Class 11 Biology · NCERT Chapter 16

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Excretory Products and Their Elimination Class 11 Notes

Exam-ready notes on excretory products and their elimination: ammonotelism, ureotelism and uricotelism, invertebrate excretory structures, the human excretory system and nephron, urine formation (GFR, JGA), the countercurrent mechanism, hormonal regulation (ADH, renin-angiotensin, ANF), micturition, accessory excretory organs and renal disorders.

Chapter:Excretory Products & Their EliminationClass:11Subject:BiologyBoard:CBSE · NEET

8 Key Formulas3 Solved Examples40 Practice MCQs

DWritten byDeep Narayan

UpdatedSeptember 2026

Key Concept Summary

What are the three processes of urine formation?

Answer-first: urine formation involves (1) glomerular filtration — ultrafiltration of blood plasma at the glomerulus (GFR ≈ 125 mL/min = 180 L/day), producing a protein-free filtrate; (2) tubular reabsorption — selective recovery of essential nutrients, electrolytes and water back into the blood, mainly in the PCT (>99% of the filtrate); and (3) tubular secretion — transfer of H⁺, K⁺ and ammonia from the blood into the filtrate, maintaining pH and ionic balance.

Table of Contents13 sections

Revision & Practice

Modes of Excretion — Ammonotelism, Ureotelism and Uricotelism

Ammonia, urea and uric acid are the major nitrogenous wastes excreted by animals. Which one an animal excretes depends mainly on its habitat and the availability of water. Ammonia is the most toxic and requires large volumes of water for elimination; uric acid, being the least toxic and nearly insoluble, can be removed with a minimum loss of water.

Definition

Ammonotelism

The process of excreting ammonia. Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic. Being readily soluble, ammonia is excreted by diffusion across body surfaces or through gill surfaces (in fishes) as ammonium ions; the kidneys play no significant role.

Definition

Ureotelism

Excretion of urea, a less toxic nitrogenous waste that needs less water. Mammals, many terrestrial amphibians and marine fishes are ureotelic. Ammonia produced by metabolism is converted into urea in the liver, released into the blood, and filtered and excreted by the kidneys. Some urea may be retained in the kidney matrix to maintain a desired osmolarity.

Definition

Uricotelism

Excretion of uric acid as a pellet or paste, with minimum loss of water. Reptiles, birds, land snails and insects are uricotelic.

Protonephridia or flame cells — excretory structures in Platyhelminthes (e.g. Planaria), rotifers, some annelids and the cephalochordate Amphioxus; concerned primarily with ionic and fluid-volume regulation (osmoregulation).
Nephridia — tubular excretory structures of earthworms and other annelids; remove nitrogenous wastes and maintain fluid and ionic balance.
Malpighian tubules — excretory structures of most insects including cockroaches; help in removal of nitrogenous wastes and osmoregulation.
Antennal glands or green glands — perform excretory function in crustaceans like prawns.

NEET favourite

Remember the pairing: bony fishes → ammonotelic; mammals and elasmobranchs → mostly ureotelic; reptiles, birds, insects and land snails → uricotelic. The mode of excretion reflects water availability: more toxic + more water needed = ammonia (aquatic); least toxic + least water = uric acid (terrestrial/egg-laying).

MCQ Questions

Which nitrogenous waste is the most toxic and requires the largest volume of water for elimination?

Bony fishes and aquatic amphibians are typically —

Reptiles and birds excrete nitrogenous wastes mainly as —

Ammonia, being readily soluble, is chiefly excreted by —

Which excretory structure is primarily concerned with osmoregulation in flatworms?

1 Mark Questions

1
Define ammonotelism with one example.
2
Define ureotelism and name the organ where urea is formed.
3
What are malpighian tubules? Name an organism that has them.
4
Name the excretory structure of crustaceans like prawns.
5
What is osmoregulation?

2 Mark Questions

1
Why does ammonia need large volumes of water for elimination while uric acid needs the least?
2
Distinguish between ammonotelism, ureotelism and uricotelism with one example of each.
3
Name the four invertebrate excretory structures and their functions.

3 Mark Questions

1
Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic. Justify, using the toxicity and solubility of the nitrogenous wastes.
2
Survey the variety of excretory structures in the animal kingdom — flame cells, nephridia, malpighian tubules and green glands — and state the function of each.

Human Excretory System — Organs

In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a urethra. Kidneys are reddish-brown, bean-shaped structures situated between the levels of the last thoracic and third lumbar vertebra, close to the dorsal inner wall of the abdominal cavity.

Each kidney of an adult human measures 10–12 cm in length, 5–7 cm in width and 2–3 cm in thickness, with an average weight of 120–170 g.
Towards the centre of the inner concave surface is a notch called the hilum, through which the ureter, blood vessels and nerves enter.
Inner to the hilum lies a broad, funnel-shaped space called the renal pelvis, with projections called calyces.
A pair of ureters carry urine from each kidney to the urinary bladder, which stores it until a voluntary signal causes its release through the urethra.

Figure 16.1 — human urinary system — From NCERT Class 11 Biology · Fig 16.1 — Human urinary system.

Exam pointer

The renal pelvis → calyces → urinary bladder → urethra is the urine outflow path. The hilum is the entry notch for ureter, blood vessels and nerves.

MCQ Questions

The human excretory system consists of —

The kidneys are situated between the levels of —

The average weight of an adult human kidney is —

The ureter, blood vessels and nerves enter the kidney through the —

The funnel-shaped cavity of the kidney into which the calyces project is the —

1 Mark Questions

1
List the organs of the human excretory system.
2
Where are the kidneys located in the body?
3
Give the average weight and dimensions of an adult human kidney.
4
What is the hilum of the kidney?
5
Define calyx and renal pelvis.

2 Mark Questions

1
Explain the roles of the ureters, urinary bladder and urethra in urine transport and storage.
2
Describe the hilum and renal pelvis of the kidney with their significance.
3
Distinguish between the renal cortex and renal medulla.

3 Mark Questions

1
Describe the position, shape, size and weight of the human kidney, mentioning the hilum and renal pelvis.
2
Trace the path of urine from the kidney to the external urethral opening, naming each part involved.

Structure of the Kidney — Cortex, Medulla and Pyramids

The outer layer of the kidney is a tough capsule. Inside the kidney there are two zones: an outer cortex and an inner medulla. The medulla is divided into a few conical masses — the medullary pyramids — that project into the calyces. The cortex extends in between the medullary pyramids as renal columns called the Columns of Bertini.

Figure 16.2 — longitudinal section (diagrammatic) of the kidney — From NCERT Class 11 Biology · Fig 16.2 — Longitudinal section (diagrammatic) of the kidney: capsule, cortex, medulla, pyramids, columns of Bertini, pelvis and calyces.

Definition

Columns of Bertini

The portions of the renal cortex that extend between the medullary pyramids. Also called renal columns.

MCQ Questions

In the human kidney, the medulla is divided into a few conical masses called —

The cortex extends between the medullary pyramids as —

The outer layer of the kidney is a —

The projections of the renal pelvis into which the medullary pyramids project are the —

1 Mark Questions

1
Name the two zones of the kidney.
2
What are medullary pyramids?
3
Define the Columns of Bertini.
4
What are the projections of the renal pelvis called?

2 Mark Questions

1
Describe the internal structure of the kidney — capsule, cortex, medulla, pyramids, pelvis and calyces.
2
Distinguish between the cortex and the medullary pyramids of the kidney.
3
How do the collecting ducts of the nephrons open into the renal pelvis?

3 Mark Questions

1
Give a labelled account of the longitudinal section of the human kidney and describe the medullary organisation.
2
Explain the relationship between the medullary pyramids, calyces and renal pelvis in draining urine.

Nephron — Structure and Types

Definition

Nephron

The functional unit of the kidney. Each kidney has nearly one million nephrons. A nephron has two parts: the glomerulus and the renal tubule.

The glomerulus is a tuft of capillaries formed by the afferent arteriole — a fine branch of the renal artery. Blood from the glomerulus is carried away by an efferent arteriole. The renal tubule begins with a double-walled cup-like structure, Bowman's capsule, which encloses the glomerulus. Glomerulus together with Bowman's capsule is called the malpighian body or renal corpuscle.

The tubule continues as a highly coiled proximal convoluted tubule (PCT).
A hairpin-shaped loop of Henle follows, with a descending and an ascending limb.
The ascending limb continues as the distal convoluted tubule (DCT).
The DCTs of many nephrons open into a straight collecting duct; many collecting ducts converge and open into the renal pelvis through the medullary pyramids in the calyces.

Figure 16.3 — diagrammatic representation of a nephron — From NCERT Class 11 Biology · Fig 16.3 — A diagrammatic representation of a nephron showing blood vessels, duct and tubule.

Figure 16.4 — Malpighian body (renal corpuscle) — From NCERT Class 11 Biology · Fig 16.4 — Malpighian body (renal corpuscle): glomerulus enclosed by Bowman's capsule.

Definition

Cortical vs juxta medullary nephrons

In most nephrons the loop of Henle is short and extends only a little into the medulla — these are cortical nephrons. In others the loop of Henle is very long and runs deep into the medulla — these are juxta medullary nephrons.

The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries. A minute vessel of this network runs parallel to the loop of Henle forming a U-shaped vasa recta. The vasa recta is absent or highly reduced in cortical nephrons.

Don't mix these up

Glomerulus (tuft of capillaries) + Bowman's capsule = malpighian body / renal corpuscle. The PCT, loop of Henle and DCT together form the renal tubule.

MCQ Questions

The functional unit of the kidney is the —

The glomerulus is a tuft of capillaries formed by the —

The malpighian body (renal corpuscle) is formed of the —

In which nephrons does the loop of Henle run deep into the medulla?

The vasa recta is —

1 Mark Questions

1
Define a nephron and name its two main parts.
2
What is the malpighian body?
3
How is the glomerulus formed?
4
Name the parts of the renal tubule in order.
5
Define vasa recta. In which nephrons is it absent or highly reduced?

2 Mark Questions

1
Distinguish between cortical and juxta medullary nephrons.
2
Describe the structure of the renal tubule starting from Bowman's capsule up to the collecting duct.
3
Trace the fate of the efferent arteriole after it leaves the glomerulus.

3 Mark Questions

1
Describe the structure of a nephron along with its blood supply — glomerulus, Bowman's capsule, PCT, loop of Henle, DCT, collecting duct, peritubular capillaries and vasa recta.
2
Why is the malpighian corpuscle also called the renal corpuscle? Describe its parts and location in the kidney.

Urine Formation — Glomerular Filtration, GFR and JGA

Urine formation involves three main processes — glomerular filtration, reabsorption and secretion — taking place in different parts of the nephron.

1. Glomerular Filtration (Ultrafiltration)

On average, 1100–1200 mL of blood is filtered by the kidneys per minute, roughly 1/5th of the blood pumped out by each ventricle in a minute. The glomerular capillary blood pressure forces blood through three layers — the endothelium of glomerular blood vessels, the epithelium of Bowman's capsule, and the basement membrane between them. The epithelial cells of Bowman's capsule, called podocytes, are arranged intricately so as to leave minute spaces called filtration slits or slit pores.

Blood is filtered so finely that almost all constituents of plasma except proteins pass into the lumen of Bowman's capsule — hence it is a process of ultrafiltration.

Glomerular filtration rate (GFR)

GFR \approx 125 mL/min = 180 L/day

Definition

Juxta glomerular apparatus (JGA)

A special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. A fall in GFR activates the JG cells to release renin, which stimulates glomerular blood flow and brings the GFR back to normal.

Exam pointer

Compare the 180 L of filtrate formed per day with the ~1.5 L of urine released: this tells you that nearly 99% of the filtrate is reabsorbed. That is the whole point of tubular reabsorption.

2. Reabsorption and 3. Secretion (overview)

Tubular epithelial cells reabsorb substances from the filtrate actively (glucose, amino acids, Na⁺) or passively (nitrogenous wastes; water in the initial segments). During urine formation the tubular cells also secrete substances such as H⁺, K⁺ and ammonia into the filtrate — this maintains the ionic and acid–base balance of body fluids.

MCQ Questions

The GFR in a healthy individual is approximately —

A GFR of 125 mL/min corresponds to how much filtrate per day?

Which of the following is NOT one of the three main processes of urine formation?

Ultrafiltration at the glomerulus passes blood through —

The JGA is formed by cellular modifications in the —

1 Mark Questions

1
Define glomerular filtration.
2
State the value of GFR in a healthy adult.
3
What is ultrafiltration?
4
Name the three processes of urine formation.
5
What are filtration slits?

2 Mark Questions

1
How much blood is filtered per minute and what fraction of the ventricular output is it?
2
Explain the role of the JGA in regulating GFR.
3
Blood is ultrafiltered at the glomerulus — which constituents pass and which are retained?

3 Mark Questions

1
Describe the three layers of the glomerular filtration membrane and explain how ultrafiltration occurs.
2
Explain the autoregulatory mechanism of GFR with the help of the juxta glomerular apparatus.

Function of the Tubules — PCT, Loop of Henle, DCT, Collecting Duct

Figure 16.5 — reabsorption and secretion of major substances at different parts of the nephron — From NCERT Class 11 Biology · Fig 16.5 — Reabsorption and secretion of major substances at different parts of the nephron (arrows indicate the direction of movement of materials).

Definition

Proximal convoluted tubule (PCT)

Lined by simple cuboidal brush border epithelium, which increases the surface area for reabsorption. Nearly all the essential nutrients and 70–80% of electrolytes and water are reabsorbed here. The PCT also maintains pH and ionic balance by selective secretion of hydrogen ions and ammonia and by absorption of HCO₃⁻.

Definition

Loop of Henle

Reabsorption is minimum in its ascending limb, but the loop is significant in maintaining the high osmolarity of the medullary interstitial fluid. The descending limb is permeable to water but almost impermeable to electrolytes (concentrating the filtrate); the ascending limb is impermeable to water but allows transport of electrolytes actively or passively (diluting the filtrate).

Definition

Distal convoluted tubule (DCT)

Performs conditional reabsorption of Na⁺ and water; also reabsorbs HCO₃⁻ and selectively secretes hydrogen and potassium ions and NH₃ to maintain pH and the sodium–potassium balance of the blood.

Definition

Collecting duct

Extends from the cortex to the inner medulla. Large amounts of water can be reabsorbed here to produce concentrated urine. It allows small amounts of urea into the medullary interstitium to keep up the osmolarity, and secretes H⁺ and K⁺ selectively.

Common mistake

Don't write that the PCT 'reabsorbs 65% of the filtrate'. The NCERT figure to quote: the PCT reabsorbs nearly all essential nutrients and 70–80% of electrolytes and water.

MCQ Questions

Nearly all essential nutrients and 70–80% of electrolytes and water are reabsorbed by the —

Which part of the loop of Henle is permeable to water but almost impermeable to electrolytes?

Which segment is impermeable to water but allows active or passive transport of electrolytes?

Small amounts of urea pass into the medullary interstitium to maintain osmolarity through the —

Which segment performs conditional reabsorption of Na⁺ and water and secretes H⁺, K⁺ and NH₃?

1 Mark Questions

1
What is the function of the brush border in the PCT?
2
Which segment of the nephron reabsorbs the maximum electrolytes and water?
3
State the permeability properties of the descending and ascending limbs of the loop of Henle.
4
Which part of the nephron allows small amounts of urea into the medullary interstitium?
5
What does tubular secretion help the body to maintain?

2 Mark Questions

1
Why is the ascending limb of the loop of Henle impermeable to water, and what role does this play in the medullary osmolarity?
2
List the functions of the PCT.
3
Explain how the DCT maintains the pH and sodium–potassium balance of the blood.

3 Mark Questions

1
Describe the functions of the PCT, loop of Henle, DCT and collecting duct with reference to reabsorption and secretion.
2
Discuss which substances are reabsorbed actively and which passively in different nephron segments, and how tubular secretion maintains the pH of body fluids.

Countercurrent Mechanism — Concentration of the Filtrate

Definition

Counter current mechanism

The special transport arrangement between the loop of Henle and the vasa recta: filtrate flows in opposite directions in the two limbs of the loop, and blood also flows in a counter current pattern through the two limbs of the vasa recta. This maintains an increasing osmolarity towards the inner medullary interstitium — from about 300 mOsmolL⁻¹ in the cortex to about 1200 mOsmolL⁻¹ in the inner medulla.

The gradient is caused mainly by NaCl and urea. NaCl is transported by the ascending limb of the loop of Henle and exchanged with the descending limb of the vasa recta, then returned to the interstitium by the ascending portion of the vasa recta.
Small amounts of urea enter the thin segment of the ascending limb of the loop of Henle and are transported back to the interstitium by the collecting tubule.
The interstitial gradient allows easy passage of water from the collecting tubule, concentrating the filtrate (urine).
Human kidneys can produce urine nearly four times more concentrated than the initial filtrate.

Exam pointer

Quote the gradient numbers with units every time: cortex ≈ 300 mOsmolL⁻¹ → inner medulla ≈ 1200 mOsmolL⁻¹, built by NaCl and urea, maintained by the counter current arrangement of the loop of Henle and vasa recta.

MCQ Questions

The osmolarity of the inner medullary interstitium is approximately —

The osmolarity gradient in the kidney goes from about —

The medullary interstitial gradient is caused mainly by —

The counter current in the kidney involves the —

Human kidneys can produce urine that is concentrated about —

1 Mark Questions

1
Define the counter current mechanism.
2
Give the osmolarity values of the kidney cortex and inner medulla.
3
Which two substances mainly build the medullary osmotic gradient?
4
How much more concentrated than the initial filtrate can human urine be?

2 Mark Questions

1
Explain the role of the vasa recta as a counter current exchanger.
2
How does the ascending limb of the loop of Henle contribute to building the medullary gradient?
3
How does urea enter the medullary interstitium and why does this matter?

3 Mark Questions

1
Give a brief account of the counter current mechanism and the role of the loop of Henle and vasa recta in concentrating urine.
2
Explain why the special arrangement of the loop of Henle and the vasa recta is called a counter current mechanism, and how the interstitial gradient it builds helps concentrate the filtrate.

Regulation of Kidney Function — ADH, Renin-Angiotensin and ANF

Hormonal regulation of kidney function

Definition

Antidiuretic hormone (ADH) / vasopressin

Osmoreceptors are activated by changes in blood volume, body fluid volume and ionic concentration. Excessive loss of fluid activates them, stimulating the hypothalamus to release ADH from the neurohypophysis. ADH facilitates water reabsorption from the latter parts of the tubule, preventing diuresis. An increase in body fluid volume switches off the osmoreceptors and suppresses ADH release to complete the feedback.

ADH also has constrictory effects on blood vessels, increasing blood pressure; an increased blood pressure increases glomerular blood flow and hence the GFR.

Definition

Renin-Angiotensin mechanism

A fall in glomerular blood flow / blood pressure / GFR activates the JG cells to release renin, which converts angiotensinogen in the blood to angiotensin I and then to angiotensin II. Angiotensin II is a powerful vasoconstrictor that raises glomerular blood pressure and GFR; it also activates the adrenal cortex to release aldosterone, which causes reabsorption of Na⁺ and water from the distal parts of the tubule — again raising blood pressure and GFR.

Definition

Atrial natriuretic factor (ANF)

An increase in blood flow to the atria of the heart causes the release of ANF, which causes vasodilation and thereby decreases blood pressure. The ANF mechanism acts as a check on the renin-angiotensin mechanism.

MCQ Questions

ADH is released from the —

Which hormone's release prevents diuresis by facilitating water reabsorption from the latter parts of the tubule?

Angiotensin II is a powerful —

Aldosterone, which causes reabsorption of Na⁺ and water, is secreted by the —

ANF, which acts as a check on the renin-angiotensin mechanism, is released by —

1 Mark Questions

1
What is ADH and from where is it released?
2
What is vasopressin?
3
Name the two hormones and one factor that regulate kidney function.
4
What is the effect of ANF on blood pressure?

2 Mark Questions

1
Explain the role of osmoreceptors and ADH in regulating the water balance of the body.
2
Outline the renin-angiotensin mechanism from renin release to aldosterone action.
3
How does ANF act as a check on the renin-angiotensin mechanism?

3 Mark Questions

1
Describe the hormonal feedback regulation of kidney function involving the hypothalamus, the JGA and the heart.
2
Explain how an excessive loss of fluid from the body is corrected by the ADH mechanism, and how an increase in body fluid volume completes the feedback.

Micturition and Accessory Excretory Organs

Urine formed by the nephrons is carried to the urinary bladder and stored until a voluntary signal from the CNS. Stretching of the bladder as it fills activates stretch receptors in its walls, which send signals to the CNS. The CNS sends motor messages that contract the smooth muscles of the bladder and simultaneously relax the urethral sphincter, releasing urine. This release is called micturition and the neural mechanism is the micturition reflex.

An adult human excretes on average 1–1.5 L of urine per day. Urine is a light-yellow, watery, slightly acidic fluid (pH ≈ 6.0) with a characteristic odour; on average 25–30 g of urea is excreted per day. Glycosuria (glucose) and ketonuria (ketone bodies) indicate diabetes mellitus.

Role of Other Organs in Excretion

Lungs — remove large amounts of CO₂ (approximately 200 mL/minute) and significant quantities of water every day.
Liver — the largest gland; secretes bile containing bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs, which mostly pass out with digestive wastes.
Skin — sweat glands secrete a watery fluid containing NaCl, small amounts of urea and lactic acid; sebaceous glands eliminate sterols, hydrocarbons and waxes through sebum. Small amounts of nitrogenous wastes can also be eliminated through saliva.

MCQ Questions

The process of release of urine from the body is called —

The micturition reflex is initiated by the stretching of the —

A healthy adult human excretes on average how much urine per day?

Normal human urine is slightly acidic, with a pH of about —

Glycosuria and ketonuria together are indicative of —

The lungs remove approximately how much CO₂ per minute?

1 Mark Questions

1
Define micturition and the micturition reflex.
2
Give the average daily urine output and the average urea excretion of an adult human.
3
Name the excretory products of the sweat glands.
4
Which organ secretes bile containing bilirubin and biliverdin?
5
What do glycosuria and ketonuria indicate?

2 Mark Questions

1
Explain the neural mechanism of micturition.
2
Describe the role of the liver and skin in excretion.
3
Mention the characteristics of normal urine and what their analysis reveals.

3 Mark Questions

1
Describe the role of the lungs, liver and skin in the elimination of excretory wastes.
2
Explain micturition — how urine is stored and released through the micturition reflex.

Disorders of the Excretory System — Uremia, Hemodialysis, Renal Calculi

Definition

Uremia

Malfunctioning of the kidneys leads to accumulation of urea in the blood — a highly harmful condition that may lead to kidney failure.

Definition

Hemodialysis

Removal of urea from the blood of a uremic patient using an artificial kidney. Blood drained from a convenient artery is pumped into a dialysing unit after adding an anticoagulant (heparin). The unit contains a coiled cellophane tube surrounded by a dialysing fluid having the same composition as plasma except nitrogenous wastes. Urea and other wastes diffuse out through the porous cellophane membrane along the concentration gradient, and the cleared blood is pumped back to the body through a vein after adding anti-heparin.

Kidney transplantation — the ultimate method for correcting acute renal failure; a functioning kidney from a donor, preferably a close relative, to minimise rejection by the host's immune system.
Renal calculi — stone or insoluble mass of crystallised salts (e.g. oxalates) formed within the kidney.
Glomerulonephritis — inflammation of the glomeruli of the kidney.

MCQ Questions

Accumulation of urea in the blood is called —

During hemodialysis, an anticoagulant added to the blood drained from the artery is —

The dialysing fluid has the same composition as plasma except for —

A stone or insoluble mass of crystallised salts formed within the kidney is called —

Inflammation of the glomeruli of the kidney is —

1 Mark Questions

1
What is uremia?
2
Define renal calculi.
3
What is glomerulonephritis?
4
Why is heparin added to blood during hemodialysis?

2 Mark Questions

1
Describe how hemodialysis removes nitrogenous wastes using the artificial kidney.
2
Why is a functioning kidney for transplantation preferred from a close relative?
3
Distinguish between renal calculi and glomerulonephritis.

3 Mark Questions

1
Explain the principle and working of hemodialysis, from blood drainage to return of cleared blood.
2
Describe the main disorders of the excretory system — uremia, renal calculi, glomerulonephritis, and the corrective methods of hemodialysis and kidney transplantation.

NCERT Exercise Questions

From the textbook

All NCERT questions for this chapter — NCERT Biology, Part II, Chapter 16 (Excretory Products and Their Elimination). Questions keep their NCERT numbering so you can match them to the book.

Exercises (NCERT Q1–Q12)

1) Define Glomerular Filtration Rate (GFR).
2) Explain the autoregulatory mechanism of GFR.
3) Indicate whether the following statements are true or false: (a) Micturition is carried out by a reflex. (b) ADH helps in water elimination, making the urine hypotonic. (c) Protein-free fluid is filtered from blood plasma into the Bowman's capsule. (d) Henle's loop plays an important role in concentrating the urine. (e) Glucose is actively reabsorbed in the proximal convoluted tubule.
4) Give a brief account of the counter current mechanism.
5) Describe the role of liver, lungs and skin in excretion.
6) Explain micturition.
7) Match the items of column I with those of column II: Column I — (a) Ammonotelism, (b) Bowman's capsule, (c) Micturition, (d) Uricotelism, (e) ADH; Column II — (i) Birds, (ii) Water reabsorption, (iii) Bony fish, (iv) Urinary bladder, (v) Renal tubule.
8) What is meant by the term osmoregulation?
9) Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic — why?
10) What is the significance of juxta glomerular apparatus (JGA) in kidney function?
11) Name the following: (a) A chordate animal having flame cells as excretory structures. (b) Cortical portions projecting between the medullary pyramids in the human kidney. (c) A loop of capillary running parallel to the Henle's loop.
12) Fill in the gaps: (a) Ascending limb of Henle's loop is ______ to water whereas the descending limb is ______ to it. (b) Reabsorption of water from distal parts of the tubules is facilitated by hormone ______. (c) Dialysis fluid contains all the constituents as in plasma except ______. (d) A healthy adult human excretes, on average, ______ gm of urea per day.

Answers at a glance

1
Q16.1 — GFR is the amount of filtrate formed by the kidneys per minute; ≈ 125 mL/min (≈ 180 L/day) in a healthy individual.
2
Q16.2 — A fall in GFR activates the JG cells of the JGA to release renin, which stimulates glomerular blood flow and restores the GFR to normal (autoregulation).
3
Q16.3 — (a) True; (b) False — ADH increases water reabsorption, making urine concentrated, not hypotonic; (c) True; (d) True; (e) True.
4
Q16.4 — The loop of Henle and the vasa recta run in opposite directions (counter current). NaCl transported by the ascending limb and urea returned by the collecting tubule maintain an osmolarity gradient from 300 mOsmolL⁻¹ (cortex) to 1200 mOsmolL⁻¹ (inner medulla), allowing the kidney to produce concentrated urine.
5
Q16.5 — Liver secretes bile with bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs (which pass out with digestive wastes); lungs remove CO₂ (~200 mL/min) and water; skin sweat glands remove NaCl, urea and lactic acid, and sebaceous glands remove sterols, hydrocarbons and waxes.
6
Q16.6 — Micturition is the release of urine: bladder distension stimulates stretch receptors → signals to the CNS → motor messages contract bladder smooth muscle and relax the urethral sphincter. The neural mechanism is the micturition reflex.
7
Q16.7 — (a)–(iii) Bony fish; (b)–(v) Renal tubule; (c)–(iv) Urinary bladder; (d)–(i) Birds; (e)–(ii) Water reabsorption.
8
Q16.8 — Osmoregulation is the maintenance of ionic balance and fluid volume (osmotic concentration) of body fluids by excretory structures such as protonephridia (flame cells) and nephridia.
9
Q16.9 — Ammonia is highly toxic and needs large volumes of water for elimination; terrestrial animals conserve water by converting ammonia to the less toxic urea (ureotelic) or almost insoluble uric acid (uricotelic), which need far less water.
10
Q16.10 — The JGA autoregulates GFR: on a fall in GFR, its JG cells release renin, which restores glomerular blood flow and hence normal GFR.
11
Q16.11 — (a) Amphioxus (a cephalochordate); (b) Columns of Bertini (renal columns); (c) Vasa recta.
12
Q16.12 — (a) impermeable, permeable; (b) ADH (vasopressin); (c) nitrogenous wastes; (d) 25–30 gm.

CBSE Pattern Questions

How CBSE asks this chapter

In the CBSE Class 11 Biology paper (and NEET), this chapter is tested through definitions and values (GFR, osmolality), one-mark differences and matching, and diagram-based and description questions on the nephron, countercurrent mechanism, hormonal regulation (ADH, renin-angiotensin, ANF) and disorders such as uremia and hemodialysis.

MCQ Questions

The dialysing unit used in hemodialysis contains a coiled —

Which of the following increases blood pressure by powerful vasoconstriction?

The portion of the renal cortex that projects between the medullary pyramids is called —

Atrial natriuretic factor (ANF) —

Nearly 99% of the glomerular filtrate is —

1 Mark Questions

1
Define GFR and give its value.
2
Give the osmolarity range from the kidney cortex to the inner medulla.
3
Name the hormone that prevents diuresis.
4
What is renal calculi?
5
Define micturition.

2 Mark Questions

1
Why are reptiles and birds uricotelic?
2
Explain tubular secretion and its significance.
3
State the significance of the juxta glomerular apparatus.
4
Distinguish between cortical and juxta medullary nephrons.

3 Mark Questions

1
Explain the counter current mechanism of urine concentration.
2
Describe how ADH regulates the water balance of the body.
3
Describe the functions of the PCT and the loop of Henle.

5 Mark Questions

1
(a) Describe the three processes of urine formation — filtration, reabsorption and secretion — with a note on the JGA. (b) Explain how ADH and aldosterone regulate water and ionic balance.
2
(a) Give a labelled account of a nephron. (b) Describe the principle and working of hemodialysis. (c) Why is the ureotelic mode of excretion advantageous to mammals?

PDF: Assignments & Tests

Printable study material

Free downloadable PDFs for this chapter — two topic-wise assignments and two full CBSE-pattern tests (each 90 minutes, 40 marks) mirroring the board paper.

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Practice path: complete Assignment 1 first (topic-by-topic), then Assignment 2 (higher difficulty, with integrated problems), then attempt the two timed CBSE-pattern tests.

Excretory Products and Their Elimination Assignment 1 — Topic-wise Questions

Walks every topic of the chapter in order — modes of excretion, nephron structure, urine formation, tubule functions, countercurrent mechanism, regulation, micturition and disorders.

excretory-products-and-their-elimination-class-11-notes-assignment-1.pdf

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Excretory Products and Their Elimination Assignment 2 — Topic-wise Questions (Higher Difficulty)

Higher-difficulty second set with integration of multi-topic problems — concentration gradient calculations, hormone feedback pathways and diagram-based questions on the nephron and countercurrent mechanism.

excretory-products-and-their-elimination-class-11-notes-assignment-2.pdf

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Excretory Products and Their Elimination Test 1 — CBSE Pattern (90 min, 40 marks)

Full board-pattern test: 1M MCQs/VSA, 2M, 3M, 5M long answers → totals 40 marks; time 90 minutes; answer key included.

excretory-products-and-their-elimination-class-11-notes-test-1-cbse.pdf

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Excretory Products and Their Elimination Test 2 — CBSE Pattern (90 min, 40 marks)

Second full paper with different questions, same 40-mark / 90-minute blueprint — urine formation, countercurrent mechanism, hormonal regulation and disorders, with answer key.

excretory-products-and-their-elimination-class-11-notes-test-2-cbse.pdf

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Quick Revision

Key formulas at a glance

Memorise these equations — direct application numericals and derivations in CBSE & JEE frequently hinge on these.

Glomerular filtration rate

GFR \approx 125 mL/min = 180 L/day

amount of filtrate formed per minute by the kidneys.

Blood filtered per minute

1100 - 1200 mL/min \approx \frac{1}{5} of ventricular output

ultrafiltered at the glomerulus.

Urine volume

Urine output \approx 1 - 1.5 L/day

Reabsorption percentage

Reabsorbed \approx 99% of filtrate

Medullary osmolarity gradient

300 mOsmolL^{- 1} (cortex) \to 1200 mOsmolL^{- 1} (inner medulla)

built by NaCl and urea.

Urine pH

Urine pH \approx 6.0 (slightly acidic)

Urea excreted per day

25 - 30 g urea/day

CO₂ removed by lungs

CO_{2} \approx 200 mL/min

Exam Strategy

How this chapter is asked

High-yield question patterns observed across CBSE boards, JEE Main & Advanced, and NEET.

About 1200 mL of blood is filtered per minute — roughly 1/5 of the blood pumped out by each ventricle.
GFR ≈ 125 mL/min = 180 L/day; only 1–1.5 L is voided as urine, so >99% of the filtrate is reabsorbed.
The PCT reabsorbs nearly all essential nutrients and 70–80% of electrolytes and water — the main site of reabsorption.
Ultrafiltration: podocytes leave filtration slits, so the filtrate is essentially protein-free plasma.
JGA autoregulates GFR — a fall in GFR triggers renin release, which restores glomerular blood flow.
Countercurrent mechanism builds a medullary osmolarity gradient of 300 mOsmolL⁻¹ (cortex) → 1200 mOsmolL⁻¹ (inner medulla), produced mainly by NaCl and urea.
ADH (vasopressin) from the neurohypophysis facilitates water reabsorption from the latter parts of the tubule, preventing diuresis.
RAAS: renin → angiotensin I → angiotensin II (vasoconstrictor) → aldosterone → Na⁺ and water reabsorption; ANF opposes this by vasodilation.
Bony fishes are ammonotelic; mammals and marine fishes are mostly ureotelic; reptiles, birds, insects and land snails are uricotelic.
An adult excretes about 25–30 g of urea daily; glycosuria and ketonuria point to diabetes mellitus.
Hemodialysis uses a dialysing fluid identical to plasma except nitrogenous wastes, over a porous cellophane membrane; heparin is added as an anticoagulant.

Practice Numericals

Step-by-step worked examples

Standard exam-level problems solved with clear conceptual breakdowns.

Percentage of filtrate reabsorbed

Problem StatementA person produces about 1.5 L of urine per day. If the GFR is 125 mL/min, what percentage of the glomerular filtrate is reabsorbed?

Step-by-Step Solution

1Total filtrate per day = 125 mL/min × 60 min × 24 h = 180,000 mL = 180 L.
2Urine produced = 1.5 L, so reabsorbed = 180 − 1.5 = 178.5 L.
3Percentage reabsorbed = (178.5 / 180) × 100 ≈ 99.2%.
4This confirms that over 99% of the filtrate is reabsorbed, mainly by the PCT.

Final Answer

≈ 99.2%

Effect of water load on urine concentration

Problem StatementExplain why a person who drinks a large quantity of water produces dilute urine, while a dehydrated person produces concentrated urine.

Step-by-Step Solution

1When water intake is high, blood osmolarity falls, osmoreceptors are suppressed, and the hypothalamus reduces ADH release from the neurohypophysis.
2With low ADH, the latter parts of the tubule reabsorb little water, so a large volume of dilute urine is produced.
3During dehydration, blood osmolarity rises, osmoreceptors activate, ADH release increases, and more water is reabsorbed — producing a small volume of concentrated urine.
4This is the ADH feedback loop that prevents diuresis and conserves body water.

Why the medullary gradient concentrates urine

Problem StatementThe osmolarity in the kidney rises from about 300 mOsmolL⁻¹ in the cortex to about 1200 mOsmolL⁻¹ in the inner medulla. How does this gradient help concentrate urine, and by how much?

Step-by-Step Solution

1The gradient is built by the countercurrent arrangement of the loop of Henle and vasa recta, accumulating NaCl and urea in the medullary interstitium.
2As filtrate (and later urine) passes down the collecting duct through this high-osmolarity interstitium, water is drawn out by osmosis.
3The nearer the medulla, the greater the osmotic pull, so the final urine becomes highly concentrated.
4Because of this mechanism human kidneys produce urine nearly four times more concentrated than the initial filtrate.

Final Answer

≈ 4× the filtrate

FAQ

Frequently asked questions

What are the three processes of urine formation?

The three processes are: (1) glomerular filtration — ultrafiltration of blood at the glomerulus (GFR ≈ 125 mL/min); (2) tubular reabsorption — recovery of essential nutrients, electrolytes and water, mainly in the PCT (>99% of the filtrate); and (3) tubular secretion — transfer of H⁺, K⁺ and ammonia from blood into the filtrate to maintain pH and ionic balance.

What is the role of ADH (vasopressin) in kidney function?

When body fluid volume or ionic concentration changes, osmoreceptors activate the hypothalamus to release ADH from the neurohypophysis. ADH facilitates water reabsorption from the latter parts of the tubule, preventing diuresis and producing concentrated urine. An increase in body fluid volume switches off the osmoreceptors and suppresses ADH release to complete the feedback.

How does the countercurrent mechanism concentrate urine?

The loop of Henle and the vasa recta run in opposite directions, forming a counter current. NaCl transported by the ascending limb and urea returned by the collecting tubule maintain an osmolarity gradient from 300 mOsmolL⁻¹ (cortex) to 1200 mOsmolL⁻¹ (inner medulla). Water is drawn out of the collecting duct by this interstitial gradient, so the kidney produces urine nearly four times more concentrated than the filtrate.

Why are terrestrial animals ureotelic or uricotelic and not ammonotelic?

Ammonia is the most toxic nitrogenous waste and needs large volumes of water for elimination. Terrestrial animals conserve water, so they convert ammonia into the less toxic urea (mammals — ureotelic) or into almost insoluble uric acid excreted as a pellet (reptiles, birds — uricotelic). Uric acid needs the least water of all.

What is hemodialysis and when is it needed?

Hemodialysis removes urea accumulated in the blood (uremia) using an artificial kidney. Blood is drained from an artery, mixed with heparin, and passed through a coiled cellophane tube immersed in a dialysing fluid identical to plasma except nitrogenous wastes; wastes diffuse out and the cleared blood is returned with anti-heparin. It is needed in kidney failure, and kidney transplantation is the ultimate corrective method.

What is the significance of the juxta glomerular apparatus (JGA)?

The JGA is a region formed by modifications in the DCT and afferent arteriole at their contact. A fall in GFR activates its JG cells to release renin, which stimulates glomerular blood flow and brings the GFR back to normal — the autoregulatory mechanism of the kidney.

Which structures perform excretion in invertebrates?

Protonephridia (flame cells) in Platyhelminthes, rotifers, some annelids and Amphioxus; nephridia in earthworms; malpighian tubules in insects; and antennal (green) glands in crustaceans like prawns. They remove nitrogenous wastes and regulate ionic/fluid balance (osmoregulation).

What do lungs, liver and skin excrete?

Lungs remove CO₂ (≈ 200 mL/min) and water; the liver secretes bile carrying bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs; skin sweat contains NaCl, urea and lactic acid, and sebaceous glands eliminate sterols, hydrocarbons and waxes.

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