In growth curves, which phase features a balance of cell division and cell death, leading to no net change in population size?

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

Answer: (C)

The main idea is the balance between how fast cells divide and how fast they die during growth. In the stationary phase, nutrients are running low and waste builds up, so the environment can’t support net growth. Here, the rate at which new cells are produced is about equal to the rate at which cells die, so the total population size stays roughly the same. This happens as cells slow their metabolism and switch to maintenance modes, with some cells even entering dormant states, allowing the culture to persist without increasing in number.

For contrast, during the lag phase cells adapt to their surroundings and divide slowly, so there isn’t yet a net gain in numbers; in the log (exponential) phase cells divide rapidly and outpace death, causing the population to rise quickly; and in the death phase death outpaces division, so the population declines.