Final answer:
An anaerobic organism benefits from a symbiotic relationship with an aerobic organism by exploiting low-oxygen environments and utilizing the metabolic byproducts as nutrients, a situation similar to the evolutionary origin of mitochondria in eukaryotic cells.
Step-by-step explanation:
What would be the advantage for an anaerobic organism to be in symbiosis with an aerobic organism? The primary advantage is that an anaerobic organism can exploit environments with low oxygen availability by relying on an aerobic partner to consume oxygen, creating beneficial anaerobic conditions. For instance, this is seen within biofilms where aerobic microorganisms create anaerobic regions. This symbiotic arrangement allows anaerobic organisms to thrive in otherwise inhospitable environments. Moreover, the aerobic respiration of the partner organism can provide metabolic byproducts that can serve as nutrients for the anaerobic organism. This relationship mimics the endosymbiotic events that gave rise to eukaryotic cells with organelles like mitochondria, derived from aerobic bacteria, which became beneficial to the host cell in a similar, mutually advantageous arrangement.