lecture 2-17 plants II - Chapter 36 (pp.738-755) Plant...

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Chapter 36 (pp.738-755) – Plant transport (continued) Learning Objectives: Describe the mechanism of root pressure; how it moves xylem sap. Explain how transpirational ‘pull’ moves xylem sap up from the root tips to the leaves. Explain this statement: “The ascent of xylem sap is ultimately solar powered.” Explain how and when stomata open and close. Describe the cues that trigger stomatal opening at dawn. Describe the process of translocation. Trace the path of phloem sap from a primary sugar source to a sugar sink. Describe the process of sugar loading and unloading. Terms to know include…mycorrhizae, flaccid, turgid, turgor pressure, plasmolyse, bulk flow, tracheid, vessel cell, transpiration, guttation, root pressure…
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Functions of the Symplast and Apoplast in Transport Water and minerals can travel through a plant by one of three routes: Transmembrane route (Out of one cell, across a cell wall & membrane, and into another cell – repeat…) Via the symplast route (The cytoplasmic continuum) Along the apoplast route (the continuum of cell walls plus extracellular spaces)
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Some concepts about plant transport • Roots absorb water and minerals from the soil • Water and minerals ascend from roots to shoots through the xylem • Stomata help regulate the rate of transpiration • Organic nutrients are translocated through the phloem
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Figure 36.9 Lateral transport of minerals and water in roots 1 2 3 Uptake of soil solution by the hydrophilic walls of root hairs provides access to the apoplast. Water and minerals can then soak into the cortex along this matrix of walls. Minerals and water that cross the plasma membranes of root hairs enter the symplast. As soil solution moves along the apoplast, some water and minerals are transported into the protoplasts of cells of the epidermis and cortex and then move inward via the symplast. Within the transverse and radial walls of each endodermal cell is the Casparian strip, a belt of waxy material (purple band) that blocks the passage of water and dissolved minerals. Only minerals already in the symplast or entering that pathway by crossing the plasma membrane of an endodermal cell can detour around the Casparian strip and pass into the vascular cylinder. Endodermal cells and also parenchyma cells within the vascular cylinder discharge water and minerals into their walls (apoplast). The xylem vessels transport the water and minerals upward into the shoot system. Casparian strip Pathway along apoplast Pathway through symplast Plasma membrane Apoplastic route Symplastic route Root hair Epidermis Cortex Endodermis Vascular cylinder Vessels (xylem) Casparian strip Endodermis 4 5 2 1 3 4 5
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Concept: Roots absorb water and minerals from the soil Water and dissolved minerals from the soil
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This note was uploaded on 03/19/2008 for the course BIO 311D taught by Professor Reichler during the Spring '08 term at University of Texas at Austin.

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lecture 2-17 plants II - Chapter 36 (pp.738-755) Plant...

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