Final answer:
The terms phototroph and chemotroph refer to an organism's source of energy. Phototrophs use light, while chemotrophs use chemical compounds for their energy needs, with chemotrophs broken down into organotrophs and lithotrophs.
Step-by-step explanation:
The terms phototroph and chemotroph refer to an organism's source of energy. Phototrophs are organisms that obtain their energy for electron transfer from light, while chemotrophs obtain energy from the transfer of electrons originating from chemical compounds. There are two main types of chemotrophs: organotrophs and lithotrophs. Organotrophs, like humans and fungi, derive energy from organic compounds, whereas lithotrophs obtain energy from inorganic compounds such as hydrogen sulfide (H₂S) and reduced iron. Lithotrophy is a concept unique to the microbial world.
For instance, organisms like chemoheterotrophs get their energy and carbon from organic sources. They are common among eukaryotes, including humans. In contrast, photoautotrophs use light energy and carbon dioxide as their carbon source. However, when looking specifically at organisms that rely on chemical energy and use an inorganic source for their carbon, we refer to them as chemolithoautotrophs. These organisms are able to live in environments without light by using inorganic compounds as a source of energy.