What type of cells are characterized by the absence of a nucleus?

Prokaryotic cells are defined by their lack of a membrane-bound nucleus and other membrane-bound organelles. Instead of a nucleus, prokaryotic cells have a nucleoid region where their genetic material (DNA) is located. This structural characteristic distinguishes them from eukaryotic cells, which contain a nucleus encased in a nuclear membrane. Prokaryotic cells are typically smaller and simpler in structure compared to eukaryotic cells, which can be found in both unicellular and multicellular organisms, including animals and plants.

In contrast, eukaryotic cells are characterized by the presence of a nucleus, making them fundamentally different from prokaryotic cells. Animal cells and plant cells are both types of eukaryotic cells, and therefore they do not fit the criteria of having an absence of a nucleus.