How is generation time defined?

• A. The time required for a population to triple in numbers during the exponential phase
• B. The time required for a population to double in numbers during the exponential phase
• C. The time required for cells to become VBNC
• D. The time required for nutrient depletion to halt growth

Answer: (B)

Generation time is the time it takes for a microbial population to double in number during the exponential (log) phase. This doubling interval reflects a constant rate of cell division under steady, nutrient-rich conditions, and it can be described mathematically as the time needed for N to become twice N, so the population grows as N = N0 × 2^(t/g). If you use the natural-growth rate k, the doubling time equals ln(2) divided by k (about 0.693/k). This is different from a time to triple or from timescales associated with cells entering a non-growing state or growth stopping due to nutrient depletion, which are not the same as the generation time.