Canadian National Institute of Health (CNIH) Entrance Practice Exam

A eukaryote is characterized by having cells that contain membrane-bound organelles. This distinction is fundamental to the structure of eukaryotic cells, which include a variety of organelles such as the nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus, each enclosed by membranes. These organelles allow for compartmentalization of various cellular processes, enhancing the complexity and efficiency of eukaryotic cells, as compared to prokaryotes, which lack such structures.

The presence of a nucleus is particularly significant as it houses the cell's genetic material. This allows for more complex regulation of gene expression and cellular processes. Eukaryotic cells can be unicellular, like yeast, or multicellular, as seen in plants, animals, and fungi, which further highlights the diversity within this group.

The other options presented do not accurately define a eukaryote. For instance, the absence of a cell membrane is not a characteristic of eukaryotes, as they have a cell membrane. Being a single-celled organism does not inherently define a eukaryote, as both eukaryotes and prokaryotes can be unicellular. Lastly, not all eukaryotes perform photosynthesis