Which growth phase is considered the exponential phase?

• A. Lag
• B. Log
• C. Stationary
• D. Death

Answer: (B)

During bacterial growth, the exponential (log) phase is the period when cells divide at a constant rate, so the population increases rapidly and doubles at regular intervals. This balanced, continuous division causes an exponential rise in cell numbers, which is why plotting population on a log scale yields a straight line. The other phases describe different dynamics: the lag phase is adaptation with little growth, the stationary phase has no net growth due to nutrient depletion or waste buildup, and the death phase is when cells die faster than they’re produced. So the phase characterized by constant-rate, rapid division is the log (exponential) phase.