Plasma 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 Terminology Solute Solvent

This 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.

Diffusion Two 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

Osmosis A form of simple diffusion where the solvent, water is

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

Osmosis Diagram

Tonicity Hypertonic 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 in Plants Isotonic- Natural

tonicityhttp://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 Animals Isotonic- 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 Prokaryotes Isotonic- natural tonicity

Hypertonic- plasmolysis, cell shrinking due to water leaving the cell.

Hypotonic- cell swelling and sometimes lysis depending on the thickness of the cell wall.

Facilitated Diffusion Large 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 Diffusion In 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 Facilitated

Occurs 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