In an experiment, bacteria were grown on agar. Four paper discs, A, B, C and D, were placed on top of the agar. Each paper disc contained a different antibiotic. The diagram shows the agar after 48 hours. The clear areas show where bacteria are not growing. Which antibiotic are the bacteria most resistant to?
▶️ Answer/Explanation
Ans: B
In antibiotic resistance tests, clear zones (inhibition zones) indicate where bacteria cannot grow due to the antibiotic’s effectiveness. Smaller or absent clear zones suggest resistance.
In the diagram, disc B shows the smallest or no clear zone, meaning bacteria continue growing near it. Thus, the bacteria are most resistant to antibiotic B.
The graph shows changes in the resistance of the bacterium Escherichia coli to two different antibiotics between 2005 and 2023.
Which statement describes the changes that occurred between 2005 and 2023?
A) Between 2010 and 2015, the percentage of bacteria resistant to antibiotic 2 increased by 6%.
B) Between 2011 and 2016, the percentage of bacteria resistant to antibiotic 1 continually increased.
C) Between 2016 and 2023, the percentage of bacteria resistant to antibiotic 2 continually decreased.
D) Between 2020 and 2022, the percentage of bacteria resistant to antibiotic 2 decreased.
▶️ Answer/Explanation
Ans: A
From the graph, antibiotic 2 resistance increased from ~12% (2010) to ~18% (2015), showing a 6% rise (A is correct). Option B is incorrect as resistance to antibiotic 1 decreased between 2012-2014. Option C is wrong as antibiotic 2 resistance fluctuated (not continual decrease). Option D is incorrect as resistance increased from ~20% to ~22% (2020-2022).
The only accurate statement is A, confirmed by direct graph analysis of the specified time periods.