Several experiments may be carried out to test what substances/conditions are necessary for photosynthesis to take place. Tests may also be done to verify the use of carbon dioxide and water in the photosynthetic process. To confirm the products, additional tests may also be done.
In testing for the substances/conditions necessary, experiments may be done in controlled environments where only the substance being tested for is lacking. If the substance missing is indeed essential for the photosynthetic process, there will be some hindrance to the process. However, if the condition/substance is unnecessary, photosynthesis will occur regardless of the absence of that particular condition/substance.
If tests are being carried out to determine whether a leaf photosynthesizes, the leaves have to be de-starched before experimentation. This can be done by leaving the leaves in a very dark area for at least 24 hours. The iodine test can then be performed to verify the absence of starch in the leaf.
In a previous lesson, it was said that plants photosynthesize to make sugars, mostly glucose. This glucose is often converted to starch. Hence, leaves can be tested for starch as a means of proving that the leaf is photosynthetic. Iodine solution is used for the starch test and a positive result is indicated by a blue-black colour after iodine has been added to the leaf.
It is important that leaves being tested for starch are boiled and decolourised before testing is done.