NCERT Solutions for Class 11 Biology Chapter 19 – Excretory Products and their Elimination
Every living cell produces metabolic waste, and the body needs efficient systems to get rid of these substances before they become toxic. Chapter 19 of Class 11 Biology, Excretory Products and their Elimination, is all about how the human body filters blood, produces urine, and removes nitrogenous wastes along with other harmful substances.
This is one of the highest-weightage chapters for NEET and CBSE exams, and students often struggle with topics like the counter-current mechanism and the role of ADH. The NCERT Solutions for Class 11 Biology Chapter 19, provided on Myclass24, explain every concept from the structure of the nephron to the hormonal regulation of urine formation in clear, easy-to-understand language. These solutions are designed to help you build a strong foundation rather than rote-learn answers, making your revision both effective and lasting.
Download PDF – NCERT Solutions for Class 11 Biology Chapter 19 Excretory Products and their Elimination
The chapter-wise PDF for NCERT Solutions Class 11 Biology Chapter 19 is available for free on Myclass24. The PDF includes answers to all NCERT exercise questions, important diagrams like the labelled nephron, and additional NEET-level questions. It is optimised for mobile viewing so students can revise on the go without needing a large screen.
Chapter 19 Excretory Products and their Elimination – Detailed Notes and Key Facts
Excretion is the process of removal of metabolic waste products from the body. Different animals have different excretory products depending on the availability of water and their evolutionary adaptations. Understanding the type of nitrogenous waste an organism produces is a key exam topic. Check out NCERT Solutions for Class 11 Biology and NCERT Solutions for Class 11 for the rest of the chapters.
Animals that excrete ammonia are called ammonotelic (most aquatic animals like bony fishes and aquatic amphibians). Ammonia is highly toxic and needs large quantities of water to dilute it. Animals that excrete urea are called ureotelic (humans, frogs, most mammals). Urea is less toxic than ammonia and needs moderate water for excretion. Animals that excrete uric acid are called uricotelic (reptiles, birds, insects, land snails). Uric acid is the least toxic form and requires minimal water, making it ideal for organisms conserving water.
| Type | Waste Product | Examples | Water Requirement |
|---|---|---|---|
| Ammonotelic | Ammonia | Bony fishes, aquatic amphibians | Very high |
| Ureotelic | Urea | Humans, frogs, most mammals | Moderate |
| Uricotelic | Uric acid | Birds, reptiles, insects, land snails | Very low |
The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. The kidneys are reddish-brown, bean-shaped organs located in the abdominal cavity, one on each side of the vertebral column. The right kidney is slightly lower than the left due to the liver. Each kidney weighs about 120–170 grams. The outer region is the cortex and the inner is the medulla. The medulla is divided into pyramids, and each pyramid has its apex pointing towards the renal pelvis, which collects urine and passes it to the ureter.
The functional unit of the kidney is the nephron. Each kidney contains about 1 million nephrons. Each nephron has a Malpighian body (glomerulus + Bowman's capsule) and a renal tubule. The tubule consists of the Proximal Convoluted Tubule (PCT), the Loop of Henle, and the Distal Convoluted Tubule (DCT), which finally opens into the collecting duct. Nephrons can be cortical (short loop of Henle, located mostly in cortex) or juxtamedullary (long loop of Henle, extending deep into medulla, important for concentrating urine).
Urine formation occurs in three steps. First, glomerular filtration takes place in the Bowman's capsule. Blood is filtered under pressure (glomerular hydrostatic pressure), and the filtrate contains glucose, amino acids, urea, ions, and water, but not proteins or RBCs. The Glomerular Filtration Rate (GFR) is approximately 125 mL per minute or 180 litres per day. Most of this filtrate is reabsorbed, and only about 1–1.5 litres of urine is produced per day. Must check the CBSE resources and NCERT Solutions.
Second, tubular reabsorption occurs throughout the nephron. In the PCT, about 70–80% of filtrate is reabsorbed, including all glucose, amino acids, most water, sodium, and chloride. The loop of Henle is responsible for concentrating the filtrate through the counter-current mechanism. In the ascending limb, sodium and chloride are actively transported out but the limb is impermeable to water. This creates a concentration gradient in the medullary interstitium that facilitates water reabsorption from the descending limb. The DCT fine-tunes pH and ion balance.
Third, tubular secretion allows certain substances like hydrogen ions, potassium ions, and ammonia to be actively secreted from blood into the tubular filtrate. This is important for acid-base balance of blood.
Functions of Different Parts of the Nephron
| Part of Nephron | Key Function |
|---|---|
| Bowman's Capsule / Glomerulus | Ultrafiltration of blood; GFR = 125 mL/min |
| Proximal Convoluted Tubule (PCT) | Reabsorption of glucose, amino acids, water, Na⁺, Cl⁻ |
| Descending Loop of Henle | Water reabsorption; permeable to water, impermeable to solutes |
| Ascending Loop of Henle | Active transport of Na⁺, Cl⁻; impermeable to water |
| Distal Convoluted Tubule (DCT) | Conditional reabsorption of water and ions under hormonal control |
| Collecting Duct | Concentration of urine; ADH acts here |
Hormonal regulation of kidney function is an important topic. Antidiuretic Hormone (ADH), also called vasopressin, is secreted by the posterior pituitary. It acts on the collecting duct to increase water reabsorption, producing concentrated urine. When blood pressure drops, the Renin-Angiotensin-Aldosterone System (RAAS) is activated. Renin from the kidneys converts angiotensinogen to angiotensin I, which becomes angiotensin II. Angiotensin II stimulates aldosterone secretion from the adrenal cortex, causing sodium and water reabsorption in DCT, thus raising blood pressure. Atrial Natriuretic Factor (ANF), secreted by the heart atria when blood pressure is high, opposes the RAAS and promotes sodium and water excretion.
Normal human urine is pale yellow due to the pigment urochrome, slightly acidic (pH around 6), and has a specific gravity of 1.003–1.030. It contains urea, creatinine, uric acid, ions, and water. The presence of glucose (glycosuria), proteins (proteinuria), ketone bodies (ketonuria), RBCs (haematuria), or excessive proteins in urine indicates kidney disorders or metabolic diseases like diabetes.
Kidney failure can be treated with haemodialysis (dialysis), where blood is filtered through an artificial kidney machine. The dialysis fluid has the same composition as plasma without waste products. Blood passes through a cellophane membrane, and wastes diffuse out by dialysis. Kidney transplant is the permanent cure for chronic kidney failure.
Other Excretory Organs in Humans
| Organ | Excretory Product |
|---|---|
| Kidneys | Urea, uric acid, creatinine, excess salts, water |
| Lungs | CO₂, water vapour |
| Skin (Sweat Glands) | Water, NaCl, small amounts of urea |
| Liver | Bile pigments (bilirubin, biliverdin), cholesterol |
| Intestine | Calcium, iron, bile salts |
For complete, step-by-step NCERT Solutions, NEET important questions, and free downloadable PDFs for Class 11 Biology Chapter 19, visit Myclass24. All content is verified by experienced biology teachers and is aligned with the latest CBSE and NTA guidelines.