Final answer:
The carbon used in cellular respiration comes from carbon dioxide, a waste product of respiration. During photosynthesis, plants convert carbon dioxide into glucose, which is used for energy through cellular respiration. The carbon atoms in glucose are released back into the environment as carbon dioxide.
Step-by-step explanation:
The carbon needed for cellular respiration comes from carbon dioxide (CO₂), which is a byproduct of both respiration in living organisms and also photosynthesis in plants. In photosynthesis, plants absorb light energy and convert carbon dioxide from the air into carbohydrates, such as glucose, which have carbon backbones. These carbohydrates are then consumed by other organisms, and through cellular respiration, these organisms convert the carbohydrates back into energy and release carbon dioxide back into the atmosphere. This process completes a biological cycle essential for life.
In photosynthesis, chloroplasts capture energy to build carbohydrates. Conversely, aerobic cellular respiration in the cytoplasm and mitochondria releases energy by using oxygen to metabolize these carbohydrates. Both life-sustaining processes are interconnected with the carbon dioxide released during cellular respiration being utilized again by plants for photosynthesis, showing how the ecosystem conserves and recycles carbon atoms indefinitely.