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Transport in Plants

Transport in Plants. Review of Diffusion. Diffusion: natural tendency for particles to move from areas of high concentration to low concentration (concentration gradient). Review of Osmosis.

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Transport in Plants

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  1. Transport in Plants

  2. Review of Diffusion Diffusion: natural tendency for particles to move from areas of high concentration to low concentration (concentration gradient).

  3. Review of Osmosis Osmosis: the natural tendency of water to flow from area of low waterconcentration to high waterconcentration.

  4. Vascular Tissue • Vascular plants have specialized tissue for transporting material from one location to another. • TUBES! • In animals, material is transported through the ________________ system.

  5. Vascular Bundles

  6. Xylem • Transports water and dissolved minerals • Xylem: • Tracheidsand/or Vessel elements: cells which grow end-to-end, but living contents eventually die, leaving non-living cell walls as the ‘tube.’ • Gymnosperms: contain only tracheids • Angiosperms: contain both tracheids and vessel elements.

  7. Which is found in gymnosperms? Angiosperms?

  8. Plants are not like animals... • Plants do not have muscles to push substances up against gravity. • Plants do not have valves to keep substances from flowing the other way.

  9. 3 Theories of Translocation in Plants • Root Pressure • Capillary Action • Cohesion-tension

  10. 1) Root Pressure • Water builds up in xylem of roots either by: • Cells actively pump water into xylem • Cells actively pump ions into xylem, creating a concentration gradient  osmosis. • Accumulation of water in xylem builds pressure and forces water upward.

  11. Problems with the Root Pressure Theory • for tall tree to raise water 100m, need difference in pressure in roots and leaves of 1000 kPa. • Pressure gradient has never been demonstrated in real life.

  12. 2) Capillary Action • Relies on adhesive properties of water • Adhesion: attraction of water to other polar molecules. • The cause of a meniscus  clings onto side of capillary. Drawback: can only explain movement of water of 60-90 cm.

  13. 3) Cohesion-tension • Also called transpiration pull. • Most widely accepted explanation of how water moves up a tall plant. • As each water molecule evaporates from stomata (in leaf), another molecule is right behind it. • Pulls up second molecule due to cohesion: attraction of water molecules to each other. • Loss of water from leaf pulls up another water molecule. • Limitation: we still do not know how water begins to move up a maple tree in the spring, before the leaves are out (therefore, no transpiration). CAREER EXPLORATION?

  14. Phloem • Translocation: the transportation of food from on region of a plant part to another region. • Phloem transports plant food (glucose/sucrose). • Why would glucose or sucrose be NEEDED by different tissues of the plant?

  15. Mass-flow Theory • Most broadly accepted theory of phloem transport. • Combination of osmosis and pressure dynamics.

  16. CLASSWORK/HOMEWORK Page 326, #1-8.

  17. Classwork/Homework (2) Read pages 531-534. SR # 1-7.

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