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Digestion and Absorption – CBSE NCERT Study Resources

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11th

11th - Biology

Digestion and Absorption

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Overview of the Chapter

This chapter explores the processes of digestion and absorption in the human body. It covers the structure and functions of the digestive system, the role of enzymes, and the mechanisms by which nutrients are absorbed and assimilated.

Digestion: The breakdown of complex food substances into simpler absorbable forms.

Absorption: The process by which digested nutrients pass through the intestinal mucosa into the blood or lymph.

Human Digestive System

The human digestive system consists of the alimentary canal and associated glands. The alimentary canal includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. Associated glands include the salivary glands, liver, and pancreas.

Mouth and Buccal Cavity

Digestion begins in the mouth where food is mechanically broken down by chewing and mixed with saliva. Saliva contains the enzyme salivary amylase, which initiates carbohydrate digestion.

Stomach

The stomach secretes gastric juice containing hydrochloric acid, pepsinogen, and mucus. Pepsinogen is converted to pepsin, which digests proteins.

Small Intestine

The small intestine is the primary site for digestion and absorption. It receives secretions from the liver (bile) and pancreas (pancreatic juice), which aid in digestion.

Digestion of Macromolecules

Different enzymes act on carbohydrates, proteins, and fats to break them down into simpler molecules:

  • Carbohydrates: Broken down into monosaccharides by enzymes like amylase, maltase, and sucrase.
  • Proteins: Digested into amino acids by enzymes like pepsin, trypsin, and peptidases.
  • Fats: Emulsified by bile salts and hydrolyzed into fatty acids and glycerol by lipases.

Absorption of Nutrients

Absorption occurs primarily in the small intestine, which has specialized structures called villi and microvilli to increase surface area. Nutrients are absorbed into the bloodstream or lymphatic system.

Disorders of Digestive System

Common disorders include:

  • Jaundice: Yellowing of skin due to bile pigment accumulation.
  • Diarrhea: Frequent, loose stools due to infection or malabsorption.
  • Constipation: Difficulty in bowel movements due to low fiber intake.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Name the enzyme that breaks down starch in the mouth.
Answer:
Definition: Salivary amylase
Question 2:
Which cells in the stomach secrete hydrochloric acid?
Answer:
Definition: Parietal cells
Question 3:
What is the function of bile in digestion?
Answer:

Emulsifies fats for easier digestion.

Question 4:
Where does the absorption of water primarily occur?
Answer:
Definition: Large intestine
Question 5:
Name the final product of protein digestion.
Answer:
Definition: Amino acids
Question 6:
Which hormone stimulates gastric juice secretion?
Answer:
Definition: Gastrin
Question 7:
What is the role of villi in the small intestine?
Answer:

Increase surface area for nutrient absorption.

Question 8:
Name the enzyme that digests lactose.
Answer:
Definition: Lactase
Question 9:
Which part of the digestive system contains rugae?
Answer:
Definition: Stomach
Question 10:
What is the function of pepsinogen?
Answer:

Inactive precursor of pepsin for protein digestion.

Question 11:
Where is trypsin secreted from?
Answer:
Definition: Pancreas
Question 12:
Name the disorder caused by vitamin C deficiency.
Answer:
Definition: Scurvy
Question 13:
Which nutrient is absorbed via lymphatic vessels?
Answer:
Definition: Fats
Question 14:
What is the role of intestinal microflora?
Answer:

Aid digestion and synthesize vitamins like B12.

Question 15:
Name the enzyme present in saliva that breaks down starch.
Answer:

The enzyme present in saliva is salivary amylase (ptyalin), which breaks down starch into maltose.

Question 16:
What is the role of hydrochloric acid in the stomach?
Answer:

Hydrochloric acid (HCl) in the stomach:
1. Activates pepsinogen to pepsin.
2. Kills harmful microbes.
3. Provides an acidic medium for enzyme action.

Question 17:
Define peristalsis.
Answer:

Peristalsis is the rhythmic contraction and relaxation of smooth muscles in the alimentary canal to push food forward.

Question 18:
Which cells in the stomach secrete mucus?
Answer:

Goblet cells or mucous cells in the stomach lining secrete mucus to protect the stomach wall from HCl.

Question 19:
Where does the absorption of water mainly occur in the digestive system?
Answer:

Most water absorption occurs in the large intestine, particularly the colon.

Question 20:
Name the final product of protein digestion.
Answer:

The final products of protein digestion are amino acids, absorbed in the small intestine.

Question 21:
Which hormone stimulates the secretion of gastric juice?
Answer:

The hormone gastrin stimulates gastric glands to secrete gastric juice.

Question 22:
What is the function of trypsin in the pancreas?
Answer:

Trypsin breaks down proteins into peptides and is secreted by the pancreas in its inactive form, trypsinogen.

Question 23:
Why is the small intestine called the primary site of digestion?
Answer:

The small intestine is the primary site because:
1. Most enzymatic digestion occurs here.
2. Major nutrient absorption happens here.

Question 24:
Name the disorder caused by the deficiency of lactase enzyme.
Answer:

The deficiency of lactase causes lactose intolerance, leading to bloating and diarrhea.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Name the enzyme present in saliva and its function.
Answer:

The enzyme present in saliva is salivary amylase (ptyalin).
It breaks down starch into maltose and dextrin during digestion in the mouth.

Question 2:
What is the role of hydrochloric acid in the stomach?
Answer:

Hydrochloric acid (HCl) in the stomach:
1. Activates pepsinogen to pepsin for protein digestion.
2. Kills harmful microbes in food.
3. Provides an acidic medium for enzyme action.

Question 3:
Define peristalsis.
Answer:

Peristalsis is the rhythmic contraction and relaxation of smooth muscles in the alimentary canal.
It helps push food forward through the digestive tract.

Question 4:
Name the cells that secrete mucus in the stomach lining.
Answer:

Mucus is secreted by goblet cells and mucous neck cells in the stomach lining.
It protects the stomach wall from HCl and digestive enzymes.

Question 5:
What is the function of bile in digestion?
Answer:

Bile helps in:
1. Emulsification of fats to increase surface area for enzyme action.
2. Neutralizing acidic chyme from the stomach.
3. Excretion of waste products like bilirubin.

Question 6:
What are villi? State their function.
Answer:

Villi are finger-like projections in the small intestine.
They increase the surface area for nutrient absorption and contain blood capillaries and lacteals for transport.

Question 7:
What is the role of trypsin in digestion?
Answer:

Trypsin is a pancreatic enzyme that breaks down proteins into smaller peptides.
It works in the small intestine and is activated from trypsinogen by enterokinase.

Question 8:
Why is the small intestine called the 'site of complete digestion'?
Answer:

The small intestine is called so because:
1. It receives secretions from liver, pancreas, and intestinal glands.
2. All major nutrients (carbs, proteins, fats) are fully digested here.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
What is the significance of bile in digestion?
Answer:

Bile, produced by the liver and stored in the gallbladder, has key digestive functions:

  • It emulsifies fats, breaking them into smaller droplets for easier digestion by lipases.
  • It neutralizes the acidic chyme from the stomach, making it alkaline for pancreatic enzyme action.
  • It helps in the excretion of waste products like bilirubin and cholesterol.

Bile does not contain enzymes but is essential for fat digestion and absorption.

Question 2:
Explain the term peristalsis and its role in digestion.
Answer:

Peristalsis refers to the rhythmic, wave-like contractions of smooth muscles in the alimentary canal:

  • It helps push food forward from the esophagus to the stomach and intestines.
  • It ensures thorough mixing of food with digestive juices for efficient digestion.
  • Peristalsis continues even during fasting, known as hunger contractions.

This involuntary movement is crucial for the mechanical breakdown and propulsion of food.

Question 3:
How does the large intestine contribute to digestion?
Answer:

The large intestine primarily aids in:

  • Water absorption from undigested food, converting it into semi-solid feces.
  • Harboring beneficial gut bacteria (microflora) that synthesize vitamins like B12 and K.
  • Storing and eliminating waste through the rectum and anus.

Unlike the small intestine, it does not secrete digestive enzymes but plays a vital role in maintaining fluid balance and gut health.

Question 4:
Explain the role of hydrochloric acid in the stomach during digestion.
Answer:

The hydrochloric acid (HCl) in the stomach plays multiple crucial roles in digestion:

  • It activates the enzyme pepsinogen into its active form pepsin, which digests proteins.
  • It provides an acidic medium (pH 1.5-2.5) necessary for the action of gastric enzymes.
  • It kills harmful microbes present in ingested food, preventing infections.
  • It also helps in the breakdown of food particles by denaturing proteins.
Question 5:
Describe the process of absorption of digested food in the small intestine.
Answer:

The absorption of digested food occurs mainly in the small intestine, specifically in the jejunum and ileum:

  • Monosaccharides (glucose, fructose) and amino acids are absorbed into blood capillaries via active transport or facilitated diffusion.
  • Fatty acids and glycerol are absorbed into the lymphatic system (lacteals) after being reconverted into triglycerides.
  • Water and minerals are absorbed through osmosis and active transport.

The villi and microvilli increase the surface area for efficient absorption.

Question 6:
Differentiate between bolus and chyme.
Answer:

Bolus and chyme are two forms of food during digestion:

  • Bolus is the soft, rounded mass of chewed food mixed with saliva in the mouth, ready to be swallowed.
  • Chyme is the semi-fluid, partially digested food mixed with gastric juices in the stomach.

While bolus is formed in the buccal cavity, chyme is formed in the stomach after mechanical and chemical digestion.

Question 7:
Describe the process of emulsification of fats and its significance.
Answer:

Emulsification is the breakdown of large fat globules into smaller droplets, primarily by bile salts in the small intestine. Here's how it works:

1. Bile salts act as detergents, reducing the surface tension of fats.
2. Large fat molecules are broken into micelles, increasing the surface area for lipase enzyme action.

Significance:
- Enhances fat digestion by pancreatic lipase.
- Facilitates absorption of fat-soluble vitamins (A, D, E, K).
- Prevents fat clumping, ensuring efficient digestion.

Question 8:
Differentiate between peristalsis and segmentation movements in the alimentary canal.
Answer:

Peristalsis and segmentation are two types of movements in the digestive tract:

  • Peristalsis:
    - Involves rhythmic, wave-like contractions of smooth muscles.
    - Pushes food forward in a single direction (esophagus to intestines).
    - Primary role is propulsion of food.
  • Segmentation:
    - Involves localized contractions and relaxations.
    - Mixes food with digestive juices (mostly in small intestine).
    - Enhances absorption by exposing nutrients to intestinal walls.

Question 9:
How does the structure of villi enhance absorption in the small intestine?
Answer:

The villi are finger-like projections in the small intestine designed for maximum nutrient absorption:

1. Increased surface area: Villi (and microvilli on their surface) expand the absorptive area by 30-40 times.
2. Thin epithelium: Single-layered cells allow quick diffusion of nutrients.
3. Rich blood supply: Each villus contains a capillary network and a lacteal (lymph vessel) for transporting absorbed nutrients.
4. Specialized transport: Carrier proteins and channels facilitate active/passive uptake of glucose, amino acids, and fats.

Question 10:
Explain the term chyme and its transition into chyle.
Answer:

Chyme is the semi-fluid mass of partially digested food mixed with gastric juices that exits the stomach. Key points:

1. Composition: Contains HCl, pepsin, and partially broken-down proteins/carbohydrates.
2. Transition to chyle: In the small intestine, chyme mixes with bile, pancreatic juices, and intestinal enzymes.
3. Chyle formation: After fat emulsification and further digestion, the milky, lymph-rich fluid (chyle) is absorbed via lacteals.
4. pH adjustment: Bicarbonate from the pancreas neutralizes acidic chyme for enzyme action.

Question 11:
What are the functions of salivary amylase and lingual lipase?
Answer:

The enzymes in saliva initiate digestion:

Salivary amylase:
- Breaks down starch into smaller sugars like maltose and dextrins.
- Works optimally at pH 6.8 (neutral to slightly acidic).
- Activity stops in the stomach due to low pH.

Lingual lipase:
- Secreted by Ebner’s glands on the tongue.
- Begins fat digestion, especially for milk fats in infants.
- Remains active in the stomach, aiding gastric lipase.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the role of enzymes in the digestion of carbohydrates, proteins, and fats in the human alimentary canal.
Answer:
Theoretical Framework

We studied that enzymes are biological catalysts that speed up digestion. Carbohydrates are broken down by amylase and maltase, proteins by pepsin and trypsin, and fats by lipase.

Evidence Analysis
  • Amylase in saliva starts starch digestion.
  • Pepsin acts in the stomach, while trypsin works in the small intestine.
  • Lipase, with bile, emulsifies fats.
Critical Evaluation

Without enzymes, digestion would be too slow to sustain life. Their specificity ensures efficient nutrient breakdown.

Future Implications

Research on enzyme deficiencies, like lactose intolerance, highlights their importance in health.

Question 2:
Describe the absorption of digested food in the small intestine with reference to villi and microvilli.
Answer:
Theoretical Framework

The small intestine is the primary site for nutrient absorption. Villi and microvilli increase surface area for efficient uptake.

Evidence Analysis
  • Villi are finger-like projections containing blood capillaries and lacteals.
  • Microvilli form the brush border, enhancing absorption.
  • Glucose and amino acids enter blood; fats enter lymph.
Critical Evaluation

This structure maximizes absorption, but disorders like celiac disease damage villi, impairing nutrient uptake.

Future Implications

Understanding villi function aids in treating malabsorption syndromes.

Question 3:
Compare and contrast the digestion and absorption of fats and proteins in humans.
Answer:
Theoretical Framework

Fats and proteins are digested differently due to their chemical structures. Fats require bile for emulsification, while proteins need acidic and alkaline environments.

Evidence Analysis
  • Fats: Lipase breaks them into fatty acids + glycerol.
  • Proteins: Pepsin and trypsin break them into amino acids.
  • Fats are absorbed via lacteals; proteins enter blood directly.
Critical Evaluation

Fat digestion is slower due to emulsification, whereas protein digestion is faster but pH-dependent.

Future Implications

Studying these processes helps design diets for metabolic disorders.

Question 4:
Explain the significance of peristalsis and segmentation in the digestive process.
Answer:
Theoretical Framework

Peristalsis and segmentation are muscular movements that propel and mix food. Peristalsis is wave-like; segmentation is churning.

Evidence Analysis
  • Peristalsis moves food from esophagus to stomach.
  • Segmentation in the small intestine mixes food with enzymes.
  • Both ensure efficient digestion and absorption.
Critical Evaluation

Without these movements, digestion would be incomplete. Disorders like gastroparesis disrupt peristalsis.

Future Implications

Research on motility disorders can improve treatments for digestive ailments.

Question 5:
Discuss the role of liver and pancreas in digestion, highlighting their secretions.
Answer:
Theoretical Framework

The liver produces bile, while the pancreas secretes digestive enzymes and bicarbonate.

Evidence Analysis
  • Bile emulsifies fats; stored in the gallbladder.
  • Pancreatic amylase, trypsin, and lipase break down macromolecules.
  • Bicarbonate neutralizes stomach acid.
Critical Evaluation

Liver and pancreas are vital; their dysfunction (e.g., cirrhosis or pancreatitis) severely impacts digestion.

Future Implications

Advances in organ transplants can save lives affected by these disorders.

Question 6:
Analyze the consequences of dehydration on digestion and absorption in the human body.
Answer:
Theoretical Framework

Dehydration reduces water availability, impairing enzyme function and nutrient transport.

Evidence Analysis
  • Less saliva and gastric juice production slows digestion.
  • Reduced blood volume limits nutrient absorption.
  • Constipation occurs due to hard stools.
Critical Evaluation

Chronic dehydration can lead to malnutrition and electrolyte imbalances, as seen in diarrhea.

Future Implications

Public awareness on hydration can prevent digestive disorders.

Question 7:
Explain the process of digestion of proteins in the human alimentary canal. Highlight the role of enzymes and the sites where digestion occurs.
Answer:

The digestion of proteins begins in the stomach and is completed in the small intestine. Here's a step-by-step breakdown:

  • In the stomach: Gastric glands secrete pepsinogen, which is activated to pepsin by hydrochloric acid (HCl). Pepsin breaks proteins into smaller peptides.
  • In the small intestine: Pancreatic juice contains trypsinogen, which is converted to trypsin by enterokinase. Trypsin further breaks peptides into dipeptides and tripeptides.
  • Final digestion: Brush border enzymes like peptidases in the intestinal mucosa convert dipeptides/tripeptides into amino acids for absorption.

Key enzymes involved are pepsin, trypsin, and peptidases, each acting at specific pH levels. The stomach provides an acidic environment, while the small intestine is alkaline, ensuring optimal enzyme activity.

Question 8:
Describe the absorption of digested food in the small intestine. Include the mechanisms and adaptations that enhance this process.
Answer:

The small intestine is the primary site for absorption due to its specialized structures and mechanisms:

  • Villi and microvilli: These finger-like projections increase the surface area for absorption. Each villus contains blood capillaries and a lacteal (lymph vessel) to transport nutrients.
  • Mechanisms:
    1. Simple diffusion: Small nutrients like water and lipids pass passively.
    2. Facilitated diffusion: Glucose and amino acids use carrier proteins.
    3. Active transport: Minerals like sodium are absorbed against concentration gradients.

Adaptations include:
- Long length (~6 meters) for prolonged contact time.
- Rich blood supply to maintain concentration gradients.
- Mucosal folds to further increase surface area.

Question 9:
Discuss the disorders of the digestive system with emphasis on jaundice and constipation. Include causes, symptoms, and preventive measures.
Answer:

Digestive disorders disrupt normal nutrient processing. Two common conditions are:

  • Jaundice:
    - Causes: Excess bilirubin due to liver damage (e.g., hepatitis), bile duct obstruction, or RBC destruction.
    - Symptoms: Yellowing of skin/eyes, dark urine, fatigue.
    - Prevention: Vaccination (e.g., Hepatitis B), avoiding alcohol, and hygienic food practices.
  • Constipation:
    - Causes: Low fiber intake, dehydration, or lack of physical activity.
    - Symptoms: Infrequent bowel movements, hard stools, bloating.
    - Prevention: High-fiber diet (fruits, vegetables), adequate water intake, and regular exercise.

Both disorders highlight the importance of a balanced diet and lifestyle for digestive health.

Question 10:
Explain the process of digestion of proteins in the human alimentary canal. Highlight the role of enzymes and the sites where they act.
Answer:

The digestion of proteins begins in the stomach and is completed in the small intestine. Here is a step-by-step breakdown:


1. Stomach: The gastric glands secrete pepsinogen, which is activated to pepsin by hydrochloric acid (HCl). Pepsin breaks down proteins into smaller fragments called peptones and proteoses.


2. Small Intestine: The partially digested proteins enter the duodenum, where pancreatic juice (containing trypsinogen and chymotrypsinogen) is released. Enterokinase (from intestinal mucosa) converts trypsinogen to trypsin, which further activates other enzymes. Trypsin and chymotrypsin break peptones into dipeptides.


3. Final Breakdown: The intestinal brush border enzymes like peptidases hydrolyze dipeptides into absorbable amino acids.


Key Enzymes: Pepsin (stomach), Trypsin, Chymotrypsin (pancreas), and Peptidases (intestine). Each enzyme acts optimally at specific pH levels, ensuring efficient protein digestion.

Question 11:
Describe the absorption of digested food in the small intestine. Include the mechanisms involved and the significance of villi.
Answer:

The small intestine is the primary site for nutrient absorption due to its specialized structure, the villi and microvilli, which increase surface area. Here’s how absorption occurs:


1. Mechanisms:

  • Simple Diffusion: Small nutrients like water and glycerol pass passively.
  • Facilitated Diffusion: Fructose is absorbed with the help of carrier proteins.
  • Active Transport: Glucose, amino acids, and ions are absorbed against concentration gradients using ATP.

2. Role of Villi: The villi are finger-like projections lined with capillaries and a lacteal (lymph vessel). They enhance absorption by:

  • Providing a large surface area.
  • Containing blood vessels for transporting glucose and amino acids to the liver.
  • Lacteals absorb fatty acids and glycerol into the lymphatic system.

Significance: Efficient absorption ensures optimal nutrient utilization for energy, growth, and repair. The villi’s structure maximizes contact with digested food, ensuring no nutrient is wasted.

Question 12:
Explain the process of digestion of proteins in the human alimentary canal, highlighting the role of enzymes and the sites of their action. (5 marks)
Answer:

The digestion of proteins begins in the stomach and is completed in the small intestine. Here's a step-by-step breakdown:


1. In the Stomach:
- The gastric glands secrete pepsinogen, which is activated to pepsin by HCl.
- Pepsin breaks down proteins into smaller fragments called peptones and proteoses.
- HCl also provides an acidic medium for pepsin activity.


2. In the Small Intestine:
- The pancreatic juice contains enzymes like trypsinogen (activated to trypsin by enterokinase).
- Trypsin further breaks down proteins into dipeptides.
- Chymotrypsin and carboxypeptidase also act on peptide bonds.
- The intestinal juice contains dipeptidases and aminopeptidases, which convert dipeptides into amino acids.


Key Points:
- Protein digestion is a stepwise process involving multiple enzymes.
- The end products (amino acids) are absorbed in the jejunum and ileum.

Question 13:
Explain the process of digestion of proteins in the human alimentary canal, highlighting the role of enzymes and the sites of their action.
Answer:

The digestion of proteins begins in the stomach and is completed in the small intestine. Here’s a step-by-step breakdown:


1. In the Stomach: The gastric glands secrete pepsinogen, which is activated to pepsin by hydrochloric acid (HCl). Pepsin breaks down proteins into smaller fragments called peptones and proteoses.


2. In the Small Intestine: The pancreatic juice contains trypsinogen and chymotrypsinogen, which are activated by enterokinase (from intestinal mucosa) into trypsin and chymotrypsin. These enzymes further break down proteins into dipeptides.


3. Final Breakdown: The intestinal brush border enzymes like dipeptidases and aminopeptidases convert dipeptides into amino acids, which are then absorbed.


Key Points:

  • HCl provides an acidic medium for pepsin activation.
  • Trypsin also activates other enzymes, ensuring efficient digestion.
  • The small intestine is the primary site for protein absorption.

Question 14:
Explain the process of digestion of proteins in the human alimentary canal, highlighting the role of enzymes and the sites of their action.
Answer:

The digestion of proteins in the human alimentary canal involves a series of enzymatic reactions at different sites. Here's a step-by-step breakdown:


1. Mouth: No protein digestion occurs here as the mouth lacks proteolytic enzymes.

2. Stomach: Gastric glands secrete pepsinogen, which is activated to pepsin by HCl. Pepsin breaks proteins into smaller peptides (proteoses and peptones).

3. Small Intestine:
  • Pancreatic juice contains trypsinogen and chymotrypsinogen, activated by enterokinase into trypsin and chymotrypsin. These enzymes further break peptides into smaller peptides.
  • Carboxypeptidases (from pancreas) and aminopeptidases (from intestinal brush border) convert peptides into amino acids.

Key Points: Protein digestion is completed in the small intestine, where amino acids are absorbed. HCl provides an acidic medium for pepsin, while bile neutralizes chyme for pancreatic enzymes.

Question 15:
Explain the process of digestion and absorption of carbohydrates in the human alimentary canal with a focus on the role of enzymes and the final absorption mechanism.
Answer:

The digestion and absorption of carbohydrates in the human alimentary canal involve multiple steps and enzymes. Here's a detailed breakdown:

1. Mouth: Digestion begins in the buccal cavity where salivary amylase (ptyalin) breaks down starch into maltose and dextrins. This action is optimal at a slightly alkaline pH (6.8-7.0).

2. Stomach: The acidic environment inactivates salivary amylase, halting carbohydrate digestion temporarily.

3. Small Intestine: The majority of digestion occurs here with the help of pancreatic and intestinal enzymes:

  • Pancreatic amylase further breaks down remaining starch into maltose and isomaltose.
  • Brush border enzymes (e.g., maltase, sucrase, lactase) convert disaccharides into monosaccharides like glucose, fructose, and galactose.

4. Absorption: Monosaccharides are absorbed in the jejunum and ileum via:

  • Facilitated diffusion (fructose).
  • Active transport (glucose and galactose with Na+ co-transport).

Value-added note: Fiber (cellulose) remains undigested due to the lack of cellulase in humans but aids in bowel movement.

Question 16:
Explain the process of digestion of proteins in the human alimentary canal. Include the role of enzymes and the sites of their secretion.
Answer:

The digestion of proteins in the human alimentary canal involves a series of enzymatic reactions that break down complex protein molecules into absorbable amino acids. The process occurs in multiple stages across different regions of the digestive system.

1. Mouth: No protein digestion occurs here as the mouth lacks proteolytic enzymes. However, mechanical digestion through chewing helps break down food into smaller pieces.

2. Stomach: Protein digestion begins in the stomach due to the action of gastric juice, which contains hydrochloric acid (HCl) and the enzyme pepsinogen.
- HCl activates pepsinogen into its active form, pepsin.
- Pepsin breaks proteins into smaller polypeptides and peptones by hydrolyzing peptide bonds.

3. Small Intestine: Further digestion occurs in the duodenum and jejunum with the help of pancreatic and intestinal enzymes.
- Pancreatic juice contains trypsinogen, chymotrypsinogen, and procarboxypeptidase, which are activated into trypsin, chymotrypsin, and carboxypeptidase, respectively.
- Trypsin and chymotrypsin further break polypeptides into smaller peptides.
- Carboxypeptidase removes terminal amino acids from peptides.
- Intestinal juice (succus entericus) contains aminopeptidases and dipeptidases, which convert peptides into free amino acids.

Final Absorption: The end products (amino acids) are absorbed by the villi in the small intestine and transported to the bloodstream for utilization by cells.

Value-Added Note: Protein digestion is crucial for growth and repair. Inadequate protein intake can lead to conditions like kwashiorkor or marasmus, highlighting the importance of a balanced diet.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A patient reports bloating and indigestion after meals. Tests reveal reduced bile secretion. Explain how bile aids digestion and analyze the consequences of its deficiency.
Answer:
Case Deconstruction

Bile, produced by the liver, emulsifies fats into smaller droplets, increasing surface area for lipase action. It also neutralizes stomach acid.

Theoretical Application
  • Deficiency reduces fat digestion, causing steatorrhea (fatty stools).
  • Bloating occurs due to undigested fats fermenting in the colon.
Critical Evaluation

Our textbook shows bile salts are recycled via enterohepatic circulation. Disruption here may worsen deficiency. Example: Gallstones blocking bile flow cause similar symptoms.

Question 2:
Compare villi and microvilli in nutrient absorption. Why do celiac patients show villous atrophy leading to malnutrition?
Answer:
Case Deconstruction

Villi are finger-like projections in the small intestine, while microvilli are hair-like structures on villi cells, increasing surface area.

Theoretical Application
  • Villi absorb nutrients; microvilli further enhance absorption via enzymes like lactase.
  • Celiac disease triggers immune damage to villi, reducing absorption.
Critical Evaluation

We studied that villous atrophy causes deficiencies. Example: Iron malabsorption leads to anemia. Gluten-free diets can reverse damage.

Question 3:
Analyze how pepsinogen activation and mucus secretion maintain stomach homeostasis. What happens if mucus production decreases?
Answer:
Case Deconstruction

Pepsinogen converts to pepsin in acidic pH, digesting proteins. Mucus protects the stomach wall from acid.

Theoretical Application
  • Low mucus exposes epithelium to HCl, causing gastric ulcers.
  • Example: NSAIDs like aspirin reduce mucus, increasing ulcer risk.
Critical Evaluation

Our textbook shows pepsinogen activation is pH-dependent. Chronic acidity may damage parietal cells, reducing acid production over time.

Question 4:
A study links gut microbiota to obesity. Explain how bacterial fermentation of dietary fiber produces short-chain fatty acids (SCFAs) affecting metabolism.
Answer:
Case Deconstruction

Gut bacteria ferment fiber into SCFAs like butyrate, which colon cells use for energy.

Theoretical Application
  • SCFAs regulate appetite hormones (e.g., leptin) and reduce fat storage.
  • Example: High-fiber diets correlate with lower obesity rates.
Critical Evaluation

We studied that dysbiosis (microbial imbalance) may alter SCFA production. Probiotics can restore healthy flora, improving metabolism.

Question 5:
A patient reports bloating and indigestion after meals. Tests reveal low bile secretion. Explain how bile deficiency affects lipid digestion and suggest dietary adjustments.
Answer:
Case Deconstruction

Bile emulsifies fats, increasing surface area for lipase action. Its deficiency causes incomplete lipid digestion, leading to bloating.

Theoretical Application
  • Bile salts convert large fat globules to micelles for enzyme access.
  • Low bile reduces fat-soluble vitamin absorption (A, D, E, K).
Critical Evaluation

Dietary adjustments: Consume medium-chain triglycerides (coconut oil) as they don't require bile. Avoid heavy fried foods. Example: Replace butter with olive oil.

Question 6:
Compare peristalsis and segmentation in the small intestine using two parameters. How do they aid nutrient absorption?
Answer:
Case Deconstruction

Peristalsis propels food, while segmentation mixes chyme. Both optimize nutrient absorption.

Theoretical Application
ParameterPeristalsisSegmentation
MovementUnidirectionalBack-and-forth
FunctionTransitMixing
Critical Evaluation

Example: Segmentation ensures enzyme-chyme contact, while peristalsis moves digested food to villi. Our textbook shows coordinated contractions increase absorption efficiency by 60%.

Question 7:
Analyze why peptic ulcers occur despite the stomach's mucous barrier. Link this to Helicobacter pylori infection and acid secretion.
Answer:
Case Deconstruction

H. pylori degrades mucus and triggers excess acid secretion, eroding the stomach lining.

Theoretical Application
  • Bacteria produce urease, neutralizing local pH for survival.
  • Inflammation reduces mucous cell activity.
Critical Evaluation

Example: Proton pump inhibitors (omeprazole) reduce acid, allowing healing. Our studies show 90% ulcers are H. pylori-related, proving microbial role.

Question 8:
A child with lactose intolerance experiences diarrhea. Explain the biochemical basis and propose an enzyme-based solution.
Answer:
Case Deconstruction

Deficiency of lactase causes undigested lactose to ferment in the colon, drawing water osmotically.

Theoretical Application
  • Lactase breaks lactose into glucose + galactose.
  • Unhydrolyzed lactose increases gut osmotic pressure.
Critical Evaluation

Solution: Lactase supplements (e.g., Lactaid) predigest milk. Example: Fermented dairy (yogurt) has lower lactose due to bacterial action.

Question 9:
A patient reports chronic diarrhea and nutrient deficiency. Tests reveal damaged villi in the small intestine. Explain how this affects digestion and absorption.
Answer:
Case Deconstruction

The damaged villi reduce surface area, impairing nutrient absorption. Chronic diarrhea further dehydrates the body and flushes out undigested food.

Theoretical Application
  • Villi contain microvilli for absorbing nutrients like glucose and amino acids.
  • Damage disrupts enzyme secretion (e.g., lactase), causing lactose intolerance.
Critical Evaluation

Our textbook shows villi increase absorption by 600x. Without them, malnutrition occurs despite adequate intake, as seen in celiac disease.

Question 10:
Compare pepsin and trypsin in terms of their secretion, activation, and role in protein digestion.
Answer:
Case Deconstruction

Pepsin is secreted as pepsinogen in the stomach, activated by HCl, while trypsin is secreted as trypsinogen in the pancreas, activated by enterokinase.

Theoretical Application
  • Pepsin works at pH 1.5-2, breaking proteins into peptides.
  • Trypsin (pH 8) further digests peptides in the duodenum.
Critical Evaluation

We studied that pepsin’s acidic environment denatures proteins, whereas trypsin’s alkaline action complements it, ensuring complete digestion, as in cystic fibrosis patients with pancreatic insufficiency.

Question 11:
Analyze how bile aids fat digestion despite lacking enzymes. Include its emulsification mechanism.
Answer:
Case Deconstruction

Bile salts break large fat globules into smaller micelles via emulsification, increasing surface area for lipase action.

Theoretical Application
  • Bile is stored in the gallbladder and released into the duodenum.
  • It neutralizes stomach acid, creating an alkaline pH for pancreatic enzymes.
Critical Evaluation

Our textbook shows bile’s role in absorbing fat-soluble vitamins (A, D, E, K). Without it, as in gallstones, undigested fats cause steatorrhea.

Question 12:
A study links gut microbiota to vitamin B12 synthesis. Discuss their role in digestion and consequences of dysbiosis.
Answer:
Case Deconstruction

Gut microbiota ferment indigestible fibers, producing short-chain fatty acids and synthesizing vitamins like B12.

Theoretical Application
  • They compete with pathogens, maintaining gut health.
  • Dysbiosis (imbalance) leads to inflammatory bowel disease or malnutrition.
Critical Evaluation

We studied that antibiotics disrupt microbiota, reducing B12 availability. Probiotics, like yogurt, restore balance, highlighting their symbiotic relationship.

Question 13:
Rahul experienced severe stomach pain and indigestion after consuming a heavy meal rich in fats. His doctor diagnosed him with a condition where his gallbladder was not functioning properly.

Explain how the malfunctioning of the gallbladder affects the digestion of fats and the role of bile in this process.

Answer:

The gallbladder stores and concentrates bile, a digestive juice produced by the liver. Bile contains bile salts that emulsify fats, breaking them into smaller droplets. This increases the surface area for lipase (an enzyme) to act upon.


If the gallbladder malfunctions, bile is not released efficiently into the small intestine. As a result:

  • Fats remain large and undigested due to lack of emulsification.
  • Lipase cannot act effectively, leading to incomplete fat digestion.

This causes symptoms like indigestion, pain, and fatty stools (steatorrhea). Bile also helps in the absorption of fat-soluble vitamins (A, D, E, K), so its deficiency may lead to vitamin deficiencies.

Question 14:
Priya noticed that her grandmother takes a digestive enzyme supplement before meals. Upon researching, she found it contains pepsin and trypsin.

Compare the roles of these two enzymes in protein digestion, including their sites of action and optimal pH conditions.

Answer:

Pepsin and trypsin are proteolytic enzymes that break down proteins, but they function in different parts of the digestive system:


  • Pepsin:
    - Acts in the stomach.
    - Optimal pH: 1.5-2 (highly acidic).
    - Converts proteins into peptones and proteoses.
    - Secreted as inactive pepsinogen, activated by HCl.

  • Trypsin:
    - Acts in the small intestine.
    - Optimal pH: 7.5-8 (alkaline).
    - Breaks down proteins into smaller peptides.
    - Secreted as inactive trypsinogen, activated by enterokinase.

While pepsin works in acidic conditions, trypsin requires an alkaline environment. Both enzymes ensure complete protein digestion, but in different regions of the gut.

Question 15:
Rahul experienced severe stomach pain and indigestion after consuming a heavy meal rich in fats. His doctor diagnosed him with gallstones, which obstructed the bile duct. Explain how this condition affects the digestion and absorption of fats in the small intestine.
Answer:

The presence of gallstones blocking the bile duct severely impacts fat digestion because bile, produced by the liver and stored in the gallbladder, cannot reach the duodenum. Bile emulsifies large fat globules into smaller micelles, increasing the surface area for lipase enzyme action.


Without bile:

  • Fat digestion slows down as lipase cannot efficiently break down large fat droplets.
  • Fat-soluble vitamins (A, D, E, K) and fatty acids are poorly absorbed due to incomplete digestion.

This leads to steatorrhea (fatty stools) and malnutrition over time. Rahul’s symptoms, like pain and indigestion, arise due to undigested fats irritating the gut lining.

Question 16:
Priya noticed that her grandmother, who lacks teeth, struggles to digest fibrous foods like salads but manages soft foods like dal-rice easily. Explain the role of mechanical digestion in the mouth and its impact on the subsequent stages of digestion.
Answer:

Mechanical digestion in the mouth involves mastication (chewing) by teeth, which breaks down food into smaller particles. This process is crucial because:

  • It increases the surface area for salivary amylase to act on starch.
  • Softens food for easier swallowing and passage through the esophagus.

In Priya’s grandmother’s case:

  • Without teeth, fibrous foods remain large and undigested, causing strain on the stomach and intestines.
  • Soft foods like dal-rice are already broken down, so gastric and intestinal enzymes can act efficiently.

Poor mechanical digestion leads to incomplete chemical digestion and nutrient absorption, emphasizing the mouth’s role as the first step in digestion.

Question 17:
Rahul experienced severe stomach pain and indigestion after consuming a heavy meal rich in fats. His doctor diagnosed him with gallstones, which obstructed the bile duct. Explain how this condition affects the digestion and absorption of fats in Rahul's body.
Answer:

The presence of gallstones in the bile duct blocks the flow of bile, a digestive juice produced by the liver and stored in the gallbladder. Bile plays a crucial role in the digestion of fats through the following steps:

  • Emulsification: Bile salts break down large fat globules into smaller micelles, increasing the surface area for lipase (a fat-digesting enzyme) to act.
  • Absorption: Bile helps in the absorption of fat-soluble vitamins (A, D, E, K) and fatty acids in the small intestine.

Due to the obstruction, undigested fats remain in the intestine, leading to:

  • Reduced fat digestion and malabsorption.
  • Steatorrhea (fatty stools) due to undigested fats.
  • Deficiency of fat-soluble vitamins, causing related disorders.

Thus, Rahul's condition severely impacts fat metabolism and nutrient absorption.

Question 18:
Priya noticed that her grandmother, who had undergone partial removal of the stomach (gastrectomy), often complained of weakness and fatigue. The doctor attributed this to vitamin B12 deficiency. Explain why the removal of a part of the stomach leads to this deficiency and its consequences.
Answer:

The stomach's parietal cells secrete intrinsic factor, a glycoprotein essential for the absorption of vitamin B12 in the ileum. After partial gastrectomy, the following occurs:

  • Reduced parietal cells → decreased intrinsic factor production.
  • Vitamin B12 cannot be absorbed efficiently without intrinsic factor.

Consequences of vitamin B12 deficiency include:

  • Pernicious anemia: Impaired RBC production due to defective DNA synthesis.
  • Neurological issues like numbness and memory loss due to myelin sheath damage.
  • Chronic fatigue and weakness due to reduced oxygen transport.

Thus, Priya's grandmother's condition arises from impaired B12 absorption post-surgery, leading to systemic deficiencies.

Question 19:
Rahul experienced severe stomach pain and vomiting after consuming stale food. Upon examination, the doctor diagnosed him with food poisoning caused by bacterial toxins.

Explain how the digestive system responds to such toxins and the role of villi in nutrient absorption during normal digestion.

Answer:

When harmful bacterial toxins enter the digestive system, the body triggers defensive mechanisms like vomiting and diarrhea to expel them quickly. The stomach lining may also increase mucus secretion to protect itself from irritation.


In normal digestion, villi are finger-like projections in the small intestine that greatly increase the surface area for absorption. They contain:

  • Microvilli for further surface expansion
  • Blood capillaries to absorb glucose and amino acids
  • Lacteals (lymph vessels) for fat absorption

During food poisoning, villi function may be temporarily impaired due to inflammation, reducing nutrient absorption efficiency.

Question 20:
A patient was found to have insufficient bile juice production, leading to difficulty digesting fatty foods.

Analyze the consequences of this condition on digestion and suggest two dietary modifications to help the patient.

Answer:

Bile juice, produced by the liver and stored in the gallbladder, plays crucial roles in fat digestion:


1. Emulsification: Bile salts break large fat globules into smaller droplets (micelles) for lipase enzyme action
2. Absorption of fat-soluble vitamins (A, D, E, K)


Without sufficient bile, the patient may experience:

  • Steatorrhea (fatty stools)
  • Vitamin deficiencies
  • Bloating after fatty meals

Dietary modifications:

  1. Consume medium-chain triglycerides (found in coconut oil) that don't require bile for absorption
  2. Increase intake of pre-digested fats like yogurt and fermented foods
Question 21:
Rahul experienced severe stomach pain and indigestion after consuming a meal rich in fried food. Upon medical examination, it was found that his gallbladder was not functioning properly. Explain how the malfunctioning of the gallbladder affects the digestion of fats and the role of bile in this process.
Answer:

The gallbladder stores and concentrates bile, a digestive juice produced by the liver. Bile plays a crucial role in the digestion of fats through the following steps:

  • Emulsification: Bile salts break down large fat globules into smaller droplets, increasing the surface area for lipase enzyme action.
  • Neutralization: Bile neutralizes the acidic chyme from the stomach, creating an alkaline environment for pancreatic enzymes.

Since Rahul's gallbladder is malfunctioning, bile secretion is impaired, leading to incomplete fat digestion. Undigested fats remain in the intestine, causing discomfort, bloating, and pain. Additionally, fat-soluble vitamins (A, D, E, K) may not be absorbed efficiently.

Question 22:
Priya noticed that her grandmother, who lacks teeth, struggles to digest raw vegetables but can comfortably eat boiled or mashed ones. Explain the significance of mechanical digestion in the oral cavity and how the absence of teeth affects the overall digestive process.
Answer:

Mechanical digestion in the oral cavity involves the physical breakdown of food by chewing (mastication) using teeth. Its significance includes:

  • Surface Area Increase: Chewing breaks food into smaller particles, allowing enzymes like salivary amylase to act efficiently.
  • Mixing with Saliva: Food is moistened and formed into a bolus for easy swallowing.

Since Priya's grandmother lacks teeth, mechanical digestion is incomplete. Raw vegetables, being fibrous, remain undigested, causing strain on the stomach and intestines. Boiled or mashed foods are pre-processed, compensating for the lack of chewing and easing digestion. This highlights the interdependence of mechanical and chemical digestion for efficient nutrient absorption.

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