During which growth phase is the cell division rate at its maximum?

• A. Lag phase
• B. Stationary phase
• C. Death phase
• D. Log (exponential) phase

Answer: (D)

In microbial growth, the stage where cells split and multiply most rapidly is the exponential, or log, phase. Here, nutrients are abundant and waste products haven’t yet built up to inhibitory levels, so the cellular machinery for DNA replication and binary fission operates at full capacity. The population increases in a true exponential fashion, with a constant generation time. In contrast, the lag phase involves little or no division as cells adapt; the stationary phase arises when nutrients run low and waste accumulates, slowing growth to a halt; and the death phase features more cell death than production. So the greatest division rate is seen during the exponential growth phase.