1. Chapter 7.2

2. selective permeability
Chapter 7.2
Membrane Structure
results in
selective permeability
Membrane- A supramolecular structure. Many molecules ordered into a higher level of organization.
Membrane regulates the cells molecular traffic. A steady traffic of small molecules and ions moves across the plasma membrane in both directions.
Cell is selective permeability, to allow a variety of small molecules, but then excluding the ones it does not want. The membrane can also determine what rate the substances travel in and out.

3. The Permeability of the Lipid Bilayer
Chapter 7.2
The Permeability
of the Lipid Bilayer
Hydrophobic molecules can dissolve in the lipid bilayer of a membrane and cross it with ease without the aid of membrane proteins.
Polar molecules only pass slowly through the membranes lipid bilayer.

4. Transport Proteins Chapter 7.2
There are many kinds that transport substances in many different ways, some cells membranes differ from others.
Transport Proteins- Allows hydrophilic substances to avoid contact with the lipid bilayer by passing through this. They also span the membrane.
An example of this is aquaporins. These are channel proteins that facilitate the passage of water molecules through the membrane in certain cells.
Carrier proteins hold on to its “passengers” and then changes shape in a way that shuttles them across the membrane.
The selective permeability of a membrane depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins built into the membrane.

5. Chapter 7.3

6. Passive Transport is diffusion of a substance across a membrane with
Chapter 7.3
Passive Transport is diffusion of a substance across a membrane with
no energy investment
A result of thermal motion is diffusion
Diffusion- the tendency for molecules of any substance to spread out evenly into the available space.
Any substance will diffuse down its concentration gradient.
Concentration gradient- in the absence of other forces, a substance will diffuse from where it is more concentrated to were it is less concentrated.
Diffusion is spontaneous.
The diffusion of substance across a biological membrane is called passive transport because the cell does not have to expend energy to make it happen.

7. Effects of Osmosis on Water Balance
Chapter 7.3
Effects of Osmosis on
Water Balance
Osmosis- the diffusion of water across a selectively permeable membrane.
The movement of water across cell membranes and the balance of water between cell and its environment are crucial to organisms.

8. Water Balance of Cells Without Walls
Chapter 7.3
Water Balance of Cells
Without Walls
Tonicity- the ability of a solution to cause a cell to gain or lose water.
Isotonic – iso means same
So the isotonic solution would be the same environment as the cell.
Hypertonic- hyper means more
So, in the instance of a cell, the hypertonic solution would have more non-penetrating solutes than the cell.
-causes water to leave cell and shrivel and die
Hypotonic- hypo means less
For a cell in a hypotonic solution with less non-penetrating solutes, water will enter the cell faster than it leaves.
-causes cell to swell and burst or lyse
Osmoregulation- the control of water balance
Animals and other organisms without rigid cell walls living in hypertonic or hypotonic environments must have special adaptations for osmoregulation.

9. Water Balance of Cells with Walls
Chapter 7.3
Water Balance of
Cells with Walls
Flaccid- limp
If the cells and their surroundings are isotonic, there is no net tendency for water to enter, and the cell becomes this.
Turgid- very firm
Elastic walls of cells will only expand so much before it exerts a back pressure on the cell that opposes further water uptake.
*Like a Bush*

10. Facilitated Diffusion
Chapter 7.3
Facilitated Diffusion
Facilitated diffusion- when polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane.
-material moves down concentration gradient
Channel proteins simply provide corridors that allow specific molecules or ions to cross the membrane.
An ion channel is one of these groups. Many of these function as gated channels. Gated channels are stimulated to open and close by electrical or chemical stimulus's.
Carrier proteins simply change conformational shape as they bind to and transport solutes across the membrane