In extended aeration, maintaining a very low F/M ratio keeps microbes near starvation. What term describes this metabolic state?

• A. Deficient respiration
• B. Endogenous
• C. Anoxic
• D. Dynamic equilibrium

Answer: (B)

When there isn’t enough substrate to support growth, microbes switch to using their own internal energy stores to meet maintenance needs. In extended aeration with a very low F/M ratio, the cells keep respiring, but they don’t proliferate; they rely on stored materials to survive. This metabolic state is endogenous respiration, where energy comes from inside the cells rather than from external substrate. The other terms don’t describe this situation: anoxic refers to a lack of oxygen, dynamic equilibrium implies a balance between growth and decay, and deficient respiration isn’t the standard term used here.