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It is the 1st chapter from Class 10 Biology. It is about human digestive system from new book.

Solved Exercise

A. Select the correct answers for the following questions (Class 10 Biology).

1. The three portions of the small intestine, in the correct order, are;

 a) Duodenum, jejunum, ileum (Correct)

 b) Ileum, duodenum, jejunum

 c) Colon, caecum, rectum

 d) Caecum, colon, rectum

2. The wavelike movement of muscles that pushes food through the digestive system is called;

 a) Chemical digestion

 b) Mechanical digestion

 c) Peristalsis (Correct)

 d) Absorption

3. The part of the digestive system where no chemical digestion takes place is;

 a) Oral cavity

 b) Oesophagus (Correct)

 c) Stomach

 d) Duodenum

4. Which group of enzymes breaks up starches?

 a) Proteases

 b) Lipases

 c) Amylases (Correct)

 d) Pepsin

5. The pancreas produces digestive enzymes and releases them into;

 a) Colon

 b) Gall bladder

 c) Liver

 d) Duodenum (Correct)

6. In stomach, pepsinogen is converted into pepsin by the action of;

 a) Bile salts

 b) Hormones

 c) HCl (Correct)

 d) Bicarbonate

7. In which part are the carbohydrates, lipids and proteins digested?

 a) Oral cavity

 b) Stomach

 c) Small intestine (Correct)

 d) Large intestine

8. The enzyme trypsin is found in;

 a) Pancreatic juice (Correct)

 b) Bile

 c) Gastric juice

 d) Saliva

9. The common bile duct carries bile from gall bladder to;

 a) Stomach

 b) Duodenum (Correct)

 c) Colon

 d) Pancreas

10. Why does the small intestine have many folds and contain villi and microvilli?

 a) To slow down the passage of food.

 b) To promote food absorption (Correct)

 c) To prevent the backflow of chyme.

 d) To produce enzymes.

B. Write short answers to the following questions (Class 10 Biology).

1. State the role of salivary glands in digestion.

Salivary glands secrete saliva into the oral cavity, which helps in digestion in two main ways:

• Chemical Digestion: Saliva contains the enzyme salivary amylase, which breaks down complex starches into simpler sugars like maltose.
• Mechanical Assistance: It moistens and lubricates the food, turning it into a soft mass called a bolus so that it can be easily swallowed.

2. What do the terms swallowing and peristalsis mean?

• Swallowing: The process of moving food (bolus) from the oral cavity, past the pharynx, and down into the esophagus. It starts as a voluntary action but continues involuntarily.
• Peristalsis: The rhythmic, wave-like contractions and relaxations of the smooth muscles in the walls of the digestive tract. This continuous movement pushes food forward through the alimentary canal.

3. What are the functions of HCl in gastric juice?

Hydrochloric acid (HCl) secreted by the stomach lining serves three major functions:

• Activation of Enzymes: It creates a highly acidic medium (pH 1.5–2.5) required to convert inactive pepsinogen into the active protein-digesting enzyme, pepsin.
• Antiseptic Action: It kills harmful bacteria and other pathogens that enter the stomach along with food.
• Softening Food: It helps dissolve and soften tough food particles, preparing them for further chemical breakdown.

4. State the role of pancreatic juice in digestion of food.

Pancreatic juice is released by the pancreas into the duodenum (small intestine). It contains sodium bicarbonate to neutralize acidic chyme from the stomach, alongside three essential enzymes:

• Pancreatic Amylase: Digests remaining carbohydrates and starches into simpler sugars.
• Trypsin: Breaks down proteins and polypeptides into smaller peptides.
• Lipase: Converts fats (lipids) into fatty acids and glycerol after they have been emulsified by bile.

5. Write a brief note on the structure of villi.

Villi (singular: villus) are tiny, finger-like projections that line the inner wall of the small intestine. Their structural features include:

• Surface Area: They massively increase the inner surface area of the small intestine to maximize nutrient absorption.
• Epithelial Layer: Each villus is covered by a single layer of epithelial cells (bearing microscopic microvilli) to allow rapid diffusion of digested food.
• Internal Network: Inside each villus lies a dense network of blood capillaries (which absorb glucose and amino acids) and a central lymphatic vessel called a lacteal (which absorbs fatty acids and glycerol).

6. What are the causes and symptoms of ulcers?

A peptic ulcer is a sore or wound that develops on the protective inner lining of the stomach or duodenum.

C. Write answers in detail.

1. Describe the absorption of food in the small intestine.
2. Explain the role of the oral cavity in the digestive system.
3. Explain the structure and functions of the stomach.
4. Justify the importance of liver and pancreas in digestion.

D. Inquisitive Questions

1. Why does someone with liver disease have difficulty in digesting fats?

The liver produces bile, which contains bile salts responsible for the emulsification of large fat droplets into tiny droplets. Emulsification increases the surface area for the enzyme lipase to break down fats effectively. In liver disease, bile production decreases, leading to poor emulsification and difficulty in fat digestion.

2. Why is it important to maintain a healthy balance of gut bacteria?

A healthy balance of gut bacteria is critical because they assist in synthesizing essential vitamins (like Vitamin K and certain B vitamins), break down indigestible dietary fibers, protect the intestinal lining against harmful pathogenic bacteria, and strengthen the body’s immune system response.

3. How can a malfunction in the cardiac sphincter lead to acid reflux?

The cardiac sphincter acts as a one-way valve at the junction between the esophagus and the stomach. If it malfunctions or weakens, it fails to close completely. This allows the highly acidic stomach contents (chyme mixed with HCl) to flow backward (reflux) into the esophagus, irritating its sensitive lining and causing heartburn.

4. Why is it necessary to store bile in the gallbladder before it is released?

The liver produces bile continuously, but food is only present in the digestive tract periodically. The gallbladder stores bile when digestion is not happening and concentrates it by absorbing water. When fatty food enters the duodenum, the gallbladder contracts to release a highly potent, concentrated dose of bile to immediately assist in fat digestion.