Final answer:
Symbiosis plays a critical role in cellulose digestion in herbivores and certain insects by providing them with microorganisms that produce cellulase, an enzyme necessary to break down cellulose into absorbable glucose.
Step-by-step explanation:
Cellulose digestion in animals relies extensively on the symbiotic relationship between herbivorous animals and the microorganisms that reside in their digestive systems. Due to the rigidity and high tensile strength of cellulose, humans and other non-herbivores cannot digest it as it requires special enzymes to break down the ß 1-4 glycosidic linkages. These microorganisms, such as bacteria and protists, produce the enzyme cellulase that breaks down cellulose into glucose monomers that can be used as an energy source by the animal. Termites also have cellulase-secreting microorganisms in their bodies, allowing them to break down cellulose for energy.
Herbivores like cows, koalas, and buffalos, however, harbor specialized flora within their rumen, or a part of their digestive system, hosting bacteria and protists which secrete cellulase. This enzyme efficiently splits cellulose into glucose monomers, which can then be absorbed and used as an energy source by the animal. Insects such as termites also benefit from similar symbiotic relationships that allow them to consume and derive nutrition from cellulose-rich diets, like wood.