What is a common metabolic byproduct of anaerobic respiration in bacteria?

A common metabolic byproduct of anaerobic respiration in bacteria is lactic acid. In anaerobic conditions, when oxygen is not available, certain bacteria, such as Lactobacillus, utilize fermentation pathways to generate energy. During this process, glucose is partially oxidized, and in lieu of oxygen, lactic acid is produced as a result of pyruvate conversion. This metabolic pathway is particularly prevalent in muscle cells as well, where lactic acid accumulates during intense exercise when oxygen levels are low.

Oxygen is not produced in anaerobic respiration; in fact, the absence of oxygen is what characterizes anaerobic processes. Carbon dioxide is also produced during some fermentation processes, but lactic acid specifically refers to a process that yields lactate. Glucose, on the other hand, is the substrate used in these reactions rather than a byproduct. Therefore, lactic acid is the expected outcome of anaerobic respiration in the context of certain bacteria, making it the correct answer.