Chapter 16: Digestion and Absorption – Long Answer Type Questions
CBSE Class 11 Biology Chapter 16 – Digestion and Absorption | Long Answer Type Questions (NCERT)
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)
Question Type: Long Answer Type Questions
Answer Length: 120–150 words
Syllabus: Strictly as per NCERT Biology Textbook
Section A: Human Digestive System (Q1–Q9)
Q1. Describe the human digestive system and its major functions.
Answer:
The human digestive system consists of the alimentary canal and associated digestive glands. The alimentary canal extends from the mouth to the anus and includes the mouth, pharynx, oesophagus, stomach, small intestine, and large intestine. Digestive glands include salivary glands, liver, and pancreas. The system performs several vital functions such as ingestion of food, mechanical and chemical digestion, absorption of nutrients, assimilation of absorbed substances, and egestion of undigested waste. Mechanical digestion breaks food into smaller particles, while chemical digestion converts complex molecules into simple absorbable forms. Absorbed nutrients are utilized by body cells for energy, growth, and repair, making digestion essential for survival.
Q2. Explain the role of the buccal cavity in digestion.
Answer:
The buccal cavity plays an important role in both mechanical and chemical digestion. Mechanical digestion occurs through mastication, where teeth break food into smaller pieces, increasing surface area for enzyme action. The tongue helps in mixing food with saliva and aids swallowing. Chemical digestion begins here with the action of saliva secreted by salivary glands. Saliva contains salivary amylase, which converts starch into maltose. Mucus present in saliva lubricates food, facilitating smooth swallowing. The slightly alkaline nature of saliva provides an ideal medium for enzyme activity. Thus, the buccal cavity initiates digestion and prepares food for further processing.
Q3. Describe the structure and functions of the stomach.
Answer:
The stomach is a J-shaped muscular organ located below the diaphragm. It is divided into cardiac, fundic, and pyloric regions. The stomach temporarily stores food and churns it mechanically to mix with gastric juice. Gastric glands secrete hydrochloric acid, pepsinogen, mucus, and rennin in infants. Hydrochloric acid creates an acidic environment, activates pepsinogen into pepsin, and kills microbes. Pepsin begins protein digestion by converting proteins into proteoses and peptones. Mucus protects the stomach lining from acid and enzymes. The stomach converts food into a semi-fluid mixture called chyme for further digestion.
Q4. Explain the role of hydrochloric acid in the stomach.
Answer:
Hydrochloric acid plays a crucial role in digestion within the stomach. It creates a highly acidic environment necessary for activating the inactive enzyme pepsinogen into pepsin. This acidic medium also helps denature proteins, making them easier for enzymes to digest. Additionally, hydrochloric acid kills harmful microorganisms present in food, preventing infections. It maintains the optimal pH for gastric enzyme activity and supports effective protein digestion. Without hydrochloric acid, protein digestion would be inefficient, and the stomach lining would be more susceptible to microbial growth.
Q5. Describe the structure and functions of the small intestine.
Answer:
The small intestine is the longest part of the alimentary canal and consists of three parts: duodenum, jejunum, and ileum. The duodenum receives bile and pancreatic juice for digestion. The jejunum and ileum are primarily involved in digestion and absorption. The inner lining has finger-like projections called villi and microvilli that greatly increase surface area. Most digestion and absorption of nutrients occur here. The small intestine provides an alkaline medium essential for enzyme activity. Absorbed nutrients are transported through blood capillaries and lymph vessels to different body parts.
Q6. Explain the functions of the large intestine.
Answer:
The large intestine consists of caecum, colon, and rectum. Its main function is absorption of water and electrolytes from undigested food. This helps in maintaining water balance in the body. Beneficial bacteria present in the colon synthesize certain vitamins like vitamin K. The large intestine also compacts undigested material into faeces. The rectum temporarily stores faeces until defecation. Thus, the large intestine plays an important role in waste formation and elimination.
Q7. Describe the role of the liver in digestion.
Answer:
The liver is the largest gland in the human body and plays a vital role in digestion by producing bile. Bile contains bile salts that help in emulsification of fats, breaking large fat globules into smaller droplets for efficient lipase action. Bile also neutralizes acidic chyme from the stomach, providing an alkaline medium for intestinal enzymes. Although bile contains no digestive enzymes, it is essential for fat digestion and absorption. The liver also stores glycogen, detoxifies harmful substances, and metabolizes nutrients.
Q8. Explain the digestive role of the pancreas.
Answer:
The pancreas is a mixed gland with both exocrine and endocrine functions. Its exocrine part secretes pancreatic juice into the duodenum. Pancreatic juice contains enzymes such as amylase, trypsinogen, chymotrypsinogen, lipase, and nucleases. These enzymes digest carbohydrates, proteins, fats, and nucleic acids. Pancreatic juice is alkaline, which neutralizes acidic chyme and provides an ideal environment for enzyme activity. Thus, the pancreas plays a key role in completing digestion in the small intestine.
Q9. What is peristalsis and why is it important?
Answer:
Peristalsis is the rhythmic contraction and relaxation of circular and longitudinal muscles of the alimentary canal. It helps propel food forward through different parts of the digestive system. Peristalsis occurs in the oesophagus, stomach, small intestine, and large intestine. It ensures movement of food irrespective of body posture. In addition to movement, peristalsis helps mix food with digestive juices, facilitating efficient digestion and absorption. Without peristalsis, food would not move smoothly through the alimentary canal.
Section B: Digestive Enzymes (Q10–Q17)
Q10. Describe digestion of carbohydrates in humans.
Answer:
Carbohydrate digestion begins in the mouth with the action of salivary amylase, which converts starch into maltose. In the stomach, carbohydrate digestion temporarily stops due to acidic conditions. In the small intestine, pancreatic amylase continues digestion of starch into disaccharides. Intestinal enzymes such as maltase, sucrase, and lactase then convert disaccharides into monosaccharides like glucose, fructose, and galactose. These monosaccharides are the final products of carbohydrate digestion and are readily absorbed through the intestinal lining into the bloodstream.
Q11. Explain digestion of proteins in humans.
Answer:
Protein digestion begins in the stomach. Pepsinogen secreted by gastric glands is activated into pepsin by hydrochloric acid. Pepsin converts proteins into proteoses and peptones. In the small intestine, pancreatic enzymes such as trypsin and chymotrypsin further break proteins into smaller peptides. Intestinal peptidases finally convert peptides into amino acids. These amino acids are absorbed into blood capillaries and transported to body cells for protein synthesis, growth, and repair.
Q12. Describe digestion of fats in humans.
Answer:
Fat digestion occurs mainly in the small intestine. Bile salts secreted by the liver emulsify fats into small droplets, increasing surface area for enzyme action. Pancreatic lipase then digests emulsified fats into fatty acids and glycerol. Fat digestion requires an alkaline medium, which is provided by bile and pancreatic juice. The final products are absorbed through the intestinal lining and transported via lymph as chylomicrons.
Q13. Explain digestion of nucleic acids.
Answer:
Nucleic acids are digested in the small intestine by pancreatic nucleases. These enzymes break nucleic acids into nucleotides. Intestinal enzymes further digest nucleotides into nitrogenous bases, sugars, and phosphates. These simpler components are absorbed into the bloodstream and used by the body for synthesis of nucleic acids and other metabolic processes.
Q14. Why is bile important in fat digestion though it has no enzymes?
Answer:
Bile plays a crucial role in fat digestion despite lacking digestive enzymes. Bile salts emulsify large fat globules into smaller droplets, increasing surface area for pancreatic lipase action. Bile also neutralizes acidic chyme, creating an alkaline environment required for lipase activity. Without bile, fat digestion and absorption would be inefficient.
Q15. Explain the role of intestinal juice in digestion.
Answer:
Intestinal juice contains enzymes such as maltase, sucrase, lactase, peptidases, and lipase. These enzymes complete digestion of carbohydrates, proteins, and fats into their absorbable forms. Intestinal juice ensures final digestion at the brush border of intestinal cells, enabling efficient absorption of nutrients.
Q16. Why is trypsinogen activated only in the intestine?
Answer:
Trypsinogen is activated into trypsin by enterokinase present in the intestinal mucosa. This prevents self-digestion of pancreatic tissue. Activated trypsin further activates other proteolytic enzymes, ensuring efficient protein digestion in the intestine.
Q17. Explain lactose intolerance.
Answer:
Lactose intolerance is a condition caused by deficiency of the enzyme lactase. Without lactase, lactose cannot be digested into glucose and galactose. Undigested lactose leads to bloating, diarrhoea, and abdominal discomfort after consuming dairy products.
Section C: Absorption Process (Q18–Q25)
Q18. Define absorption and explain its significance.
Answer:
Absorption is the process by which digested nutrients pass through the intestinal mucosa into blood or lymph. It is significant because only absorbed nutrients can be transported to body cells for energy, growth, repair, and maintenance of physiological functions.
Q19. Describe the structural adaptations of the small intestine for absorption.
Answer:
The small intestine has villi and microvilli that greatly increase surface area. Each villus contains blood capillaries and a lacteal for nutrient transport. Thin epithelial lining allows rapid absorption.
Q20. Explain absorption of carbohydrates and proteins.
Answer:
Carbohydrates are absorbed as monosaccharides by active transport or facilitated diffusion. Proteins are absorbed as amino acids through active transport into blood capillaries.
Q21. Describe absorption of fats.
Answer:
Fatty acids and glycerol form micelles, enter intestinal cells, re-form fats, and are transported as chylomicrons through lymph.
Q22. Explain absorption of vitamins and minerals.
Answer:
Water-soluble vitamins are absorbed into blood, while fat-soluble vitamins are absorbed with fats. Minerals are absorbed by diffusion or active transport.
Q23. What is assimilation?
Answer:
Assimilation is the utilization of absorbed nutrients by body cells for energy, growth, repair, and maintenance.
Q24. Explain defecation.
Answer:
Defecation is the elimination of faeces through the anus. It is controlled by neural reflexes and voluntary muscles.
Q25. Explain diarrhoea and its effects.
Answer:
Diarrhoea is frequent passage of watery stools due to infection or increased motility. It causes loss of water and electrolytes, leading to dehydration.