Which of the following describes bacteria that reproduce most rapidly during growth?

• A. Dormant phase
• B. Active growth phase
• C. Death phase
• D. Lag phase

Answer: (B)

Bacteria reproduce most rapidly when nutrients are plentiful and conditions are favorable, which is the exponential (log) growth phase, also known as the active growth phase. In this stage, cells divide quickly and the population grows at a constant, rapid rate, often doubling in a short period. The other phases describe slower or negative growth: during the lag phase, cells are adapting to their environment and dividing slowly; in the stationary phase, resources become limited and growth levels off; and in the death phase, more cells die than are produced. This is why the active growth phase best describes the period of the fastest bacterial reproduction.