Final answer:
A bacterium that uses light for energy but requires organic carbon sources is known as a photoheterotroph, which is different from chemoheterotrophs that use organic compounds for both energy and carbon.
Step-by-step explanation:
A bacterium that requires a carbon source other than carbon dioxide and can convert light energy to chemical energy is called a photoheterotroph. These organisms are capable of using light energy to support their chemical energy needs but must obtain carbon in an organic form from other organisms. An example of a photoheterotrophic organism would be purple non-sulfur bacteria. In contrast, chemoheterotrophs obtain both their energy and carbon from organic compounds and do not utilize light. Humans are an example of chemoheterotrophs. Photoautotrophs such as plants, algae, and cyanobacteria, use light energy to convert carbon dioxide into organic matter.