2 Osmosis… …is the diffusion of water molecules …happens across a semi-permeable membrane
3 ONLY WATERWater is a small but extremely important molecule that makes up most of the liquid part of the cytoplasm in living things.Deals ONLY with the diffusion of WATERThe molecules (in this case, water - not solute molecules) will tend to move from an area of high (water) concentration to an area of low(water)concentration until equilibrium is reached.
5 OSMOSIS: FACILITATED DIFFUSION OF WATER ACROSS A CELL MEMBRANE Why would water molecules normally have a hard time getting across the cell membrane?The inside of a cell’s lipid bilayer is hydrophobic (water hating)Click me!
6 Aquaporins Most cells have special water channel proteins Known as – AquaporinsAllow H2O to pass right through them by facilitated diffusion.This EXTREMELY important process is = OSMOSIS
7 By knowing the concentrations of solute and solvent on the inside and outside of a cell, we can predict the direction of osmosis and the result on the cell.Solutions on the outside of a cell can be described based on how they affect the cellhypERtonichypOtonicisotonic
8 NOTE: (*tonic = solute. [High] solute means [low] water) Solutions on the outside of a cell (in its environment) can be described based on how they affect the cell:Hypertonic“Above Strength”Cell ShrinksThe solution outside the cell has a [higher] of solutes than insideWater moves OUT of cellHypotonic“Below Strength”Cell SwellsThe solution outside the cell has a [lower] of solutes than insideWater moves INTO the cellIsotonic“Same Strength”Cell stays the samethe solution outside the cell has the [SAME] of solutes than insideWater moves EQUALLY in/out of the cellNOTE: (*tonic = solute. [High] solute means [low] water)"HYPER" = HIGH; "HYPO" = LOW; "ISO" = equal or same.
9 VISUALIZE HYPERTONIC What will happen? a) net movement of water _______of cellb) cell will ________c) solution is hypertonic to the cellCell with 2% solute, 98% solventBeaker with 3% solute, 97% solventH2OH2OH2OBEFOREAFTER
10 VISUALIZE HYPOTONIC What will happen? a) net movement of water _______of cellb) cell will ________c) solution is hypotonic to the cellCell with 2% solute, 98% solventBeaker with 1% solute, 988% solventH2OH2OH2OBEFOREAFTER
11 VISUALIZE ISOTONIC What will happen a) no net movement Cell with 2% solute concentration, 98% solventBeaker = 2% solute, 98% solventWhat will happena) no net movementb) cell won’t change in sizec) solution = isotonic to the cell
12 Common mistakes when discussing hyper-, hypo-, and isotonic solutions The solutions are named for the concentrations of the SOLUTESThe substance that moves to balance the solute concentration is the WATERThe solutes to not “pull” or “suck” the water across the membrane – the water simply diffuses from where it is in high concentration to low concentration
13 Solute and solvent concentrations can be expressed as percentages of the entire solution. When added together, the solute and solvent concentrations must equal 100%.A solution with a 10 % solute concentration has a 90% solvent concentration.
14 Let’s do some math!What is the solvent concentration of a solution with a 3% concentration of solute?What is the solvent concentration of a solution with a 15% concentration of glucose?What is the solute concentration of a solution with 98% solvent?What is the solute concentration of a solution with 75% water?
15 Osmotic PressureDriven by differences in solute concentration, the net movement of water into or out of a cell produces a force known as osmotic pressure
16 Almost always hypertonic… Because cells contain a variety of solutes such as:sugars, proteins, salts, etc.they are almost always hypertonic(*the environment = HYPOtonic!) to fresh water;as a result, a typical cell exposed to fresh water will tend to swell up quickly from the entering water.This may in fact cause an animal cell to swell like an overinflated balloon.
17 Plant cells contain a central vacuole which stores excess water - shrinking and swelling as water enters or exits the cell. Plant cells wouldn't generally burst thanks to their protective cell walls.In fact, most cells in large organisms are not in contact with fresh water on a regular basis - rather, they tend to be bathed in blood or other isotonic fluids which have solute concentrations approximately equal to themselves.Cells which are plump and rigid in hypotonic environments are called turgid; when a cell shrinks in a hypertonic environment this is called plasmolysis
18 Fill in… Conditions Water will… Environment is... Solute concentration in the environment is equal to that in the cellSolute concentration in the environment is greater than the cellSolute concentration in the environment is less than the cellMove in and out in equal amountsNo net movementIsotonic to the cellCell is isotonic to its environmentMove OUT of the cellThe Cell ShrinksHypertonic to the cellCell is hypotonic to its environmentMove INTO the cellThe Cell SwellsHypotonic to the cellCell is hypertonic to its environment
20 Animal cell (blood cell) Show what happens to plant and animal cells subjected to isotonic, hypertonic, and hypotonic solutions in the environment:ConditionsPlant Cell (leaf cell)Animal cell (blood cell)EnvironmentBeforeAfterSolute concentration in the environment is equal to that in the cell:Isotonic solutionSolute concentration in the environment is greater than the cell:Hypertonic SolutionSolute concentration in the environment is less than the cell:Hypotonic Solution