Early embryonic development (metaphase in mitosis) over time, from upper left to lower right with tubulin (microtubules) labeled, showing the elongation of the mitotic spindle prior to the first cell division. Courtesy of Ahna Skop, Skop Lab.
A class of organisms composed of one or more cells containing a membrane-enclosed nucleus and organelles. This class constitutes one of three distinct evolutionary lineages (eubacteria, eukaryotes & archaea) of modern-day organisms. Includes all organisms except viruses and prokaryotes (mostly bacteria).