Role of mouth in digestion of food:
 (a) Ingestion of food happens through mouth.
(b) Mastication of food breaks the food into smaller particles.
(c) Saliva makes the food slippery so that it becomes easy to swallow the food.
(d) Salivary amylase converts starch into sugar

Gastric glands secrete hydrochloric acid, pepsin and mucus. They have following functions:
(a) Hydrochloric acid kills any germ which may be present in food. It makes the environment in the stomach acidic; which is essential for functioning of gastric enzyme.
 (b) Pepsin digests protein.
(c) Mucus prevents the inner lining of stomach from getting damaged by hydrochloric acid. 

Column (A)	Column (B)
(a) Trypsin	(i) Pancreas
(b) Amylase	(ii) Liver
(c) Bile	(iii) Gastric glands
(d) Pepsin	(iv) Saliva

Ans. (a)- i (b)- iv (c)- ii (d)- iii

(a) Trypsin
 Ans. Protein
(b) Amylase
 Ans. Starch
(c) Pepsin
 Ans. Protein
(d) Lipase
 Ans. Fat 

Blood flow through vein does not exert pressure on the walls of veins. Due to this, they do not need thick walls. Hence, veins have thin walls as compared to arteries.

Platelets play an important role in clotting of blood. Clotting of blood is defense mechanism. It prevents excess loss of blood in case of injury. Lack of platelet will not allow the blood to clot. This will result in excess loss of blood in case of injury. This may prove fatal for the person.

Plants remain fixed at a place because they do not need to move in search of food. As a result, plants do not need to have locomotion, the way animals do. Moreover, most of the movements of substances in plants happen through passive transport; which does not need energy. Due to this, the energy requirement in plants is low as compared to animals.

Root hairs have thin walls. Due to this, water enters the root hairs because of osmosis. Water from root hairs continuously moves into the root xylem. To maintain the osmotic gradients, the cells of root hairs take up ions from the soil.