Microbial Growth: Conditions, Curve & Control
Learning targets
- Describe lag, exponential, stationary and death phases of a microbial growth curve.
- Explain how temperature, pH, nutrients and oxygen affect growth.
- Interpret growth data and connect aseptic technique to reliable microbiology.
1 · Four phases
Lag
Cells adapt; enzyme systems become active.
Exponential
Rapid binary fission; population rises exponentially.
Stationary
Nutrients become limiting and waste accumulates; births ≈ deaths.
Death
Viable population declines.
2 · Environmental factors
Temperature changes enzyme activity and membrane function; pH alters proteins and transport; nutrient availability limits biosynthesis; oxygen requirement depends on organism metabolism.
When interpreting data, identify the trend, quote evidence, then explain the biological cause.
Watch and focus
Pause after each major idea and write one sentence linking the visual evidence to the lesson objective.
Quick check
Exam-style practice
Applied question. Two cultures begin with equal cell numbers. Culture A reaches stationary phase earlier than culture B. Give two plausible environmental explanations and state one measurement that could test each explanation.