GCSE Biology (AQA)

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Measuring Zones of Inhibition

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Cell Biology Cell Structure

Measuring Zones of Inhibition

3:29 Microorganisms and Measurements
Spec 4.1.1.6
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  • The zone of inhibition is a clear area around an antibacterial substance where bacteria cannot grow.
  • This zone can be used to test and compare different antibiotics or antiseptics, or different concentrations of the same substance, to determine the most effective concentration for inhibiting bacterial growth.
  • In a petri dish, filter paper discs soaked in an antibiotic are placed on an agar plate spread with bacteria to observe the zone of inhibition.
  • The clear space around the disc indicates the zone of inhibition, while the yellow color shows bacterial growth.
  • The efficacy of an antibiotic is measured by the area of the zone of inhibition, calculated using the formula for the area of a circle (��r��).
  • The radius (r) of the zone of inhibition is measured in millimeters or centimeters, and the area can be calculated in square millimeters or square centimeters.
  • A larger zone of inhibition indicates a more effective antimicrobial agent.
  • To measure the zone of inhibition, first measure the diameter of the clear space, then calculate the radius by dividing the diameter by two, and finally use the radius in the formula ��r�� to find the area.
  • This method is a required practical for GCSE biology and understanding it is crucial for exams.

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