What is a defining feature of eukaryotic cells?

A defining feature of eukaryotic cells is the presence of a nucleus. Eukaryotic cells are characterized by having a membrane-bound nucleus that contains their genetic material (DNA), which is organized into chromosomes. This structure allows for greater regulation of gene expression and more complex processes such as mitosis and meiosis. The presence of the nucleus distinguishes eukaryotes from prokaryotic cells, which do not have a nucleus; instead, their DNA is located in a region called the nucleoid.

In contrast, the other options highlight characteristics that do not define eukaryotic cells. Eukaryotic cells are known for having various organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus, which perform specialized functions. They can be larger than prokaryotic cells, contradicting the idea that they are generally smaller. Additionally, all cells, including eukaryotic cells, have ribosomes, which are essential for protein synthesis, further emphasizing that the absence of ribosomes does not apply to eukaryotic cells.