Biology - 2.3 - transport across cell membranes (processes)
define simple diffusion
movement of molecules from a high to low concentration, down a concentration gradient until equilibirum has been reached. passive process.
why are there limitations to simple diffusion
only small or non-polar molecules may diffuse directly through phospholipid bilayer, like oxygen and carbon dioxide
why may polar molecules not diffuse through the P.B.
they are hydrophilic and cannot travel through the centre lipid layer
define facilitated diffusion
channel or carrier proteins facilitate the diffusion of large, polar, charged, and lipid insoluble moleules which cannot diffuse through the P.B.
what is the role of carrier proteins in facilitated diffusion
facilitate diffusion of water insoluble molecules
how do carrier proteins work
receptors only allow a specific molecules to bind
once binded, protein changes shape to allow molecule to move through
what do carrier proteins rely on
kinetic energy of diffusion molecule
how do channel proteins work
forms pores in the membrane to allow ions to travel through