1. Water Balance & Potential AP BIOLOGY

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3. Water Balance Hypotonic – A solution has less solutes than the solution on the other side of the membrane Isotonic – A solution has the same solute concentration as the solution on the other side of the membrane Hypertonic – A solution has more solutes than the solution on the other side of the membrane

4. Water Balance

5. Osmosis Water moves from an area of low solute concentration to region of high solute concentration In equilibrium, the solute concentrations will be equal

6. Water Potential Water potential tendency of water to leave one place in favor of another measure of the degree to which osmosis occurs water moves from higher water potential to lower water potential Area with low H 2 O concentration has lower water potential  water tends to move into areas with low water potential water potential is affected by: Pressure Amount of solute

7. What affects water potential? water potential is affected by: Pressure potential Amount of pressure on the container surrounding the solution Exertion of pressure on a solution Solute potential Looking at effect of solute concentration Pure water has a solute potential of zero. As solute is added to water, solute potential becomes more negative. As solute is added, water potential of solution drops, and water moves into the solution. Water potential = solute potential + pressure potential Ψ = Ψs + Ψp

8. Osmotic Potential Osmotic potential = relative concentration of solutes in the two solutions Looking at potential of water to move between regions of differing concentrations Water potential = solute potential + pressure potential Ψ = Ψs + Ψp Water potential = osmotic potential + pressure potential Ψ = Ψs + Ψπ Osmotic (solute) potential is negative because adding solutes to pure water makes the potential negative

9. Osmotic Potential Isotonic solution = zero osmotic potential Hypotonic solution (less solutes/more water) = solution has higher osmotic potential Hypertonic solution (more solutes/less water) = solution has lower osmotic potential

10. Examples Red blood cell is placed in distilled water Water moves into the cell, causing it to expand and stretching the membrane. Eventually, the pressure of incoming water will cause the cell to pop. Plant cell is placed in distilled water Water moves into the cell, causing the cell to expand. There is pressure of incoming water, but there is also pressure exerted back by the cell wall.

11. Osmotic Pressure Osmotic pressure = the pressure exerted by the flow of water across a semi-permeable membrane When a red blood cell is in a hypotonic environment, water flows into the cell, causing it to expand (due to osmotic pressure).