Here's why:
* Nucleus: Eukaryotic cells have their genetic material (DNA) enclosed within a membrane-bound nucleus. This distinguishes them from prokaryotic cells, which lack a nucleus and have their DNA freely floating in the cytoplasm.
* Other characteristics: While other characteristics like the presence of organelles (like mitochondria and Golgi apparatus) are common in eukaryotes, they aren't universally present in all eukaryotic cells. For example, some eukaryotes are single-celled and lack complex organelles.
Therefore, the presence of a nucleus is the most fundamental and defining characteristic of all eukaryotic cells.
