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In 1988 a scientist called Richard Lenski and his group used a single ancestral genome of *Escherichia coli* to put 12 genetically identical populations in 12 identical environments - VCE - SSCE Biology - Question 11 - 2023 - Paper 1
Question 11
In 1988 a scientist called Richard Lenski and his group used a single ancestral genome of *Escherichia coli* to put 12 genetically identical populations in 12 identi... show full transcript
Worked Solution & Example Answer:In 1988 a scientist called Richard Lenski and his group used a single ancestral genome of *Escherichia coli* to put 12 genetically identical populations in 12 identical environments - VCE - SSCE Biology - Question 11 - 2023 - Paper 1
Step 1
b. What effect would you expect this mutation to have on subsequent generations of this group of bacteria and why?
Answer
The mutation allowing some E. coli to utilize citrate as an energy source would likely lead to a significant increase in the growth and reproduction rate of those mutated bacteria in environments where citrate is present. This is because access to an additional nutrient means that these bacteria could exploit a resource that others cannot, resulting in higher reproductive success. Over time, this could result in an increased frequency of this mutation in subsequent generations due to positive selection.
Step 2
c. Describe how you would conduct an experiment to investigate the effect of different glucose concentrations on the mutant citrate phenotype.
Answer
To conduct this experiment, I would use the following steps:
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Experimental Design
Create multiple flasks with varying concentrations of glucose (e.g., 0%, 1%, 5%, 10%) while keeping citrate concentration constant in each flask. This would allow isolation of the glucose variable while maintaining consistency in other conditions. -
Control Group
Include a control group in which E. coli is provided only with glucose and no citrate to compare the effects of the independent variable. -
Sample Size
Use large sample sizes for each glucose concentration to ensure the results are statistically significant. -
Incubation Conditions
Maintain consistent incubation temperatures and times across all samples to reduce variability in results. -
Data Collection
Measure the growth of bacteria over time (e.g., through optical density measurements) to evaluate how different glucose levels affect the frequency of the mutant citrate phenotype.