In certain ways, photosynthesis and breathing are related. We know that the breathing of carbohydrates involves the oxidation of energy. Since carbohydrates are prepared for breathing during photosynthesis, breathing can therefore not take place without photosynthesis. In addition, breathing also needs oxygen that is a photosynthesis by-product. Similarly, carbon dioxide is an important raw material for photosynthesis and much of the carbon dioxide comes as a by-product of respiration.