Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture the energy that originates from sunlight and converts it into chemical compounds (carbohydrates) that every organism uses to power its metabolism.
It is also a source of oxygen necessary for many living organisms. In brief, the energy of sunlight is “captured” to energize electrons, whose energy is 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 350 to 200 million years ago during the Carboniferous Period.
Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis.
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 sunlight’s energy, but by extracting energy from inorganic chemical compounds. For this reason, they are referred to as chemoautotrophs.