CBSE Class 11 Biology Revision Notes Chapter 16 Excretory Products and Their Elimination

Excretory Products and Their Elimination explains how animals remove nitrogenous wastes and maintain water, salt and acid-base balance. In CBSE Class 11 Biology, this chapter covers excretory products, human kidneys, nephron, urine formation, kidney regulation and excretory disorders.

Excretory Products and Their Elimination explains how animals remove waste substances produced during metabolism. Ammonia, urea and uric acid are the major nitrogenous wastes. The type of waste removed depends mainly on habitat, water availability and body organisation.

Use CBSE Class 11 Biology Revision Notes Chapter 16 for 2026–27 to revise nitrogenous wastes, ammonotelism, ureotelism, uricotelism, human excretory system, nephron structure, urine formation, GFR, tubular functions, counter current mechanism, micturition and disorders of the excretory system.

Key Takeaways

• Excretion: Removal of metabolic wastes such as ammonia, urea, uric acid, carbon dioxide, water and ions.
• Nitrogenous wastes: Ammonia is most toxic, urea is less toxic and uric acid is least toxic.
• Nephron: The functional unit of the kidney.
• Urine formation: Includes glomerular filtration, reabsorption and tubular secretion.

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Excretory Products and Their Elimination Class 11 Biology Notes: Chapter Overview

Animals produce metabolic wastes during cellular activities. These wastes must be removed fully or partly to maintain normal body functions.

Excretion also helps maintain ionic balance, water balance and acid-base balance.

Nitrogenous Wastes in CBSE Class 11 Biology Notes Chapter 16

Ammonia, urea and uric acid are the major nitrogenous wastes excreted by animals.

The type of nitrogenous waste depends on the habitat and water availability.

Ammonotelism, Ureotelism and Uricotelism

Animals are classified based on the main nitrogenous waste they excrete.

Ammonotelism

Ammonotelism is the process of excreting ammonia. Ammonia is readily soluble and is generally removed by diffusion through body surfaces or gill surfaces.

Kidneys do not play a major role in ammonia removal.

Ureotelism

Ureotelic animals excrete urea. Ammonia produced during metabolism is converted into urea in the liver.

Some urea may be retained in the kidney matrix to maintain osmolarity.

Uricotelism

Uricotelic animals excrete uric acid. Uric acid is excreted as a pellet or paste with minimum water loss.

This is an important adaptation for water conservation.

Excretory Structures in Animals

Different animal groups have different excretory structures.

In most invertebrates, excretory structures are simple tubular forms. Vertebrates have complex tubular kidneys.

Human Excretory System in Class 11 Biology Chapter 16 Notes

The human excretory system removes nitrogenous wastes and maintains fluid balance.

Humans have a pair of kidneys, one pair of ureters, a urinary bladder and a urethra.

Structure of Human Kidney

Kidneys are reddish-brown, bean-shaped organs present close to the dorsal inner wall of the abdominal cavity.

Each kidney has a notch on the inner concave surface called hilum. Ureter, blood vessels and nerves enter through the hilum.

Internal Structure of Kidney

The medulla is divided into conical masses called medullary pyramids.

Nephron in Excretory Products and Their Elimination Class 11 Notes

Each kidney has nearly one million nephrons. Nephron is the functional unit of the kidney.

Each nephron has two main parts: glomerulus and renal tubule.

Glomerulus and Renal Tubule

Glomerulus is formed by the afferent arteriole, a branch of the renal artery. Blood from the glomerulus is carried away by the efferent arteriole.

The renal tubule begins with Bowman’s capsule and continues as PCT, Henle’s loop, DCT and collecting duct.

Cortical and Juxtamedullary Nephrons

Nephrons are of two main types based on the length of Henle’s loop.

Juxtamedullary nephrons help in producing concentrated urine.

Peritubular Capillaries and Vasa Recta

The efferent arteriole forms capillaries around the renal tubule.

Vasa recta is important in the counter current mechanism.

Urine Formation in CBSE Class 11 Biology Revision Notes Chapter 16

Urine formation has three main processes.

These processes occur in different parts of the nephron.

Glomerular Filtration

Glomerular filtration is the first step of urine formation. It occurs due to glomerular capillary blood pressure.

Blood is filtered finely through these layers. Almost all plasma constituents pass into Bowman’s capsule except proteins. This is why it is called ultrafiltration.

Glomerular Filtration Rate or GFR

The amount of filtrate formed by kidneys per minute is called glomerular filtration rate.

Nearly 99% of the filtrate is reabsorbed by renal tubules.

Juxta Glomerular Apparatus or JGA

The kidneys have a built-in mechanism to regulate GFR. One such mechanism is the juxta glomerular apparatus.

JGA is important in kidney function regulation.

Reabsorption in Urine Formation

Reabsorption returns useful substances from filtrate to blood.

Reabsorption prevents loss of useful substances from the body.

Tubular Secretion

Tubular secretion adds certain substances from tubular cells into the filtrate.

Tubular secretion is important for ionic and acid-base balance.

Function of Tubules in Class 11 Biology Chapter 16 Notes

Different parts of the nephron perform different functions.

Proximal Convoluted Tubule or PCT

PCT is lined by simple cuboidal brush border epithelium. This increases surface area for reabsorption.

PCT is the major site of reabsorption.

Henle’s Loop

Henle’s loop has descending and ascending limbs.

Henle’s loop helps maintain high osmolarity in the medullary interstitium.

Distal Convoluted Tubule or DCT

DCT helps in conditional reabsorption and secretion.

DCT maintains pH and sodium-potassium balance in blood.

Collecting Duct

The collecting duct extends from the cortex to the inner medulla.

The collecting duct plays an important role in final urine concentration.

Counter Current Mechanism in Excretory Products and Their Elimination Class 11 Notes

Mammals can produce concentrated urine. Henle’s loop and vasa recta are important for this.

The osmolarity increases from about 300 mOsmol/L in the cortex to about 1200 mOsmol/L in the inner medulla.

Role of NaCl and Urea

The concentration gradient is mainly caused by NaCl and urea.

This arrangement helps maintain the osmotic gradient in the medulla.

Importance of Counter Current Mechanism

Counter current mechanism is a key concept in this chapter.

Regulation of Kidney Function

Kidney function is regulated by hormonal feedback mechanisms involving the hypothalamus, JGA and heart.

Role of ADH in Kidney Function

Osmoreceptors detect changes in blood volume, body fluid volume and ionic concentration.

ADH also causes blood vessel constriction, which can increase blood pressure and GFR.

Renin-Angiotensin-Aldosterone Mechanism

A fall in glomerular blood flow, glomerular blood pressure or GFR activates JG cells.

This mechanism helps restore blood pressure and GFR.

Role of Atrial Natriuretic Factor or ANF

ANF acts as a check on the renin-angiotensin mechanism.

ANF helps prevent excessive rise in blood pressure.

Micturition in CBSE Class 11 Biology Notes Chapter 16

Micturition is the release of urine from the urinary bladder.

The neural mechanism causing urination is called the micturition reflex.

Normal Urine Characteristics

Urine analysis helps in clinical diagnosis. Glucose in urine is called glycosuria. Ketone bodies in urine are called ketonuria. Both may indicate diabetes mellitus.

Role of Other Organs in Excretion

Kidneys are the main excretory organs, but lungs, liver and skin also help in excretion.

Lungs remove about 200 mL of carbon dioxide per minute.

Disorders of Excretory System

Kidney malfunction can cause waste accumulation and serious health problems.

Uremia and Hemodialysis

Uremia is harmful and may lead to kidney failure. Urea can be removed by hemodialysis.

Hemodialysis helps remove nitrogenous wastes from blood.

Kidney Transplantation

Kidney transplantation is the ultimate method for correcting acute renal failure. A functioning kidney from a donor is transplanted into the patient.

A close relative is preferred as donor to reduce the chances of rejection by the immune system.

Nitrogenous Wastes Comparison

Filtration, Reabsorption and Secretion Difference

PCT, Henle’s Loop, DCT and Collecting Duct Difference

Important Terms from Excretory Products and Their Elimination Class 11 Notes

NCERT-Based Exam Points

• Ammonia, urea and uric acid are major nitrogenous wastes.
• Ammonia is the most toxic nitrogenous waste.
• Uric acid is the least toxic nitrogenous waste.
• Ammonotelic animals excrete ammonia.
• Ureotelic animals excrete urea.
• Uricotelic animals excrete uric acid.
• Protonephridia are also called flame cells.
• Nephridia occur in earthworms and other annelids.
• Malpighian tubules occur in insects such as cockroach.
• Antennal glands occur in crustaceans such as prawns.
• Human excretory system has kidneys, ureters, urinary bladder and urethra.
• Kidney has an outer cortex and inner medulla.
• Columns of Bertini are cortical extensions between medullary pyramids.
• Nephron is the functional unit of kidney.
• Each kidney has nearly one million nephrons.
• Malpighian body includes glomerulus and Bowman’s capsule.
• Urine formation includes filtration, reabsorption and secretion.
• Glomerular filtration is also called ultrafiltration.
• GFR is about 125 mL per minute.
• Kidneys form about 180 litres of filtrate per day.
• About 99% of filtrate is reabsorbed.
• PCT reabsorbs nearly all essential nutrients.
• Descending limb of Henle’s loop is permeable to water.
• Ascending limb of Henle’s loop is impermeable to water.
• DCT helps maintain pH and sodium-potassium balance.
• Collecting duct helps produce concentrated urine.
• Counter current mechanism involves Henle’s loop and vasa recta.
• Medullary osmolarity increases from 300 to 1200 mOsmol/L.
• ADH increases water reabsorption.
• Renin-angiotensin mechanism increases blood pressure and GFR.
• ANF decreases blood pressure.
• Micturition is caused by a neural reflex.
• Normal urine is slightly acidic with pH around 6.0.
• Uremia is accumulation of urea in blood.
• Hemodialysis removes nitrogenous wastes from blood.
• Renal calculi are kidney stones.
• Glomerulonephritis is inflammation of glomeruli.

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