Office Hours: Fri Feb 7 526 12:20-1:10 pmWed Feb 12 526 12:20:1:10 pmFri Feb 14 412 2:30-3:30 pmToday:How are plants different from animals fundamentally?- Animals: circulatory system (pumped), osmosisTransport in plants- Diamorpha (1 inch)- Dolystrichem (1 inch)- Helianthus porteri (3 ft)- Ferns (1 ft)- Redwood sequoia (379 ft = tallest)- Osmosis is involved; vascular tissue used in long distanceChallenges- Water: take up enough to support transpiration while maintaining turgor in living cellso Transpiration: water evaporation out of leaveso turgor: only happens with cells that have cell walls- Nutrient: take up enough and distribute where neededo Sugar transport both ways to wherever it is needed o To roots that are growing or to leaves that are developing- Photosynthetic products (carbs): move from where produced or stored to where neededFocus on:- What is being moved?- Scale and location of movemento Short: across membraneso Longer: vascular tissue (phloem & xylem)- How’s it being moved?o Diffusion o Osmosis o Bulk flowOutline over next two lectures- Water movement across cell membraneso Osmosiso Water potentials Todayo Turgor pressure- Water and nutrient acquisition by roots- Transpiration and xylem transport- Phloem transportHypotonic solution: solution has lower solute concentration than inside the cell; why water moves in- Animal cell: Cell could lyse (explode)- Plant cell: Turgid (normal); dynamic equillibriumIsotonic: solute concentrations are equal in solution to inside the cell- Normal- Plant cell: flaccid (no turgor)Hypertonic: solution has higher solute concentration than inside the cell; why water leaves the cell- Cell shrivels- Plasmolyzed Clicker: Main feature that makes substantial turgor possible in living plant cells?A vacuole B cell membrane C cell wall D chloroplasts E chlorophyll- Vacuole is not substantial enoughHow can plant cell water exchange be in equilibrium if solution is hypotonic to the cell?Explains how solute concentration is not the only reason for water exchange in plant cellsNet transport processes- Diffusion: movement of substance down concentration/electrochemical gradient (driving force)- Osmosis: diffusion of water across a selectively permeable membrane where physical property that predicts direction of water is water potentialo Better definition: movement of water across a cell membrane down a water potential gradientProcess: water movement across membranesTransport process: osmosisDriving force: water potential gradient (units MPa)Rules for predicting how water will move across living cell membranes- When crossing one or more cell membranes, water moves from areas of higher potential to areas of lower potential, until equilibrium- Potential made of 2 components: potential = potential solute + pressure potentialo increasing solutes in water lowers Ψs (gets more negative)o Pressure increases Ψp (positive) and tensions decreases (negative pressure potential)Living plant cells are “osmometers” with relatively rigid cell walls that can build up torgor (positive Ψp)Putting numbers on Ψ, Ψs, Ψp for plant cellsExercise in class: what happens when an individual plant cell is put into one of the solutions below (assume cell wall rigid and that cell cytoplasm volume doesn’t change)?- Initial flaccid cell: Ψp = 0, Ψs = -0.7 MPa, Ψ = -0.7 MPa- 0.4 M sucrose solution (water moving out by osmosis)o Solution: Ψp = 0, Ψs = -0.9, Ψ = -0.9o Plasmolyzed cell at equilibrium with surroundings: Ψp = 0, Ψs = -0.9, Ψ = -0.9- Distilled water:o solution: Ψp = 0,Ψs = 0,Ψ = 0o Turgid cell: Ψp = 0.7, Ψs = -0.7, Ψ = 0o At equilibrium: Ψ = 0Question for studying later: what would happen if a flaccid cell with a Ψs of 1.0 is put into the distilled water and the 0.4 M sucrose solution, or into a 0.8 M sucrose solution? Clicker: In order to maintain water