Final answer:
Once an herbivore swallows plant material, it travels to the rumen, a section of its stomach filled with bacteria that aid in the digestion of cellulose.
Step-by-step explanation:
Herbivores such as cows, koalas, buffalos, and horses have a digestive system that includes a section called the rumen. The rumen is filled with bacteria and protists that help break down cellulose, a complex carbohydrate found in plant material. These microorganisms secrete an enzyme called cellulase, which can break down the cellulose into glucose monomers that the animal can use as an energy source.