Cells and cellular diversity

The cell is the root of all cell diversity because diversity begins in the cell. Cells are categorized by the organelles they do or do not contain, their shape and size, the complexity and type of genetic information they carry, and the basic structure of it. Plants cells and animal cells differ, for example, because plant cells do not contain mitochondria, but instead have chloroplasts to gather energy from the sun and large vacuoles to store their food.
Animal cells and plant cells are even categorized into their own separate category from other cells; they are considered eukaryotes because they are more complex and contain DNA, as opposed to the simpler prokaryotes which contain single stranded genetic information and are typically smaller. These microscopic differences within the cells account for the tissues they may or may not make up and the functions of the tissues which root from the functions of the cells.