Activity 6.2 NCERT class 10 science chapter 6 Life processes
Activity 6.2 asks us to test for starch in a plant with iodine, and compare it with the plant kept with potassium hydroxide.
- Leaf of plant kept without potassium hydroxide turn blue with iodine solution.
- The plant with potassium hydroxide does not turn blue.
Potassium hydroxide is a highly reactive compound. It reacts with the carbon dioxide of the bell and forms its carbonate.
KOH + CO2 —————>K2CO3 + H2O
As a result, no carbon dioxide is available for the plant. In the absence of Carbon dioxide plant is unable to do photosynthesize and form starch. So, iodine does not turn the leaf blue.
The plant kept in bell without Potassium hydroxide can do photosynthesis and form starch. So, iodine solution here turns the leaf blue.
This experiment shows that carbon dioxide is necessary for photosynthesis and starch formation.
Ref: Biology Discussion.