Question

How are cellular respiration and photosynthesis related to each other?

Answer 1

They rely on each other to function.
Photosynthesis produces oxygen which cellular respiration needs and in turn cellular respiration produces carbon dioxide that photosynthesis. 

Answer 2

Photosynthesis is related to cellular respiration because cellular respiration uses glucose and O2, then produces carbon dioxide and water plus ATP, and then photosynthesis uses carbon dioxide and water to produce glucose and O2. They are basically doing different things but helping each other in an endless loop of what is created and used by another and what is used and recreated by another.