Understand the processes of photosynthesis and cellular respiration: Photosynthesis is the process by which plants use sunlight, carbon dioxide (CO₂), and water (H₂O) to produce glucose (C₆H₁₂O₆) and oxygen (O₂). Cellular respiration is the process by which humans and other organisms use oxygen (O₂) to break down glucose (C₆H₁₂O₆) into carbon dioxide (CO₂), water (H₂O), and energy (ATP).