In cell biology, the cytoplasm is the material within a living cell, excluding the cell nucleus. It comprises cytosol and the organelles – the cell's internal sub-structures. All of the contents of the cells of prokaryotic organisms (such as bacteria, which lack a cell nucleus) are contained within the cytoplasm. The mitochondrion is a double membrane-bound organelle found in all eukaryotic organisms. Some cells in some multicellular organisms may, however, lack them.
