The separation of cell components by differential centrifugation. The tissue is broken down in a homogenizer and the homogenate is spun in the cell of an ultracentrifuge. Protoplasmic particles settle out in order of size and weight, separation also depending on the speed and duration of centrifugation. The rate of sedimentation is expressed as the *sedimentation coefficient
, s. After sedimentation is complete the fractions can be identified by their biochemical activity and by electron microscopy.