In biology, particularly cell biology, the term organelle is used to describe any one of a number of types of subcellular structures, historically identified through the use of some form of microscopy.
A few large organelles probably originated from endosymbiont bacteria:
... 45 to 64, and 28.1% who are 65 years of age or older. The median age is 50 years. For every 100 females there are 86.7 males. For every 100 females age 18 and over, there ...