What is considered the main characteristic of prokaryotic cells?

The main characteristic of prokaryotic cells is their lack of a membrane-enclosed nucleus. This fundamental distinction sets prokaryotic cells apart from eukaryotic cells, which do have a defined nucleus where their genetic material is housed. In prokaryotes, the DNA is typically found in a region called the nucleoid, but it is not surrounded by a lipid membrane, which is a hallmark feature of eukaryotic cells.

Considering the other options, the presence of a nucleus and organelles is associated with eukaryotic cells, not prokaryotic. The claim that prokaryotic cells are only found in plants is incorrect, as prokaryotes, such as bacteria, are diverse and can inhabit a wide range of environments, including those outside of plants. Additionally, prokaryotic cells do not possess extensive Golgi apparatus; this is another feature that characterizes eukaryotic cells, where the Golgi apparatus plays a crucial role in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. Thus, the absence of a membrane-enclosed nucleus is indeed the defining trait of prokaryotic cells.