Question

recent work in classification of life on earth has shown that what were once called prokaryotes are much more diverse than ever suspected. the prokaryotae are now divided into two domains, the bacteria and the archaea, as different from each other as either is from the eukaryota. one organism, the blue - green algae or cyanobacteria, has left a fossil record that dates back nearly 3.5 billion years and is among the oldest fossils known. these blue - green algae had cell walls and were photosynthetic. a few hundred years ago, this organism was classified as a plant, then as a protist. today it is classified in the bacteria because it
a is prokaryotic.
b is photosynthetic.
c is the ancestor of land plants.
d has cell walls and chloroplasts.

Explanation:

The question concerns the classification of blue-green algae (cyanobacteria). The key point is that prokaryotes (including Bacteria and Archaea) lack a nucleus, while eukaryotes (plants, protists, etc.) have one. Cyanobacteria are prokaryotic, which is why they are now classified in Bacteria instead of eukaryotic groups like plants or protists. Photosynthesis (B) or being an ancestor (C) does not define prokaryotic vs eukaryotic classification; having chloroplasts (D) is a eukaryotic trait, which cyanobacteria lack.

Answer:

A. is prokaryotic.