Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Chapter 36 Transport in Vascular Plants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Forces that drive transport in plants Physical forces drive the transport of materials in plants over a range of distances Transport in vascular plants occurs on three scales – Transport of water and solutes by individual cells, such as root hairs – Short-distance transport of substances from cell to cell at the levels of tissues and organs – Long-distance transport within xylem and phloem at the level of the whole plant Water Uptake in Plants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Minerals H2OH2O CO 2 O2O2 O2O2 H2OH2O Sugar Light Physical Processes A variety of procceses are involved in the different types of transport Sugars are produced by photosynthesis in the leaves. 5 Sugars are transported as phloem sap to roots and other parts of the plant. 6 Through stomata, leaves take in CO 2 and expel O 2. The CO 2 provides carbon for photosynthesis. Some O 2 produced by photosynthesis is used in cellular respiration. 4 Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 3 Water and minerals are transported upward from roots to shoots as xylem sap. 2 Roots absorb water and dissolved minerals from the soil. 1 Figure 36.2 Roots exchange gases with the air spaces of soil, taking in O 2 and discharging CO 2. In cellular respiration, O 2 supports the breakdown of sugars. 7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Selective Permeability of Membranes: A Review The selective permeability of a plant cell’s plasma membrane – Controls the movement of solutes into and out of the cell Specific transport proteins – Enable plant cells to maintain an internal environment different from their surroundings – Mineral Uptake Mineral Uptake

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Central Role of Proton Pumps Proton pumps in plant cells – Create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work – Contribute to a voltage known as a membrane potential Figure 36.3 CYTOPLASM EXTRACELLULAR FLUID ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Proton pump generates membrane potential and H + gradient. – – – – –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy for Solute Transport Plant cells use energy stored in the proton gradient and membrane potential – To drive the transport of many different solutes + CYTOPLASM EXTRACELLULAR FLUID Cations (, for example) are driven into the cell by the membrane potential. Transport protein K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ – – – + + (a) Membrane potential and cation uptake – – + + Figure 36.4a

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cotransport In the mechanism called cotransport – A transport protein couples the passage of one solute to the passage of another Figure 36.4b H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ NO 3 – – – – – – – (b) Cotransport of anions H+H+ of through a cotransporter. Cell accumulates anions (, for example) by coupling their transport to the inward diffusion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ S S S S S Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. S H+H+ – – – – – + + – Figure 36.4c H+H+ H+H+ S + – (c) Contransport of a neutral solute Cotransport The “coattail” effect of cotransport – Is also responsible for the uptake of the sugar sucrose by plant cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of Differences in Water Potential To survive – Plants must balance water uptake and loss Osmosis – Determines the net uptake or water loss by a cell – Is affected by solute concentration and pressure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of Differences in Water Potential Water potential – Is a measurement that combines the effects of solute concentration and pressure – Determines the direction of movement of water Water – Flows from regions of high water potential to regions of low water potential

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Standard for measuring Standard for measuring  Pure water is the standard. Pure water in an open container has a water potential of zero at one atmosphere of pressure.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How Solutes and Pressure Affect Water Potential Both pressure and solute concentration – Affect water potential The solute potential of a solution – Is proportional to the number of dissolved molecules Pressure potential – Is the physical pressure on a solution

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Quantitative Analysis of Water Potential The addition of solutes – Reduces water potential Figure 36.5a 0.1 M solution H2OH2O Pure water  P = 0  S =  0.23  =  0.23 MPa  = 0 MPa (a)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Solute Potential Solute Potential  S Solutes bind water molecules 1.reducing the number of free water molecules  2. lowers waters ability to do work. The Effect of Solutes on Water Potential

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water Potential: an artificial model (a) addition of solutes on right side reduces water potential.  S = Water flows from “hypo” to “hyper” Or from hi  on left to lo  on right

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pressure Potential Pressure Potential  P  P is the physical pressure on a solution.  P can be negative  transpiration in the xylem tissue of a plant (water tension)  P can be positive  water in living plant cells is under positive pressure (turgid)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Application of physical pressure – Increases water potential H2OH2O  P = 0.23  S =  0.23  = 0 MPa (b) H2OH2O  P = 0.30  S =  0.23  = 0.07 MPa  = 0 MPa (c) Figure 36.5b, c The Effect of Pressure on Water Potential

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water Potential: an artificial model (b) adding pressure with plunger  no net flow of water (c) applying pressure increases water potential solution now has  of Water moves right to left

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Negative pressure – Decreases water potential H2OH2O  P = 0  S =  0.23  =  0.23 MPa (d)  P =  0.30  S = 0  =  0.30 MPa Figure 36.5d The Effect of Pressure on Water Potential

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (d) negative pressure or tension using plunger decreases water potential on the left. Water moves from right to left Water Potential: an artificial model

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Effect of Water Potential on Plant Cells Water potential – Affects uptake and loss of water by plant cells If a flaccid cell is placed in an environment with a higher solute concentration – The cell will lose water and become plasmolyzed Figure 36.6a 0.4 M sucrose solution: Initial flaccid cell: Plasmolyzed cell at osmotic equilibrium with its surroundings  P = 0  S =  0.7  P = 0  S =  0.9  P = 0  S =  0.9  =  0.9 MPa  =  0.7 MPa  =  0.9 MPa

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If the same flaccid cell is placed in a solution with a lower solute concentration – The cell will gain water and become turgid Distilled water: Initial flaccid cell: Turgid cell at osmotic equilibrium with its surroundings  P = 0  S =  0.7  P = 0  S = 0  P = 0.7  S =  0.7 Figure 36.6b  =  0.7 MPa  = 0 MPa  =  0 MPa The Effect of Water Potential on Plant Cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Effect of Water Loss Turgor loss in plants causes wilting – Which can be reversed when the plant is watered Figure 36.7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Calculating Solute potential Need solute concentration Use the equation  S = - iCRT i = # particles molecule makes in water C = Molar concentration R = pressure constant liter bar mole o K T = temperature in degrees Kelvin = o C

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Solve for water potential Knowing solute potential, water potential can be calculated by inserting values into the water potential equation.  =  P +  S In an open container,  P = 0

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Practice Problems

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Aquaporin Proteins and Water Transport Aquaporins – Are transport proteins in the cell membrane that allow the passage of water – Do not affect water potential