Which graph best represents the general rate at which bacteria reproduce in a closed system over time?

• A. A sigmoidal (S-shaped) curve showing lag, exponential, stationary, and death phases
• B. A straight line indicating constant growth rate
• C. A flat line indicating no change in cell number
• D. A bell-shaped curve peaking at mid-time

Answer: (A)

Verified step by step guidance

1. Understand that bacterial growth in a closed system typically follows distinct phases: lag, exponential (log), stationary, and death phases.
2. Recognize that during the lag phase, bacteria adapt to the environment with little to no increase in cell number, so the graph starts off relatively flat.
3. In the exponential phase, bacteria reproduce rapidly, causing a steep upward slope in the graph representing exponential growth.
4. The stationary phase occurs when nutrient depletion and waste accumulation slow growth, balancing cell division and death, resulting in a plateau on the graph.
5. Finally, the death phase shows a decline in viable cell numbers due to unfavorable conditions, causing the graph to slope downward.