NCERT Class 11 Biology Chapter 16 Notes Excretory Products And Their Elimination- Download PDF Notes

Q: 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).

NCERT Class 11 Biology Chapter 19 Notes Excretory Products And Their Elimination- Download PDF Notes

Edited By Irshad Anwar | Updated on Apr 01, 2025 06:53 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
Micturition
Role of Other Organs in Excretion
Disorders of the Excretory System

NCERT Class 11 Biology Chapter 19 Notes Excretory Products And Their Elimination- Download PDF Notes

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,

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.

human excretory system

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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kidney

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.

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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.

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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.

Chapter-Wise NCERT Class 11 Notes Biology

The chapterwise notes are given below:

NCERT Class 11 Biology Chapter 1 The Living World Notes

NCERT Class 11 Biology Chapter 2 Biological Classification Notes

NCERT Class 11 Biology Chapter 3 Plant Kingdom Notes

NCERT Class 11 Biology Chapter 4 Animal Kingdom Notes

NCERT Class 11 Biology Chapter 5 Morphology of Flowering Plants Notes

NCERT Class 11 Biology Chapter 6 Anatomy of Flowering Plants Notes

NCERT Class 11 Biology Chapter 7 Structural Organisation in Animals Notes

NCERT Class 11 Biology Chapter 8 Cell the Unit of Life Notes

NCERT Class 11 Biology Chapter 9 Biomolecules Notes

NCERT Class 11 Biology Chapter 10 Cell cycle and cell division Notes

NCERT Class 11 Biology Chapter 11 Photosynthesis in Higher Plants Notes

NCERT Class 11 Biology Chapter 12 Respiration in Plants Notes

NCERT Class 11x Biology Chapter 13 Plant Growth and Development Notes

NCERT Class 11 Biology Chapter 14 Breathing and Exchange of Gases Notes

NCERT Class 11 Biology Chapter 15 Body Fluids and Circulation Notes

NCERT Class 11 Biology Chapter 16 Excretory Products and Their Elimination Notes

NCERT Class 11 Biology Chapter 17 Locomotion and Movement Notes

NCERT Class 11 Biology Chapter 18 Neural Control and Coordination Notes

NCERT Class 11 Biology Chapter 19 Chemical Coordination and Integration Notes

Knowledge of the excretory system and its role is important in understanding how organisms regulate homeostasis through the elimination of waste products. The mechanism of urine production, concentration, and control ensures the elimination of toxic substances while retaining necessary nutrients and water. Knowledge of prevalent disorders assists in early detection of symptoms and the initiation of proper medical care.

Students studying for Class 11 Biology Chapter 16 can rely on these notes for a good understanding of Excretory Products and Their Elimination. Along with this, going through NCERT Solutions and Exemplars can also contribute to good exam preparation.

Subject Wise NCERT Exemplar Solutions

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.

11. What are the disorders related to the excretory system?

Common disorders include kidney stones, urinary tract infections (UTIs), nephritis, polycystic kidney disease, and chronic kidney disease (CKD), which impair filtration, leading to toxin buildup and potential organ damage.

12. How does dialysis help in kidney failure?

Dialysis removes waste, excess fluids, and toxins from the blood when kidneys fail. Hemodialysis uses an external machine, while peritoneal dialysis utilizes the peritoneum as a natural filter, sustaining life until a transplant.

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Option 1) $0.34\; J$	Option 2) $0.16\; J$
Option 3) $1.00\; J$	Option 4) $0.67\; J$

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up ? Fat supplies 3.8×10⁷J of energy per kg which is converted to mechanical energy with a 20% efficiency rate. Take g = 9.8 ms⁻² :

Option 1)

2.45×10⁻³ kg

Option 2)

6.45×10⁻³ kg

Option 3)

9.89×10⁻³ kg

Option 4)

12.89×10⁻³ kg

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1) $2,000 \; J - 5,000\; J$	Option 2) $200 \, \, J - 500 \, \, J$
Option 3) $2\times 10^{5}J-3\times 10^{5}J$	Option 4) $20,000 \, \, J - 50,000 \, \, J$

A particle is projected at 60⁰ to the horizontal with a kinetic energy $K$ . The kinetic energy at the highest point

Option 1) $K/2\,$	Option 2) $\; K\;$
Option 3) $zero\;$	Option 4) $K/4$

In the reaction,

$2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}$

Option 1) $11.2\, L\, H_{2(g)}$ at STP is produced for every mole $HCL_{(aq)}$ consumed	Option 2) $6L\, HCl_{(aq)}$ is consumed for ever $3L\, H_{2(g)}$ produced
Option 3) $33.6 L\, H_{2(g)}$ is produced regardless of temperature and pressure for every mole Al that reacts	Option 4) $67.2\, L\, H_{2(g)}$ at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, $Mg_{3}(PO_{4})_{2}$ will contain 0.25 mole of oxygen atoms?

Option 1) 0.02	Option 2) 3.125 × 10^-2
Option 3) 1.25 × 10^-2	Option 4) 2.5 × 10^-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1) decrease twice	Option 2) increase two fold
Option 3) remain unchanged	Option 4) be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1) Molality	Option 2) Weight fraction of solute
Option 3) Fraction of solute present in water	Option 4) Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol^-1) is

Option 1) twice that in 60 g carbon	Option 2) 6.023 × 10²²
Option 3) half that in 8 g He	Option 4) 558.5 × 6.023 × 10²³

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t²) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m² , the number of rotations made by the pulley before its direction of motion if reversed, is