Colloids and suspensions are heterogeneous mixtures of two or more physically intermixed components. In a colloid, the size of the solute particles ranges from 1 to 1000 nanometers, small enough that they are invisible individually. However, these solute particles can scatter light, making colloids appear translucent or opaque. They remain in the solution indefinitely and do not settle. Cytosol, the semifluid material inside living cells, is a colloid because of the numerous proteins and metabolites dispersed in it. In contrast, suspensions contain large particles, usually over 10000 nanometers, often visible to the naked eye. When left undisturbed, these particles settle down as sediments. Blood is an example of a suspension. When freshly drawn blood is left undisturbed for some time, the red blood cells settle at the bottom of the container. The upper liquid portion, called the blood plasma, is a solution of small solutes as well as a colloid containing larger plasma proteins.