The human kidney removes nitrogenous waste — primarily urea — from blood and regulates body fluid composition. NEET questions on this topic frequently test the structural detail of the nephron and the functional distinction between its segments, so confusing which segment does what is a reliable way to lose marks.
Excretory products across organisms. Animals are classified by their dominant nitrogenous waste: ammonotelic (ammonia — aquatic animals like bony fish), ureotelic (urea — mammals, adult amphibians), and uricotelic (uric acid — birds, reptiles, insects). Humans are ureotelic; urea is synthesised in the liver via the ornithine cycle and excreted by the kidneys (NCERT Class 11 Biology Chapter 16, page 205).
Kidney gross structure. Each bean-shaped kidney has an outer cortex and inner medulla. The medulla is organised into medullary pyramids (renal pyramids) whose tips (papillae) open into minor calyces → major calyces → renal pelvis → ureter. The hilum is the concave notch where the renal artery, renal vein, and ureter connect.
The nephron — structural and functional unit. Each kidney contains roughly 1 million nephrons. A nephron has two parts:
Glomerulus + Bowman's capsule (renal corpuscle) — located in the cortex. The glomerulus is a tuft of capillaries supplied by the afferent arteriole and drained by the efferent arteriole. Bowman's capsule is a double-walled cup that collects the filtrate.
Renal tubule — Proximal Convoluted Tubule (PCT) in the cortex → Loop of Henle (descending and ascending limbs dipping into the medulla) → Distal Convoluted Tubule (DCT) in the cortex → Collecting Duct (CD) passing through the medulla.
Cortical vs juxtamedullary nephrons. Most nephrons (~85%) are cortical — short loops of Henle confined mostly to the cortex. Juxtamedullary nephrons (~15%) have long loops extending deep into the medulla and are critical for concentrating urine.
Watch-out: NEET stems often test whether a structure is cortical or medullary, and whether the vasa recta is associated with cortical or juxtamedullary nephrons. Vasa recta are prominent only in juxtamedullary nephrons.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Humans are classified as ureotelic organisms. Which of the following is the primary nitrogenous waste product excreted by human kidneys?
Answer: A. Humans are ureotelic — urea is the dominant nitrogenous waste, synthesised in the liver via the ornithine cycle and excreted by the kidneys (NCERT Class 11 Biology Chapter 16, page 205).
Why B is wrong: B is wrong because ammonia is the primary waste of ammonotelic organisms (bony fish, aquatic larvae). Humans convert ammonia to the less toxic urea in the liver.
Why C is wrong: C is wrong because uric acid is the primary waste of uricotelic organisms (birds, reptiles, insects). Humans excrete small amounts of uric acid but are classified as ureotelic.
Why D is wrong: D is wrong because creatinine is a waste product of muscle metabolism and is excreted by the kidneys, but it is not the primary nitrogenous waste — urea is produced in far greater quantities.
Which of the following correctly describes the location of the renal corpuscle in the kidney?
Answer: B. The renal corpuscle (glomerulus + Bowman's capsule) is located in the cortex of the kidney (NCERT Class 11 Biology Chapter 16).
Why A is wrong: A is wrong because medullary pyramids contain loops of Henle and collecting ducts, not renal corpuscles.
Why C is wrong: C is wrong because the renal pelvis is a funnel-shaped collecting space that channels urine from calyces to the ureter — no nephron components are located there.
Why D is wrong: D is wrong because minor calyces receive urine from the tips of medullary pyramids (papillae); they are part of the drainage system, not the filtration apparatus.
Which of the following organisms is uricotelic?
Answer: C. Birds (including pigeons) are uricotelic — they excrete uric acid as their primary nitrogenous waste, which is semi-solid and conserves water (NCERT Class 11 Biology Chapter 16).
Why A is wrong: A is wrong because bony fish are ammonotelic — they excrete ammonia directly into the surrounding water.
Why B is wrong: B is wrong because adult frogs are ureotelic (though tadpoles are ammonotelic). The shift from ammonotelism to ureotelism occurs during metamorphosis.
Why D is wrong: D is wrong because humans are ureotelic — the primary nitrogenous waste is urea.
The vasa recta is a network of peritubular capillaries that runs parallel to the loop of Henle. It is prominently associated with which type of nephron?
Answer: D. Vasa recta are prominent only in juxtamedullary nephrons, where they run alongside the long loops of Henle deep into the medulla and help maintain the medullary osmotic gradient (NCERT Class 11 Biology Chapter 16).
Why A is wrong: A is wrong because cortical nephrons have short loops of Henle that barely enter the medulla, and vasa recta are absent or rudimentary in these nephrons.
Why B is wrong: B is wrong because no nephrons are located in the renal pelvis. The renal pelvis is a urine-collecting funnel, not a site of filtration or reabsorption.
Why C is wrong: C is wrong because vasa recta are NOT equally present in both types — they are prominent only in juxtamedullary nephrons (~15% of total nephrons).
A student labels the parts of a nephron. She marks the segment that connects Bowman's capsule to the loop of Henle. Which structure has she marked?
Answer: C. The proximal convoluted tubule (PCT) is the segment of the renal tubule that directly follows Bowman's capsule and leads into the loop of Henle (NCERT Class 11 Biology Chapter 16).
Why A is wrong: A is wrong because the DCT comes after the loop of Henle, not before it. The correct sequence is: Bowman's capsule → PCT → Loop of Henle → DCT → Collecting duct.
Why B is wrong: B is wrong because the collecting duct comes after the DCT — it is the terminal segment, not the one connected to Bowman's capsule.
Why D is wrong: D is wrong because the afferent arteriole is a blood vessel that brings blood into the glomerulus — it is not a tubular segment of the nephron.
Approximately what percentage of nephrons in the human kidney are juxtamedullary?
Answer: A. About 15% of nephrons are juxtamedullary (with long loops of Henle extending deep into the medulla). The remaining ~85% are cortical nephrons with short loops (NCERT Class 11 Biology Chapter 16).
Why B is wrong: B is wrong because 85% represents cortical nephrons, not juxtamedullary. This is a common confusion — the majority type is cortical.
Why C is wrong: C is wrong because the split is not equal — cortical nephrons vastly outnumber juxtamedullary ones (~85:15).
Why D is wrong: D is wrong because not all nephrons are juxtamedullary. Only ~15% have the long loop and prominent vasa recta characteristic of juxtamedullary nephrons.
The efferent arteriole of a glomerulus has a smaller diameter than the afferent arteriole. What is the functional significance of this arrangement?
Answer: B. The narrower efferent arteriole creates resistance to outflow, raising hydrostatic pressure within the glomerular capillaries. This elevated pressure drives ultrafiltration of plasma into Bowman's capsule (NCERT Class 11 Biology Chapter 16).
Why A is wrong: A is wrong because a narrower efferent arteriole increases (not decreases) pressure inside the glomerulus. If the efferent were wider, pressure would drop and filtration would decrease.
Why C is wrong: C is wrong because blood must pass through the glomerular capillary network — it cannot bypass the glomerulus. The afferent arteriole feeds into the capillary tuft, which drains via the efferent arteriole.
Why D is wrong: D is wrong because blood flows from afferent → glomerulus → efferent (not the reverse). The names indicate direction: afferent = arriving, efferent = exiting.
A kidney has approximately 1 million nephrons. If 85% are cortical and the remaining are juxtamedullary, and each juxtamedullary nephron has a loop of Henle approximately 4 cm long while each cortical nephron's loop is approximately 1 cm long, what is the approximate total length of all loops of Henle in one kidney?
Answer: A. Cortical nephrons: 850,000 × 1 cm = 850,000 cm. Juxtamedullary nephrons: 150,000 × 4 cm = 600,000 cm. Total = 850,000 + 600,000 = 1,450,000 cm. This requires identifying the two nephron populations, calculating each contribution, and summing.
Why B is wrong: B is wrong because this assumes all 1 million nephrons have 1 cm loops (ignoring juxtamedullary nephrons entirely). Juxtamedullary nephrons have much longer loops (~4 cm).
Why C is wrong: C is wrong — this swaps the two loop lengths, giving cortical nephrons 4 cm and juxtamedullary nephrons 1 cm: 850,000 × 4 + 150,000 × 1 = 3,550,000 cm.
Why D is wrong: D is wrong — this would result from using 1 million × 1 cm + 150,000 × 4 cm = 1,600,000, which double-counts by not subtracting the juxtamedullary fraction from the total.
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Given
Five parts of a nephron listed in scrambled order. We must arrange them in the direction of filtrate/urine flow.
Required
The correct sequential order from the site of filtration to the final collecting structure.
Concept
The nephron is a tube that begins at Bowman's capsule (where filtrate is collected from the glomerulus) and continues through defined segments in a fixed anatomical order. Each segment has a specific function, and the filtrate moves through them in one direction only.
Formula / Rule
No mathematical formula applies. The ordering rule is:
Bowman's capsule → PCT → Loop of Henle → DCT → Collecting duct.
Substitution
Mapping the given labels:• (v) Bowman's capsule → first• (iii) PCT → second• (iv) Loop of Henle → third• (i) DCT → fourth• (ii) Collecting duct → fifth
Sequence assembly
(v) → (iii) → (iv) → (i) → (ii)
Final answer
Option A: (v) → (iii) → (iv) → (i) → (ii) is correct.
Common trap
The most frequent confusion is swapping DCT and Loop of Henle (option D), placing DCT before the loop. This likely arises because "distal" suggests "far from the start," but students forget that "distal" refers to distance from Bowman's capsule along the tubule — and the loop comes between the proximal and distal segments.
Similar NEET-style question
"Which of the following is the correct sequence of structures through which urine passes after leaving the collecting duct?
(A) Minor calyx → Major calyx → Renal pelvis → Ureter
(B) Major calyx → Minor calyx → Renal pelvis → Ureter
(C) Renal pelvis → Minor calyx → Major calyx → Ureter
(D) Ureter → Renal pelvis → Major calyx → Minor calyx"
Answer: A.
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Ammonotelic (fish): NH3 — toxic, requires water. Ureotelic (mammals, amphibians): urea. Uricotelic (birds, reptiles, insects): uric acid — water-saving. Kidneys, ureters, bladder, urethra; nephron is functional unit.
-- NCERT Class 11 Biology, Chapter 16, p. 205More in Human Physiology: 33 exam traps and mistakes · 2 formulas · 1 question pattern from its other lessons.
6 questions from NEET 2022, 2023, 2024. Answers verified against NTA official keys.
Choose the correct statement given below regarding juxta medullary nephron.
Nitrogenous waste is excreted in the form of pellet or paste by :
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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