Diffusion and Osmosis

1. Diffusion and Osmosis

2. Membrane Architecture • The cellular membrane is an organelle that allows materials in and out of the cell.It is very similar to a guard at a gate. • The basic building block of the membrane is a Phospholipids, which has both polar and nonpolar regions. • The structure is a bilayer of the Phospholipids which repel each other with their heads facing in one direction and their tails facing in another direction.

3. Membrane • The lipid bilayer has two main characteristics.: • Polar molecules can not travel across the membrane • The bilayer is movable not rigid. Think of them as life perseveres they are capable of floating around and changing shape to fit their function.

4. Diffusion • Movement of molecules from an area of high concentration to an area of low concentration. • The difference in the concentrations is called concentration gradient. • Diffusion is driven entirely by kinetic energy the molecules possesses.

5. Diffusion • Molecules are always in motion, they move randomly, and are constant. • When molecules encounter an object they bounce off the object and move in another direction. • When molecules do not encounter another object they will continue in that direction and then move to an area of lower concentration.

6. Diffusion • In the absence of other influences, diffusion will eventually cause the concentration of molecules to be the same throughout the space in which the molecules occupy. This is called equilibrium.

7. Diffusion • In order for a molecule to diffuse across a membrane, there are some things to consider. • 1. Size and type of molecule • 2. Chemical nature of the membrane

8. Osmosis • Osmosis is the movement of water across a membrane. • Hypotonic means that the cell is lacking water. Therefore causing water to enter the cell and the cell swells. • Hypertonic means that the cell has too much water. Therefore causing the cell to loose water and making the cell shrink. • Isotonic means that there is the same solute concentration on the outside of the cell as there is in the inside of the cell. • Osmosis like diffusion, the molecules are in constant motion and always moving in and out of the cell to reach equilibrium.

9. Facilitative Transport • Active transport: That requires no extra energy of the cell, but the molecules need help crossing the membrane. • This is used when molecules can not diffuse across the membrane quickly. • Molecules that need help moving across the membrane are assisted by carrier proteins. These proteins carry the molecule from an area of high concentration to an area of low concentration.

10. Carrier Proteins • When the carrier protein binds to the molecule it then changes it’s shape. • Once the shape changes the molecule is transported across the membrane. • Glucose is an example: no extra energy

11. Sodium-Potassium PumpExtra Energy Needed • A sodium-potassium pump is one example of active transport in an animal cell. • This protein carries Na and K ions up their concentration gradient. • To function normally most animal cells must have a higher concentration of Na on the outside of the cells and a higher concentration of K on the inside of the cell.

12. Sodium-Potassium Pump • The sodium potassium pump works to maintain the difference in concentrations. • During the transfer 3 Na ions bond to the carrier protein and released ATP (energy source) allowing the molecules to move across the membrane. • Once Na has been transferred 2 K ions are able to bond and then be release inside the cell. • Na always wants to go outside of the cell and K wants to move inside the cell.