Before the Starch Test:
Just before the starch test, the green portions (A) of the variegated leaf would appear green, indicating the presence of chlorophyll. Chlorophyll is the green pigment responsible for capturing light energy during photosynthesis.

After the Starch Test:
After conducting the starch test, the green portions (A) would turn blue-black. This color change indicates the presence of starch, which is a product of photosynthesis. The blue-black color is due to the formation of a complex between starch and iodine used in the starch test.
Equation of Photosynthesis:
The overall equation for photosynthesis is:
6CO2 + 6H2O + Chlorophyll + sunlight —> C6H12O6 +6O2

This equation represents the conversion of carbon dioxide (CO2, obtained from the air) and water (H2O) as splitting of water results in formation of Hydrogen (used for making glucose) and oxygen (by-product) in the presence of light energy.

By-Product and Its Origin:

The by-product of photosynthesis is oxygen gas (O2), and it is obtained from the splitting of water molecules during the light-dependent reactions of photosynthesis. The oxygen released during photosynthesis comes from the water molecules, not from carbon dioxide. The oxygen is released as a by-product into the atmosphere. The process of photosynthesis involves two main stages: the light-dependent reactions, which occur in the thylakoid membranes, and the light-independent reactions (Calvin cycle), which take place in the stroma of the chloroplasts.