Scientific investigation
Glowing bacteria from a plasmid
- Unit 6
- 4 points
- About 10 minutes
You can use a calculator on this question, just like on exam day.
A short question about a described lab investigation. You describe a concept behind it, identify part of the method such as a control or a variable to hold constant, state a null hypothesis or predict a result, and justify a prediction. On the exam: Question 3 of 6 in Section II; about 10 minutes suggested.
The question and its sources
Plasmid pFL carries two genes: one gives resistance to the antibiotic ampicillin, and the other codes for a fluorescent protein that makes cells glow under ultraviolet (UV) light. Students tried to transform a strain of E. coli that is killed by ampicillin and does not glow.
Investigation
The students split the E. coli into two tubes. Tube + was given plasmid pFL and treated to help cells take up DNA. Tube − was treated the same way but given no plasmid.
They spread the same volume of cells from each tube onto four plates: Plate 1, cells from tube − on nutrient agar; Plate 2, cells from tube − on nutrient agar with ampicillin; Plate 3, cells from tube + on nutrient agar; Plate 4, cells from tube + on nutrient agar with ampicillin. After 24 hours at 37°C, they counted the colonies on each plate and checked them under UV light.
Source: Hypothetical study
Suggested time: 10 minutes
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Part (a)
1 pointDescribe bacterial transformation.
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Part (b)
1 pointIdentify the purpose of Plate 1 in this investigation.
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Part (c)
1 pointPredict whether the colonies on Plate 4 will glow under UV light.
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Part (d)
1 pointJustify your prediction in part (c).
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