Final answer:
A photoheterotroph is an organism that uses light to generate energy and needs organic sources for carbon. Examples include certain bacteria. They play a crucial role in the food web by providing energy to other consumers.
Step-by-step explanation:
A photoheterotroph is an organism that uses light energy to generate ATP but must obtain carbon in organic form, typically by consuming other organisms. Unlike photoautotrophs that use carbon dioxide as their carbon source, photoheterotrophs rely on complex organic substances. Common examples include purple non-sulfur bacteria, green non-sulfur bacteria, and heliobacteria. In the food web, photoheterotrophs play a role in transferring energy they obtained from light into the ecosystem by providing nutrients for other organisms when consumed.
Chemoheterotrophs, on the other hand, obtain both their energy and carbon from organic sources. This includes most eukaryotes, like humans, who consume organic molecules such as sugars to survive. These chemoheterotrophs are essential as consumers in food webs, depending on photoautotrophs and other heterotrophs as their food sources.