Microbial Metabolism Practice Test

Photoautotrophs use light energy to drive the fixation of CO2 into organic matter, meaning they convert inorganic carbon into sugars through photosynthesis. Cyanobacteria are photosynthetic bacteria and algae are photosynthetic eukaryotes, so both are classic examples of organisms that rely on light to build their own carbon skeletons. They also contribute to oxygen production through oxygenic photosynthesis. The other options describe organisms that rely on organic carbon from their surroundings (heterotrophs) rather than fixing CO2 themselves, or are not known for photosynthesis, so they don’t fit the definition of photoautotrophs.