The carbon-oxygen cycle illustrates the interconnection between photosynthesis and respiration, where plants absorb carbon dioxide (CO2) and release oxygen (O2) during photosynthesis, while animals inhale O2 and exhale CO2 through respiration. Carbon from fossil fuels is released into the atmosphere as CO2 when burned, which can then be absorbed by plants for photosynthesis, transforming it into organic matter. The O2 produced by plants originates not from CO2 but from water during photosynthesis, while the CO2 exhaled by animals is derived from the breakdown of sugars. This highlights that the carbon that constitutes plant matter comes primarily from atmospheric carbon, not soil nutrients. Understanding these processes emphasizes the cyclical nature of matter in ecosystems.