How are photosynthesis and respiration related to each other? a: both are performed by all plants and animals. b: the products of photosynthesis, oxygen and glucose, are the starting substances of cellular respiration. two of the products of respiration, carbon dioxide and water, are the starting substances of photosynthesis. plants and animals depend on each other and these two important processes to survive. c: photosynthesis and respiration are not related to each other.