Decribe the importance of photosynthesis in the producers

In many humans, exposing the skin to sunlight over prolonged periods of time results in the production of more pigment by the skin cells (tanning). this change in skin color provides evidence that -

Omg substrates with the same size and shape as the active site will bind to the enzyme. why is the key labeled the “bad” substrate?

Does anyone know what the schooling version of sos mean? example