Testing for organisms in the soil.

Testing for organisms in the soil.

ZIMSEC O Level Combined Science Notes: Experiment: Testing for the presence of micro-organisms in soil

Material:2 test tubes, lime water/bicarbonate indicator, cotton thead, corks, muslin cloth or cotton material, burner


  1. Put a sample of fresh soil (about 50g mass) in a muslin bag
  2. Bake another soil using the burner and put a sample of about 50g into another bag
  3. The baked soil acts as the control to the experiment as baking will kill all the micro-organisms in the soil
  4. Seal the test tubes with a cork using the string to make sure that they do not fall into the lime water
  5. Leave the apparatus for a day or two
  6. Record the results


  • The lime water in the test tube with the fresh water turns milky
  • This indicates the presence of carbon dioxide
  • The lime water in the test tube with baked soil remains clear
  • Conclusion
  • Since the test tubes are sealed to prevent outside air from entering the test tubes
  • The carbon dioxide is a result of micro-organisms in the fresh soil sample respiring and thus producing
  • carbon dioxide whose presence is shown by the lime water
  • There are no micro-organisms in the baked soil sample as a result the lime water remains unchanged
  • The test tubes are sealed to prevent air from entering them from the outside and thus influencing results
  • Micro-organisms such as bacteria and fungi live in the soil

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