In cell biology, an organelle is one of several structures with specialized functions, suspended in the cytoplasm of a eukaryotic cell. Organelles were historically identified through the use of some form of microscopy and were also identified through the use of cell fractionation.

A few large organelles probably originated from endosymbiont bacteria:

• chloroplast
• mitochondrion

Other organelles include:

• centriole
• endoplasmic reticulum
• golgi apparatus
• lysosome
• myofibril
• plastids
• nucleus
• peroxisome
• ribosome
• vacuole
• vesicle
• melanosome

Other related structures:

• flagellum
• cytosol
• endomembrane system
• nucleosome
• microtubule
• cell membrane