Final answer:
Photosynthesis and cellular respiration are considered complementary processes because they involve reciprocal reactions and use each other's products as reactants.
Step-by-step explanation:
Photosynthesis and cellular respiration are considered complementary processes because they involve reciprocal reactions. The products of photosynthesis, such as glucose and oxygen, are used as reactants in cellular respiration to produce ATP and carbon dioxide. Similarly, the products of cellular respiration, such as ATP and carbon dioxide, are used as reactants in photosynthesis to produce glucose and oxygen.