Biosc 0150 Foundations of Biology I Review 8 Chapters 37 and 39 Review Chapter 37 Water and sugar transport 1 What is transpiration Water loss due to evaporation a What two conditions must be met for transpiration to occur Stomata must be open and the air surrounding the leaves is drier than the air inside the leaves b How does water move up a tree Does it require ATP Which direction does it move Water always moves passively It requires no ATP it moves by differences in water potential from high to low c If a plant has a high solute concentration it has a high low solute potential Low d How do solute potential and water potential combine to make up water potential When selectively permeable membranes are present water tends to move by osmosis from areas of high solute potential to areas of low solute potential However when no membranes are present water moves from areas of high pressure potential to low pressure potential e Why are solute potentials always negative Because they are measured relative to that of pure water which has 0 Mpa Since there is always some solutes inside a cell the water inside always has a solute potential lower that that of pure water f How do the terms flaccid and pressure potential relate to one another A cell that is flaccid means it has no turgor pressure and thus a pressure potential of 0 g Application Why don t red blood cells pop in the bloodstream Red blood cells don t pop because the blood provides an isotonic environment for the cells 2 Work with Water Potential a If a cell with a solute potential of 0 2 MPa and a pressure potential of 0 4 MPa is placed in a chamber filled with pure water that is pressurized with 0 5 MPa what will happen Water will flow into the cell c b You place a piece of potato weighing 0 3 grams with a water potential of 1 MPa in a beaker of Pepsi After 10 minutes you remove the potato piece and it now weighs 0 25 grams What can you conclude about Pepsi s water potential Pepsi s water potential was less than 1 MPa If you could turn a plant upside down without affecting the function of the major organs roots shoots and leaves would transport of water in xylem move upwards toward the roots or would it still move toward the leaves Would transport of sugar in phloem change as a result of this inversion Water would still move towards the leaves in the xylem of your inverted plant Roots don t have stomata for water to move through and there is not a mechanism for water to move from the ground into leaves and then exit through the roots via transpiration Transpiration would still move water out through the leaves but this would stop as the roots dried out Transport in the phloem would not be altered Sugars would still move from the source to the sink as described by the pressure flow model for phloem transport d Compare and Contrast i The pressure potential of wet soils vs dry soils Wet soils have almost no pressure potential while dry soils have a highly negative pressure potential because the few water molecules present cling to soil particles ii The solute potential of salty soils vs typical soils Salty soils have extremely low solute potentials compared to typical soils because the concentration of solutes is high 3 The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2 5M a True or False If false explain Adel Anthony Kathleen Megan Dr Swigonova Page 1 of 16 Biosc 0150 Foundations of Biology I Review 8 Chapters 37 and 39 i Initially solute concentration is greater outside the cell than inside True ii Water will enter the cell because solute potential is lower inside the cell than outside False water will leave the cell because solute potential is higher inside the cell than outside iii The cell will become flaccid because the pressure potential is greater outside the cell than inside False the cell will become more flaccid because the solute potential is greater inside the cell than outside iv Initially the cytoplasm is hypertonic to the surrounding solution False the cell is hypotonic to the surrounding solution v Initially the numerical value of the solute potential is more negative inside the cell than outside False it is more negative outside the cell than inside vi Net diffusion of water will be from inside the cell to outside the cell True vii At equilibrium the molarity of the cytoplasm will have increased True viii At equilibrium the pressure potential inside the cell will have increased False the pressure potential inside the cell will remain zero 4 When the pressure potential is negative there is a net water flow When is positive there is net flow of water When 0 Into the cell out of the cell there is no net water flow into or out of the cell 5 What is the advantage of transpiration being a passive process What is the disadvantage It is advantageous for plants to move water through a passive process like transpiration because water in a tree needs to move great distances in order to get to where it is needed especially in the top leaves of very tall trees There is no energy expenditure for this which frees energy for use in other processes The disadvantage of this is that transpiration can occur rapidly in dry climates and result in a high water loss for the tree risking dehydration 6 The Cohesion Tension Theory a Explain the theory in your own words It is the regulation of long distance water movement It all starts with the transpiration from leaf surfaces as water is pulled up out of the menisci from all the way down in the roots It is a constant pulling as long as the atmosphere is drier and the stomata are open b What is most responsible for creating the steep concentration gradients between the leaf interior and its surroundings Along the water transpiration continuum where is the water potential the lowest most negative If you could name one thing that drives or powers this whole process what would it be not stomata Stomata the outside of the stomata or atmosphere the sun water transport is solar powered c Why is root pressure and capillary action not enough to regulate water movement in plants i e why did anyone hypothesize the cohesion tension theory in the first place Because menisci are so small how does their lowering of pressure have any effect on water movement in a significant way since the tension they create is so little Root pressure and capillary action assist in the movement of water However these forces alone would not