The Open Door Web Site
Experiments on Soil Index
Testing for the Presence of Living Organisms in the Soil
When living organisms breathe they give out carbon dioxide gas as a waste product. Carbon dioxide gas can be detected (identified) using a carbon dioxide indicator solution called bromothymol blue.
To find out if there are living organisms present in the four different levels of soil taken from the deciduous forest.
1. Set up the apparatus as shown in the diagram using a sample of the leaf litter (A).
2. Label your test tube. (NB. You should put your initials, science group code, the date and the letter A to identify the sample. The label should be placed near the top of the test tube).
3. Repeat points 1. and 2. with the three remaining soil layer samples B, C and D (see the table above).
4. Set up a fifth tube like the one shown in the diagram but with no soil sample. This test tube will be your control.
5. Leave the five test tubes in the same place for one week.
6. After one week observe and record the results.
If carbon dioxide has been given out by living organisms, the bromothymol blue will change colour
Write a conclusion to this experiment.
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