The food of ruminants like grass is rich in cellulose (a type of carbohydrate). Ruminants have a large sac-like structure between the small intestine and large intestine. The cellulose of the food is digested here by the action of certain bacteria which are not present in humans. In this way ruminants can digest the cellulose but many animals including human can not digest cellulose. 

When the ingest food in our mouth, salivary glands of the mouth secrete saliva which moistens the food. It also converts the starch into sugar. The tongue helps in chewing by moving the food in various directions. Saliva contains enzyme called salivary amylase which converts starch into sugar.

From mouth, food goes into food pipe called oesophagus. As food enters into the food pipe, muscles of its wall starts contraction and relaxation movement. This movement is called peristaltic movement that pushes the food into the stomach. The peristaltic movement occurs throughout the alimentary canal. The oesophagus leads the food to a saclike structure called stomach. The food is churned and partly digested in the stomach. The semi-solid food passes from the stomach to much coiled tube-like structure called the small intestine. The small intestine serves two purposes-digestion and absorption of the digested food. It is about 20 feet long. The inner surface of the small intestine has a large number of finger-like projections called villi. The villi increase the surface area for the absorption of digested food. The absorbed food enters into the blood stream and carried away to various parts of the body for assimilation. The undigested food moves from the small intestine to the large intestine where mainly absorption of water from the undigestion takes place. From the large intestine, the undigested food passes to the rectum which pushes it out of the body through the opening called the anus as faeces.

Oral rehydration solution is the solution of sugar and salt in a particular ratio in the clean water. When a person passes out watery stools frequently, the disease is called diarrhoea. In this condition there is a loss of water and salt from the body of a person.
This is called dehydration which may be fatal if not cured at proper time. In order to prevent dehydration, the person or patient should be given ORS. ORS makes up the loss of water and salts in the body and sugar provides energy which helps in the recovery of disease. It should be given to a patient suffering from diarrhoea at a regular interval.
At home the ORS can be prepared by dissolving a teaspoonful of sugar and pinch of salt in a glass of clean water. The water used for preparing ORS should be first boiled and then cooled so that all the microorganisms or harmful bacteria may be killed.

(a) Diarrhoea.
(b) Oral Rehydration Solution (ORS). It is given to a person suffering from diarrhoea to prevent the dehydration.
(c) She is sincere, curious and has interest in science.

(i) The problem is of tooth decay which causes toothache.
(ii) One should clean the teeth with a toothbrush twice a day. Chocolates should be avoided.
(iii) She is aware and concerned about the problems arising in the teeth especially of younger children.