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Lecture 33

BIOLOGY 172 Lecture 33: Xylem and Phloem

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Stephen Clark

Biology 172 Dr. Clark- Winter 2017 Lecture 33 Transport of water, sugar and nutrients through vascular tissue Water loss is an inevitable consequence of photosynthesis Transpiration is process where plants have to get carbon dioxide and open stomata to release oxygen and water Also loses water in photosystem II when oxidizes water Stomata are made of two guard cells  provide gas exchange in plant tissue (CO2 in, O2 and H2O out)  >100 molecules of H2O for every CO2 used stomata opening is tightly controlled epidermal cells are covered by a thick waxy coat that prevents water loss water follows the solute solute/water in  swells  stomata open solute/water out  shrink  stomata close increasing atmospheric carbon dioxide levels would be expected to cause water loss to DECREASE  increase in CO2, it is more likely to get CO2 in  the stomata needs to be open for less time  less water loss Pure water has increased water potential High water potential near roots//low at atmosphere Increase push from soil up against the gravity to reach leaves Water moves from roots to leaves passively Water outside is absorbed by epidermal root hair cells  high surface area to volume ration plant cell wall resists the tendency of water to dilute the solutes in the cell turgor pressure is the presence of water counteracted by structural rigidity of cell wall water moves through the root of a vascular system via xylem (dead cells with lignin and cellulose structure)  tracheids: very small perforated straws  vessels: small perforated straws Designed so water can move rapidly through the system via capillary actions (DEAD CELLS) Water
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