Phototrophs
Organisms are usually classified based on their nutritional need, and according to this criterion, there are two distinct groups, the phototrophs and the chemotrophs. Phototrophs rely on energy from the sun to manufacture their food in the form of ATP (Parker et al., 2017). The sunlight oxidizes organic molecules to produce energy, which is crucial for cellular functions. Green plants are examples of phototrophs as they contain chlorophyll that enables them to trap sunlight for food manufacture through photosynthesis. Photosynthesis is the process by which green phototrophs convert organic compounds into important energy for their survival. Phototrophs are classified into two broad groups, the photoautotrophs and the photoheterotrophs. Photoautotrophs contain chlorophyll and use it to manufacture food after capturing sunlight, while photoheterotrophs rely on a process called photophosphorylation to produce ATP (Parker et al., 2017). While photoautotrophs chemically act on carbon dioxide to produce energy, photoheterotrophs lack such capacity. They act on organic carbon products of other organisms to produce ATP as a source of energy.
Chemotrophs
Chemotrophs are chemoautotrophs or chemoheterotrophs and depend on the combustion of chemical substances to make food instead of depending on sunlight. The process chemotrophs use to obtain energy is called chemosynthesis and involves the chemical oxidation of various compounds (Parker et al., 2017). Chemoautotrophs rely on reducing agents such as hydrogen sulfide, sulfur, and ammonium to synthesize carbohydrates from carbon dioxide. These organisms reside in extreme habitats, such as the deep sea, where sufficient sunlight is not available for photosynthesis (Parker et al., 2017). These organisms include halophiles, methanogens, and sulfur oxidizers. Chemoheterotrophs rely on organic components for energy and carbon source. They devour foods, for instance, starch, fats, and proteins, from other creatures and are the most plentiful organisms, including bacteria.
Reference
Parker, N., Schneegurt, M., Forster, B. M., & Lister, P. (2017). Microbiology. OpenStax. Web.