During respiration, plants mainly release oxygen gas. This process happens primarily during photosynthesis, where plants convert sunlight, carbon dioxide, and water into glucose and oxygen. While plants also undergo respiration—breaking down glucose for energy—they typically release more oxygen through photosynthesis than they consume during respiration, contributing positively to the atmosphere. This release of oxygen is critical for sustaining life on Earth, as it provides the essential gas needed for the respiration of most living organisms, including humans. Thus, the balance between photosynthesis and respiration is crucial for ecological health.