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

Method

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

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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