What is photosynist?

It seems like there might be a typo in your question, as "photosynist" does not appear to be a recognized term. If you meant "photosynthesis," it is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide and water to produce glucose and oxygen. This process is essential for life on Earth, as it provides the primary source of energy for nearly all living organisms. If you meant something else, please clarify!