Chapter 23, Problem 3RQ

To determine

If all carbohydrates are digestible by humans or not.

Answer to Problem 3RQ

All the carbohydrate are not digestible by human beings, one of them is cellulose. It is so because of the absence of cellulase enzyme in digestive system of humans.

Explanation of Solution

Carbohydrates which upon hydrolysis give a large number of monosaccharide molecules are considered as polysaccharides. The one of the polysaccharide is not digestible by human. The name of that polysaccharide is cellulose.

The molecular mass of cellulose varies from $\text{50000}$ to $\text{500000}$ suggesting thereby that cellulose may contain $\text{300}-3000$ glucose units. It is insoluble in water but dissolved in Schweitzer’s reagent that is ammoniacal solution of cupric hydroxide from which it can be precipitated by addition of acid or salts.

The human digestive system does not contain enzyme cellulase which can hydrolyse cellulose into glucose and hence cannot digest cellulose. However,the enzyme cellulaseenzyme is present in stomach of ruminant mammals that is grazing animals where they are produced by intestinal bacteria such as cows, buffalo, and many others.

Thus, the grazing animals can use cellulose of grass and plants as food by covering then into glucose.

Hence, all the carbohydrates are not digestible by human beings.

Conclusion:

The carbohydrate which is not digestible by human beings is cellulose. This is so because there is the absence of cellulase enzyme in digestive system of the humans.