Diffusion  Diffusion is moving particles from an area where there are many particles to an area where there are less particles.  When the particles are spread out evenly or equally we say the solution has reached equilibrium.  Even in equilibrium, particles move back and forth in equal distribution, but there is no change in concentration.

Examples of Diffusion Example one: if cookies are baking in the kitchen the aroma will eventually make its way to all the rooms in the house. Example two: You add a drop of blue food coloring to a glass of water the food coloring will continue to travel out until all the water is blue.

Concentration Gradient Look at the picture below….there are two sides Rate of movement is determined by the concentration gradient.

Diffusion

Osmosis Water can move freely in and out of the cell. So, how is equilibrium achieved? Osmosis is how water diffuses across the cellular membrane. Water moves from an area of low particle concentration to an area of high particle concentration until equilibrium is achieved.

Three Types of Solution  Isotonic Solution is when the particles and water inside and outside the cell are equal.  Hypotonic Solution is when the particles inside the cell is greater than the particles outside the cell causing too much water to enter the cell. The cell may swell and burst.

 Hypertonic Solution is when the concentration of the particles outside the cells is greater than the concentration inside the cell causing the water to leave the cell. The cell shrivels up.

Passive Transport  The cell membrane uses Facilitated Diffusion to bring substances through a protein channel that have a charge (positive or negative) and cannot get through the cell membrane.  These substances are escorted by a carrier protein that protects the substance as it is passing through.

 In both Diffusion and Facilitated Diffusion particles move from high concentration to low concentration and require no extra input of energy.

Active Transport Active Transport is when substances have to move from lower to higher concentration against the passive movement. This movement requires energy! Think about walking up a hill against the wind on an extremely windy day.

Active Transport The cell uses a pump to transport particles against the concentration gradient. 3 Na + atoms go out and 2 K + atoms come in. Energy in the form of ATP is required for this process. A phosphate breaks away from ATP and binds to the pump. Na + and K + hook up to ATP to get the job done.

Examples  Diffusion- Lipids, carbon dioxide, oxygen, and alcohol.  Osmosis- Water.  Facilitated diffusion- sugar  Active transport- Sodium and potassium.

Questions 1. In your own words, what is the difference between facilitated diffusion and active transport? 2. What is a concentration gradient? 3. How does the cell transport sodium ions outside the cell?

4.How many sodium ions leave the cell in one event? How many potassium ions enter the cell? 5. What substances cross the membrane by Facilitated Diffusion? Active Transport? Osmosis?

Transport of Large Particles  Endocytosis is when a substance is too large to enter the protein channel and cannot diffuse across the membrane. The cell membrane stretches and surrounds the substance and then takes it into the cell.

Endocytosis  Phagocytosis-Moving solid material into the cell.  Pintocytosis-Moving liquid material into the cell.  Receptor Mediated Endocytosis- Receptors bind to substance to move into the cell.

Transport of Large Particles Exocytosis is when a particle needs to get out of the cell and can not diffuse through the membrane nor can it leave through the protein channel. The cell forms a bulge and then pinches off from the rest of the cell. Ex. Hormones and waste.

Signal Molecule A molecule that carries information to nearby cells. Ex. Hormones – Are made in one part of the body and are carried in the blood to another part of the body where they have their effect.

Receptor Protein Signal molecules are received at the target cells by binding to the cells receptor protein. The cell then responds to the signal. Ex. When a person is exercising the muscle would not be able to contract without the use of signal molecules and receptor proteins that tell the molecule when to contract and when to relax.

Receptor proteins cont……  Signal molecule binds to receptor protein that is embedded in the cell membrane.  The part of receptor protein that binds to signal is located on the outside of the cell.  This binding causes a change in the cell.

Change Can Occur In Three Ways 1. Change the permeability of the cell. 2. Trigger the formation of a second messenger inside the cell. 3. Activate enzymes inside the cell.

Questions  1. What are the three ways the binding of signal molecules can cause the cell to change?  2. What is a receptor protein?  3. What is a signal molecule? Give an ex.

1. Changes in Permeability  Receptor protein may be coupled with a protein ion channel, the binding causes the gate (door) to open. Ex. Na/ K pump Very important in the nervous system.

2. Second Messengers  The receptor protein causes the formation of a second messenger inside the cell.  The second messenger amplifies the message of the first signal.  The second mesenger can activate an enzyme  Or can change permeability by opening protein channels inside the cell.

Second messenger

3. Enzyme Action Receptor Proteins can act as enzymes (speeding up a reaction) or can trigger an enzyme to speed up a reaction. Ex1, Heroin acts as a signal molecule and binds to receptor proteins altering the functions of cells.

 Ex2. Some signal molecules cause increase in heart rate. Patients with irregular heart beat can take Beta Blockers. These drugs block signal molecules from binding. So heart beat stays normal.