Cytosol is the cytoplasm excluding organelles and nucleus, and cytoplasm is cytosol plus organelles, but not the nucleus. Cytosol is an aqueous semifluid solution that surround organelles and nucleus that can be up to more than half of the cell volume of the animal cells, whereas in mature plant cells the majority of the cellular volume is occupied by vacuolae.
Cytosol mostly consists of water containing a large amount of organic molecules and ions. The concentration of molecules and ions can be so high that makes cytosol a viscous gel-like solution. Unlike the extracellular space, cytosol has a higher concentration of potassium and a lower concentration of sodium and calcium. It is buffered, about pH 7 to 7,4.
An intense molecular activity takes place in the cytosol: many metabolic reactions like glycolysis, translation of mRNA to proteins by free ribosomes, signaling cascades for cell communication and for communication between cellular compartments, etcetera. Ions, second messengers, and large molecules diffuse through the cytosol. Vesicles also move in cytosol from the source compartments toward the target compartments.
Cytoskeleton is also located in the cytosol. Cytoskeleton is a set of proteins organized in filaments that work as the skeleton and the muscles of the cell. These filaments are really versatile to accomplish the cell needs. In the cytosol, there are also stores of lipids as lipid droplets, and carbohydrates as glycogen.