Question

Why is it impossible for humans to digest food that contains cellulose?

Short answer

Humans cannot digest the food that contains cellulose as they lack the enzymes which can digest cellulose.

Step-by-step solution

Cellulose

Cellulose is a polysaccharide that is made up of many glucose units. The glucose units in cellulose are linked together by the beta 1, 4 glycosidic linkages.

Digestive enzymes 

In humans, the digestive enzymes can break the alpha 1, 4, and alpha 1, 6 glycosidic linkages but are unable to break the beta 1, 4 glycosidic linkages and hence is unable to digest the food containing cellulose.