Final answer:
Plants use carbon dioxide for photosynthesis to form glucose and oxygen. When they die, decomposers break down their parts to release carbon dioxide back into the atmosphere.
Step-by-step explanation:
Plants play a major role in the carbon cycle by using carbon dioxide for photosynthesis, a process that forms glucose and releases oxygen. During photosynthesis, energy from the sun converts carbon dioxide and water into glucose and oxygen, as represented by the general equation 6CO₂(g) + 6H₂O(l) → C₆H₁₂O₆(s) + 6O₂(g). When plants die, decomposers, such as bacteria and fungi, break down their parts, releasing carbon dioxide back into the atmosphere. This process contributes to the carbon cycle, which involves the transfer of carbon among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.