Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. when animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. the presence of phosphatidylserine on the cell surface serves as a signal that direct the rapid removal of the dead cell. how might a cell actively engineer this phospholipid redistribution?