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Excretory Products and Their Elimination

NCERT Class 11 Biology Chapter 16

Excretory Products and Their Elimination for Class 11 Biology and NEET: modes of excretion, the nephron, urine formation, kidney regulation and disorders.

9 topics Updated 8 Nov 2026

For: Class 11 and NEET, unless a topic says otherwise

In the syllabus: NEET Class 11 syllabus

With your textbook

NCERT Biology (Class 11), Chapter 16 “Excretory Products and their Elimination”, reprint 2026-27.

Open the official NCERT chapter (PDF, 1.8 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Modes of excretion: ammonotelism to uricotelism

    Ammonia, urea and uric acid, NCERT’s examples of each, and excretory organs from flame cells to kidneys.

    NEET only 11 min read 5 solved examples 6 practice questions

  2. Human excretory system and the nephron

    Structure of kidney and nephron with labelled diagrams, cortical vs juxtamedullary nephrons, and vasa recta.

    NCERT Section 16.1 10 min read 5 solved examples 6 practice questions

  3. Urine formation: filtration, reabsorption, secretion

    Glomerular filtration, reabsorption and secretion, GFR of 125 mL a minute and the JGA, with diagrams and examples.

    NCERT Section 16.2 11 min read 6 solved examples 6 practice questions

  4. Functions of the renal tubules

    What the PCT, both limbs of Henle’s loop, the DCT and collecting duct reabsorb and secrete, with a diagram.

    NCERT Section 16.3 8 min read 4 solved examples 6 practice questions

  5. Counter current mechanism and urine concentration

    Henle’s loop and vasa recta, the 300 to 1200 mOsmol per litre gradient, NaCl and urea, with a diagram.

    NCERT Section 16.4 8 min read 3 solved examples 6 practice questions

  6. Regulation of kidney function

    ADH and osmoreceptors, renin–angiotensin, aldosterone, ANF and diabetes insipidus, with flow diagrams.

    NCERT Section 16.5 12 min read 5 solved examples 6 practice questions

  7. Micturition and the composition of urine

    The micturition reflex, composition of urine (1 to 1.5 litres a day, pH 6.0, 25–30 g of urea), glycosuria and ketonuria.

    NCERT Section 16.6 7 min read 5 solved examples 6 practice questions

  8. Role of lungs, liver and skin in excretion

    Role of other organs in excretion for Class 11 Biology and NEET: what the lungs, the liver through bile, and the sweat and sebaceous glands remove.

    NCERT Section 16.7 6 min read 3 solved examples 6 practice questions

  9. Disorders of the excretory system

    Uraemia, haemodialysis and artificial kidney, transplantation, renal calculi, glomerulonephritis.

    NCERT Section 16.8 10 min read 4 solved examples 6 practice questions

Key formulas in this chapter

Modes of excretion

  • toxicity: ammonia > urea > uric acid
  • water needed: ammonia > urea > uric acid
  • ammonotelic: many bony fishes, aquatic amphibians, aquatic insects
  • ureotelic: mammals, many terrestrial amphibians, marine fishes
  • uricotelic: reptiles, birds, land snails, insects

Human excretory system

  • excretory system: 2 kidneys + 2 ureters + urinary bladder + urethra
  • nephron = glomerulus + renal tubule
  • renal corpuscle = glomerulus + Bowman’s capsule
  • renal tubule: Bowman’s capsule → PCT → Henle’s loop → DCT; many DCTs → one collecting duct
  • blood: afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries, vasa recta

Urine formation

  • excreted amount = filtered amount − reabsorbed amount + secreted amount
  • GFR ≈ 125 mL a minute ≈ 180 L a day
  • reabsorbed ≈ (180 − 1.5) ÷ 180 ≈ 99 per cent
  • filter: endothelium + basement membrane + podocyte epithelium
  • secreted: H, K, ammonia

Functions of the tubules

  • PCT: nutrients + 70–80 per cent of electrolytes and water reabsorbed
  • descending limb: water out → filtrate concentrates
  • ascending limb: electrolytes out → filtrate dilutes
  • DCT: conditional Na and water; secretes H, K, NH
  • collecting duct: ADH permits water reabsorption; urea recycling; H and K secretion

Counter current mechanism

  • counter current: opposite flows in the two limbs of Henle’s loop and of the vasa recta
  • medullary gradient: 300 → about 1200 mOsmol L
  • concentration factor: 1200 ÷ 300 = 4
  • gradient made mainly by NaCl and urea

Regulation of kidney function

  • fluid loss → osmoreceptors → hypothalamus → ADH → water reabsorbed
  • renin: angiotensinogen → angiotensin I; ACE (beyond NCERT): angiotensin I → angiotensin II
  • angiotensin II → vasoconstriction + aldosterone → GFR and blood pressure up
  • ANF → vasodilation → blood pressure down

Micturition

  • reflex: stretch → stretch receptors → CNS → bladder contracts + sphincter relaxes
  • urine: 1 to 1.5 L a day, pH about 6.0
  • urea: 25–30 g a day
  • glycosuria and ketonuria: possible diabetes clues, not specific diagnoses

Other organs in excretion

  • lungs: CO about 200 mL a minute + water
  • liver: bile → bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins, drugs
  • sweat: water + NaCl + a little urea + lactic acid
  • sebum: sterols + hydrocarbons + waxes

Disorders of the excretory system

  • uraemia: urea accumulates in blood
  • haemodialysis: artery → heparin → cellophane tube in dialysing fluid → anti-heparin → vein
  • dialysing fluid = plasma − nitrogenous wastes
  • renal calculi: crystallised salts (oxalates); glomerulonephritis: inflamed glomeruli

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