First, a quick review of respiration vs. fermentation (from the Bacteriology 102 lab manual): In our introductory laboratory courses, we deal mostly with chemotrophic bacteria – primarily the chemoheterotrophs. Depending on the abilities of any specific chemotrophic organism and the environment in which it is found, the catabolic pathway is involved with either oxidative or substrate-level phosphorylation. If the former, the organism is obtaining energy by respiration; if the latter, the process is fermentation. Relative comparisons are made between respiration and fermentation in the following outline. (The three kinds of "phosphorylation" are diagrammed under respiration, fermentation and phototrophy on the catabolism page.