Final answer:
The correct answer is option A Carbon dioxide and water are the reactants of photosynthesis and the products of cellular respiration.
Step-by-step explanation:
The correct answer is A: Carbon dioxide and water are the reactants of photosynthesis and the products of cellular respiration. In the process of photosynthesis, plants absorb carbon dioxide from the atmosphere and use water to produce glucose and oxygen.
Conversely, during cellular respiration, organisms break down glucose in the presence of oxygen and release carbon dioxide and water as byproducts, along with energy. Both processes are thus inversely related and crucial for maintaining the balance of oxygen and carbon dioxide in Earth's atmosphere.