Osmosis & Diffusion Packet #8 Sections 7.3 & 36.1

Diffusion

Introduction {Figure 7.11} Atoms and molecules, above absolute zero, exhibit motion. This random motion allows particles to move from an area of higher concentration to an area of lower concentration in an attempt to reach equilibrium.

Rate of Diffusion… Depends on four factors Temperature Size of the molecule Electrical charges Concentration gradient

Categories of Diffusion I Regular Diffusion Movement of molecules down the concentration gradient High to low Facilitated Diffusion Movement of molecules down the concentration gradient via a channel In cells, these channels are found in proteins More to come later Active transport Movement of molecules against the concentration gradient via channels and with the use of energy.

Osmosis Special Case of Diffusion

Osmosis {Figure 7.12} Concise Definition Friday, November 16, 2018Friday, November 16, 2018 Concise Definition The diffusion of water (liquid solvent) across a selectively permeable membrane Detailed Definition Transfer of a liquid solvent through a semi permeable membrane, that does not allow dissolved solids (solutes) to pass from an area of high concentration to an area of low concentration

Osmotic Pressure, Osmotic Potential & Solute Potential

Osmotic Pressure Osmotic Pressure Friday, November 16, 2018Friday, November 16, 2018 Osmotic Pressure Is a measure of the tendency of water to move into a solution. The driving force for the water and is the difference in water pressure on both sides of the membrane. The differences in pressure provides a net pressure that is exerted by the flow of water as it moves through the semi-permeable membrane. Class Illustration Use students to illustrate the differences in pressure. Five on side A and 2 on side B—most pressure going forward will be on side A giving a net pressure as the water moves from side A to side B. If a solution is separated from pure water by a semi-permeable membrane, the pressure which must be applied to prevent osmosis is called the osmotic pressure

Osmotic Potential = Osmotic Pressure Friday, November 16, 2018Friday, November 16, 2018 Osmotic Potential Difference in osmotic pressure that draws water from an area of less osmotic pressure to an area of greater osmotic pressure. The potential of a solution to pull in water Value is always negative The more concentrated the solution, the more negative its osmotic potential

Osmotic Potential = Osmotic Pressure = Solute Potential Friday, November 16, 2018Friday, November 16, 2018 The presence of solutes, in the solutions, impact the direction of the movement of water. The ability of a solution to pull in water depends on the number of solute particles present. The higher the amount of solutes in the solution, the lower the solute potential. The solution is more concentrated. Remember, from previous slide, the value is always suppose to be negative.

Osmotic Potential = Osmotic Pressure = Solute Potential Friday, November 16, 2018Friday, November 16, 2018 All three terms represent a measure of the ability of a solution to pull in water. The value is always negative. The more solutes present, the more negative the value. Represented by s

Osmotic Potential = Osmotic Pressure = Solute Potential Friday, November 16, 2018Friday, November 16, 2018 When two solutions have the same osmotic potential, they are said to be isotonic. Where one solution has a greater osmotic potential compared to the other, it is described as being hypertonic. i.e. It is more concentrated. The solution with the lower osmotic potential is described as being hypotonic. Less concentrated.

Pressure Potential {Figure 36.5} Friday, November 16, 2018Friday, November 16, 2018 Solutions/Water are also under the influence of external pressures. These external pressures are measure as pressure potential. This force (pressure) is not the same as the one caused by the movement of the liquid solvent (water). Represented by p Negative or positive depending on conditions.

Water Potential Measure of the tendency of water to leave a solution. Friday, November 16, 2018Friday, November 16, 2018 Measure of the tendency of water to leave a solution. Combination of the sum of osmotic potential/solute potential and pressure potential.  = s + p

Water Potential II Friday, November 16, 2018Friday, November 16, 2018 When measuring the water potential of two solutions, the solution with the lower water potential receives water from the solution with higher water potential Osmosis!

Friday, November 16, 2018 Cells and Osmosis

Pressure Potential in Plant Cells Friday, November 16, 2018Friday, November 16, 2018 In plant cells, the cell contents press the plasma membrane against the cell wall—producing an external force called turgor pressure. Results in a turgid plant cell Pressure potential is positive A plant cell can be considered as a solution of salts and sugars in the vacuole surrounded by a semi-permeable membrane

Pressure Potential in Plant Cells II Friday, November 16, 2018Friday, November 16, 2018 Special plant cells that make up xylem, tissue that conducts water in plants, undergoes transpiration. This transpiration results in a negative pressure potential.

Cells & Osmosis {Figure 36.6} Friday, November 16, 2018Friday, November 16, 2018

Cells & Osmosis {Figure 7.14} Friday, November 16, 2018Friday, November 16, 2018