PASSIVE TRANSPORT

• Requires no energy input because all molecules still move down their concentration gradient
• All channels and many transporters work via passive transport

CHANNELS

• Somewhat specific, only allowing a molecule through if it is the right size and charge
• Allow for faster transport than transporters or diffusion
• Some channels require a signal before solutes can travel through
• Aquaporins are an example of channels – increase the rate of water travel

TRANSPORTERS

• Also called carrier proteins
• Very specific for the molecules that they transport
• Transporters can reverse direction if the concentration gradient flips
• Glucose transporter is an example

ELECTROCHEMICAL GRADIENT

• Concentration gradient is important for movement of molecules, but voltage difference between the two sides of the membrane can also play a role

Electrochemical gradient

Combined force due to the membrane voltage and concentration gradient

Electrochemical gradient when molecules are non-charged

• Movement based on concentration gradient ONLY, voltage difference plays no role

Electrochemical gradient when molecules are charged and voltage and concentration gradient work together

• Larger electrochemical gradient when voltage and concentration gradient work in the same direction

Electrochemical gradient when molecules are charged and voltage and concentration gradient oppose one another

• Smaller electrochemical gradient when voltage and concentration work in opposite directions