Cell Transport Chapter 4

Framing Question: How does a cell transport materials across the cell membrane?

Passive Transport Movement of molecules WITHOUT the use of energy by the cell. ◦ Diffusion ◦ Facilitated diffusion ◦ Osmosis

Diffusion Molecules constantly move randomly. Over time, molecules move from areas of high concentration to areas of low concentration.

Dynamic Equilibrium Eventually the molecules are evenly dispersed. This is known as equilibrium. THE MOLECULES CONTINUE TO MOVE.

Diffusion Across Membranes Particles will move across membranes if there is a concentration difference.

Dynamic Equilibrium Particles continue to move across the membrane in both directions even after equilibrium is reached. However, there is no net change in concentration. PARTICLES STILL MOVE.

Checkpoint: How will the molecules move in the following diagram?

Question: Why can’t the cell rely on diffusion for transport?

Facilitated Diffusion Molecules that are small and uncharged can easily move across the membrane. ◦ E.g. oxygen, carbon dioxide

Facilitated Diffusion Some molecules that cannot pass directly through the membrane can pass through using protein channels. This is known as facilitated diffusion.

Facilitated Diffusion Movie _Zhz8AY _Zhz8AY

Two kinds of facilitated diffusion Ion channels ◦ This is a special kind of protein that has a polar pore in the middle ◦ Ions have a charge, so they will be attracted to the polar pore and can diffuse through it.

Carrier Proteins Some molecules are just too big to get through the semi-solid membrane. A protein carrier will help transport each across Biggest example – GLUCOSE.

Checkpoint: How do diffusion and facilitated diffusion differ?