Which type of cells are characterized by being small, simple, and lacking a nucleus?

The correct response identifies prokaryotic cells, which are indeed small and simple compared to their eukaryotic counterparts. These cells are primarily characterized by their lack of a true nucleus; instead, their genetic material is found in a region called the nucleoid. Prokaryotic cells also lack membrane-bound organelles, which distinguishes them from eukaryotic cells, which are generally more complex and larger, containing a defined nucleus and various organelles.

This simplicity is an advantage for prokaryotic cells, allowing them to reproduce quickly and thrive in a variety of environments. Their structure typically includes a cell membrane, a rigid cell wall, and sometimes additional features like flagella for movement or pili for attachment. These features have allowed prokaryotic cells—such as bacteria and archaea—to adapt successfully to many ecological niches.

In contrast, eukaryotic cells are more complex and contain a nucleus, along with various organelles. Multicellular organisms refer to life forms composed of multiple cells working together, and complex cells would imply advanced organization and structure that prokaryotic cells do not possess. Therefore, prokaryotic cells stand out for their simplicity and lack of a nucleus.