H the teeth are not cleaned regularly, they become covered with a sticky yellowish layer W of food particles and bacteria. Since layer W covers the teeth, the alkaline liquid X secreted by glands Y inside the mouth cannot reach the teeth surface to neutralise the acid formed by the action of organisms Z on sugary food, and hence tooth decay sets in.

(a) What is W known as?

(b) What is (i) X, and (ii) Y?

(c) What are organisms Z?

(d) State one way of removing layer W from the teeth.

Which of the following is the correct sequence of parts as they occur in the human alimentary canal ?

When a person eats sugary food, then organisms A present in his mouth act on sugar to produce a substance B. The substance B first dissolves the calcium salts from the top part C of the tooth and then from its middle part D forming holes E. These holes ultimately reach the part F in the lower part of tooth which contains nerves and blood vessels. The substance B irritates the nerve endings inside the tooth causing toothache.

(a) What are (i) organisms A, and (ii) substance B?

(b) What are (i) part C, and (ii) part D, of tooth known as?

(c) By what name are the holes E in the tooth known?

(d) Name the part F of the tooth.

(e) What will happen if organisms A reach part F of the tooth ?

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 an enzyme for digestion. The partially digested food then enters into small intestine for further digestion.

(a) What is (i) gland A

(ii) substance B, and (iii) enzyme C?

(b) Name the tube D.

(c) What is the movement E known as?

(d) What are (i) F (ii) G, and (iii) H?

The partially digested food coming from the stomach of a person enters a long and narrow organ A in his body. The organ A receives the secretions of two glands : liver and pancreas. Liver secretes a greenish yellow liquid B which is normally stored in the organ C. Pancreas secretes pancreatic juice which contains three digestive enzymes D, E and F. The intestinal juice completes the process of digestion of food. The inner wall of organ A has millions of tiny finger-like projections G which help in the rapid absorption of digested food into blood stream. The undigested part of food then passes into wider tube H which absorbs most of the water from undigested food. The last part of tube H called I stores this undigested food (or waste) for some time. The undigested food is then passed out though opening J as faeces in the process known as K.

(a) Name the organ A

(b) Name (t) liquid B, and (it) organ C.

(c) What are the digestive enzymes D, E and F?

(d) Name the projections G present on the inner wall of organ A.

(e) Name (i) tube H (ii) part I (iii) opening J, and (iv) process K.