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Experiments on Soil Index

Testing the pH of Soil
Investigating the Presence of Micro-organisms in Different Soil Layers
The Tullgren Funnel

Biology Practical Work index

 

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PRACTICAL WORK

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Testing for the Presence of Living Organisms in the Soil

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).

 

Experiment apparatus ©  Shirley Burchill

 

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

pH colours

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? explanation for this?

 

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