An organism is said to have a prokaryotic cell if its cell is a very simple one that does not contain any true nucleus and which do not have membrane bound organelles. Prokaryotes are usually unicellular organisms, examples are bacteria. One key feature of prokaryotic cell is a piece of circular, double stranded DNA which is usually found in the cell.
24 because the sun has to be over his head again...?
It allows people in different places and different countries to use the same units, avoid mistakes and understand each other more easily. The common base 10 of all units makes it easier and has more accurate calculations that are made without cumbersome conversion factors.