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Transport Within Plants

Transport Within Plants. Packet #55 Chapter #36. Reasons for Transport Within Plants. Absorption of water and minerals by roots Transport of xylem sap Control of transpiration Transport of organic nutrients within phloem. Review of Important Terms. Water Potential Solution Solvent

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Transport Within Plants

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  1. Transport Within Plants Packet #55 Chapter #36

  2. Reasons for Transport Within Plants • Absorption of water and minerals by roots • Transport of xylem sap • Control of transpiration • Transport of organic nutrients within phloem

  3. Review of Important Terms • Water Potential • Solution • Solvent • Solute • Hypotonic • Hypertonic • Isotonic • Diffusion • Osmosis • Dialysis • Movement of a solute from an area of high concentration to an area of low concentration across a semi-permeable membrane • Cohesion • Adhesion • Osmotic Pressure • Plasmolysis • Turgidity

  4. Water Movement Through Xylem

  5. Introduction • Plants take up water through the roots and release “excess” through the stomata. • The release of water through the stomata is called transpiration. • *About 90% of all water entering the roots leaves the leaves via the stomatas without ever taking part in plant’s metabolic reactions.

  6. Water Movement Through Xylem I • Water movement, through the xylem, is due to the differences in water potential between the soil, root, stem, leaf and atmosphere. • The water potential becomes higher (more negative) as water flows from the soil up and out into the atmosphere through the stomata of the leaf. • Shoot tension

  7. Water Movement Through the Xylem II • As water enters the root, from the soil, it may travel different routes in order to reach the xylem. • Two of those routes are the: - • Apoplastic Route • Symplastic Route

  8. Apoplastic Pathway • An apoplast consists of interconnected pourous cell walls of a plant, along which water and nutrient mineral ions move freely. • Water and minerals diffuse freely without ever entering a living cell.

  9. Symplastic Pathway • A symplast is a continuum of living cytoplasm, which is connected from one cell to the next by cytoplasmic bridges called plasmodesmata.

  10. Reasons Behind the Movement of Water Through the Xylem Transpiration Pull

  11. Introduction I • There are three ways to describe the movement of solutes, or fluids, from one end of the plant to another. • Bulk Flow • Hydrostatic Pressure • Transpiration Pull

  12. Bulk Flow • Movement of fluid that is driven by pressure • Osmotic Pressure** • Roots to leaves • Overall movement of water in response to differences in the potential energy of water.

  13. Hydrostatic Pressure • The pressure at a point in a fluid at rest due to the weight of the fluid above it. • Also known as gravitational pressure.

  14. Transpiration Pull • Tension, or negative pressure, due to the evaporation of water from a leaf • Based on cohesion, adhesion and differences in pressure.

  15. Transpiration Pull II • In the leaf, water diffuses from the xylem into the spaces inside the spongy layer, out through the stomata and into the atmosphere.

  16. Transpiration Pull III • Tension is generated as water is pulled from between the cells. • The tension formed is negative pressure. • This pressure “pulls” water from areas of greater hydrostatic pressure into areas of lower hydrostatic pressure. • Fluid filled areas such as xylem vessels are areas of higher hydrostatic pressure.

  17. Reasons Behind the Movement of Water Through the Xylem Root Pressure

  18. Root Pressure • Caused by the movement of water into roots from the soil as a result of the active absorption of nutrient mineral ions from the soil

  19. Root Pressure II • At night, depending on the species of plant, stomata close and transpiration ceases. • Water potential decreases • However, root cells still pump nutrients into the xylem • Minerals accumulate in the steele • As minerals aggregate, the water potential in the roots becomes higher in comparison to that in the leaf. • Water is “pushed” up into the stem and into the leaves because of the differences in water potential that has been produced as a result of the minerals accumulating in the steele • Root Pressure.

  20. Water & Nutrient Movement Through the Phloem.

  21. Introduction • Unlike the movement of xylem sap, phloem sap requires the use of energy.

  22. Movement Within Phloem • Sugars are moved through the phloem and to their final location via the use of proton pumps, transport protein (Sucrose-H+ co-transporter) and co-transport.

  23. Important Definitions • Source • Any location in a plant where sugar is either produced or stored. • Sink • Location in a plant where sugar is used.

  24. Review

  25. Review I

  26. Review II

  27. Review III

  28. Review IV

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