Name the phases of the bacterial growth curve.

• A. Lag, log (exponential), stationary, and death (decline) phases
• B. Lag, exponential, stationary, decline phases
• C. Phase I, II, III, IV
• D. Initiation, Acceleration, Plateau, Decline

Answer: (A)

Bacterial growth curves progress through four distinct phases as a culture responds to available nutrients and accumulating waste. The first phase is the lag period, when cells adapt to their environment and there is little increase in cell number, though metabolic activity is high. Next comes the log, or exponential, phase, where cells divide at a constant, rapid rate and population size grows exponentially. After nutrients thin and waste builds up, growth levels off in the stationary phase, where the rate of cell division roughly equals the rate of cell death, so the total population remains steady. Finally, in the death, or decline, phase, more cells die than are produced, and the culture population decreases. This sequence—lag, log (exponential), stationary, and death (decline)—is the standard description of the bacterial growth curve. Other option phrasings use nonstandard names or omit the explicit death phase, so they don’t match the typical four-phase progression.