What key characteristic distinguishes prokaryotes from eukaryotes?

The key characteristic that distinguishes prokaryotes from eukaryotes is primarily their size and cell organization. Prokaryotic cells are generally smaller and simpler in structure compared to eukaryotic cells. Prokaryotes lack membrane-bound organelles, including a defined nucleus, which is a hallmark of eukaryotic cells. Instead, prokaryotic DNA is typically found in a nucleoid region instead of being enclosed in a nucleus. This fundamental difference in organization and complexity dictates many of the functional capabilities and evolutionary biology of the two groups.

While the presence of ribosomes, the shape of DNA, and the type of cell membrane can differ between the two types of cells, these factors are either not unique to prokaryotes or do not universally apply in the same way that size and organizational structure do. For instance, both prokaryotes and eukaryotes possess ribosomes, albeit in different sizes and compositions, and while prokaryotic DNA is often circular, eukaryotic DNA is linear. Additionally, the type of cell membrane can vary among different organisms and is not a defining characteristic that sets them apart. Thus, size and cell organization serve as the most critical distinguishing feature between prokaryotes