1. Choose the correct option.
a. The type of nutrition in which animals consume the solid or liquid food which is later broken down by the body is called ______.
i. parasitic nutrition
ii. symbiotic nutrition
iii. saprotrophic nutrition
iv. holozoic nutrition
Answer: iv. holozoic nutrition
b. Organism X is a parasite. It obtains its nutrition from inside the body of the host. Identify organism X.
i. Tick
ii. Louse
iii. Leech
iv. Mite
Answer: ii. Louse
c. Which part of the human teeth that is richly supplied with blood vessels and nerves?
i. Dentine
ii. Crown
iii. Pulp
iv. Root
Answer: iii. Pulp
d. Which part of the stomach stores cud in ruminants?
i. Rumen
ii. Reticulum
iii. Omasum
iv. Abomasum
Answer: i. Rumen
2. Assertion-Reasoning questions.
(i) Assertion (A): Gastric juices secreted by the stomach contain hydrochloric acid.
Reason (R): Hydrochloric acid provides the acidic environment necessary for digestion of food.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Explanation: The Assertion is correct as HCl is a key component of gastric juice. The Reason is also correct and explains why HCl is present—to create an acidic medium for the enzyme pepsin to work.
(ii) Assertion (A): Our mouth has the salivary glands which secrete saliva.
Reason (R): The saliva has no action on the food we eat.
(c) Assertion (A) is true, but Reason (R) is false.
Explanation: The Assertion is true as salivary glands do secrete saliva. However, the Reason is false because saliva contains the enzyme salivary amylase, which begins the chemical digestion of starch.
(iii) Assertion (A): Bacteria present in our mouth act on the food particles present in the gaps between our teeth and form plaque.
Reason (R): Plaque converts sugar and starch in the food items into acids.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Explanation: Both statements are factually correct. The Reason correctly explains how the bacteria in plaque contribute to tooth decay by producing acids.
3. Answer the following questions in one sentence.
a. What is chemical digestion?
Answer. Chemical digestion is the process where complex food molecules are broken down into simpler, soluble substances with the help of enzymes and digestive juices.
b. State the function of the epiglottis.
Answer. The epiglottis acts as a flap that closes the windpipe (trachea) during swallowing to prevent food from entering it.
c. In which part of the alimentary canal does absorption of water take place?
Answer. The absorption of water takes place primarily in the large intestine.
4. Answer the following questions in 2-3 sentences.
a. Name the organ that secretes bile and the one that stores it. State the function of bile.
Answer. Bile is secreted by the liver and stored in the gall bladder. Its main function is to emulsify fats, which means it breaks down large fat globules into smaller ones, providing a larger surface area for enzymes to act upon.
b. What is mastication? How does it help in the process of digestion?
Answer. Mastication is the process of chewing food in the mouth using the teeth. It helps in digestion by physically breaking down large food pieces into smaller ones, which increases the surface area for digestive enzymes to act upon more effectively.
5. Answer the following questions in 3-4 sentences.
a. How is digestion in human beings different from that in grass-eating animals?
Answer. Digestion in humans is different mainly because grass-eating animals (ruminants) have a specialized stomach with four chambers—rumen, reticulum, omasum, and abomasum. They can digest cellulose, a component of grass, with the help of bacteria present in the rumen. They also regurgitate their food (cud) to chew it again. In contrast, humans have a single-chambered stomach and cannot digest cellulose.
b. What do the gastric juices secreted by the stomach contain? State their role in the chemical digestion of food.
Answer. The gastric juices secreted by the stomach contain hydrochloric acid, the enzyme pepsin, and mucus.
- Hydrochloric acid kills harmful bacteria and creates an acidic medium for pepsin to work.
- Pepsin breaks down complex proteins into simpler peptides.
- Mucus protects the inner lining of the stomach from being digested by its own juices.