Here's why:

* Lack of a Nucleus: Prokaryotes lack a membrane-bound nucleus, and their DNA is located in a region called the nucleoid. Cyanobacteria fit this description.

* Simple Cell Structure: Prokaryotes generally have a simpler cell structure compared to eukaryotes. They lack membrane-bound organelles like mitochondria, Golgi apparatus, and endoplasmic reticulum. Cyanobacteria also exhibit this characteristic.

* Size: Prokaryotes are typically much smaller than eukaryotes. Cyanobacteria are relatively small, aligning with the prokaryotic size range.

While cyanobacteria perform photosynthesis like plants, they are fundamentally different in their cellular structure and organization.