Testing the Squeeze Model Diffusion and Osmosis

Review Goal: How does lead get into our cells? 3 Models Egg experiment Squeeze Channel Active Egg experiment Test to see if squeeze model works with real cell membranes

Squeeze Model = Passive Transport No energy required Molecules move from area of HIGH to LOW concentration

Passive Transport: Diffusion The process of random movement toward equilibrium At equilibrium, particles continue to move, but there is no net change in distribution

Diffusion

Solute moves down the concentration gradient (from HIGH to LOW) Diffusion is the net movement of a substance from regions of high concentration to regions of low concentration Solute moves down the concentration gradient (from HIGH to LOW)

Diffusion Examples A membrane is not needed for diffusion Food coloring A membrane is not needed for diffusion Diffusion causes many substances to move across a cell membrane but NO ENERGY IS NEEDED

Egg Experiment Results With your group, Analyze the data table What happened in the egg experiment? Draw a Model explaining the results

Data Table Oil No Very Large None 150 Glucose Large 90 5 DDT High 100 Substance Charge of molecule Size of molecule Toxicity of molecule Outside the egg at Start (mL) Inside egg after 24hrs (per mL) Oil No Very Large None 150 Glucose Large 90 5 DDT High 100 10 Carbon Monoxide Small 110 Water Iodine Low 99 Calcium Yes Modify your egg experiment models based on the new information in the table. Individually explain and justify the changes you have made in response to the complex data table.

Egg Experiment Results What happened in the egg experiment The water crossed the membrane, the oil did not Why did the water move from the cup into the egg? Why did the water move from the egg into the oil?

Membrane properties affect the diffusion of solutes

Small molecules (H2O) and lipid soluble, hydrophobic molecules (O2, CO2) move through easily Molecules that pass through the phospholipid bilayer easily: Hydrophobic molecules (oil soluble): O2, N2 Nonpolar: benzene Small uncharged polar molecules: H2O, CO2, urea, glycerol

Ions, hydrophilic molecules larger than water, and large molecules such as proteins cannot move through the membrane on their own. Molecules that don’t pass through the phospholipid bilayer easily Large uncharged: glucose Polar molecules: sucrose Ions (charged): H+, Na+, Cl-, Mg 2+, HCO3, K+Ca 2+

Membrane properties affect the diffusion of solutes 3 characteristics of a molecule that determine the permeability of the membrane to that substance: Polarity (hydrophobic vs. hydrophilic) Charge (charged vs. uncharged) Size (large vs. small)

What about Lead?! Is it possible that lead can just squeeze through the membrane? It is toxic…. It is small…. AND It is ______________

OSMOSIS Another form of passive transport

Egg Experiment Results Osmosis (water diffusion) Water diffuses from a region of high concentration to one of low concentration. Move across the membrane until equilibrium is reached.

Descriptions of Solutions (in comparison to another) Isotonic Solution Equal [solute] in both solutions Hypertonic Solution Higher [solute] in the solution Hypotonic Solution Lower [solute] in the solution

Cell in Isotonic Solution 10% NaCl 90% H2O ENVIRONMENT CELL NO NET MOVEMENT 10% NaCl 90% H2O What is the direction of water movement?

Osmosis: Isotonic Isotonic- special equilibrium case where there is no net movement of water Hypotonic:A condition in which the inside of the animal or plant cell has a higher solute concentration than its environment. Osmosis causes a net flow of water into the cell, causing swelling and expansion. This swelling may cause cells without a rigid cell wall to burst. Hypertonic:A condition in which the environment has a higher solute concentration than inside the animal or plant cell. Osmosis pressure causes water to flow out of the cells and causing the cell to shrink

Cell in Hypotonic Solution 10% NaCl 90% H2O CELL 20% NaCl 80% H2O What is the direction of water movement?

Osmosis: Hypotonic Solution Hypotonic- a condition in which the environment has a lower solute concentration than inside the animal or plant cell. Water flows into the cell, causing swelling Swelling = breakage Hypotonic: A condition in which the inside of the animal or plant cell has a higher solute concentration than its environment. Osmosis causes a net flow of water into the cell, causing swelling and expansion. This swelling may cause cells without a rigid cell wall to burst. Hypertonic: A condition in which the environment has a higher solute concentration than inside the animal or plant cell. Osmosis pressure causes water to flow out of the cells and causing the cell to shrink Swollen

Cell in Hypertonic Solution 15% NaCl 85% H2O ENVIRONMENT CELL 5% NaCl 95% H2O What is the direction of water movement?

Osmosis: Hypertonic Solution Hypertonic- a condition in which the environment has a higher solute concentration than inside the animal or plant cell. Water flows out of cell into environment, cell shrinks Hypotonic: A condition in which the inside of the animal or plant cell has a higher solute concentration than its environment. Osmosis causes a net flow of water into the cell, causing swelling and expansion. This swelling may cause cells without a rigid cell wall to burst. Hypertonic:A condition in which the environment has a higher solute concentration than inside the animal or plant cell. Osmosis pressure causes water to flow out of the cells and causing the cell to shrink

Osmosis

Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

Cytolysis & Crenation Crenation Cytolysis Cyto = cell Plasm= Lysis = break Crenation Cytolysis

Plasmolysis vs. Turgid in Plant Cells

Osmosis With the egg in water: With the egg in oil: The water solution is hypotonic. Water will move into the egg until it becomes swollen With the egg in oil: The oil solution is hypertonic Water will move out of egg into the oil. Oil

Let’s Practice Some Problems