Membrane Transport Passive & Active Transport

What does selective permeability of cell membranes do?

Regulates what enters & exits the cell

How is selective permeability able to regulate what enters and exits the cell?

Due to hydrophobic interior (tails) preventing polar/charged molecules from passing through

What does selective permeability create/maintain?

Concentration Gradients of solutes across the membrane

What are the two main types of transport across a membrane?

Passive & Active

What is passive transport?

Transport of a molecule that does not require energy from the cell because a solute is moving with its concentration/electrochemical gradient

What is passive transport involved in?

The import of materials and export of waste

What are some examples of passive transport?

1. Diffusion

2. Osmosis

3. Facilitated Diffusion

What is diffusion?

A spontaneous process resulting from the constant motion of molecules

What concentration do substances move from?

From high to low concentration

What direction do substances move on the concentration gradient?

Down

What do molecules do in diffusion?

They diffuse directly across the membrane

What are different rates of diffusion for?

For different molecules

Even with diffusion, the membrane is still what?

Selectively Permeable

What is Osmosis?

The diffusion of water down its concentration gradient across a selectively permeable membrane

What is Facilitated Diffusion?

The diffusion of molecules through the membrane via channel or carrier proteins

Facilitated Diffusion does not require what?

Energy

In Facilitated Diffusion, molecules still move down their what?

Concentration Gradient

What do channel proteins do?

1. Form an open pore/channel in the membrane

2. Moves charged ions like Na+ and K+ (Most are not permanently open)

“Gates” can open/close in response to what?

Stimuli (signaling molecules, changes in electric potential across membrane)

Ion channels are highly what?

Selective

Direction of flow is determined by what?

Electrochemical gradient (concentration and charge)

What can movement do to the membrane?

Polarize the membrane (affect the change across the membrane)

What are Aquaporins?

Specialized channel proteins for water