use organic compounds, such as glucose, or inorganic substances such as iron, nitrate, ammonia, or sulfur, as sources of energy
cannot fix carbon; they use organic molecules produced by other organisms as the building blocks from which they synthesize the carbon compounds they need.
use light energy to make ATP and other molecules that temporarily hold chemical energy but are unstable and cannot be stockpiled in the cell.
able to use light energy but unable to carry out carbon fixation. must obtain carbon from organic compounds
prokaryotes obtain their energy from the oxidation of reduced inorganic molecules such as hydrogen, sulfide, or ammonia.