Question

When a person puts food in his mouth, then teeth cut it into small pieces, chew and grind it. The glands A in the mouth secrete a substance B which is mixed with the food by tongue. The substance B contains an enzyme C which starts the digestion of food in the mouth. The slightly digested food from the mouth goes down a tube D. The special type of movements E in the walls of tube D push the food into stomach for further digestion. The stomach wall secretes gastric juice containing three substance F, G and H. One of the functions of F is to kill bacteria which may enter the stomach with food. The substance G protects the inside layer of stomach from the damaging effect of substance F whereas substance H is and enzyme for digestion. The partially digested food then enters into small intestine for further digestion.

1. What are (i) gland A, (ii) substance B, and (iii) enzyme C?
2. Name the tube D.
3. What is the movement E known as?
4. What are (i) F, (ii) G, and (iii) H?

Answer 1

(a)

1. Gland A: Salivary glands (located in the mouth).
2. Substance B: Saliva (the watery fluid secreted by the salivary glands).
3. Enzyme C: Salivary amylase (historically called ptyalin, which breaks down starch into sugar).

(b) Name of the Tube D is the oesophagus (commonly known as the food pipe).

(c) The movement E is a peristaltic movement (or Peristalsis). These are the rhythmic, wave-like contractions and relaxations of the muscles in the walls of the food pipe that push food down toward the stomach.

(d) 

1. Substance F: Hydrochloric acid ($\text{HCl}$). It creates an acidic medium for the gastric enzyme to work and kills harmful bacteria that enter with food.
2. Substance G: Mucus. It forms a protective barrier over the inner lining of the stomach, preventing the lining from being eroded or digested by the stomach's hydrochloric acid.
3. Substance H: Pepsin. This is the active protein-digesting enzyme that breaks down complex proteins into smaller peptides in an acidic environment.