A level Biology B · Edexcel 9BI0 · Topic 6B
Bacterial growth
Key points
- Lag phase: little growth while bacteria make enzymes and adjust to the medium.
- Log (exponential) phase: numbers double each generation as resources are plentiful.
- Stationary phase: birth rate equals death rate as nutrients run low and toxic waste builds up.
- Death (decline) phase: deaths exceed new cells.
- Because numbers rise so fast, growth curves are plotted on a log scale.
- Number of bacteria after generations: ; the generation time is the time for one doubling.
- Growth rate constant gives generations per unit time.
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In a closed culture a bacterial population follows a predictable pattern: a slow start, explosive doubling, a plateau and then decline. You need to explain each phase and handle the logarithms that describe exponential growth.
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