Water Treatment Class 3-A Practice Test

The main idea here is that microorganisms obtain energy by using organic matter as their food source and oxidizing it. In water treatment and environmental microbiology, this is described as biodegradation through oxidation, which often occurs via aerobic respiration—bacteria break down the organic material, and the energy released from that oxidation fuels their growth and activity. The statement that organic matter serves as food for bacteria and energy results from its oxidation captures exactly this process. Therefore, it is the best choice because it directly describes the biological oxidation of organics as the energy-producing mechanism for microbes.

The other options describe non-biological or unrelated processes: settling of solids is a physical separation step, formation of leaves is a plant process, and evaporation of water is a phase change. None of those involve microorganisms using organic matter for energy through oxidation.