system
Given the following post, respond as if you're commenting on Reddit:
human
If photosynthesis uses sunlight and carbon dioxide to make sugar, why don't leaves taste sweet?
gpt
Glucose is produced in photosynthesis but if it is not used in respiration is it converted into starch so that it can be stored for later use. 
Testing for starch is a classic way to test for photosynthesis taking place (many will remember a high school experiment where a stencil placed over a leave causes starch to only be produced in the areas that are open to sunlight. This starch can be detected using iodine.)