Experiment: Do plants release carbon dioxide when they respire?

Aim: To determine whether all living things, including plants, release carbon dioxide when they respire.

Materials: bell jar or a large container, 3 boiling tubes/flasks glass or rubber tubing, lungs, suction pump, potassium hydroxide, lime water or bicarbonate indicator and a potted plant/rat/frog.

Method

Respiration chain. Image credit oldschool.com.sg

1. Set up the respiratory chain apparatus using the materials above as shown in the diagram.
2. The respiratory chain compares the amount of carbon dioxide in the air before and after respiration by an organism.
3. The potassium hydroxide solution removes carbon dioxide from the air before it enters the apparatus.
4. In the above diagram air is filtered through a additional flask/boiling tube containing potassium hydroxide on the left side of the apparatus shown as Liquid A.
5. The rat in the diagram can be replaced by any living organism for example a plant/frog as shown below.

Respiratory chain with a plant instead of a rat. Image credit slideshare.net

Results

Lime water turns milky indicating the presence of carbon dioxide. Image credit calpoly.edu

• The same result will be observed if a frog is used instead. The lime water in flask A will turn milky to show that the frog is respiring.
• If the plant is left overnight the lime water in flask A will turn milky indicating the presence of carbon dioxide.

Conclusion

• All living things such as frogs and plants and produce carbon dioxide when they respire.

NB. This experiment can also be used to test whether germinating seeds respire and produce carbon dioxide during the germination process.

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