What type of cells are characterized as simple cells without a nucleus or membrane-bound organelles?

Prokaryotes are indeed characterized as simple cells that lack a nucleus and membrane-bound organelles. This classification is foundational in biology, differentiating them from eukaryotic cells, which have complex structures including a defined nucleus and various organelles such as mitochondria and the endoplasmic reticulum. Prokaryotic cells, which include bacteria and archaea, have a more simplistic organization. They typically consist of a cell membrane, cytoplasm, and genetic material that is not enclosed within a nucleus but instead resides in a region called the nucleoid. This structural simplicity allows prokaryotes to reproduce rapidly and adapt quickly to different environments, making them incredibly versatile and widespread in various habitats. The other options do not accurately describe cells without a nucleus or membrane-bound organelles, with eukaryotes being the direct opposite due to their complex cellular architecture. Multicellular organisms consist of eukaryotic cells and stem cells are a specific type of eukaryotic cell with the potential to differentiate into various cell types.