Step 1: Begin by understanding the processes of photosynthesis and cellular respiration. Photosynthesis is the process by which plants convert light energy into chemical energy, using carbon dioxide (CO$_2$) and water (H$_2$O), and releasing oxygen (O$_2$) as a byproduct. Cellular respiration is the process by which cells break down glucose to produce energy, using oxygen (O$_2$) and releasing carbon dioxide (CO$_2$) as a byproduct.