Passive TransportPlasma Membrane Part 2- Diffusion, Osmosis,

and facilitated diffusion.

The Cell Membrane and Transport The main function of the plasma membrane is

to regulate what enters and leaves the cell. This can be done passively through the

processes of simple diffusion and facilitated diffusion.

IN GENERAL PASSIVE TRANSPORT DOES NOT REQUIRE ENERGY BECAUSE IT GOES WITH THE CONCENTRATION GRADIENT….

Particles move from areas of high concentration to low concentration.

Solution TerminologySolute SolventThis substance that is

dissolved into the solvent.

The substance that dissolves the solute.

When learning about the plasma membrane we have to remember that in biological systems substances are in their aqueous form. Water is the universal solvent for all biological substances. Since we are speaking in terms of solutions we must always be aware of what is the solvent and the solute in each situation.

DiffusionTwo types of Diffusion: Simple and Facilitated.Both solvent and solute particles will move with

the concentration gradient in an effort to reach equilibrium.

Evolutionarily speaking the reason that cells are so small is because of diffusion. http://www.youtube.com/watch?v=xuG4ZZ1GbzI&safety_mode=true&persist_safety_mode=1

Understanding the process of diffusion has allowed us to save countless lives with dialysis and other disease treatments. http://www.youtube.com/watch?v=shFSW8VE3Gs&safety_mode=true&persist_safety_mode=1

Diffusion Diagram

OsmosisA form of simple diffusion where the solvent,

water is moving with its concentration gradient in an effort to reach equilibrium.

TonicityHypertonic Solution- has more solute particles than

solvent particles. Hypertonic cell- has more solute particles outside of

the cell than in which makes the water rush out of the cell.

Isotonic Solution- has a balanced number of solute and solvent particles.

Isotonic cell- has a balanced solute ration inside and outside of the cell, water will not move in either direction.

Hypotonic solution- has more solvent particles than solute particles

Hypotonic cell- has more solute particles inside the cell that outside which makes water rush into the cell.

Osmosis Diagram

Osmosis in PlantsIsotonic- Natural tonicity

http://www.youtube.com/watch?v=BB5rvjZzgFU

Hypertonic- plasmolysis, the cytoplasm shrinks and the membrane shrinks away form the cell wall. http://www.youtube.com/watch?v=SooSsKkJo1o

Hypotonic- swelling of the cell which makes the cells appear packed closely together in microscopy. Cell lysis does not occur because of the plant cell wall. http://www.youtube.com/watch?v=2b2xYv-2B1g&safe=active

Osmosis in AnimalsIsotonic- natural tonicity. Hypertonic- plasmolysis, shrinking of the cell

as the water leaves.Hypotonic- swelling of the cell to the point of

cell lysis, or cell bursting, as water enters the cell.

Video:http://www.youtube.com/watch?v=OYoaLzobQmk

http://www.youtube.com/watch?v=dHc05E7BijQ&safety_mode=true&persist_safety_mode=1

Osmosis in ProkaryotesIsotonic- natural tonicityHypertonic- plasmolysis, cell shrinking due to

water leaving the cell. Hypotonic- cell swelling and sometimes lysis

depending on the thickness of the cell wall.

Facilitated DiffusionLarge or charged molecules require a

pore/channel or a carrier in the cell membrane for diffusion to occur.

Cholera, a digestive disease caused by a bacteria, cause death for many years before facilitated diffusion was understood and could be utilized to save patients.

Heat stroke and other dehydration sicknesses have also been helped by our current understanding of facilitated diffusion.

Facilitated DiffusionIn facilitated diffusion an opening created by the

pore of channel allows the diffusing particle to cross the cell membrane.

This process DOES NOT require energy. Pores/channels are openings, like a straw in the

cell membrane. Carriers usually involve the binding of the target

substances, a conformational change in the protein carrier, then a dissociation of the substance on the other side of the membrane.

Video:http://www.youtube.com/watch?v=fupBv22Eh6Y&safe=active

Passive Transport Overview- occurs with the concentration gradient!Simple FacilitatedOccurs due to concentration

difference. Semi permeability of the

membrane allows molecules to move to reach equilibrium.

Does not require energy. Includes osmosis.

Isotonic -osmotically balanced, water doesn’t move.

Hypertonic- too much solute, water flows out

Hypotonic- too much solvent, water flows in

Occurs due to concentration difference.

Requires protein pores/channels/carriers for molecules to move to reach equilibrium.

Pores/channels/carriers are specific to the molecule they transport.

Does not require energy.

Video:http://www.youtube.com/watch?v=JShwXBWGMyY&safe=active