Final answer:
Carbon dioxide is a reactant in photosynthesis, and water is both used in photosynthesis and produced in cellular respiration. Photosynthesis and cellular respiration function in a reciprocal relationship: the products of one process are the reactants of the other, showing their critical roles in the carbon cycle.
Step-by-step explanation:
Cellular respiration and photosynthesis work together to maintain the cycling of carbon and oxygen among Earth's systems. In this cyclical relationship, carbon dioxide and water play crucial roles. Carbon dioxide is a reactant in photosynthesis, a process that occurs in chloroplasts, where light energy is absorbed to build carbohydrates. Water is also consumed in this process, and oxygen is produced as a byproduct. Conversely, in cellular respiration, which takes place in the cytoplasm and mitochondria of cells, oxygen is used to metabolize carbohydrates, producing ATP, the energy currency of cells. During this process, carbon dioxide and water are released as products.
Therefore, the correct answer to the question of what describes the roles of carbon dioxide and water in these two processes is D. Carbon dioxide and water are the reactants of photosynthesis and the products of cellular respiration. This illustrates the reciprocal nature of the two processes in the carbon cycle, both of which are essential to life on Earth.