What is a phototroph?

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A phototroph is defined by harvesting energy from light to drive cellular metabolism. This energy source distinguishes phototrophs from chemotrophs, which obtain energy from chemical compounds. In terms of carbon, phototrophs can either fix carbon dioxide (photoautotrophs) or use organic carbon (photoheterotrophs), so the carbon source is a separate axis from how energy is obtained. Some phototrophs are aerobic and others can be anaerobic, so requiring oxygen isn’t what defines them. The key idea is that light provides the energy.