Chapter 16: Digestion and Absorption – Study Modules with Revision Notes
CBSE Class 11 Biology Chapter 16 – Digestion and Absorption | NCERT-Based Study Module & Revision Notes
Course & Examination Details
Course: CBSE Class 11 Biology
Unit: Unit V – Human Physiology
Chapter: Chapter 16 – Digestion and Absorption
Board: Central Board of Secondary Education (CBSE)
Examination Level: CBSE Class 11 – Annual Examination
Curriculum: Strictly as per NCERT Biology Textbook
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CBSE Class 11 Biology Chapter 16 – Digestion and Absorption | NCERT-Based Study Module & Revision Notes
Introduction to Digestion and Absorption
Digestion and Absorption is a crucial chapter under Unit V: Human Physiology, dealing with the structure and functioning of the human digestive system, the role of digestive enzymes, and the mechanism of absorption of nutrients. This chapter explains how complex food materials are broken down into simpler, absorbable forms and transported to body tissues for energy, growth, and repair.
Questions from this chapter are frequently asked in CBSE Class 11 examinations, internal assessments, and form a strong conceptual base for Class 12 Biology and NEET preparation.
Section 1: Human Digestive System
1.1 Overview of the Digestive System
The human digestive system consists of:
- Alimentary canal
- Associated digestive glands
Its primary functions are:
- Ingestion of food
- Digestion of food
- Absorption of nutrients
- Assimilation
- Egestion
1.2 Alimentary Canal
The alimentary canal is a continuous muscular tube extending from the mouth to the anus.
Major parts include:
- Mouth
- Buccal cavity
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Rectum and anus
1.3 Mouth and Buccal Cavity
The mouth is the opening of the alimentary canal and leads into the buccal cavity.
Components of Buccal Cavity:
- Teeth
- Tongue
- Salivary glands
Functions:
- Mechanical breakdown of food
- Mixing of food with saliva
- Initiation of digestion
1.4 Teeth and Tongue
Teeth:
- Help in mastication
- Humans have heterodont dentition
- Dental formula: 2123 / 2123
Tongue:
- Muscular organ
- Helps in swallowing
- Contains taste buds
- Assists in speech
1.5 Salivary Glands
There are three pairs:
- Parotid
- Submaxillary (Submandibular)
- Sublingual
Saliva contains:
- Salivary amylase (ptyalin)
- Mucus
- Electrolytes
Function:
Salivary amylase initiates digestion of starch into maltose.
1.6 Pharynx and Oesophagus
- Pharynx: Common passage for food and air
- Oesophagus: Muscular tube that transports food to the stomach by peristalsis
No digestion occurs here.
1.7 Stomach
The stomach is a J-shaped muscular organ located below the diaphragm.
Regions:
- Cardiac
- Fundic
- Pyloric
Gastric glands secrete:
- Hydrochloric acid (HCl)
- Pepsinogen
- Mucus
- Rennin (in infants)
Functions of Stomach
- Temporary storage of food
- Mechanical churning
- Partial digestion of proteins
- Formation of chyme
1.8 Small Intestine
The small intestine is the longest part of the alimentary canal and is divided into:
- Duodenum
- Jejunum
- Ileum
It is the major site of digestion and absorption.
1.9 Large Intestine
Divided into:
- Caecum
- Colon
- Rectum
Functions:
- Absorption of water and electrolytes
- Formation of faeces
- Egestion
Section 2: Digestive Glands
2.1 Liver
The liver is the largest gland in the body.
Functions:
- Produces bile
- Detoxification
- Storage of glycogen
- Metabolism of carbohydrates, fats, and proteins
Bile:
- Contains bile salts
- No enzymes
- Helps in emulsification of fats
2.2 Gall Bladder
- Stores and concentrates bile
- Releases bile into the duodenum
2.3 Pancreas
The pancreas is a mixed gland with:
- Exocrine function
- Endocrine function
Pancreatic juice contains:
- Amylase
- Trypsinogen
- Chymotrypsinogen
- Lipase
- Nucleases
Section 3: Digestive Enzymes
3.1 Digestion of Carbohydrates
Mouth:
- Salivary amylase converts starch into maltose
Small intestine:
- Pancreatic amylase converts starch into disaccharides
- Intestinal enzymes (maltase, sucrase, lactase) convert disaccharides into monosaccharides
3.2 Digestion of Proteins
Stomach:
- Pepsin converts proteins into proteoses and peptones
- HCl activates pepsinogen
Small intestine:
- Trypsin and chymotrypsin convert proteins into peptides
- Peptidases convert peptides into amino acids
3.3 Digestion of Fats
Small intestine:
- Bile salts emulsify fats
- Pancreatic lipase converts fats into fatty acids and glycerol
Fat digestion occurs only in the alkaline medium of the intestine.
3.4 Digestion of Nucleic Acids
- Pancreatic nucleases convert nucleic acids into nucleotides
- Intestinal enzymes further break them into sugars, bases, and phosphates
Section 4: Absorption of Digested Products
4.1 Definition of Absorption
Absorption is the process by which digested food molecules pass through the intestinal mucosa into the blood or lymph.
4.2 Absorptive Structures of Small Intestine
- Villi
- Microvilli
These structures:
- Increase surface area
- Enhance absorption efficiency
4.3 Mechanisms of Absorption
a) Passive Diffusion
- Simple diffusion
- Facilitated diffusion
- For fatty acids and glycerol
b) Active Transport
- Requires energy
- Used for amino acids, glucose, electrolytes
4.4 Absorption of Different Nutrients
- Carbohydrates: Absorbed as glucose, fructose, galactose
- Proteins: Absorbed as amino acids
- Fats: Absorbed as micelles → chylomicrons → lymph
- Vitamins: Fat-soluble and water-soluble
- Minerals: Absorbed by active or passive transport
4.5 Absorption in Other Parts
- Mouth: No absorption
- Stomach: Limited absorption (alcohol, some drugs)
- Large intestine: Water, salts, vitamins
Section 5: Assimilation and Egestion
5.1 Assimilation
Assimilation is the utilization of absorbed nutrients by body cells for:
- Energy
- Growth
- Repair
- Maintenance
5.2 Egestion
Egestion is the removal of undigested and unabsorbed food through the anus.
Section 6: Disorders of Digestive System (NCERT Mentioned)
- Indigestion
- Constipation
- Diarrhoea
- Vomiting
- Jaundice
Section 7: Revision Notes – Key Exam Points
Important Definitions
- Digestion: Breakdown of complex food
- Absorption: Entry of nutrients into blood
- Assimilation: Utilization of nutrients
- Egestion: Removal of waste
Key Enzymes to Remember
- Salivary amylase
- Pepsin
- Trypsin
- Lipase
- Maltase, Sucrase, Lactase
NCERT-Based Exam Tips
- Diagram-based questions are common
- Enzyme-action questions are frequent
- Functions of liver and pancreas are important
- Absorption mechanisms are concept-based
Conclusion
The chapter Digestion and Absorption provides a detailed understanding of how food is processed within the human body. A clear grasp of the human digestive system, digestive enzymes, and absorption mechanisms is essential for scoring well in CBSE Class 11 Biology examinations. Thorough revision of enzyme actions, absorption pathways, and structural adaptations ensures conceptual clarity and exam success.