The cytoplasm is the parts of a cell that are enclosed within the plasma membrane. It is eighty percent water and usually clear in color. The cytoplasm is a viscous (thick) gel that liquefies when shaken or stirred. Cytoplasm means cell substance. In eukaryotic cells the cytoplasm contains organelles, such as mitochondria, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes. It is also the site where most cellular activities occur, such as many metabolic pathways, and processes such as cell division.
The part of the cytoplasm that is not held within organelles is called the cytosol. The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol is a gel, with a network of fibers dispersed through water. Due to this network of pores and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution. This crowding effect alters how the components of the cytosol interact with each other.