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PSU BIOL 240W - Long Distance Water and Mineral Movement

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BIOL 240W 1st Edition Lecture 8 Outline of Last Lecture I. Plant EvolutionII. Three Transport Routes for Water and SoluteIII. Solute TransportIV. Short-Distance Water TransportV. Solutions and OsmosisOutline of Current Lecture I. Short Distance Water MovementII. Bulk FlowIII. TranspirationIV. Water and Mineral Uptake by RootsV. TransportCurrent LectureI. Short Distance Water Movementa. Flaccid plant cells placed in a solution with lower solute concentration (hypotonic), water moves into the cells making them turgidb. This is why watering plants makes them less wiltedc. Plasomolysis occurs when water leaves the cell and the cell membrane detaches from the cell wall. This is in the presence of a hypertonic solution.II. Bulk Flowa. Long distance transport through xylem and phloemb. Dependent on pressure gradient; material always flows from higher pressure to lower pressurec. Independent of solute in or out of the celld. Movement through tracheids and vessel elements of xylem; sieve-tube elements of phloeme. Active transport and diffusion still occurIII. Transpirationa. Transpiration is the movement and exaporative loss of water from the plantb. Drives transport of water and minerals from roots to the shoots via the xylemc. Dilemma of the stomataThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. The whole plant needs movement of water and dissolved nutrients from roots up to the shoots/leavesii. Stomata must be open to let in carbon dioxide for photosynthesis, but this leads to loss of waterIV. Water and Mineral Uptake by Rootsa. Water and minerals want to get to xylem and phloem, but movement must start at the root hairs.b. Walls of the endodermis have a waxy barrier called the casparian strip that inhibits apoplastic entry into the vascular bundlei. Minerals moving through the symplast only move through cytosol through plasmodesmata and do not interact with casparian stripii. In the apoplast, the cell has selectivity with what can move into the rest of the plant. In order to make for minerals to make their way to the xylemfrom the apoplast, they must cross a plasma membrane to enter the symplastic route.V. Transporta. When water has entered the xylem, long-distance transport is rapidb. Faster than diffusion or active transportc. Force of movement is due to root pressure and transpirationi. Root pressure1. Active transport of solutes into root stele lowers the water potential2. Water movement into the stele increases pressure, forcing water up the xylem to a lower pressure environment3. This is a minor mechanism of xylem bulk flowii. Transpiration1. Pulls xylem sap upward. Loss of water by evaporation is pulling force for upward movementiii. Cohesion- water molecules attracted to each otheriv. Adhesion- water molecules attracted to other polar molecules1. These two forces are the reason surface tension exists.2. Water has a high surface tension (negative pressure potential)d. Cohesion and Adhesion in the Ascent of Xylem Sapi. Water molecules adhere to cellulose in xylem cellii. Water molecules are also attracted to each other through cohesion, which makes it possible to pull a column of xylem


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