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lecture13 - Transpiration is regulated by opening and...

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5/10/09 1 Water in Plants Water, Diffusion, and Osmosis Water Movement in the Xylem Cohesion Tension Theory Sugar Movement in the Phloem Reading: Botany for Gardeners Pages 152-158 Polar molecule Sticks to other molecules - adhesion Cohesion - water sticks to itself Water is a Strange Molecule Osmosis - diffusion of water through a differentially permeable membrane Diffusion is driven by a concentration gradient Diffusion: high concentration to low concentration Diffusion is driven by random movement of molecules. Turgor Pressure Turgor pressure - pressure that is exerted against the cell wall as a result of water entering the cell Transpiration Water loss in leaves occurs by diffusion. Transpiration - the diffusion of water vapor from a leaf to the air
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5/10/09 2 Turgor pressure of guard cells controls stomatal opening
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Unformatted text preview: Transpiration is regulated by opening and closing of stomata The Cohesion-Tension Theory • Transpiration and the cohesion of water causes an upward flow of water from soil to roots to leaves • The adhesion of water to walls of xylem cells also helps resist gravity Cohesion, Tension, and Adhesion in the Ascent of Water 90 % of dry matter in phloem is sugar (mainly sucrose) Aphid Stylet Aphid Sugars are transported in the phloem • Root Pressure- the pressure that develops, due to osmosis, in living cells of a root, forcing water up the xylem • Guttation- droplets of water that form on leaf margins in a humid environment as a result of water being pushed up the xylem by root pressure • Imbibition- the process of water absorption by a dry substance or structure, causing it to swell...
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