The main purpose of photosynthesis is to convert radiant energy from the sun into chemical energy that can be used for food. Cellular respiration is the process that occurs in the mitochondria of organisms (animals and plants) to break down sugar in the presence of oxygen to release energy in the form of ATP.
https://orise.orau.gov/resources/k12/documents/lesson-plans/intro-to-photosynthesis.pdf
