Correct Response: C. Phytoplankton are microscopic marine plants that fix atmospheric carbon dioxide as they use sunlight to make organic molecules during photosynthesis. Coral polyps are marine animals in the phylum Cnidaria and do not fix atmospheric carbon dioxide (A). While one phylum of bacteria (B) (i.e., cyanobacteria or blue-green algae) do photosynthesize and fix carbon dioxide, the vast majority of bacteria do not. Protozoa (D) digest the food they take in from their environment in vacuoles and do not fix atmospheric carbon dioxide. Although protozoa constitute a complex and diverse group of microscopic eukaryotes, they were traditionally considered to be animal- like to distinguish them from photosynthesizing phytoplankton and because of their motility and predatory behavior.
