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

NCERT Class 11 Biology Chapter 16 Notes: Download PDF

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Class 11 Biology Chapter 16 Excretory Products And Their Elimination Notes

The Excretory Products and Their Elimination chapter explores how the human body gets rid of waste to stay healthy and balanced, the structure of the excretory system, and how our kidneys manage to filter blood. Excretory Products and their Elimination Class 11 Notes are prepared by subject experts, following the latest NCERT guidelines.

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:

1. 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.
2. Ureotelic animals: These animals produce urea, which is less toxic and uses less water for removal. Examples: Mammals, amphibians, and cartilaginous fishes.
3. Uricotelic animals: These animals expel uric acid, which is the least toxic and is removed with the least water loss. Examples: Birds, reptiles, and insects.
4. Humans are ureotelic, i.e., they mainly excrete urea.

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.
• Henle's loop: Responsible for urine concentration.
• Distal Convoluted Tubule (DCT): Regulates pH and ion balance.
• Collecting Duct: Collects and transports urine to the renal pelvis.

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⁻¹, i.e., the kidneys filter 180 litres of fluid daily, and only 1.5 liters is excreted as urine.

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.

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 passes about 1–1.5 L 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

The human excretory system can face several disorders that affect its normal function. These conditions may disturb waste removal and harm overall health if left untreated. Here are some important disorders you should know about:

• 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.

Also Read

• NCERT Notes for Class 11 Physics

• NCERT Notes for Class 11 Chemistry

• NCERT Notes for Class 11 Mathematics

Chapter 16 Biology: Previous Year Questions and Answers

Some of the questions that have come in past years from the chapter are given below. For quick reference to all the topics, students can refer to the NCERT Class 11 Biology Chapter 16 Notes Excretory Products and their Elimination.

Question 1. Which one of the following is also known as an antidiuretic hormone?

Option 1. Oxytocin

Option 2. Vasopressin

Option 3. Adrenaline

Option 4. Calcitonin

Answer :

The hypothalamus produces the peptide hormone vasopressin, sometimes referred to as antidiuretic hormone (ADH), which is secreted by the posterior pituitary gland. Its main function is to control blood pressure and the body's water balance. By increasing the permeability of the collecting ducts, vasopressin works on the kidneys to increase water reabsorption, which lowers urine production and conserves water. Overproduction of vasopressin leads to excessive water retention in the body.

Hence, the correct answer is option (2) Vasopressin

Question 2. We can produce concentrated/dilute urine. This is facilitated by a special mechanism. Identify the mechanism.

Option 1. Reabsorption from PCT

Option 2. Reabsorption from the collecting duct

Option 3. Reabsorption/secretion in DCT

Option 4. Counter-current mechanism in Henle loop/Vasa recta

Answer :

The two limbs of Henle's loop, as well as the vasa recta, witness countercurrents. When we move towards the descending limb, the concentration increases, whereas it is diluted as we move towards the ascending limb. This countercurrent mechanism in Henle's loop helps concentrate urine and conserve water, ensuring efficient reabsorption of water and electrolytes. The vasa recta, by maintaining a countercurrent flow, preserves the osmotic gradient in the renal medulla, aiding in the production of concentrated urine.

Hence, the correct answer is option (4) Counter-current mechanism in Henle's loop/Vasa recta.

Question 3. Which one of the following statements is incorrect?

Option 1. The medullary zone of the kidney is divided into a few conical masses called medullary pyramids projecting into the calyces.

Option 2. Inside the kidney, the cortical region extends between the medullary pyramids as the renal pelvis

Option 3. The Glomerulus, along with Bowman's capsule, is called the renal corpuscle

Option 4. Renal corpuscle, proximal convoluted tubule (PCT), and distal convoluted tubule (DCT) of the nephron are situated in the cortical region of the kidney

Answer :

The cortical region does not extend as far as the renal pelvis between the medullary pyramids. Instead, the cortical tissue extends between medullary pyramids as columns of Bertini (renal columns), while the renal pelvis is a funnel-shaped structure that collects urine and channels it to the ureter. Therefore, that statement is incorrect because the cortical tissue extends between the medullary pyramids as renal columns (columns of Bertini), not as the renal pelvis.

Hence, the correct answer is option (2). Inside the kidney, the cortical region extends between the medullary pyramids as the renal pelvis

Also Read:

• NCERT Solutions
• NCERT Solutions for Class 11
• NCERT Solutions for Class 11 Biology

How to Use Excretory Products And Their Elimination Class 11 Notes Effectively?

The excretory system plays an important role in removing harmful wastes from the body and maintaining homeostasis. Well-structured notes can make learning this complex process much easier and help in clear revision.

1. Focus on diagrams like the nephron structure and urine formation steps, as they make understanding faster and easier.

2. Use Class 11 Biology Chapter 16 Excretory Products and Their Elimination Notes to revise the mechanisms of osmoregulation and nitrogenous waste elimination in different organisms.

3. Important terms and flowcharts are highlighted in the NCERT Class 11 Biology Notes to improve learning before exams.

4. Compare examples of excretory products in animals and humans through the Class 11 Biology Chapter 16 Excretory Products and Their Elimination Notes.

5. Practice previous year questions along with the notes to improve application-based understanding.

Chapter-Wise NCERT Class 11 Notes Biology

Students can refer to the table below, which provides well-structured notes for every chapter of Class 11 Biology for effective revision.