Exchange Across Cell Membranes - Diffusion Flashcards
What is diffusion?
Diffusion is the net movement of particles from an area of high conc to an area of low conc
Which way to molecules diffuse?
Both ways but the net movement will be to the area of lower conc
How do particles diffuse?
Down a concentration gradient?
Does diffusion require energy?
No - it’s a passive process
What is simple diffusion?
When molecules diffuse directly through a cell membrane
What molecules can’t pass directly through a cell membrane?
- Larger molecules because they’re too big
- Charged particles because they’re water soluble and the centre of the bilayer is hydrophobic
What is facilitated diffusion?
When large or charged particles diffuse through carrier proteins or channel proteins in the membrane
Does facilitated diffusion use energy?
No, it’s a passive process
What do carrier proteins do?
They move large molecules across membranes, down their conc gradient
How do carrier proteins work?
First, a large molecule attaches to a carrier protein in the membrane. Then, the protein changes chase and releases the molecule on the opposite side of the membrane
How do channel proteins work?
They form pores in the membrane for charges particles to diffuse through, down their conc gradient
What three things affect the rate of simple diffusion?
- The conc gradient
- The thickness of the exchange surface
- The surface area
How does the conc gradient affect the rate of simple diffusion?
The higher it is, the faster the rate of diffusion. As diffusion takes place, the difference in conc between the two sides of the membrane decreases over time until it reaches an equilibrium - rate of diffusion slows over time
How does the thickness of the exchange surface affect the rate of simple diffusion?
The thinner the exchange surface, the quicker the rate of diffusion
How does the surface area affect the rate of simple diffusion?
The larger the surface area the faster the rate of diffusion
