Mouldy bread and their conditions. Image credit

Mouldy bread and their conditions. Image credit

ZIMSEC O Level Combined Science Notes: Experiment: Finding conditions necessary for growth of microorganisms

Aim: To determine factors affecting the growth of microorganisms in food

Materials:  3 containers with sterilized lids, brad, milk, burners, drying agent (calcium chloride)


  1. Pour equal amounts of milk into each of the three containers
  2. Seal each of the containers and put one of them into a refrigerator
  3. Boil the other milk using the burner and let it cool.
  4. Leave the other container in a warm place.
  5. In the second test make three slices of bread and put them on the floor for a while
  6. Place one piece of bread in a box with a lead
  7. Place a small container of drying agent  in the box
  8. Place the other in a similar box but with a few drops of water
  9. Wrap the third slice in a polythene bag and seal it with tape to exclude air
  10. Examine the bread after a week

NB Do not handle the fungi as it is poisonous. Also avoid breathing in the spores of the fungi

Observations and Results

  • The unsterilised(unboiled0 milk went sour first
  • The milk in the refrigerator lasted longer
  • The sterilized milk did not go sour at all
  • The bread with water had the most fungi
  • The dried bread had less fungi/none at all
  • The wrapped bread had very little fungi


  • Food goes bad due to microorganisms
  • These organisms need:
  • Air/Oxygen
  • A warm temperature
  • Moisture
  • In order for them to thrive
  • Food can be preserved by depriving the microorganisms one/some/all of these conditions

To access more topics go to the Combined Science Notes page