Please enable JavaScript.
Coggle requires JavaScript to display documents.
Cell surface membrane (Types of transport (Simple diffusion occurs down a…
Cell surface membrane
Types of transport
Simple diffusion occurs down a concentration gradient and is passive. Transport proteins are not required as the molecules that are diffusing are small and non-water soluble.
Facilitated diffusion occurs down a concentration gradient and is passive. Transport proteins are required as it involves the transport of larger molecules and water-soluble molecules.
Active transport occurs up the concentration gradient. It is active, requiring ATP, and carrier proteins.
Osmosis is the diffusion of water molecules down their water potential gradient. It is passive and requires transport proteins.
Co-transport is passive and requires a transport protein. It involves something travelling down its concentration gradient, in order for another to travel up its concentration gradient.
Cell-surface membrane
This is the thing that surrounds cells. It needs to be partially permeable, in order to let certain compounds pass through it.
Proteins are scattered throughout the cell-surface membrane, like tiles in a Mosaic.
The bilayer is fluid in the fluid mosaic model. The bilayer is fluid because the phospholipids are constantly moving.
-
-
Components
Phospholipids: Phospholipids have a hydrophilic head and two hydrophobic chains. The molecules automatically arrange themselves into a bilayer. The centre of the bilayer is hydrophobic so it doesn't let water-soluble substances pass through it. Small non-polar substances can diffuse through the membrane.
Cholesterol: Cholesterol gives the membrane stability. It is a type of lipid that's present in all membranes. Cholesterol binds to the hydrophobic tails of phospholipids, resulting in them packing closer together. This restricts the movement of phospholipids, making the membrane rigid, and less fluid. This is particularly important for free cells, e.g. red blood cells.
-