Describe an experiment to show that carbon dioxide is necessary for photosynthesis.
Answers
Procedure
Remove food reserves from the leaves of a potted plant by keeping it in the dark for 24 hours (example; in a cupboard).
Test for starch to ensure no starch is present.
Enclose one leaf (A) in a glass flask containing some soda lime to absorb the carbon dioxide.
The leave stalk should pass through a split cork.
Support the flask with a clamp on a retort stand.
Enclose a second leaf (B) in a similar flask but without the soda lime as control experiment.
Put the plant and flask in sunlight for three (3) hours.
Remove the enclosed leaves and test for the presence of starch.
Observation
Leaf A (in the flask with soda lime) tested negative for the presence of starch but leaf B (in the flask without soda lime) tested positive for the presence of starch.
Conclusion
It can therefore be concluded that, carbon dioxide is necessary for photosynthesis.
*Take a plant with destarched leaves.
*Insert a part of one if its leaves into a conical flask containing potassium hydroxide(potassium hydroxide absorbs CO2).
*Leave the plant in sunlight.
*After a few hours, test the leave for starch.
The part of the leave which was exposed to the atmospheric air becomes blue-black, and the part of the leaf inside the flask containing potassium hydroxide does not becomes blue-black, showing that CO2 is necessary dir photosynthesis. The part of the leaf outside the flask becomes the control experiment.