Cellular respiration and metabolism

Breathing is not the same as cellular respiration. Breathing, or gas exchange, is how oxygen gets in and carbon dioxide gets out of the body. Cellular respiration happens inside every living cell: glucose reacts with oxygen to release energy, and carbon dioxide and water are made. In words: glucose + oxygen → carbon dioxide + water + energy. It follows the reverse pattern of photosynthesis. Cells use the energy for movement, growth, heat and building. Energy is not a substance made like carbon dioxide: it is released from the food. Respiration goes on day and night, in animals and plants alike. Plants have no breathing system. They exchange gases through stomata in the leaves. By day photosynthesis uses carbon dioxide and releases oxygen, usually more than respiration uses. At night there is no light, so only respiration goes on, and the leaf takes in oxygen and gives out carbon dioxide. People sometimes say that cells “burn” glucose: it is only a comparison, since there is no flame in a cell.