Which growth phase is defined by rapid cell division and exponential population increase?

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

Answer: (A)

Rapid growth with an exponential increase in the population is the log phase. In this stage, cells are in a nutrient-rich, favorable environment and divide at a constant, maximal rate, leading to a doubling time and a steadily rising population. This contrasts with the lag phase, where cells are adapting and division is minimal; the stationary phase, where growth slows and births balance deaths due to limited nutrients and waste buildup; and the death phase, where conditions become so adverse that net cell numbers decline. Understanding this helps explain why the log phase is when cells are most metabolically active and often most susceptible to antibiotics.