Biology AS level OCR

It's called the fluid mosaic as the phospholipids are constantly moving. It is a bilayer as you can see there is two layers of phospholipids. The tails face each other as they are hydrophobic, and the heads face outwards as they are hydrophillic.



I did OCR and you do need to know about carrier and channel proteins. The proteins are in the bilayer and form channels - like the name suggests. Channel proteins form pores for small ions and polar molecules to move through. As it is through a protein, the movement is called facilitated diffusion, and the molecules move down their concentration gradient.



Carrier proteins are slightly different, but are also in the phospholipid bilayer. They can transport large, polar molecules and ions in or out of cells. They can do this by facilitated diffusion - if the molecule is moving down the concentration gradient. Or it can do it by active transport if it is transporting the molecule against its concentration gradient. It works when a molecule attaches to a carrier protein in the membrane. The carrier protein changes shape, which then allows the molecule to be released on the opposite side of the membrane. When the carrier protein works by active transport, it uses ATP.



I hope that answers everything!