How are photosynthesis and cellular respiration related?
They are essentially the reverse of each other.
Photosynthesis is when energy, carbon dioxide and water react to produce glucose and oxygen. It is an endothermic reaction (takes in more energy than it gives off).
Respiration is the process of producing energy from glucose. It uses glucose and oxygen to give water, carbon dioxide and energy (this making it exothermic).
As you can see from the equations, they are essentially the reverse of each other.
Another difference is how they are used. Respiration occurs in the mitochondria of all living cells, whereas only plants photosynthesise.
In plants, they make their own glucose using the sun's energy, then respire to allow them to use the glucose for energy they can use. The glucose can also be stored and used in many other ways other than in respiration.
Hope this helps:)