Active Transport
---Uses ATP to move solutes (e.g. Na+, K+, Ca++) “uphill” against concentration gradients and across a membrane
---Requires carrier proteins
---PrimaryActiveTransport:UsesATP
--- SecondaryActiveTransport:Substance pumped against its gradient can do “work” as it leaks back in.
---Coupled transport: more than one type of substrate at a time.

Types of Active Transport
----- Symport system – two substances are moved across a membrane in the same direction
-----Antiport system – two substances are moved across a membrane in opposite directions

Passive Transport: Diffusion
---Diffusion is the tendency of molecules and ions to scatter evenly throughout the environment
---Molecules move from areas of high concentration to areas of low concentration
---Kinetic energy is the driving force.
---Thus, size and temperature influence rate of
diffusion
---The plasma membrane is a physical barrier to free diffusion due to its hydrophobic core.
---Molecules will diffuse through the plasma membrane if the molecule is:
--lipid soluble
-- can pass through membrane channels
-- assisted by a carrier molecule
Simple diffusion – nonpolar and lipid-soluble substances
-----Diffuse directly through the lipid bilayer
E.g. O2 & CO2 (opposite gradients), fat-soluble
vitamins
-----Diffuse through channel
Facilitated diffusion
-----Transported substance binds to protein carriers in the plasma membrane and is ferried across or moves through water filled protein channels

24. Relate plasma membrane structure to active and passive transport mechanisms.