Diffusion Flashcards
What is diffusion?
Diffusion is the net movement of a substance from an area of high concentration to an area of lower concentration, until equilibrium is reached
Random movement of particles
Why are cells generally microscopic?
Particles move at high speeds and are constantly colliding (slows them down)
Large cell- rate of diffusion is too slow due to collisions
What are the factors affecting simple diffusion?
Temperature- higher (particles have more KE so they move at higher speeds)
Concentration difference- higher (overall movement from higher conc to lower conc is larger)
Surface area- larger
Thickness of membrane-lower
What does diffusion across membranes involve?
Particles pass through the phospholipid bilayer
Only non polar molecules can pass through the bilayer- smaller non polar molecules pass through more easily than larger ones
Ions (polar) cannot pass through because the hydrophobic interior of the membrane repels them
Small polar molecules (eg h20) can pass through the membrane but at a very slow rate
What is facilitated diffusion?
Involves the transport of polar molecules and ions. Involves channel and carrier proteins.
Why is facilitated diffusion selectively permeable?
Protein channels are usually specific to one molecule/ion
How do carrier proteins transport molecules across a membrane?
They change shape when a specific molecule binds
What is one factor that affects the rate of facilitated diffusion
Number of channel proteins available
