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Testing
for the Presence of Living Organisms in the Soil
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Introduction
...
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.
Aim
...
To find out if there
are living organisms present in the four different levels of
soil taken from the deciduous forest.
|
Letter |
Name
of Layer |
|
A |
The
Leaf Litter |
|
B |
The
Humus Layer |
|
C |
The
Humus mixed with Minerals Layer |
|
D |
The
Mineral Layer mixed with very little Humus |
Method
...
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.
Results
...
If carbon dioxide has
been given out by living organisms, the bromothymol blue will
change colour
| blue-green |
no
carbon dioxide : control |
| green |
some
carbon dioxide |
| light
green to yellow |
a
lot of carbon dioxide |
|
Test
Tube |
Observation |
|
Control |
|
|
A |
|
|
B |
|
|
C |
|
|
D |
|
Conclusion
Write a
conclusion to this experiment.
Had the bromothymol blue in the control tube changed colour?
Explain your answer.
What is this tube used for?
Compare any colour changes for the other four tubes.
What do these results indicate to you about the numbers of
living organisms in the different soil samples?
Can you think of an explanation for this?
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