All living cells have an outer cellular membrane that regulates not only what enters and exits the cell, but also how much of any given substance comes in and out. Cellular membranes are made up of proteins, called lipids, and certain nutrients use these to get into and out of the cell, while certain solvents depending on the cell are blocked by them. The make up of this membrane that protects the cell are selectively permeable meaning that the protiens embedded in the phospholipid bilayer can selectively take up and expel molecules that otherwise could not penetrate the memebrane. (Lab Manual) In doing so, these protien functions act as pores expelling fluid similar to the sweat glands that humans contain all over their bodies. Our pores secrete
