How to Use This Page
Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Digestion and Absorption covers the alimentary canal, digestive enzymes, and nutrient absorption — focus on the enzyme-substrate-product pathway.
Key Concepts (Quick Recap)
The Alimentary Canal
| Part | Function | Key Feature |
|---|
| Mouth (buccal cavity) | Mechanical digestion (chewing) + chemical (salivary amylase) | Teeth, tongue, salivary glands |
| Oesophagus (food pipe) | Transports food from mouth to stomach | Peristalsis (wave-like contractions) |
| Stomach | Chemical digestion (proteins) + storage | Gastric glands: HCl, pepsin, mucus |
| Small intestine | Complete digestion + absorption | Villi, microvilli, duodenum, jejunum, ileum |
| Large intestine | Water absorption, faeces formation | Caecum, colon, rectum |
| Rectum | Stores faeces | Defecation reflex |
| Anus | Expels faeces | Sphincter control |
Digestive Glands and Their Secretions
| Gland | Secretion | Function |
|---|
| Salivary glands | Saliva (salivary amylase) | Digests starch → maltose |
| Gastric glands (stomach) | Gastric juice (HCl, pepsin, mucus) | HCl activates pepsin, kills bacteria; Pepsin digests proteins → peptides |
| Liver | Bile | Emulsifies fats (mechanical, not chemical) |
| Pancreas | Pancreatic juice (trypsin, amylase, lipase) | Trypsin → proteins; Amylase → starch; Lipase → fats |
| Intestinal glands | Intestinal juice (maltase, sucrase, lactase, peptidases) | Final digestion of disaccharides and peptides |
Digestion Pathway (Enzyme → Substrate → Product)
MOUTH:
Salivary amylase → Starch → Maltose
STOMACH:
Pepsin (activated by HCl) → Proteins → Peptides
SMALL INTESTINE (Duodenum):
Bile (from liver) → Emulsifies fats (mechanical)
Trypsin (from pancreas) → Proteins → Peptides
Pancreatic amylase → Starch → Maltose
Pancreatic lipase → Fats → Fatty acids + Glycerol
SMALL INTESTINE (Jejunum/Ileum):
Maltase → Maltose → Glucose
Sucrase → Sucrose → Glucose + Fructose
Lactase → Lactose → Glucose + Galactose
Peptidases → Peptides → Amino acids
Absorption in the Small Intestine
| Nutrient | Absorbed as | Into |
|---|
| Carbohydrates | Glucose, fructose, galactose | Blood capillaries in villi |
| Proteins | Amino acids | Blood capillaries in villi |
| Fats | Fatty acids + glycerol | Lacteals (lymph vessels) in villi |
| Water | H₂O | Blood capillaries |
| Minerals | Na⁺, K⁺, Ca²⁺, Fe²⁺ etc. | Blood capillaries |
| Vitamins | Water-soluble (B, C) and fat-soluble (A, D, E, K) | Blood capillaries and lacteals |
Villi and Microvilli
- Villi: Finger-like projections on the inner wall of the small intestine
- Microvilli: Tiny projections on the epithelial cells of each villus
- Function: Increase surface area for absorption by ~600 times
- Each villus contains: Blood capillaries (absorb glucose, amino acids) and lacteals (absorb fatty acids and glycerol)
I. Choose the Best Answer (MCQs)
Q1. The enzyme that digests starch in the mouth is (a) Pepsin (b) Trypsin (c) Salivary amylase (d) Lipase
Answer(c) Salivary amylase — Salivary amylase (also called ptyalin) is secreted by the salivary glands and acts on starch in the mouth, breaking it down into maltose. It works optimally at pH 6.8.
Q2. Bile is produced by (a) Pancreas (b) Gallbladder (c) Liver (d) Stomach
Answer(c) Liver — Bile is produced by the liver and stored in the gallbladder. When fat enters the duodenum, the gallbladder releases bile through the bile duct. Bile emulsifies fats (breaks large fat globules into smaller droplets).
Q3. The largest gland in the human body is (a) Pancreas (b) Liver (c) Thyroid (d) Salivary gland
Answer(b) Liver — The liver is the largest gland in the human body (weighing about 1.5 kg). It produces bile, detoxifies harmful substances, stores glycogen, and performs over 500 functions.
Q4. Pepsin acts on (a) Starch (b) Proteins (c) Fats (d) Sucrose
Answer(b) Proteins — Pepsin is a protein-digesting enzyme secreted by the gastric glands in the stomach. It converts proteins into peptides. Pepsin works in acidic pH (1.5-2.0), which is provided by HCl.
Q5. The inner wall of the small intestine has villi to (a) Secrete enzymes (b) Increase surface area for absorption (c) Produce bile (d) Kill bacteria
Answer(b) Increase surface area for absorption — Villi are finger-like projections that increase the surface area of the small intestine by about 600 times, allowing efficient absorption of nutrients into the blood.
II. Fill in the Blanks
1. The alimentary canal starts at the mouth and ends at the anus. 2. Salivary amylase digests starch into maltose. 3. The stomach secretes HCl which activates pepsin and kills bacteria. 4. Pepsin digests proteins into peptides. 5. Bile is produced by the liver and stored in the gallbladder. 6. Bile emulsifies fats (breaks them into smaller droplets). 7. Trypsin is secreted by the pancreas and digests proteins into peptides. 8. Lipase digests fats into fatty acids and glycerol. 9. The small intestine has three parts: duodenum, jejunum, and ileum. 10. Villi and microvilli increase the surface area for absorption. 11. Glucose and amino acids are absorbed into blood capillaries in the villi. 12. Fatty acids and glycerol are absorbed into lacteals (lymph vessels) in the villi. 13. The wave-like muscular contractions that push food forward are called peristalsis. 14. The largest gland in the human body is the liver.
III. True or False (with corrections for false statements)
Q1. Digestion of food is completed in the stomach.
AnswerFalse — Correction: Digestion is completed in the small intestine, not the stomach. The stomach only partially digests proteins (pepsin). Carbohydrate digestion starts in the mouth, protein digestion continues in the stomach, and all digestion is completed in the small intestine by pancreatic and intestinal enzymes.
Q2. Bile digests fats chemically.
AnswerFalse — Correction: Bile does NOT digest fats chemically. It emulsifies fats mechanically — breaking large fat globules into smaller droplets, increasing the surface area for lipase to act. The chemical digestion of fats is done by lipase.
Q3. The small intestine is the main site of nutrient absorption.
AnswerTrue — The small intestine has villi and microvilli that increase its surface area about 600 times, making it the primary site for absorption of glucose, amino acids, fatty acids, glycerol, vitamins, and minerals.
Q4. HCl is secreted in the small intestine.
AnswerFalse — Correction: HCl is secreted in the stomach by gastric glands (parietal cells). The small intestine has an alkaline environment (pH 7-8) maintained by bile and pancreatic juice.
Q5. Peristalsis is a voluntary process.
AnswerFalse — Correction: Peristalsis is an involuntary process. It is the wave-like contraction of smooth muscle in the alimentary canal that pushes food forward. It is controlled by the autonomic nervous system.
IV. Match the Following
| Column A | Column B | Answer |
|---|
| 1. Salivary amylase | (a) Proteins → peptides | (b) Starch → maltose |
| 2. Pepsin | (b) Starch → maltose | (a) Proteins → peptides |
| 3. Trypsin | (c) Fats → fatty acids + glycerol | (d) Proteins → peptides (in small intestine) |
| 4. Lipase | (d) Proteins → peptides (small intestine) | (c) Fats → fatty acids + glycerol |
| 5. Bile | (e) Starch → maltose (pancreas) | (f) Emulsifies fats |
| 6. Maltase | (f) Emulsifies fats | (g) Maltose → glucose |
V. Answer Briefly (2-mark questions)
Q1. What is peristalsis? Why is it important?
Answer
Peristalsis is the wave-like muscular contractions of the alimentary canal that push food forward from the oesophagus to the rectum. Importance: (1) Moves food along the digestive tract even against gravity (we can swallow while hanging upside down), (2) Mixes food with digestive juices, (3) It is an involuntary process controlled by smooth muscle.
Q2. What is the role of HCl in the stomach?
Answer
HCl in gastric juice serves three functions: 1. Activates pepsinogen to pepsin (the active enzyme that digests proteins) 2. Kills bacteria and harmful microorganisms in food 3. Creates an acidic environment (pH 1.5-2.0) which is optimal for pepsin activity
Q3. Distinguish between digestion and absorption.
Answer
| Feature | Digestion | Absorption | |---|---|---| | Definition | Breaking down complex food into simpler substances | Taking digested nutrients into the blood | | Location | Mouth, stomach, small intestine | Small intestine (mainly) | | Process | Enzymatic breakdown | Diffusion through villi | | Example | Starch → glucose (by amylase) | Glucose enters blood capillaries in villi |
Q4. What are villi? State their function.
Answer
Villi are finger-like projections on the inner wall of the small intestine. Each villus contains: - Blood capillaries: Absorb glucose and amino acids - Lacteals (lymph vessels): Absorb fatty acids and glycerol Function: Villi (along with microvilli) increase the surface area for absorption by about 600 times, allowing efficient nutrient uptake into the blood and lymph.
VI. Answer in Detail (5-mark questions)
Q1. Describe the process of digestion in the human alimentary canal.
Answer
1. Mouth (Buccal Cavity): - Mechanical digestion: Teeth chew food, tongue mixes it with saliva - Chemical digestion: Salivary amylase (ptyalin) converts starch → maltose - Food becomes a bolus and is swallowed 2. Oesophagus (Food Pipe): - Peristalsis pushes the bolus from the mouth to the stomach - No digestion occurs here 3. Stomach: - Gastric glands secrete gastric juice containing HCl, pepsin, and mucus - HCl: Activates pepsinogen → pepsin, kills bacteria, creates acidic pH - Pepsin: Digests proteins → peptides - Mucus: Protects the stomach lining from HCl and pepsin - Food becomes a semi-liquid called chyme - Duration: 2-6 hours 4. Small Intestine (Duodenum): - Bile (from liver via gallbladder) emulsifies fats - Pancreatic juice contains: Trypsin (proteins → peptides), Pancreatic amylase (starch → maltose), Pancreatic lipase (fats → fatty acids + glycerol) 5. Small Intestine (Jejunum and Ileum): - Intestinal juice contains: Maltase (maltose → glucose), Sucrase (sucrose → glucose + fructose), Lactase (lactose → glucose + galactose), Peptidases (peptides → amino acids) - All digestion is completed here - Absorption occurs through villi and microvilli 6. Large Intestine: - No digestion occurs (no digestive enzymes) - Absorption of water and minerals - Formation of faeces (undigested waste) - Faeces stored in rectum and expelled through anus
Q2. Explain the role of the liver and pancreas in digestion.
Answer
Role of the Liver: 1. Bile production: The liver produces bile (about 500-1000 mL/day) 2. Bile storage: Bile is stored in the gallbladder and released into the duodenum when fat enters 3. Fat emulsification: Bile breaks large fat globules into smaller droplets, increasing surface area for lipase 4. Neutralisation: Bile neutralises the acidic chyme coming from the stomach, creating an alkaline pH (7-8) suitable for pancreatic enzymes 5. Other functions: Detoxification, glycogen storage, protein synthesis, vitamin storage Role of the Pancreas: The pancreas is both an exocrine and endocrine gland. Exocrine function (digestive juice — pancreatic juice): - Trypsin: Digests proteins → peptides (activated from trypsinogen by enterokinase) - Pancreatic amylase: Digests starch → maltose - Pancreatic lipase: Digests fats → fatty acids + glycerol - Pancreatic juice is alkaline (contains NaHCO₃) to neutralise acidic chyme Endocrine function (hormones into blood): - Insulin (β-cells of Islets of Langerhans): Lowers blood sugar - Glucagon (α-cells of Islets of Langerhans): Raises blood sugar
Q3. Explain the process of absorption in the small intestine.
Answer
The small intestine is the main site of absorption because: 1. It is very long (about 6 metres in humans), providing a large surface area 2. The inner wall has villi (finger-like projections) 3. Each villus has microvilli on its epithelial cells, further increasing surface area 4. Each villus has a rich network of blood capillaries and a lacteal (lymph vessel) Absorption of Different Nutrients: 1. Carbohydrates (absorbed as monosaccharides): - Glucose, fructose, galactose are absorbed by blood capillaries in villi - They enter the hepatic portal vein and are transported to the liver 2. Proteins (absorbed as amino acids): - Amino acids are absorbed by blood capillaries in villi - They enter the hepatic portal vein and are transported to the liver 3. Fats (absorbed as fatty acids and glycerol): - Fatty acids and glycerol are absorbed into the lacteals (lymph vessels) inside villi - They are reassembled into fat molecules and transported through the lymphatic system to the blood - Some short-chain fatty acids enter blood capillaries directly 4. Water and Minerals: - Water is absorbed by osmosis - Minerals (Na⁺, K⁺, Ca²⁺, Fe²⁺) are absorbed by active transport and diffusion 5. Vitamins: - Water-soluble vitamins (B, C) are absorbed into blood capillaries - Fat-soluble vitamins (A, D, E, K) are absorbed along with fats into lacteals
Common Mistakes to Avoid
- Saying digestion is completed in the stomach: Digestion is COMPLETED in the small intestine. The stomach only partially digests proteins. All final digestion (carbohydrates, proteins, fats) happens in the small intestine.
- Saying bile digests fats: Bile EMULSIFIES fats (mechanical process). Lipase DIGESTS fats (chemical process). Bile makes fat digestion easier, but does not chemically break down fats.
- Confusing the enzyme and its product: Salivary amylase: starch → maltose (NOT glucose). Pepsin: proteins → peptides (NOT amino acids). Final breakdown to monomers happens in the small intestine.
- Forgetting that fats are absorbed into lacteals, not capillaries: Fatty acids and glycerol enter the lacteals (lymph vessels), not blood capillaries. Glucose and amino acids enter blood capillaries.
- Mixing up the three parts of the small intestine: Duodenum (first — receives bile and pancreatic juice), Jejunum (middle — main absorption), Ileum (last — absorption of B12, bile salts).
- Confusing the liver and gallbladder: The liver PRODUCES bile. The gallbladder STORES bile. Both are important, but they serve different roles.
Exam Checklist
- [ ] Can you trace the path of food through the alimentary canal with functions at each stage?
- [ ] Can you list all digestive enzymes with their source, substrate, and product?
- [ ] Can you explain the role of HCl in the stomach?
- [ ] Can you explain the role of bile (production, storage, emulsification)?
- [ ] Can you explain the role of pancreatic juice (trypsin, amylase, lipase)?
- [ ] Can you describe the structure and function of villi and microvilli?
- [ ] Can you explain absorption of carbohydrates, proteins, and fats into capillaries and lacteals?
- [ ] Can you distinguish between digestion and absorption?
- [ ] Can you explain peristalsis and its importance?
- [ ] Can you describe the liver's and pancreas's dual roles in digestion?
