Plants rely on the sun for energy by using chloroplasts (located in their cells) in photosynthesis to combine sunlight with water and carbon dioxide to provide energy. Photosynthesis also creates Oxygen, which all animals need to breath. Animals use the oxygen in cellular respiration (C₆H₁₂O₆ + 0₂ → CO₂ + H₂0 + ATP) to create carbon dioxide. In this way animals and plants need the sun because if there wasn't any sunlight, then plants couldn't create oxygen which animals need to breath.
