Investigating Disinfectants

In this investigation you are going to find out how good different cleaning products are at killing micro-organisms.


  • 2 Petri dishes containing a nutrient agar.
  • A permanent marker.
  • Sticky tape
  • Cotton buds
  • Cleaning products to test.


  1. Divide each petri dish into 4 quadrants by marking the base. This gives you 8 test areas. Label them 1 to 8.
  2. Take a small piece of tape (1cm x 2cm) and stick it onto an area of the floor or a tabletop. Peel it off.
  3. Gently place the tape sticky side down into section 1 of the petri dish then remove the tape and discard it replace the lid on the dish. (This transfers any micro-organisms on the tape onto the agar surface.) This will be your control area which you can use to compare the effectiveness of the cleaners.
  4. With a cotton bud dipped in a cleaning product clean a small area of the floor or tabletop.
  5. Use a new piece of tape to transfer any micro-organisms into section 2 of the petri dish.
  6. Repeat this with all of the products you want to test. Keep a list of what you have in each quadrant. Tape the plates shut (do not seal all around the edge)
  7. The petri dishes need to be left at room temperature for about a week. After this time you can count how many colonies have grown in each section. The fewer the colonies the better the product.

Risk Assessment

Cleaning products can be caustic and so safety spectacles must be worn. The dishes must not be opened after the micro-organisms have grown there may be harmful bacteria inside.

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