Growth curve phases — During the accelerated phase (early exponential transition), what happens to cell number and division rate?

Introduction:
The accelerated phase bridges lag and exponential growth. It reflects cellular adaptation to the medium, where metabolic machinery ramps up and division frequency climbs toward its exponential-phase maximum.

Given Data / Assumptions:

• Batch culture after inoculation into fresh medium.
• Cells are viable and adapting to nutrients and conditions.
• No major inhibitory by-products initially.

Concept / Approach:
As cells complete adaptation (enzyme induction, cofactor pools, ribosome content), their specific growth rate mu increases from near zero (lag) toward mu_max in early exponential, so both cell count and division rate rise until a steady exponential rate is reached.

Step-by-Step Solution:
1) Immediately after inoculation, cells invest in adaptation rather than division (lag).2) As adaptation completes, mu increases (accelerated phase).3) Cell number increases; division rate approaches a maximum characteristic of exponential phase.

Verification / Alternative check:
Time-lapse data of OD or viable counts show curvature upward before a linear log-phase segment, consistent with increasing mu during acceleration.

Why Other Options Are Wrong:

• (b) Decrease in cell number is inconsistent with growth onset.
• (c) Division rate does not decrease in acceleration; it increases.
• (d) A “minimum” contradicts the definition of acceleration.
• (e) Constant cell number indicates lag, not acceleration.

Common Pitfalls:
Confusing accelerated phase with diauxic shifts; misreading semilog plots as linear plots and misjudging curvature.

Final Answer:
Cell number increases and the division rate increases to reach a maximum.