ORGANELLES
Organelles are substructures in a cell that perform some or other specific functions. They serve for division of a cell into sections (or, separation sections inside a cell) with different conditions. They contain different combinations of biological molecules. The size of an organelle can vary from 20 nm to 10 microns. The largest organelles, such as nucleus, mitochondria and chloroplasts, are found for the present only in eukaryotic cells. Their diameter is almost equal to the diameter of a typical prokaryotic cell (that is, 1 to 10 microns). The diameter of small organelles, like ribosomes (that are found both in eukaryotic and prokaryotic cells) is approximately 20 nm. All the organelles are in the cytoplasmic matrix.