What is diffusion?
It is overall the net, or overall, movement of particles from a higher concentration to a lower concentration, the process is passive process, it continues until equilibrium is reached where there is no difference in concentrations.
Why does diffusion happen?
The particles in a state (except solids) have kinetic energy, the movement is random and will eventually become an equal distribution, equilibrium doesn’t mean the particles aren’t moving there is no difference in concentrations.
Factors affecting the rate of diffusion
Temperature - an increase in temperature increases the kinetic energy of the particles. Concentration difference - the greater the difference in concentration between the two regions the faster the rate of diffusion, as the overall movement of molecules will be larger.
Diffusion across membranes
The movement across membranes are involved in the passing of the phospholipid billayer, or if they are permeable to the substance they will not be allowed to enter ( e.g 02) the hydrophobic interior repels charges ions
Diffusion across a membrane through protein channels is called facilitated diffusion, membranes with protein channels are selectively permeable, these protein channels are specific to molecules or ions.
Factors affecting facilitated diffusion
The rate is dependent on temperature, concentration gradient, membrane surface area and thickness, the more protein channels leads to a higher rate of diffusion.
A channel protein
Its pore can open and close but is specific to a molecule or ion, this type of facilitated diffusion has a high rate of diffusion.
A carrier protein
Its pore is open fully across a membrane, the protein changes shape when a specific molecule or ion binds to the protein causing conformational shape allowing the molecule to cross the cell membrane, this protein allows a slower rate of diffusion due to the limited carrier proteins available. The changing of the conformational shape comes from the molecule or ion to the protein, not from ATP.