Which term describes single-celled algae with calcareous plates that accumulate to form biogenic sediments?

• A. Coccolithophore
• B. Diatom
• C. Foraminiferan
• D. Lithification

Answer: (A)

The term refers to single-celled algae that build calcium carbonate plates, called coccoliths, and these plates accumulate to form biogenic sediments. These organisms are photosynthetic plankton; when they bloom, their coccoliths blanket the sea surface, and after they die the plates settle to the ocean floor, creating carbonate-rich sediments such as coccolith ooze and even large chalk deposits like the famous white cliffs of Dover. This distinguishes them from diatoms, which have silica-based shells; foraminiferans, which are protozoan organisms with calcium carbonate tests but are not algae; and lithification, which is the geological process of turning sediment into rock rather than a type of organism. So the best fit is coccolithophore.