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:
... spread out with 22.3% under the age of 18, 6.7% from 18 to 24, 28.0% from 25 to 44, 25.8% from 45 to 64, and 17.2% who are 65 years of age or older. The median age is 41 ...