Cellular respiration and photosynthesis are connect because the reactants for cellular respiration are the products for photosynthesis, and the products for cellular respiration are the reactants for photosynthesis. They are also connected because they go in a cycle. Photosynthesis gives off oxygen for us to breathe, and cellular respiration gives off carbon dioxide when we breathe out, so the plants can continue photosynthesis. They also both give energy for the organism.