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NCERT Class 11 Biology Chapter 19 Notes Excretory Products And Their Elimination- Download PDF Notes
Edited By Irshad Anwar | Updated on Apr 29, 2025 11:46 AM IST
NCERT Class 11 Biology Chapter 16 Notes Excretory Products And Their Elimination: All living creatures need to remove waste products resulting from metabolic processes and food that is not digested. These compounds, if allowed to accumulate, can cause damage to the health of the organism. The mechanism of removal of these wastes is excretion, and in animals, excretory products are generally removed in one of the following forms: ammonia, urea, or uric acid.
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This Story also Contains
- Types of Nitrogenous Wastes and Their Removal
- Human Excretory System
- Urine Formation
- Regulation of Kidney Function
- Disorders of the Excretory System
- Important Topics of Class 11 Biology Chapter 16
- Most Important Questions for Class 11 Biology Chapter 16: Excretory Products and Their Elimination
- Approach to Solve Questions of Class 11 Biology Chapter 16: Excretory Products and Their Elimination
- Chapter-Wise NCERT Class 11 Notes Biology
These NCERT Notes for Class 11 Biology give a thorough insight into excretory products, their removal, and how various organisms get rid of waste. Students revising for CBSE Board exams can refer to these notes for rapid revision and understanding.
Types of Nitrogenous Wastes and Their Removal
Metabolic processes and overconsumption of substances contribute to the body's storage of waste products. The most familiar nitrogenous waste products discharged by animals are ammonia, urea, and uric acid. According to the type of nitrogenous waste they excrete, organisms are categorized into three groups:
Ammonotelic animals: These animals expel ammonia, which is very toxic and needs a lot of water for removal. Example: Bony fishes, amphibians, and invertebrates in water.
Ureotelic animals: These animals produce urea, which is less toxic and uses less water for removal. Example: Mammals, amphibians, and cartilaginous fishes.
Uricotelic animals: These animals expel uric acid, which is the least toxic and is removed with the least water loss. Example: Birds, reptiles, and insects.
Humans are ureotelic, i.e., they mainly excrete urea.
Also, students can refer,
- NCERT Solutions for Class 11 Biology Chapter 16 Excretory Products and Their Elimination
- NCERT Exemplar Class 11 Biology Chapter 16 Solutions Excretory Products and Their Elimination
Human Excretory System
The human excretory system includes the following structures:
Kidneys: Reddish-brown, bean-shaped organs lying against the dorsal inner wall of the abdominal cavity. Each kidney measures approximately 10-12 cm in length, 5-7 cm in width, and weighs approximately 120-170 g.
Ureters: Tubes that carry urine from the kidneys to the urinary bladder.
Urinary bladder: A muscular sac that stores urine until its excretion.
Urethra: A tube that transports urine out of the body.
There are approximately one million nephrons in each kidney, which are the functional units of the kidney. Each nephron is made up of:
- Glomerulus: A capillary network where filtration takes place.
- Bowman's Capsule: A cup-like structure that surrounds the glomerulus.
- Renal Tubule: Divided further into:
- Proximal Convoluted Tubule (PCT): Reabsorbs vital nutrients, electrolytes, and water.
- Loop of Henle: Responsible for urine concentration.
- Distal Convoluted Tubule (DCT): Regulates pH and ion balance.
- Collecting Duct: Collects and transports urine to the renal pelvis.
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Urine Formation
Three processes are involved in the formation of urine:
Glomerular Filtration: The pressure of blood forces plasma constituents (excluding proteins) into the Bowman's capsule, an ultrafiltration process.
Tubular Reabsorption: Necessary nutrients and most of the filtrate (approximately 99%) are reabsorbed into the blood.
Tubular Secretion: Other waste materials are secreted into the tubule for excretion.
The Glomerular Filtration Rate (GFR) is approximately 125 ml/min, i.e., the kidneys filter 180 liters of fluid daily, and only 1.5 liters is excreted as urine.
Also read:
Mechanism of Urine Concentration
The countercurrent mechanism is responsible for urine concentration. It includes:
Henle's Loop: The descending limb is water-permeable, whereas the ascending limb actively reabsorbs NaCl, rendering the medullary interstitium very concentrated.
Vasa Recta: Parallel blood vessels to Henle's loop that preserve the osmotic gradient.
Subject Wise NCERT Solutions
- NCERT Solutions for Class 11 Mathematics
- NCERT Solutions for Class 11 Chemistry
- NCERT Solutions for Class 11 Physics
Regulation of Kidney Function
Kidney function is regulated by hormonal feedback mechanisms, primarily through:
Antidiuretic Hormone (ADH): Secreted from the hypothalamus to enhance water reabsorption in the collecting ducts.
Renin-Angiotensin System: Stimulated by decreased blood pressure, which results in the release of angiotensin II, enhancing blood pressure and GFR.
Atrial Natriuretic Factor (ANF): Released by the heart to lower blood pressure and lower GFR.
Micturition
Urine is retained in the urinary bladder and eliminated through the urethra by the mechanism of micturition, which is regulated by the micturition reflex.
As the bladder fills, stretch receptors transmit signals to the central nervous system (CNS).
The CNS initiates bladder muscle contractions and relaxation of the urethral sphincter, resulting in urine release.
On average, an adult human urinates 1 to 1.5 liters of urine daily.
Role of Other Organs in Excretion
Other organs also play a role in excretion apart from the kidneys:
Lungs: Release carbon dioxide (CO₂) and water vapor.
Liver: secretes bile pigments (bilirubin, biliverdin) and detoxifies drugs.
Skin: Excretes sweat with water, salts, and traces of urea.
Disorders of the Excretory System
Uremia: Elevated level of urea in the blood due to kidney impairment. It might need hemodialysis (artificial kidney) for its management.
Kidney Failure (Renal Failure): Kidney dysfunction, usually calling for kidney transplantation.
Renal Calculi (Kidney Stones): Deposition of salts such as oxalates within the kidneys.
Glomerulonephritis: Glomerular inflammation, impairing filtration and causing the presence of blood or protein in the urine.
Important Topics of Class 11 Biology Chapter 16
The important topics of the chapter are given below:
1. Human Excretory System
2. Urine Formation
3. Function of the Tubules
4. Mechanism of Concentration of the Filtrate
5. Regulation of Kidney Function
6. Micturition
7. Role of Other Organs in Excretion
8. Disorders of the Excretory System
Most Important Questions for Class 11 Biology Chapter 16: Excretory Products and Their Elimination
Below are a few solved questions:
Q1. Match the abnormal conditions given in Column A with their explanations given in Column B
Column A | Column B | ||
A. | Glycosuria | (i) | Accumulation of uric acid in joints |
B. | Renal calculi | (ii) | Inflammation in glomeruli |
C. | Glomerulonephritis | (iii) | Mass of crystallised salts within the kidney |
D. | Gout | (iv) | Presence of glucose in the urine |
Answer:
Glycosuria: When glucose is found in the urine, it is usually a sign of diabetes.
Renal calculi are hard deposits of minerals and salts inside the kidney that resemble kidney stones.
Inflammation of the glomeruli, the kidneys' microscopic filtering units, is known as glomerulonephritis.
Gout: A disorder caused by elevated blood uric acid levels in which uric acid crystals form in joints, resulting in discomfort and inflammation.
The correct match is A – (iv), B – (iii), C – (ii), D – (i)
Q2. What is the renal pelvis?
Answer:
Inside the kidney, the cortical region extends between the medullary pyramids as the renal pelvis.
Q3. What kind of nitrogenous waste do the insects excrete?
Answer:
Since insects are uricotelic organisms, uric acid is the main kind of nitrogenous waste that they expel. Because uric acid is comparatively insoluble in water and can be eliminated as a paste or solid with little water loss, this adaptation aids in their water conservation.
Q4. What kind of nitrogenous waste do the birds excrete, and how is it different from other kinds of excretion?
Answer:
Birds and most reptiles are uricotelic, excreting nitrogenous waste primarily as uric acid, which is insoluble in water and excreted as a semi-solid paste with minimal water loss—an adaptation crucial for water conservation, especially in arid environments. Unlike ammonotelic animals that excrete ammonia (highly toxic and requiring large water dilution) or ureotelic animals that excrete urea (less toxic but water-soluble), uricotelic organisms convert nitrogenous waste into uric acid via the inosine monophosphate (IMP) pathway in the liver, reducing toxicity and allowing efficient excretion without significant water loss.
Q5. Different types of excretory structures and animals are given below. Match them appropriately.
Excretory structure/ organ | Animals | ||
A. | Protonephridia | (i) | Prawn |
B. | Nephridia | (ii) | Cockroach |
C. | Malpighian tubules | (iii) | Earthworm |
D. | Green gland or Antennal gland | (iv) | Flatworms |
Answer:
Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids, and the cephalochordate – Amphioxus.
Nephridia are the tubular excretory structures of earthworms and other annelids.
Malpighian tubules are the excretory structures of most of the insects including cockroaches. Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation.
Antennal glands or green glands perform the excretory function in crustaceans like prawns.
Therefore, the correct match is A- (iv), B-(iii), C- (ii), D-(i)
Subject Wise NCERT Exemplar Solutions
- NCERT Exemplar Class 11 Solutions
- NCERT Exemplar Class 11 Maths
- NCERT Exemplar Class 11 Physics
- NCERT Exemplar Class 11 Chemistry
- NCERT Exemplar Class 11 Biology
Approach to Solve Questions of Class 11 Biology Chapter 16: Excretory Products and Their Elimination
The students should start by clearly understanding the types of nitrogenous waste and the concept of Osmoregulation. They should study the structure and functioning of the human excretory system carefully, concentrating on the nephron and the urine formation steps. They should pay attention to the processes like filtration, tubular absorption and secretion. They should practice drawing and labelling the diagrams neatly and prepare a flowchart for quick reference. They should always write logical answers and should practise as many questions as possible to boost confidence during the exam.
Chapter-Wise NCERT Class 11 Notes Biology
The chapterwise notes are given below:
Frequently Asked Questions (FAQs)
1. What are the main excretory products in humans?
Humans excrete nitrogenous wastes like urea, uric acid, and creatinine, along with water, salts, and carbon dioxide. These waste products are removed through urine, sweat, and exhalation to maintain homeostasis.
2. How do kidneys help in the process of excretion?
Kidneys filter blood, remove metabolic wastes, and regulate water and electrolyte balance. They form urine by filtering out toxins and excess substances, which are then excreted through the ureters, bladder, and urethra.
3. What is the structure and function of a nephron?
A nephron consists of the glomerulus, Bowman’s capsule, tubules, and loop of Henle. It filters blood, reabsorbs essential nutrients, and secretes waste into the urine, playing a key role in maintaining water and ion balance.
4. What are the different modes of excretion in animals?
Animals excrete waste via different modes: ammonotelism (ammonia – fish, amphibians), ureotelism (urea – mammals, amphibians), and uricotelism (uric acid – birds, reptiles). These modes depend on water availability and metabolic needs.
5. What is the role of the liver in excretion?
The liver detoxifies harmful substances, breaks down hemoglobin into bilirubin, converts ammonia to urea, and metabolizes drugs and toxins. It also regulates cholesterol, hormone levels, and bile production for fat digestion.
6. How is urea formed in the human body?
Urea is formed in the liver through the urea cycle (ornithine cycle) by converting toxic ammonia and carbon dioxide into urea, which is then transported to the kidneys for excretion via urine.
7. What is the difference between ammonia, urea, and uric acid?
Ammonia: Highly toxic, requires large water amounts for excretion (e.g., fish).
Urea: Less toxic, soluble, excreted by mammals.
Uric Acid: Insoluble, excreted as a paste to conserve water (e.g., birds, reptiles).
8. What is the significance of osmoregulation in excretion?
Osmoregulation maintains water and ion balance in the body, ensuring proper cellular function. It helps regulate blood pressure, prevents dehydration or overhydration, and supports metabolic homeostasis.
9. How does the human body regulate urine concentration?
The kidneys regulate urine concentration via the loop of Henle, ADH hormone, and countercurrent mechanisms. When dehydrated, concentrated urine is produced; when hydrated, diluted urine is excreted to maintain fluid balance.
10. What is the function of ADH (Antidiuretic Hormone) in excretion?
Antidiuretic Hormone (ADH) regulates water reabsorption in the kidneys. It increases water retention in response to dehydration by making the collecting ducts more permeable, reducing urine volume and preventing water loss.
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