NEET 2027 Biology — Digestion and Absorption is one of the highest-scoring chapters from NCERT Class 11 Chapter 16. Expect 3–5 direct questions from this chapter every year. This guide covers all key concepts, enzyme tables, absorption mechanisms, disorders, and 10 NEET-pattern MCQs with answer distribution across all options.
Overview: The Human Digestive System
The human digestive system is a complex arrangement of organs that processes food from ingestion to egestion. It consists of the alimentary canal (also called the gastrointestinal tract or GI tract) and associated digestive glands.
The alimentary canal begins at the mouth and ends at the anus. The organs in sequence are:
- Mouth (Oral cavity) — mechanical digestion, salivary amylase action
- Pharynx — passage for food and air
- Oesophagus — muscular tube, peristalsis moves food to stomach
- Stomach — churning, HCl secretion, pepsin action
- Small intestine — Duodenum, Jejunum, Ileum — major digestion and absorption site
- Large intestine — Caecum, Colon, Rectum — water absorption, temporary storage
- Anus — egestion of faeces
The major associated glands are: Salivary glands (parotid, submandibular, sublingual), Liver, and Pancreas.
Key Digestive Enzymes — Complete Table
Knowing which enzyme is secreted where and acts on what substrate is essential for NEET. Here is the complete enzyme reference table:
| Enzyme | Secreted By | Site of Action | Substrate → Product |
|---|---|---|---|
| Salivary amylase (Ptyalin) | Salivary glands | Mouth | Starch → Maltose |
| Pepsin | Gastric glands (as pepsinogen) | Stomach | Proteins → Peptones/Proteoses |
| Rennin | Gastric glands | Stomach (infants) | Casein (milk protein) → Paracasein |
| Trypsin | Pancreas (as trypsinogen) | Small intestine | Proteins → Peptides |
| Chymotrypsin | Pancreas | Small intestine | Proteins → Peptides |
| Pancreatic amylase | Pancreas | Small intestine | Starch → Maltose |
| Pancreatic lipase | Pancreas | Small intestine | Emulsified fats → Fatty acids + Glycerol |
| Maltase | Intestinal glands | Small intestine | Maltose → Glucose |
| Sucrase | Intestinal glands | Small intestine | Sucrose → Glucose + Fructose |
| Lactase | Intestinal glands | Small intestine | Lactose → Glucose + Galactose |
The Role of Bile — High-Yield NEET Fact
NEET High-Yield: Bile is produced by the liver, stored in the gall bladder, and released into the duodenum via the bile duct. Bile does not contain any enzymes. Its function is to emulsify fats — breaking large fat globules into smaller droplets to increase the surface area for lipase action. Bile also contains bile salts (sodium taurocholate and sodium glycocholate), bile pigments (bilirubin and biliverdin), cholesterol, and lecithin.
Structure of the Small Intestine — Villi and Absorption
The small intestine is the primary site of digestion and absorption. Its inner wall (mucosa) has several structural adaptations that massively increase surface area:
- Circular folds (plicae circulares) — permanent folds of mucosa and submucosa
- Villi — finger-like projections of mucosa, 0.5–1.5 mm long. Each villus contains a lacteal (lymph capillary) and a network of blood capillaries.
- Microvilli — tiny projections on each epithelial cell of the villus, forming the “brush border”. Each epithelial cell has ~3000 microvilli.
What Gets Absorbed Where
| Nutrient | Site of Absorption | Route |
|---|---|---|
| Glucose, Amino acids | Small intestine (jejunum) | Blood capillaries → portal vein → liver |
| Fatty acids, Glycerol | Small intestine (jejunum) | Lacteals → lymph → blood |
| Water, Vitamins, Minerals | Large intestine (mainly) | Blood capillaries |
| Iron, Calcium | Duodenum | Active transport |
| Vitamin B12, Bile salts | Ileum (terminal) | Active transport |
The process of absorption includes simple diffusion, facilitated diffusion, and active transport depending on the nutrient type.
NCERT Diagrams You Must Know
1. Transverse Section (TS) of Small Intestine
A TS of the small intestine shows four distinct layers (from inside to outside):
- Serosa — outermost layer, single layer of epithelium
- Muscularis — outer longitudinal muscle layer and inner circular muscle layer
- Sub-mucosa — connective tissue with nerves, blood vessels (Meissner’s plexus)
- Mucosa — innermost layer, contains villi and crypts of Lieberkuhn (intestinal glands)
The same four-layer arrangement applies throughout the GI tract, with regional modifications.
2. The Complete GI Tract Diagram
The NCERT diagram of the human digestive system shows: oral cavity → pharynx → oesophagus → stomach (fundus, body, pylorus) → duodenum → jejunum → ileum → ileocaecal valve → caecum (with appendix) → ascending colon → transverse colon → descending colon → sigmoid colon → rectum → anal canal → anus.
Digestive Disorders from NCERT
NCERT Class 11 Chapter 16 mentions the following disorders that are frequently asked in NEET:
1. Jaundice
Jaundice occurs when the liver is diseased or damaged, leading to excess bilirubin in the blood. The skin and eyes turn yellow due to bilirubin deposition. It can be caused by hepatitis (viral liver inflammation), obstruction of bile ducts, or excessive haemolysis of RBCs.
2. Vomiting
Vomiting (emesis) is the ejection of stomach contents through the mouth. It is controlled by the vomiting centre in the medulla oblongata. It can be caused by irritation of the stomach, motion sickness, or toxins.
3. Diarrhoea
Diarrhoea is characterised by abnormally frequent watery stools. It results from impaired absorption of water in the large intestine, often caused by infections (bacterial or viral), food poisoning, or intestinal inflammation. It can lead to dehydration.
4. Constipation
In constipation, the faeces are retained in the rectum due to irregular bowel movements. It is caused by insufficient fibre in diet, inadequate water intake, or reduced physical activity. Increased dietary roughage (fibre) helps prevent constipation.
5. Indigestion (Dyspepsia)
Indigestion is a condition where the food is not properly digested. It leads to a feeling of fullness. The causes include inadequate enzyme secretion, anxiety, food poisoning, overeating, and spicy food.
NEET Exam Strategy for Digestion Chapter
- Memorise enzyme table — substrate, site, product for each enzyme
- Remember: Liver produces bile; gall bladder only stores it
- Know the 4 layers of GI tract wall (serosa/muscularis/sub-mucosa/mucosa)
- Absorption routes: glucose/amino acids → blood; fats → lacteals → lymph
- Disorders: connect each to its pathophysiology (jaundice = bilirubin excess)
- Expect 3–5 questions from this chapter in NEET 2027
Practice more NEET Biology MCQs on our daily practice platform to test your conceptual clarity and speed.
Practice MCQs — Digestion and Absorption
Test yourself with these 10 NEET-pattern MCQs based strictly on NCERT Class 11 Chapter 16:
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Frequently Asked Questions (FAQs)
Q1. What is the difference between bile and digestive enzymes?
Bile is not an enzyme — it is a secretion of the liver that emulsifies (breaks down) large fat globules into smaller droplets. It does not chemically break down fats. In contrast, digestive enzymes like pancreatic lipase actually catalyse the hydrolysis of fats into fatty acids and glycerol. Bile makes fats accessible to lipase by increasing surface area.
Q2. Why is pepsin secreted as pepsinogen?
Pepsin is a protease (protein-digesting enzyme). If secreted in its active form directly, it would digest the protein lining of the stomach itself. By secreting it as the inactive precursor pepsinogen, the body ensures it is only activated in the acidic environment of the stomach lumen (by HCl and by existing pepsin molecules in an autocatalytic process), protecting the stomach wall. This type of inactive precursor is called a zymogen or proenzyme.
Q3. What is the role of HCl in digestion?
Hydrochloric acid (HCl) secreted by parietal (oxyntic) cells of the stomach: (1) provides an acidic pH (~2) optimal for pepsin activity; (2) converts pepsinogen to pepsin; (3) kills bacteria and other pathogens present in food; (4) stops salivary amylase action; and (5) helps in the absorption of calcium and iron by keeping them in soluble form.
Q4. How many MCQs come from Digestion in NEET every year?
Based on NEET previous year papers (2018–2024), the Digestion and Absorption chapter (NCERT Class 11 Chapter 16) typically yields 2 to 4 questions per year. Focus areas include: enzyme identification, absorption sites, bile function, disorders, and GI tract structure. High-priority topics are the enzyme table and the villus structure for absorption.