MCAT® ExamBiological and Biochemical Foundations of Living SystemsEasy
A microbiologist is culturing a bacterial strain in a nutrient-rich medium. To measure the growth rate, they perform serial dilutions and plate counts, observing the number of viable cells over time. During which phase of the bacterial growth curve would the microbiologist observe the highest rate of cell division?
- ALag phase
- BLog (exponential) phase
- CStationary phase
- DDeath phase
Show answer & explanationAnswer & explanation
Correct answer: B. Log (exponential) phase
The log (exponential) phase is characterized by a rapid and consistent rate of cell division, where the bacterial population doubles at regular intervals, assuming optimal conditions and nutrient availability.
Why the other options are wrong
- A. In the lag phase, cells are metabolically active but not dividing rapidly as they adapt to the new environment.
- C. In the stationary phase, the rate of cell division equals the rate of cell death due to nutrient depletion or waste accumulation.
- D. In the death phase, the rate of cell death exceeds the rate of cell division, leading to a decline in viable cells.
Bacterial Growth Curve
The bacterial growth curve describes the four distinct phases of growth that a bacterial population experiences in a closed system: lag, log, stationary, and death phases.
- Lag phase: adaptation, little to no division.
- Log phase: exponential growth, maximum division rate.
- Stationary phase: growth rate equals death rate.
- Death phase: more cells die than divide.
Memory trick: Bacteria 'LAUGH' (Lag), 'LIVE' (Log), 'STOP' (Stationary), 'DIE' (Death).