Cholesterol, it is thought of as a temperature buffer for the membrane, resisting changes in membrane fluidity that can be caused by changes in temperature.
Phospholipids can move within the bilayer but most of the lipids and proteins drift laterally. Flip flopping doesn't happen very often. When temperatures are cool, the fluid state goes to a solid...
The cell membrane/plamsa membrane a) maintains the internal environment of the cell by monitoring what enters and exits it b) Contains the contents of the cell, and c) Lends some sort of protection...
it is the outer coveringi dont know why im answering this i am the one who has to do a project!and i just had to read in my science book to find the answer...fingers crossed i get an A+