CBSE Class 11 Biology Chapter 19: Excretory Products and Their Elimination NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

This chapter delves into the crucial biological process of excretion, focusing on the removal of metabolic waste products from the body. The NCERT Solutions for Class 11 Biology, Chapter 19, 'Excretory Products and Their Elimination,' provide detailed explanations of the human excretory system, including the kidneys, ureters, urinary bladder, and urethra. It covers essential concepts such as the definition and regulation of Glomerular Filtration Rate (GFR), the autoregulatory mechanisms involving the juxtaglomerular apparatus, and the vital role of the counter-current mechanism (Henle's loop and vasa recta) in concentrating urine and conserving water. The solutions also clarify the functions of different parts of the nephron and the hormonal regulation of kidney function. These solutions are designed to help students grasp complex physiological processes, understand the formation of urine, and prepare effectively for their board examinations by offering clear, step-by-step explanations and accurate answers to all questions.

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Board	CBSE
Class	Class 11
Subject	Biology
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 19: Excretory Products and Their Elimination

Chapter summary

Chapter 19 of the Class 11 Biology NCERT Solutions focuses on the excretory products in humans and the mechanisms of their elimination. It explains the structure and function of the human excretory system, detailing the process of urine formation, including filtration, reabsorption, and secretion. Key concepts like Glomerular Filtration Rate (GFR), its regulation through autoregulation and hormonal control (renin-angiotensin system), and the counter-current mechanism involving Henle's loop and vasa recta for urine concentration are thoroughly covered. The solutions also address common misconceptions and provide clear answers to true/false statements related to these processes.

Learning outcomes

Define Glomerular Filtration Rate (GFR) and its normal value.
Explain the autoregulatory mechanism of GFR involving the juxtaglomerular apparatus.
Identify the truthfulness of statements regarding micturition, ADH function, filtration, Henle's loop, and reabsorption.
Describe the counter-current mechanism involving Henle's loop and vasa recta.
Understand the role of the kidneys in eliminating excretory products and conserving water.

Topics covered

Paper topics

Excretory Products and Their Elimination
Human Excretory System
Nephron Structure and Function
Glomerular Filtration Rate (GFR)
Autoregulation of GFR
Juxtaglomerular Apparatus
Counter-current Mechanism
Henle's Loop
Vasa Recta
Urine Formation
Water Conservation
Hormonal Regulation of Kidney Function

Important topics

Glomerular Filtration Rate (GFR) and its regulation
Counter-current Mechanism (Henle's Loop and Vasa Recta)
Urine Formation (Filtration, Reabsorption, Secretion)
Role of Juxtaglomerular Apparatus
Water conservation by kidneys

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Questions and Solutions

Question 1

Define Glomerular Filtration Rate (GFR).

Solution: Glomerular Filtration Rate (GFR) refers to the volume of fluid that is filtered from the glomerular capillaries into Bowman's capsule across all the nephrons in both kidneys per minute. In a healthy adult individual, this rate is approximately 125 mL per minute. The resulting glomerular filtrate is a fluid that contains essential substances like glucose, amino acids, and sodium ions, along with potassium ions, urea, uric acid, ketone bodies, and a large volume of water.

Question 2

Explain the autoregulatory mechanism of GFR.

Solution: The kidney possesses an intrinsic autoregulatory mechanism to maintain a stable Glomerular Filtration Rate (GFR) despite fluctuations in systemic blood pressure. This regulation is primarily managed by the juxtaglomerular apparatus (JGA), a specialized structure located at the junction of the afferent arteriole, efferent arteriole, and the distal convoluted tubule of the same nephron. When there is a decrease in GFR, the macula densa cells of the JGA detect this change. In response, the juxtaglomerular cells are stimulated to release renin. Renin initiates the renin-angiotensin-aldosterone system (RAAS), which leads to vasoconstriction of the efferent arteriole and, if necessary, the afferent arteriole. This action helps to increase glomerular blood flow and pressure, thereby restoring the GFR back to its normal level. Conversely, if GFR increases, renin release is inhibited, leading to vasodilation and a decrease in GFR.

Question 3

Indicate whether the following statements are true or false:

(a) Micturition is carried out by a reflex.

(b) ADH helps in water elimination, making the urine hypotonic.

(d) Henle's loop plays an important role in concentrating the urine.

(e) Glucose is actively reabsorbed in the proximal convoluted tubule.

Solution:

(a) True. Micturition, the process of expelling urine from the urinary bladder, is a reflex action controlled by the nervous system.

(b) False. ADH (Antidiuretic Hormone) promotes water reabsorption in the kidneys, which helps to conserve water and makes the urine more concentrated (hypertonic), not hypotonic.

(c) True. During glomerular filtration, a fluid that is essentially free of proteins and blood cells passes from the blood plasma in the glomerulus into the Bowman's capsule.

(d) True. Henle's loop is a critical component of the counter-current mechanism, which is essential for establishing the osmotic gradient in the renal medulla required for concentrating urine.

(e) True. Glucose is almost completely reabsorbed from the glomerular filtrate back into the blood in the proximal convoluted tubule through active transport mechanisms.

Question 4

Give a brief account of the counter current mechanism.

Solution: The counter-current mechanism is a physiological process that operates within the kidneys to conserve water and concentrate urine. It involves two main components: the counter-current multiplier (Henle's loop) and the counter-current exchanger (vasa recta). These systems work together to create and maintain a steep osmotic gradient in the renal medulla, increasing in osmolarity from the cortex (approx. 300 mOsmol/L) to the inner medulla (up to 1200 mOsmol/L).

Henle's Loop: This U-shaped tubule has two limbs (descending and ascending) where tubular fluid flows in opposite directions. The ascending limb actively transports salts (like NaCl) out into the medullary interstitium, while the descending limb is permeable to water but not salts, allowing water to move out. This differential permeability and transport create a concentration gradient.

Vasa Recta: These are peritubular capillaries that run parallel to Henle's loop. Blood flows in opposite directions in the descending and ascending vasa recta. The descending vasa recta equilibrates with the increasing osmolarity of the medulla, taking up solutes and losing water. The ascending vasa recta equilibrates with the decreasing osmolarity, losing solutes and reabsorbing water. This arrangement prevents the washout of the medullary osmotic gradient by the blood flow.

The overall effect of this mechanism is to facilitate the reabsorption of water from the collecting duct into the hypertonic medullary interstitium, resulting in the production of concentrated urine and the conservation of body water. The movement of NaCl and urea also contributes significantly to establishing and maintaining this osmotic gradient.

Common mistakes

Confusing the role of ADH in water balance (ADH conserves water, making urine hypertonic, not hypotonic).
Misunderstanding the direction of blood flow and its role in the counter-current mechanism.
Incorrectly identifying the processes of filtration, reabsorption, and secretion in the nephron.

Revision tips

Draw and label diagrams of the nephron and the counter-current system to visualize the processes.
Focus on understanding the 'why' behind each step in urine formation and GFR regulation.
Use the true/false questions to quickly test your recall of key facts.
Relate the counter-current mechanism to water conservation and the maintenance of osmotic gradients.

Practice MCQs

Q1. What is the approximate Glomerular Filtration Rate (GFR) in a healthy individual per minute?

Q2. Which part of the nephron plays a crucial role in concentrating urine?

Q3. The autoregulatory mechanism of GFR involves which specialized structure?

Q4. Which of the following substances is NOT typically found in significant amounts in the glomerular filtrate?

Q5. What is the primary function of ADH (Antidiuretic Hormone) regarding urine?

Frequently asked questions

What is Glomerular Filtration Rate (GFR)?

Glomerular Filtration Rate (GFR) is the volume of fluid filtered from all the nephrons of both kidneys per minute. In a healthy person, it is approximately 125 mL/minute.

How does the kidney regulate GFR?

The kidney regulates GFR through an autoregulatory mechanism involving the juxtaglomerular apparatus. This mechanism helps maintain a stable GFR even with fluctuations in blood pressure.

What is the counter-current mechanism and why is it important?

The counter-current mechanism involves Henle's loop and vasa recta, where fluids flow in opposite directions. It creates and maintains an osmotic gradient in the renal medulla, crucial for concentrating urine and conserving water.

Is ADH important for urine concentration?

Yes, ADH (Antidiuretic Hormone) plays a vital role by increasing the reabsorption of water in the distal convoluted tubule and collecting duct, leading to the formation of concentrated urine.

What is filtered from the blood into Bowman's capsule?

A protein-free fluid is filtered from the blood plasma into the Bowman's capsule. This filtrate contains water, glucose, amino acids, salts, urea, and other small molecules.

Are all statements in Question 3 true or false?

The statements are: (a) True, (b) False (ADH conserves water, making urine hypertonic), (c) True, (d) True, (e) True.

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