The two processes are similar in that they both produce energy, albeit in two different forms. ... The win-win of the two processes is that they both provide each other with the necessary ingredients for the process to take place: glucose and oxygen for cellular respiration, carbon dioxide and water for photosynthesis.
They are quite similar but the difference is that photosynthesis converts carbon dioxide and water into oxygen and glucose, but cellular respiration converts oxygen and glucose into water and carbon dioxide. Basically they just do the opposite things.