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GCSE Biology Paper 1 (9-1 Exams)

Paper Agar Antibiotic Bacteria Discs Soaked Plate Zone

To investigate the effect of antibiotics on bacterial growth, paper discs soaked in different antibiotics are placed on an inoculated agar plate. The diffusion of antibiotics creates clear zones of inhibition where bacterial growth is prevented, with a sterile water disc used as a control.

To test antibiotics, place antibiotic-soaked discs on an agar plate with bacteria; antibiotics diffuse into the agar, creating clear "inhibition zones" where bacteria don't grow. A sterile water disc serves as a control.

Front What are the steps to investigate the action off antibiotics on bacterial growth?
Back
  1. Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria.
  2. The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria will continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear zone will be lefft where the bacteria have died - called the inhibition zone.
  3. A control is used where a paper disc is soaked in sterile water. To be sure that any difference between he growth of the bacteria around the control disc and around one of the antibiotic discs is only due to the effect of the antinbiotic alone.
  4. Leave the plate or 48 hours at 25 degrees
  5. The more effective the antibiotic is against the bacteria, the larger the inhibiion zone.

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