Cell Membrane Discussion

Monday November 5^th

The cell membrane is made up of a bilayer made of two parts

1. Polar Phoshpate heads which are attracted to water (Hydrophilic)

2.  NonPolar Fatty Acid (lipid) Tails which are repelled by water (Hydrophobic)

Because of this, what kind of molecules can pass freely through the cell membrane? Small nonpolar molecules such as oxygen, carbon dioxide and natural steroid hormones.

Other substances (larger/polar molecules) move through membrane proteins known as  Transport Proteins (Channel and carrier proteins)

I discussed all the notes on the cell membrane and we started to get into the notes on passive transport.  We will start a lab tomorrow looking at different types of passive transport.  One demonstration I did today showed you what BASIC diffusion is and what the term "Dynamic Equilibrium" means.  The following are pics of red dye diffusing through a test tube.  This was an example of simple diffusion.  We will be looking at much more complex forms of transport throughout this week and next!

Red Dye added initially

A concentration Gradient has now formed with a high concentration
at the top and a low concentration at the bottom.

The Dye continues to sink, still setting up a concentration gradient

The Dye has now sunk to the bottom and will now
move from an area of HIGH concentration to an area of LOW
Concentration.

Red dye molecules continue to move WITH
the concentration gradient.

At this point, the test tube would be in Dynamic Equilibrium.
It is NOT that the molecules have STOPPED moving, it is
that now they have no NET movement.