(1/4) BR Osmosis review: if a selectively permeable membrane separates a hypertonic solution from a hypotonic solution, in which direction will WATER flow? Animal cell Plant cell

(3) Shriveled (crenation) Isotonic solution Hypotonic solution Hypertonic solution H2O H2O H2O H2O Animal cell (1) Normal (2) Lysed (hemolysis) (3) Shriveled (crenation) Plasma membrane H2O H2O H2O H2O Plant cell (4) Flaccid (5) Turgid (6) Shriveled (plasmolysis)

Osmosis: water moves from a hypotonic solution into a hypertonic solution Cells take in water and may burst (hemolysis) Cells lose water and shrivel (crenation) Cells stiffen and become turgid Cell body shrinks away from cell wall (wilting)

If pressure builds or is applied on the hypertonic side, it can counteract the movement of water into the solution

Water Potential: Ψ = ψs + ψp Osmosis: Water moves from area of high water potential (hypotonic solution) to low water potential (hypertonic) Ψs = solute potential Ψp = pressure potential (= 0 at atmospheric pressure) Ψs = -iCRT i  ionization constant C  molar concentration (mol/L of solute in water) R  pressure constant (0.0831 L-bars/mol-K) T  temperature in Kelvin (0C + 273) At equilibrium both sides of the membrane have equal ψ Plasma membranes typically are impermeable to solutes Animal cells have no significant Ψp Plant cells have significant Ψp in hypotonic solutions…what is this internal pressure called? When water leaves a cell, concentration (C) increases so its ψs becomes more negative

Water Potential Water molecules surround solutes, decreasing water’s free energy AND water potential Hypertonic solutions have LOW water potential

Water Potential practice Ψ = ψs + ψp The initial molar concentration of the cytoplasm inside a plant cell is 1.3M and the surrounding solution is .3M. Is it possible for the cell to be in equilibrium? Explain. If the cell is initially flaccid, in which direction will water move by osmosis? A cell is in equilibrium with its environment. The solute potential (Ψs) of the cell’s cytoplasm is –0.45 bars. The water potential of the surrounding solution is –0.32 bars. When the cell was first put into the solution, it was flaccid. In which direction did water move by osmosis? What is the pressure potential (Ψp) of the cell? Is the cell hypertonic, hypotonic, or isotonic to its surroundings?

Water Potential practice Ψ = ψs + ψp The initial molar concentration of the cytoplasm inside a plant cell is 1.3M and the surrounding solution is .3M. Yes because of turgor pressure in cell Into the cell A cell is in equilibrium with its environment. The solute potential (Ψs) of the cell’s cytoplasm is –0.45 bars. The water potential of the surrounding solution is –0.32 bars. When the cell was first put into the solution, it was flaccid. .13 bars hypertonic

Water Potential practice Ψ = ψs + ψp A cell is in equilibrium with its surroundings. The molarity of the surrounding solution is 0.5M, and the temperature is 200C. Calculate the solute potential (ψs) of the solution. What is the water potential of the solution? What is the water potential of the cell? Why can’t we calculate the solute potential of the cell? Ψs = -iCRT i  ionization constant (assume i = 1) C  molar concentration (mol/L) R  pressure constant (0.0831 L-bars/mol-K) T  temperature in Kelvin (0C + 273)

Water Potential practice Ψ = ψs + ψp A cell is in equilibrium with its surroundings. The molarity of the surrounding solution is 0.5M, and the temperature is 200C. ψs = -(1)(.5)(.0831)(273+20) = -12.2 bars -12.2 bars Because we don’t know the pressure potential (turgor pressure). If the cell is flaccid, then the solute potential is -12.2 bars because the pressure potential is zero. Ψs = -iCRT i  ionization constant (assume i = 1) C  molar concentration (mol/L) R  pressure constant (0.0831 L-bars/mol-K) T  temperature in Kelvin (0C + 273)

(1/5) Group BR: Transpiration Describe the process of transpiration in plants. Explain how capillary action works in plants. Leaves have openings called stomata, sometimes up to 1000 per mm2. Which 3 gases enter or exit through the stomata when they are open? Would you expect stomata to open more often during the day or at night? Explain. Left: Guard cells swollen and open Right: Guard cells lose water and close Stomata

Transpiration A 15 m tall maple tree has ~177,000 leaves with a total surface area of 675 m2. During a summer day, it loses 220 L of water PER HOUR via transpiration! So to prevent wilting the xylem must transport that much water up from the roots to the leaves EVERY HOUR. How? TACT! Transpiration Adhesion Cohesion Tension (negative pressure potential)

How does water reach the leaves of a plant? TACT!! Transpiration Adhesion Cohesion Tension (negative pressure potential)

Transpiration How do you think humidity affects the rate of water loss from leaves through stomata? Think about the factors that govern the movement/diffusion of water.