For life to continue, the body requires fuel in the form of oxygen and food. Respiration provides the oxygen. Our food, however, cannot be utilized by the body in the form in which it is eaten. It must be specially processed by the body before it can be of any use. This special processing is known as digestion. It is brought about by the action on the food of certain substances called enzymes which are made by the body and mixed with the food during its passage through the body.
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