why option 3 is the answer

    The trap: I correct; glucose and amino acids are reabsorbed ACTIVELY, so II is incorrect.

    What this is testing: the scale of reabsorption alongside the transport mode used for glucose and amino acids.

    Statement I: nearly 99 per cent of the filtrate is reabsorbed by the renal tubules. Correct.
    Statement II: glucose and amino acids are reabsorbed by passive transport. Incorrect — glucose and amino acids are reabsorbed by ACTIVE transport, not passive.

    Statement I is correct but Statement II is incorrect, so the answer is (3).

    The trap: it is the nitrogenous wastes and initial-segment water that move passively, not glucose and amino acids, which need active pumps.

    NCERT Class 11 Biology, page 209

20. Q20 Statement I and Statement II

    Statement IThe medullary interstitial osmolarity rises from 300 to 1200 mOsmol per litre.

    Statement IIThe gradient is mainly caused by NaCl and urea.

    1. 1.Both Statement I and Statement II are correctCorrect answer
    2. 2.Both Statement I and Statement II are incorrect
    3. 3.Statement I is correct but Statement II is incorrect
    4. 4.Statement I is incorrect but Statement II is correct

    Why option 1 is the answer

    The trap: Both statements are correct.

    What this is testing: the numerical rise in medullary osmolarity alongside the solutes that cause it.

    Statement I: the medullary interstitial osmolarity rises from 300 to 1200 mOsmol per litre. Correct.
    Statement II: the gradient is mainly caused by NaCl and urea. Correct.

    Both are correct, so the answer is (1).

    These two statements fit together as cause and figure: NaCl and urea are what build the gradient, and 300 to 1200 mOsmol/L is the range that gradient actually spans.

    NCERT Class 11 Biology, page 211

21. Q21 Match the columns

    Match the transport with its mode:

    Column I	Column II
    (a) Glucose reabsorption	(i) passive
    (b) Amino acid reabsorption	(iii) passive
    (c) Nitrogenous waste absorption	(ii) active
    (d) Water reabsorption in initial segments	(iv) active

    1. 1.(a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
    2. 2.(a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)Correct answer
    3. 3.(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
    4. 4.(a)-(i), (b)-(iv), (c)-(iii), (d)-(ii)

    Why option 2 is the answer

    The trap: Glucose and amino acids actively; wastes and water passively.

    What this is testing: matching each reabsorbed substance to whether its transport is active or passive.

    Glucose and amino acid reabsorption are both active, while absorption of nitrogenous wastes and water reabsorption in the initial segments are both passive — giving (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i), option 2.

    The trap: option 1 flips every pairing, marking glucose and amino acids as passive and the wastes and water as active, which reverses the entire active-versus-passive picture the PCT depends on.

    NCERT Class 11 Biology, page 209

22. Q22 Match the columns

    Match the substance secreted with the tubular segment:

    Column I	Column II
    (a) H+ and ammonia	(ii) collecting duct
    (b) H+, K+ and NH3	(iii) absorbed, not secreted, by the PCT
    (c) H+ and K+	(i) PCT
    (d) HCO3-	(iv) DCT

    1. 1.(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
    2. 2.(a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
    3. 3.(a)-(i), (b)-(iv), (c)-(ii), (d)-(iii)Correct answer
    4. 4.(a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

    Why option 3 is the answer

    The trap: The tubular segments secrete H+, K+ and NH3, while the PCT absorbs bicarbonate.

    What this is testing: matching each tubular segment to what it secretes, or in the PCT's case, absorbs instead.

    The PCT secretes H+ and ammonia, the DCT secretes H+, K+ and NH3, the collecting duct secretes H+ and K+, and bicarbonate is absorbed, not secreted, by the PCT — giving (a)-(i), (b)-(iv), (c)-(ii), (d)-(iii), option 3.

    The trap: option 1 swaps the PCT and DCT secretions, which mixes up two tubular segments that both secrete similar ions but at different points along the nephron.

    NCERT Class 11 Biology, page 210

23. Q23 Match the columns

    Match the osmolarity with its site:

    Column I	Column II
    (a) Cortex	(i) about four times the filtrate
    (b) Inner medulla	(ii) about 300 mOsmol per litre
    (c) Gradient solutes	(iii) about 1200 mOsmol per litre
    (d) Urine concentration	(iv) NaCl and urea

    1. 1.(a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)
    2. 2.(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)Correct answer
    3. 3.(a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
    4. 4.(a)-(i), (b)-(iii), (c)-(iv), (d)-(ii)

    Why option 2 is the answer

    The trap: 300 mOsmol in the cortex rising to 1200 in the inner medulla.

    What this is testing: matching each osmolarity figure and fact to its correct site.

    The cortex sits at about 300 mOsmol per litre, the inner medulla at about 1200, the gradient is built by NaCl and urea, and urine concentration can reach about four times the filtrate — giving (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i), option 2.

    The trap: option 1 swaps the cortex and inner medulla values, giving the cortex the higher 1200 figure and the medulla the lower 300, which reverses the direction the gradient actually rises.

    NCERT Class 11 Biology, page 211

24. Q24 Match the columns

    Match the dialysis step with its detail:

    Column I	Column II
    (a) Heparin	(i) plasma composition without nitrogenous wastes
    (b) Dialysing fluid	(ii) porous membrane allowing passage by gradient
    (c) Cellophane tube	(iii) added before returning blood
    (d) Anti-heparin	(iv) anticoagulant added before dialysis

    1. 1.(a)-(i), (b)-(iv), (c)-(ii), (d)-(iii)
    2. 2.(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)Correct answer
    3. 3.(a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)
    4. 4.(a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)

    Why option 2 is the answer

    The trap: The sequence of haemodialysis using the artificial kidney.

    What this is testing: matching each step of haemodialysis to its correct detail.

    Heparin is the anticoagulant added before dialysis, the dialysing fluid matches plasma minus the nitrogenous wastes, the cellophane tube is a porous membrane letting molecules pass by their concentration gradient, and anti-heparin is added before the blood is returned — giving (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii), option 2.

    The trap: option 1 swaps heparin and the dialysing fluid entries, describing heparin as the plasma-like fluid and the fluid as the anticoagulant, which mixes up two very different steps of the same procedure.

    NCERT Class 11 Biology, page 213

25. Q25 Exception / incorrect

    Identify the INCORRECT value:

    1. 1.blood filtered 1100-1200 mL per minute
    2. 2.GFR 125 mL per minute
    3. 3.GFR 1200 mL per minuteCorrect answer
    4. 4.filtrate 180 litres per day

    Why option 3 is the answer

    The trap: 1200 mL/min is the volume of blood filtered, not the GFR.

    What this is testing: whether you can tell apart the volume of blood filtered from the actual filtration rate.

    Roughly 1100-1200 mL of blood is filtered by the kidneys each minute, and of that, the glomerular filtration rate (GFR) is about 125 mL per minute — the two numbers together give 180 litres of filtrate per day. Stating the GFR itself as 1200 mL per minute is wrong; that is the blood-flow figure repeated under the wrong label.

    The trap: two very different quantities, blood filtered and filtrate formed, share the same units and a numeral that has already appeared once correctly in the list.

    NCERT Class 11 Biology, page 209

26. Q26 Exception / incorrect

    All are true of the JGA EXCEPT:

    1. 1.formed from the DCT and afferent arteriole
    2. 2.formed from the PCT and efferent arterioleCorrect answer
    3. 3.a sensitive region
    4. 4.releases renin when GFR falls

    Why option 2 is the answer

    The trap: The JGA arises from the DCT and afferent arteriole.

    What this is testing: the exact structures that form the juxtaglomerular apparatus (JGA).

    The JGA is a sensitive region formed where the DCT touches the afferent arteriole of the same nephron, and it releases renin when the GFR falls. Saying it forms from the PCT and efferent arteriole gets both halves wrong — it is the DCT, not the PCT, and the afferent, not the efferent, arteriole.

    The trap: PCT/DCT and afferent/efferent are two separate pairs of easily confused terms, and this option swaps both at once, which can look like just one small slip rather than two.

    NCERT Class 11 Biology, page 209

27. Q27 Sequence / ordering

    Correct order of decreasing toxicity of nitrogenous wastes:

    1. 1.ammonia → urea → uric acidCorrect answer
    2. 2.uric acid → urea → ammonia
    3. 3.urea → ammonia → uric acid
    4. 4.uric acid → ammonia → urea

    Why option 1 is the answer

    The trap: Ammonia is most toxic and uric acid least toxic.

    What this is testing: ranking ammonia, urea and uric acid from most to least toxic.

    Ammonia is the most toxic of the three nitrogenous wastes, urea is intermediate, and uric acid is the least toxic — so the correct decreasing order is ammonia, then urea, then uric acid. Any sequence that starts with uric acid or places urea first reverses this order.

    The trap: toxicity and water-cost run in opposite directions — the most toxic waste (ammonia) needs the most water to flush safely, while the least toxic (uric acid) needs almost none — mixing the two scales up is how the wrong orderings get built.

    NCERT Class 11 Biology, page 205

28. Q28 Sequence / ordering

    Correct order of increasing osmolarity:

    1. 1.inner medulla → outer medulla → cortex
    2. 2.cortex (300 mOsmol/L) → outer medulla → inner medulla (1200 mOsmol/L)Correct answer
    3. 3.cortex → inner medulla → outer medulla
    4. 4.inner medulla → cortex → outer medulla

    Why option 2 is the answer

    The trap: Osmolarity rises from cortex to inner medulla.

    What this is testing: how osmolarity changes across the kidney, from cortex to inner medulla.

    Osmolarity is lowest in the cortex at about 300 mOsmol/L, and rises steadily through the outer medulla up to about 1200 mOsmol/L in the inner medulla — an increasing gradient built by the counter-current mechanism. Any order that starts at the inner medulla, or places the cortex anywhere but first, reverses this real gradient.

    The trap: it is easy to remember "medulla is more concentrated" without fixing which end, inner or outer, is highest; the inner medulla, farthest from the cortex, is always the peak.

    NCERT Class 11 Biology, page 211

29. Q29 NEET 2023 (Manipur)

    Correct order of events in the Renin-Angiotensin mechanism:

    1. 1.Fall in GFR → Renin converts angiotensinogen to Angiotensin I, then II → Vasoconstriction and aldosterone release → Reabsorption of Na+ and water → Increase in blood pressure and GFRCorrect answer
    2. 2.Increase in GFR → Renin release → Vasoconstriction → Reabsorption → Fall in GFR
    3. 3.Fall in GFR → Vasoconstriction → Renin release → Reabsorption → Increase in GFR
    4. 4.Reabsorption → Fall in GFR → Renin release → Vasoconstriction → Increase in GFR

    Why option 1 is the answer

    The trap: A fall in glomerular filtration rate triggers renin release, generating Angiotensin II, which causes vasoconstriction and aldosterone-driven Na+/water reabsorption, restoring blood pressure and GFR.

    What this is testing: the correct order of events in the renin-angiotensin mechanism.

    A fall in GFR triggers renin, which converts angiotensinogen to angiotensin I and then II; angiotensin II causes vasoconstriction and aldosterone release, driving Na+ and water reabsorption that restores blood pressure and GFR. Options starting from an INCREASE in GFR, or placing vasoconstriction before renin, reverse this chain.

    The trap: this mechanism corrects a FALL, not a rise, in GFR, so an option starting from the wrong direction of change gets the whole chain backward from its first step.

    NCERT Class 11 Biology, page 212

30. Q30 NEET 2026 (Cancelled)

    The JGA (Juxtaglomerular Apparatus) is a special sensitive region formed by cellular modifications in ________ related to the same nephron.

    1. 1.Distal convoluted tubule and afferent renal arterioleCorrect answer
    2. 2.Distal convoluted tubule and efferent renal arteriole
    3. 3.Proximal convoluted tubule and afferent renal arteriole
    4. 4.Proximal convoluted tubule and efferent renal arteriole

    Why option 1 is the answer

    The trap: The JGA forms where the distal convoluted tubule contacts the afferent arteriole of the same nephron.

    What this is testing: the exact structures forming the juxtaglomerular apparatus (JGA).

    The JGA forms from cellular modifications in the distal convoluted tubule and the AFFERENT renal arteriole of the same nephron, at the point where they touch. Pairing it with the efferent arteriole instead, or with the proximal convoluted tubule rather than the distal, both misname one half of this specific two-part junction.

    The trap: DCT/PCT and afferent/efferent are two separate pairs of easily confused terms, and only one exact combination, DCT with afferent arteriole, is the real JGA — the other three options each swap just one half of it.

    NCERT Class 11 Biology, page 209