Final answer:
The sedimentation order in centrifugation is primarily determined by the Svedberg value (S value), which is influenced by size and mass. Ribosomes require higher speeds for collection in ultracentrifugation than nuclei because nuclei are larger and sediment at lower speeds. Higher angular velocity in centrifugation is needed for smaller and denser ribosomes to sediment properly.
Step-by-step explanation:
The primary factor that determines the sedimentation order of ribosomes and the nucleus in centrifugation is the Svedberg value (S value). The Svedberg value reflects the rate of sedimentation during centrifugation, which is influenced by the size and shape of the particles as well as their mass and buoyant density in a given medium. Because ribosomes have smaller S values compared to the nucleus, they sediment more slowly and therefore require higher speeds for collection during ultracentrifugation.
Regarding why ribosomes require higher speeds for collection compared to nuclei, it is because the nuclei are larger and sediment out of solution at lower speeds than the smaller ribosomes. Ribosomes are denser in terms of size and therefore must be spun at higher speeds to ensure their adequate separation from the solution. Also, the large angular velocity of the centrifuge quickens the sedimentation of smaller ribosomes by providing a higher centripetal force.