About Lesson
Practical Activity: To investigate whether Carbon (IV) oxide is necessary for photosynthesis
Requirements
- Potted plant
- 2 conical flasks
- Sodium hydroxide.
- Petroleum jelly
- Boiling tube
- Ethanol or methylated spirit
- Iodine solution
- Water bath
- White tile
- Means of heating
Sodium hydroxide is used to absorb Carbon (IV) oxide.
The leaves outside act as a control. They have access to all requirements for photosynthesis.
The leaf under test lacks Carbon (IV) oxide.
Procedure
- Keep the plant in the dark for 48 hours.
- Place a few pellets of Sodium hydroxide in the flask.
- Bore a hole in the cork of the same size as the petiole of the leaf being used.
- Cut the cork lengthwise.
- Remove the plant from the dark and immediately fit the petiole of a leaf A in the groove and cork the flask as shown below.
- Seal the mouth of the conical flask with petroleum jelly to make it airtight.
- Keep the set up in the light for 2 – 3 hours.
- Detach and test for the presence of starch in both leaves A and B.
- Record your observations.
Questions
(a) What is the function of the sodium hydroxide pellets?
To absorb Carbon (IV) oxide.
(b) Why was the leaf outside the flask also tested for starch?
It acts as a control experiment.
Expected Results
Leaf A turned brown showing absence of starch.
Leaf B turned blue-black indicating presence of starch.
Conclusion
Plants require carbon (IV) oxide to carry out photosynthesis.
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