Biology 9700 · AS & A Level · Antibiotics

Antibiotics — practice question

The diagram illustrates one method used to investigate the effect of an antibiotic on bacteria. Colonies of bacteria are cultured on a petri dish containing nutrient agar with bacteria. A filter paper disc that has been soaked in antibiotic is put onto the agar. The bacteria are left to grow for 5 days, and the diameter of the zone is measured each day for 5 days. The table presents the results of testing five different types of bacteria. Zones smaller than $13.0\,\text{mm}$ indicate that resistant bacteria are present. Which statement is supported by this data?

  • AAll the types of bacteria become resistant to antibiotics over time.
  • BOnly types 2, 3 and 4 of the bacteria show resistance to the antibiotic.
  • CThe antibiotic can be used to treat types 1 and 3 only.
  • DType 5 of the bacteria can never become resistant to the antibiotic.

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