Which of the following is NOT a eukaryote?

Bacteria are classified as prokaryotes, which means they lack a membrane-bound nucleus and membrane-bound organelles that are characteristic of eukaryotic cells. Eukaryotes, on the other hand, include organisms such as humans, animals, and plants, all of which possess complex cellular structures with organized nuclei.

In humans and animals, cells contain membrane-bound organelles such as mitochondria and endoplasmic reticulum, which are not found in prokaryotic cells like bacteria. Plants also have similar eukaryotic structures and additionally contain chloroplasts for photosynthesis. Thus, the distinct absence of these defining characteristics of eukaryotic cells in bacteria confirms that they are not classified as eukaryotes.