Our bodies require oxygen to break down (metabolize) carbohydrates and fats to carbon dioxide and water with the release of the energy that is required to keep our bodies running. The process of energy release from carbohydrates in living organisms is called cellular respiration. Seeds also use cellular respiration to release energy from fats or carbohydrates stored in the seed. Once the seedling begins photosynthesis, it will produce more oxygen in photosynthesis than it uses in cellular respiration. However, plants use cellular respiration 24 hours per day, even when they are photosynthesizing. Some seeds, such as rice, can germinate underwater so require very little oxygen for germination.