CBSE Class 11 Biology Chapter 16: Digestion and Absorption NCERT Solutions
This chapter delves into the intricate processes of digestion and absorption in the human body. It explains how the digestive system breaks down complex food substances into simpler molecules that can be absorbed and utilized by the body. The solutions cover the roles of various digestive organs, enzymes like pepsin and lipase, and the structure of the intestinal villi that facilitate absorption. Understanding these concepts is crucial for students to grasp the physiological mechanisms underlying nutrient uptake and energy production. These NCERT Solutions provide clear, step-by-step explanations and answers to key questions, aiding students in their exam preparation and reinforcing their knowledge of this vital biological system.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 11 |
| Subject | Biology |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 16: Digestion and Absorption |
Chapter summary
Chapter 16, Digestion and Absorption, focuses on the physiological processes involved in breaking down food and absorbing nutrients. The NCERT Solutions explain the functions of different digestive organs, the chemical actions of enzymes, and the structural adaptations of the small intestine, such as villi, for efficient absorption. Key topics include the composition of digestive juices, the activation of enzymes, and the transport of absorbed nutrients. These solutions are designed to help students understand the mechanics and chemistry of digestion and absorption.
Learning outcomes
- Understand the functions of different organs in the digestive system.
- Identify the enzymes involved in digestion and their roles.
- Explain the process of absorption of digested food.
- Describe the structure and function of villi in the small intestine.
- Differentiate between the roles of gastric juice and intestinal juice.
Topics covered
Paper topics
- Digestive System Organs
- Composition of Gastric Juice
- Role of Pepsinogen and HCl
- Function of Lipase and Rennin
- Intestinal Juice (Succus Entericus)
- Enzymes in Intestinal Juice
- Structure of Villi
- Absorption of Carbohydrates
- Absorption of Proteins
- Absorption of Fats
- Layers of the Alimentary Canal Wall
- Bile Pigments
Important topics
- Role of Villi in Absorption
- Mechanism of Enzyme Activation (Pepsinogen)
- Composition and Function of Digestive Juices
- Digestion and Absorption of Major Macronutrients
- Structure of the Alimentary Canal Wall
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Questions and Solutions
Question 1
(a) Gastric juice contains
- pepsin, lipase and rennin
- trypsin lipase and rennin
- trypsin, pepsin and lipase
- trypsin, pepsin and renin
(b) Succus entericus is the name given to
- a junction between ileum and large intestine
- intestinal juice
- swelling in the gut
- appendix
(a) The correct option is (i) pepsin, lipase, and rennin. Gastric juice, secreted by the stomach lining, contains these enzymes. Pepsin is secreted in an inactive form called pepsinogen, which is activated by hydrochloric acid (HCl). Pepsin is responsible for breaking down proteins into smaller peptides called peptones. Lipase aids in the digestion of fats, and rennin is an enzyme important for milk coagulation, particularly in infants.
(b) The correct option is (ii) intestinal juice. Succus entericus is the collective term for the intestinal juice secreted by the glands of the intestinal wall. This juice is rich in various enzymes such as maltase, sucrase, lactase, dipeptidases, nucleosidases, and intestinal lipases, which complete the digestion of carbohydrates, proteins, and fats.
Question 2
Column I
Column II
Bilirubin and biliverdin (a) (i)
Parotid (b) Hydrolysis of starch
(ii)
Bile
Digestion of fat (c) (iii)
Lipases
Salivary gland (d) (iv)
Amylases
The correct matching of Column I with Column II is as follows:
- (a) Bilirubin and biliverdin corresponds to (ii) Bile. Bilirubin and biliverdin are bile pigments, which are waste products of red blood cell breakdown and are excreted in bile.
- (b) Hydrolysis of starch corresponds to (iv) Amylases. Amylase is the enzyme responsible for breaking down starch (a carbohydrate) into smaller sugars. Salivary amylase begins this process in the mouth, and pancreatic amylase continues it in the small intestine.
- (c) Digestion of fat corresponds to (iii) Lipases. Lipases are enzymes that catalyze the breakdown of fats into fatty acids and glycerol.
- (d) Salivary gland corresponds to (i) Parotid. The parotid gland is the largest salivary gland and is a major contributor to the saliva that initiates starch digestion.
Question 3
- Why are villi present in the intestine and not in the stomach?
- How does pepsinogen change into its active form?
- What are the basic layers of the wall of the alimentary canal?
- How does bile help in the digestion of fats?
(a) Villi are microscopic, finger-like projections that line the mucosal wall of the small intestine. Their primary function is to significantly increase the surface area available for the efficient absorption of digested nutrients. The stomach, on the other hand, is primarily involved in storing food and initiating protein digestion; its mucosal lining forms folds called rugae, which allow for expansion but do not possess villi as extensive absorption does not occur here.
(b) Pepsinogen is the inactive precursor enzyme secreted by the chief cells in the stomach lining. It is converted into its active form, pepsin, by the presence of hydrochloric acid (HCl) secreted by the parietal cells. HCl provides the acidic environment necessary for this conversion and also helps denature proteins, making them more accessible to pepsin.
(c) The wall of the alimentary canal is composed of four fundamental layers, arranged from the innermost lumen to the outermost covering: the mucosa, the sub-mucosa, the muscularis (composed of inner circular and outer longitudinal smooth muscle layers), and the serosa (an outer connective tissue layer).
(d) Bile, produced by the liver and stored in the gallbladder, aids in fat digestion through a process called emulsification. Bile salts break down large fat globules into smaller, uniformly dispersed droplets. This increase in surface area allows the enzyme lipase to act more effectively, breaking down the fats into absorbable fatty acids and glycerol.
Common mistakes
- Confusing the functions of different digestive enzymes.
- Misunderstanding the activation process of enzymes like pepsinogen.
- Not clearly distinguishing between absorption in the stomach and intestine.
- Incorrectly identifying the components of digestive juices.
Revision tips
- Draw diagrams of the digestive system and label all parts.
- Create a table summarizing digestive enzymes, their sources, substrates, and products.
- Focus on the role of villi in increasing the surface area for absorption.
- Review the chemical reactions involved in the breakdown of carbohydrates, proteins, and fats.
Practice MCQs
Q1. Which of the following enzymes is primarily responsible for the digestion of fats in the small intestine?
Explanation: Lipases are enzymes that break down fats (lipids) into fatty acids and glycerol. While some lipase is present in gastric juice, the majority of fat digestion occurs in the small intestine with the help of pancreatic and intestinal lipases.
Q2. What is the primary function of villi in the small intestine?
Explanation: Villi are finger-like projections that line the inner surface of the small intestine, significantly increasing the surface area available for the absorption of digested nutrients into the bloodstream and lymphatic system.
Q3. Gastric juice contains which of the following combinations of enzymes?
Explanation: Gastric juice is known to contain pepsin (in its inactive form, pepsinogen), lipase, and rennin. Pepsin is crucial for protein digestion, lipase for fat digestion, and rennin for milk coagulation in infants.
Q4. Succus entericus is the term for:
Explanation: Succus entericus is the collective name for the intestinal juice secreted by the glands in the intestinal wall. It contains various enzymes essential for the final stages of digestion.
Q5. Which layer of the alimentary canal wall is responsible for forming rugae in the stomach?
Explanation: The mucosa, the innermost lining of the alimentary canal, forms irregular folds called rugae in the stomach. These folds allow the stomach to expand significantly when filled with food.
Frequently asked questions
What is the main function of villi in the small intestine?
Villi are finger-like projections in the small intestine that greatly increase the surface area for efficient absorption of digested food molecules into the bloodstream and lymphatic system.
How is pepsinogen activated to pepsin?
Pepsinogen, an inactive enzyme precursor, is converted into its active form, pepsin, by the action of hydrochloric acid (HCl) present in the stomach.
What is succus entericus?
Succus entericus is the name given to the intestinal juice, which is secreted by the glands of the intestinal wall and contains various enzymes necessary for the final stages of digestion.
Why are villi absent in the stomach?
Villi are absent in the stomach because the stomach's primary role is food storage and initial protein digestion, not extensive absorption. Its mucosal lining forms rugae (folds) to allow for expansion, rather than villi for absorption.
How does bile aid in fat digestion?
Bile salts emulsify fats, breaking large fat globules into smaller ones. This increases the surface area for lipase enzymes to act upon, facilitating more efficient fat digestion.
What are the four basic layers of the alimentary canal wall?
The four basic layers of the alimentary canal wall, from innermost to outermost, are the mucosa, sub-mucosa, muscularis, and serosa.
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