Cytoplasm is the viscid, semifluid matter contained within the plasma membrane of a biological cell. In contrast to the protoplasm, however, the cytoplasm does not include the cell nucleus. The watery or aqueous component of the cytoplasm is the cytosol, which includes ions and soluble macromolecules, for example enzymes. The insoluble constituents of the cytoplasm include the organelles and the cytoskeleton, which gives to the cytoplasm a gel-like structure and consistency. While all cells possess a cytoplasm, cells from the different biological domains and kingdoms can differ widely in the characteristics of their cytoplasms.