Cell Membrane: -Maintains homeostasis by controlling what substance may enter or leave cells.
Passive Transport: Substances crossing cell membrane without energy input by the cell, from high to low concentration. “Down” the concentration gradient
1) Diffusion (no facilitation)
omovement of molecules from high to low concentration
oconcentration gradient: difference in concentration of molecules across a distance
oDriven by molecules’ kinetic energy
oMolecules in constant motion, move randomly, in straight line
oEnd result: causing the concentration of solution the same throughout the space = Equilibrium
oRandom movement of molecules continues even in equilibrium
Diffusion across membranes = simple diffusion
- depends on size, type of molecules - depends on the chemical nature of the membrane
- Phospho-lipid bilayer - certain proteins can form pores in the membranes (e.g. molecules can dissolve in lipids may pass directly thruCO2 and O2 are non-polar and can dissolve in lipids.
(e.g. molecules that are very small, but not soluble in lipids may diffuse across the membrane by moving thru the poles in the membrane)