Which type of organism does not have a nucleus or membrane-bound organelles?

Prokaryotes are organisms characterized by the absence of a nucleus and membrane-bound organelles. This fundamental distinction separates prokaryotic cells from eukaryotic cells, which do have a defined nucleus and various organelles enclosed by membranes.

In prokaryotes, such as bacteria and archaea, the genetic material is not housed within a nucleus but instead is organized in a single circular strand of DNA located in the cytoplasm, known as the nucleoid. The simplicity of prokaryotic cells allows them to reproduce rapidly and occupy a wide variety of ecological niches.

Eukaryotes, including fungi and protozoa, possess complex cellular structures with a nucleus that contains the cell's DNA. Their cells contain multiple membrane-bound organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus, which perform specialized functions essential for cell survival and metabolism.

Thus, the correct identification of prokaryotes highlights their unique cellular structure, setting them apart from more complex organisms that possess nuclei and organelles.