Acolony of termites was exposed to an atmosphere of 100 percent oxygen for three days. the insects were not immediately harmed by the treatment, but the protozoa that lived in the termites' guts were eliminated. the treated termites continued to behave normally and to eat wood, but they began to starve after a short time. when the treated termites were instead fed wood contaminated with the feces of untreated termites, the treated termites regain the ability to digest wood and no longer starved. the best analysis of the results of the experiment is that