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Question 2

From Biology SL Paper 3 (November 2024, TZ2)

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  1. The growth of non-pathogenic Escherichia coli bacteria were studied in a microbiology laboratory at different temperatures with the antibiotic ampicillin. The number of bacterial colonies that grew were counted, and the mean and standard deviations calculated for five replicates per temperature.

At 25 °C, the mean number of colonies counted was 70 ± 8. The Petri dish shows the results obtained in one of the replicates at this temperature.

A photo of a Petri dish containing bacterial colonies, with labels pointing to 'growth media containing ampicillin', 'bacteria colony', and 'petri dish'. This image illustrates the results of a microbiology experiment described in Question 2.
A photo of a Petri dish containing bacterial colonies, with labels pointing to 'growth media containing ampicillin', 'bacteria colony', and 'petri dish'. This image illustrates the results of a microbiology experiment described in Question 2.

(a) State the dependent variable in this experiment. [1]

(b) Explain the need for replicates in this experiment. [2]

(c) Suggest one reason for the presence of bacterial colonies despite the use of the antibiotic ampicillin. [1]

Textbook topics in this question

Review the exact course sections assessed by each question part.

Mixed-topic question
2(a)10.3 HIV, Antibiotics and Resistance5.2 Prokaryotic Cell Structure
2(b)10.3 HIV, Antibiotics and Resistance
2(c)10.3 HIV, Antibiotics and Resistance11.2 Selection, Gene Pools and Hardy–Weinberg