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Lecture 8 - Lecture 8 2006 water relations 1 Quiz Weds Do...

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Lecture 8 2006 water relations 1 Quiz Weds. Do the reading in the text for this lecture: Chapter 36 very clear; do not need to know 739-740 transport at the cell level, but do need to know osmosis; Overview: How does water move in plants? o Short distance (cell to cell) o Long distance (roots to leaves) Answer for long distance: water is pulled from roots through xylem by evaporation from leaves. Why does this work? 1. Water has unique properties: A. HYDROGEN BONDS with itself and with other molecules B. that allow it to STRETCH, C. to COMPRESS UNDER PRESSURE, 2. For both short and long distance transport, water moves along a water potential gradient from regions of high water potential to regions of low water potential. I. Water (read all of Ch. 3) A. Hydrogen bonds 1. H 2 O: hydrogen molecules separated by an angle of 105 o
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Lecture 8 2006 water relations 2 2. oxygen has a slight negative charge, hydrogen a slight positive charge, so due to uneven distribution of electrons 3. H 2 O is a polar molecule 4. forms H-bonds (weak) with itself and other charged molecules B. Hydrogen bonds lead to unique properties of water 1. COHESION : attraction of molecules to the same type of molecule (water to water-) because of cohesion a. water in the liquid state "flows"-- one molecule follows another because of cohesion among water molecules b . SURFACE TENSION : ability of the surface to resist stretching (i.e tension) without breaking (Water has a very high surface tension.) c. TENSILE STRENGTH measure of the force required to to pull on a water column before it breaks; compared to other liquids, the tensile strength of water is high 2. ADHESION : attraction of molecules to other unlike molecules (water to cell walls, water to fabric, water to paper) C. Osmosis: (definition of solutes--substance dissolved in a solution) 1. Across a semi-permeable membrane.
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Lecture 8 2006 water relations 3 2. Water always moves from low solute concentration solution (HYPOTONIC) to high solute concentration solution (HYPERTONIC). 3. At equilibrium (equal concentration of free water (not bound to the solute)), no further movement of water.
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