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Name: Mahla
Status: other
Grade: other
Location: N/A
Country: N/A
Date: September 2008

Why herbivore can digest cellulose but humans cannot?

Cellulose is a long molecule called a polymer, which, like DNA, consists of subunits connected together by covalent bonds. In the case of cellulose the subunits are the simple sugar glucose and they are connected by a very specific bond, called a "beta-1,4-glycosidic bond". This bond makes the molecule stiff and able to pack together to create structure in the cell walls of plants.

Humans lack enzymes to break this kind of chemical bond and therefore cannot digest cellulose. Cows, and other ruminants like deer, camels, and water buffalo, have microorganisms in their guts which express enzymes capable of breaking down cellulose. These animals go through cycles of chewing, swallowing, and regurgitating, in order to reduce the particle size of the plant matter so that it can be digested and broken down with the aid of microorganisms in a process known as "ruminating".

Ethan Greenblatt
Ph.D. Candidate
Stanford Biophysics


Herbivores and people both have digestive systems. These systems produce chemicals that digest the food that is eaten. The digestive systems of herbivores, such as cows and sheep, include enzymes (digestive chemicals) that break down cellulose (a large chemical) into its building block chemicals. The human digestive system does not include the chemical factories that produce the cellulose-digesting enzymes.

Warren Young

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