Advanced Placement (AP) Biology Practice Exam

Which type of organism has evolved mechanisms to digest cellulose?

1. Carnivores

2. Herbivores

3. Omnivores

4. Detritivores

The correct answer is: Herbivores

Herbivores are organisms that primarily eat plants, and as a result, they have developed specialized adaptations to effectively digest cellulose, a complex carbohydrate found in plant cell walls. The digestion of cellulose is challenging due to its rigid structure, but many herbivores possess unique anatomical and physiological traits that facilitate this process. For instance, ruminants, such as cows and sheep, have a specialized four-chambered stomach that allows them to ferment and break down cellulose with the help of symbiotic microorganisms, such as bacteria and protozoa. These microorganisms produce enzymes that can digest cellulose, helping the herbivore extract nutrients from plant materials that would otherwise be indigestible. This mutualistic relationship enhances the herbivore's ability to utilize plant matter efficiently. In contrast, carnivores primarily consume animal tissues and do not typically need to digest cellulose, as their diet does not include plants. Omnivores eat both plant and animal matter but may not have specific adaptations for cellulose digestion since their dietary habits vary. Detritivores consume decomposing organic material, which can include some plant matter, but their primary role in the ecosystem is related to nutrient recycling rather than the specialized digestion of cellulose. Therefore, the ability of herbivores to digest