The ultimate source of energy for all organisms, except those living deep in the ocean near a thermal vent, is the sun. The process through which organisms harness this energy is called photosynthesis. To obtain this answer, you can start by understanding the basics of how organisms acquire energy. You could then narrow down the options based on the given criteria and eliminate those that are not relevant. Finally, you would arrive at the correct answer by recognizing that the sun is the primary source of energy for most organisms on Earth.
