Cells
... heads. There some pentagon shaped organelles between phospholipid heads that are called steroids. These physical features make up the cell membrane. Cells have organelles that are designed for the function of transporting molecules in and out of the cell. When a molecule passes through the lipid bilayer, membrane proteins play a very important role in this function. Two examples of how molecules can travel in and out of a cell. One of them is that the integral proteins form passages, or pores that allow molecules to travel through. Another ways is that proteins will stick to the molecule and transport it to another part of the membrane. Cell may use one of these examples as a way of transporting molecules in and out of a cell. There are different kinds of passive transport, but the simplest of them is diffusion. Diffusion is when a molecule travels from an area of high concentration to low concentration. An example of this would be when you drop a sugar cube into a glass of water. The sugar diffuses into the water; this is because the sugar was moving from high concentration to low concentration. Another type of passive transport is facilitated diffusion. When a molecule is unable to diffuse through the cell membrane it is assisted by a carrier protein. The carrier pro...