W9L1 - Transport in Plants Part 2

W9L1 - Transport in Plants Part 2 - Biol 5B: Organismal...

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1 Biol 5B: Organismal Biology Spring ’09 WEEK 8; Lecture 3 Transport in Plants – Part 2 Three major pathways of transport • Transport is also regulated by the compartmental structure of plant cells • Water and minerals can travel through a plant by three routes: – Transmembrane route: out of one cell, across a cell wall, and into another cell – Symplastic route: via the continuum of cytosol – Apoplastic route: via the cell walls and extracellular spaces
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2 Cell wall Cytosol Vacuole Plasmodesma Vacuolar membrane Plasma membrane (a) Cell compartments Key Transmembrane route Apoplast Symplast Apoplast Symplast Symplastic route Apoplastic route (b) Transport routes between cells Bulk flow in long-distance transport • Diffusion only efficient for short-distance transport • Efficient long distance transport of fluid requires bulk flow , the movement of a fluid driven by pressure • Water and solutes move together through tracheids and vessel elements of xylem, and sieve-tube elements of phloem
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3 Water and minerals are transported from roots to shoots Most water and mineral absorption occurs near root tips, where the epidermis is permeable to water and root hairs are located Root hairs account for much of the surface area of roots After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals Transport of water and minerals into the xylem Water can cross the cortex via the symplast or apoplast The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder
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4 Pathway along apoplast Casparian strip Endodermal cell Pathway through symplast Casparian strip Plasma membrane Apoplastic route Symplastic route Root hair Epidermis Cortex Endodermis Vessels (xylem) Stele (vascular
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This note was uploaded on 06/07/2009 for the course BIOL 05 taught by Professor Helen during the Spring '09 term at UC Riverside.

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W9L1 - Transport in Plants Part 2 - Biol 5B: Organismal...

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