specialized part of a cell having some specific function; a cell organ.
_membrane-bound structures w/in cell w/ specific functions isolated in separate compartments
_include nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, microbodies, vacuoles, mitochondria, chloroplasts
_separation of the organelle membrane and interior from the rest of the cell allows organelles to perform distinct functions isolated from other activities
_the separation of the organelle membrane prevents incompatible processes from mixing together; allows step-wise processes to be more strictly regulated; can make more processes more efficient by making them happen in a single constrained place
_Cytoplasm: liquid inside the cell surrounding organelles