light
every organism uses to power its metabolism. In brief, the energy of sunlight is captured and used to energize electrons, which are then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis almost 200 million years ago. Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis Figure 8.2 . Because they use light to manufacture their own food, they are called photoautotrophs literally, self-feeders using light . Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs other feeders , because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlights energy, but by extracting energy from inorganic chemical compounds; hence, they are referred to as chemoautotrophs.