What is the definition of diffusion?
the net passive movement of particles (atoms, ions or molecules) from a region of high concentration to a region of low concentration. It continues until the concentration reaches equilibrium between the two areas.
What are the two factors which affect the rate of diffusion?
Temperature and concentration
How does an increase in temperature affect the rate of diffusion?
The particles would have more kinetic energy and so would move at higher speeds
How does concentration affect the rate of diffusion?
The greater the difference in concentration between the two areas the faster the rate of diffusion because the overall movement from the higher concentration o the lower concentration would be greater
What is meant by simple diffusion?
Diffusion in the absence of a barrier or membraneq
How can you calculate the rate of diffusion?
Distance/time
Why are membranes described as partially permeable?
Because they will only allow particular substances to enter the cell
What substances move through the membrane the easiest?
Small non-polar molecules
What substances have the hardest time of trying to move through the membrane?
Large polar molecules
Why are polar molecules or ions move through the membrane slowly or not at all?
They are repelled by the hydrophobic core of the membrane (non-polar lipid tails)
What are the two factors that affect the rate at which molecules and ions move through the membrane?
Surface area and thickness of membrane
How does increasing the surface area affect the rate of diffusion of molecules and ions across the membrane?
The larger the surface area the higher the rate of diffusion
How does decreasing the thickness of the membrane affect the rate of diffusion of molecules and ions across the membrane?
The thinner the exchange surface, the higher the rate of diffusion
What is the name given to the movement of a polar molecule or ion via a channel protein or carrier protein?
Facilitated diffusion
Why are membranes with channel proteins selectively permeable/
Because most channel proteins are specific to one molecule or ion
Does facilitated diffusion require energy?
No. because the movement of molecules is still down a concentration gradient
The more protein channels…..
The higher the rate of diffusion overall
