The part of the cell that regulates what can enter or leave is the

Yes, the cell membrane regulates what enters the cell and leaves the cell. The cell membrane is a fluid mosaic consisting of a phospholipid bilayer and integral and peripheral proteins. The proteins of the membrane serve many purposes: transport, receptors, etc. The cell membrane is amphipathic, meaning is has hydrophilic and hydrophobic regions.

Ithink you should go back and learn in school rather then here asking questions