Which type of cell lacks a defined nucleus?

Prokaryotic cells are characterized by the absence of a defined nucleus. Instead of a nucleus, their genetic material, which is typically a single circular strand of DNA, is located in an area called the nucleoid. This structural difference is one of the primary distinctions between prokaryotic and eukaryotic cells.

In contrast, eukaryotic cells, which include animal and plant cells, possess a defined nucleus encased in a nuclear membrane, where their DNA is organized into multiple linear chromosomes. This separation of genetic material allows for more complex regulation of gene expression and cell function within eukaryotes.

Animal and plant cells, as subsets of eukaryotic cells, also have defined nuclei. Hence, they do not fall under the category of cells that lack a nucleus. Understanding this fundamental difference is crucial for grasping the broader concepts of cellular biology and the classification of living organisms.