CBSE Class 11 Biology NCERT Solutions: Excretory Products and their Elimination
This chapter delves into the crucial biological process of excretion, focusing on the removal of metabolic waste products from the body. It covers the various excretory products generated in animals, such as ammonia, urea, and uric acid, and discusses how their forms are adapted based on water availability and toxicity. The solutions explain the mechanisms of filtration in the kidneys, including the role of the Malpighian body, PCT, DCT, and collecting ducts. It also touches upon hormonal regulation of kidney function, like the roles of ADH and aldosterone, and the excretory functions of other organs like lungs. These NCERT Solutions are designed to provide clear, step-by-step explanations to help students grasp complex physiological processes, aiding in their preparation for exams by reinforcing key concepts and problem-solving skills.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 11 |
| Subject | Biology Exemplar |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 19 |
Chapter summary
Chapter 19 of the CBSE Class 11 Biology NCERT Solutions focuses on Excretory Products and their Elimination. It covers the types of nitrogenous wastes produced, their relative toxicity, and how different animals excrete them. The solutions detail the structure and function of the human excretory system, particularly the nephron and the process of urine formation, including filtration, reabsorption, and secretion. Key regulatory mechanisms and the role of lungs in excretion are also discussed.
Learning outcomes
- Understand the different types of excretory products and their toxicity.
- Identify the least toxic excretory product.
- Explain the process of blood filtration in the kidneys.
- Describe the functions of different parts of the nephron (PCT, DCT, Collecting Duct).
- Recognize the role of hormones like ADH and aldosterone in kidney function.
- Explain the excretory role of lungs.
Topics covered
Paper topics
- Excretory Products
- Ammonia Excretion
- Urea Excretion
- Uric Acid Excretion
- Toxicity of Waste Products
- Human Excretory System
- Nephron Structure and Function
- Glomerular Filtration
- Tubular Reabsorption
- Tubular Secretion
- Hormonal Regulation of Kidney Function
- Role of Lungs in Excretion
Important topics
- Types and toxicity of nitrogenous wastes
- Mechanism of urine formation (filtration, reabsorption, secretion)
- Functions of different parts of the nephron
- Hormonal regulation of kidney function (ADH, Aldosterone)
- Excretory role of lungs
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Questions and Solutions
Multiple Choice Questions (MCQs) - Question 1
- Urea
- Uric acid
- Ammonia
- Carbon dioxide
The toxicity of nitrogenous waste products and the amount of water required for their excretion vary significantly. Ammonia is the most toxic and requires a large volume of water for elimination. Urea is less toxic than ammonia and is excreted with a moderate amount of water. Uric acid is the least toxic and is excreted in a semi-solid form, requiring the least amount of water. Animals like birds, reptiles, and insects primarily excrete uric acid to conserve water, especially in arid environments. Carbon dioxide is a gaseous waste product removed by the lungs.
Therefore, the least toxic form among the given options is uric acid.
Answer: (b) Uric acid
Multiple Choice Questions (MCQs) - Question 2
- PCT
- DCT
- Collecting ducts
- Malpighian body
The process of filtration of blood in the kidneys occurs within the Malpighian body, also known as the renal corpuscle. The Malpighian body consists of two main parts: the glomerulus, which is a network of capillaries, and the Bowman's capsule, a cup-shaped structure that surrounds the glomerulus. Blood enters the glomerulus via the afferent arteriole and leaves through the efferent arteriole. Under pressure, water and small solutes from the blood are filtered from the glomerulus into the Bowman's capsule, forming the glomerular filtrate. The PCT, DCT, and collecting ducts are involved in subsequent processes of reabsorption and secretion, not the initial filtration of blood.
Answer: (d) Malpighian body
Multiple Choice Questions (MCQs) - Question 3
- ADH prevents conversion of angiotensinogen in blood to angiotensin
- Aldosterone facilitates water reabsorption
- ANF enhances sodium reabsorption
- Renin causes vasodilation
Let's analyze each statement:
1. ADH prevents conversion of angiotensinogen in blood to angiotensin: This statement is incorrect. ADH (Antidiuretic Hormone) primarily regulates water reabsorption. The conversion of angiotensinogen to angiotensin is initiated by renin, not ADH. Angiotensinogen is converted to angiotensin I by renin, and then to angiotensin II by ACE (Angiotensin-Converting Enzyme).
2. Aldosterone facilitates water reabsorption: This statement is correct. Aldosterone acts on the distal convoluted tubule (DCT) and collecting duct, promoting the reabsorption of sodium ions (Na+) and consequently water, helping to regulate blood volume and pressure.
3. ANF enhances sodium reabsorption: This statement is incorrect. ANF (Atrial Natriuretic Factor) opposes the action of aldosterone and renin-angiotensin system. It inhibits sodium reabsorption and promotes its excretion (natriuresis), leading to increased water excretion and decreased blood pressure.
4. Renin causes vasodilation: This statement is incorrect. Renin is an enzyme that initiates the renin-angiotensin-aldosterone system (RAAS). Angiotensin II, a product of this system, is a potent vasoconstrictor, meaning it causes blood vessels to narrow, thereby increasing blood pressure. Renin itself does not directly cause vasodilation.
Since the question asks for the incorrect statement and multiple statements appear incorrect based on standard physiological understanding, let's re-evaluate based on common textbook interpretations. Statement 1 is definitively incorrect as ADH's role is water balance, not angiotensin conversion. Statement 3 is incorrect as ANF promotes sodium excretion. Statement 4 is incorrect as renin leads to vasoconstriction via angiotensin II. However, if we must choose only one incorrect statement as is typical for MCQs, and considering the provided source's answer points to (a), let's focus on why (a) might be singled out. ADH's primary role is water reabsorption, and it does not directly interfere with the renin-angiotensinogen conversion. The source's provided answer is (a). Let's assume the question intends to test the direct actions of hormones. ADH's direct action is on water permeability. Renin's action leads to vasoconstriction. Aldosterone's action is on Na+ reabsorption. ANF's action is on Na+ excretion. Statement 1 incorrectly assigns a role to ADH. Statement 3 is incorrect as ANF inhibits Na+ reabsorption. Statement 4 is incorrect as renin leads to vasoconstriction. Given the ambiguity and potential for multiple incorrect options, and adhering to the source's implied answer, we will proceed with the explanation for why (a) is incorrect.
Revisiting the provided answer: The source indicates (a) as the incorrect statement. ADH (Antidiuretic Hormone) primarily regulates water reabsorption by increasing the permeability of the collecting ducts. It does not directly prevent the conversion of angiotensinogen to angiotensin. This conversion is part of the renin-angiotensin system. Therefore, statement (a) is indeed incorrect.
Answer: (a) ADH prevents conversion of angiotensinogen in blood to angiotensin
Multiple Choice Questions (MCQs) - Question 4
- CO2 only
- H2O only
- CO2 and H2O
- Ammonia
The lungs serve as a major excretory organ by removing metabolic waste products from the body. During cellular respiration, carbon dioxide (CO2) is produced as a waste product. This CO2 diffuses from the blood into the alveoli of the lungs and is expelled during exhalation. Additionally, a significant amount of water vapor is also lost from the body through the lungs during exhalation. Therefore, the lungs remove both CO2 and H2O in large quantities.
Ammonia is highly toxic and is primarily excreted by the kidneys after being converted to urea. While some ammonia might be present in exhaled air, it is not the primary substance removed in large quantities by the lungs.
Answer: (c) CO2 and H2O
Common mistakes
- Confusing the relative toxicity of ammonia, urea, and uric acid.
- Misidentifying the site of blood filtration in the nephron.
- Incorrectly recalling the functions of different parts of the nephron.
- Confusing the hormonal regulation of water and salt balance.
Revision tips
- Focus on understanding the toxicity and water requirements for excreting ammonia, urea, and uric acid.
- Memorize the sequence of blood flow and filtration within the Malpighian body.
- Create diagrams of the nephron and label the functions of each part (PCT, Loop of Henle, DCT, Collecting Duct).
- Review the roles of ADH, aldosterone, and ANF in maintaining homeostasis.
- Practice identifying incorrect statements about kidney function and hormonal regulation.
Practice MCQs
Q1. Which of the following excretory products is the least toxic and excreted in a semi-solid form?
Explanation: Uric acid is the least toxic nitrogenous waste product because it is insoluble in water and excreted in a semi-solid form, thus conserving water. Ammonia is highly toxic and requires a lot of water for excretion, while urea is moderately toxic.
Q2. In the human kidney, where does the primary filtration of blood occur?
Explanation: The Malpighian body, which consists of the glomerulus and Bowman's capsule, is the site where blood filtration takes place. The glomerulus acts as a filter, allowing small molecules to pass into Bowman's capsule.
Q3. Which hormone is primarily involved in facilitating water reabsorption from the collecting ducts, thus preventing excessive water loss?
Explanation: Antidiuretic Hormone (ADH), also known as vasopressin, increases the permeability of the collecting ducts and distal convoluted tubules to water, leading to increased water reabsorption and the production of concentrated urine.
Q4. What is the main excretory product removed in large quantities by the lungs?
Explanation: The lungs are responsible for removing significant amounts of carbon dioxide (CO2) as a waste product of cellular respiration, along with a considerable quantity of water vapor during exhalation.
Q5. Which of the following statements about kidney function is incorrect?
Explanation: Renin is an enzyme that initiates the renin-angiotensin-aldosterone system (RAAS). It leads to vasoconstriction (narrowing of blood vessels), not vasodilation, which helps in increasing blood pressure.
Frequently asked questions
What are the main excretory products in animals?
The main excretory products are nitrogenous wastes like ammonia, urea, and uric acid, along with carbon dioxide and water. The form excreted depends on the animal's habitat and water availability.
Which excretory product is the least toxic and why?
Uric acid is the least toxic because it is insoluble in water and excreted in a semi-solid form, requiring minimal water for elimination and thus conserving water.
Where does the filtration of blood occur in the human kidney?
Blood filtration occurs in the Malpighian body, which comprises the glomerulus and Bowman's capsule.
What is the role of ADH in the excretory system?
ADH (Antidiuretic Hormone) increases the permeability of the collecting ducts to water, promoting water reabsorption and reducing water loss in urine.
Do lungs play a role in excretion?
Yes, lungs excrete significant amounts of carbon dioxide and water vapor, which are metabolic waste products.
How do these NCERT Solutions help students?
These solutions provide clear, step-by-step explanations for each question, helping students understand the concepts of excretory products and their elimination, and reinforcing their knowledge for exams.
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