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Plants

Plants. Transport and Tissue. Transport in plants. H 2 O & minerals transport in xylem transpiration Sugars transport in phloem bulk flow Gas exchange photosynthesis CO 2 in; O 2 out stomates respiration O 2 in; CO 2 out roots exchange gases within air spaces in soil.

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Plants

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  1. Plants Transport and Tissue

  2. Transport in plants • H2O & minerals • transport in xylem • transpiration • Sugars • transport in phloem • bulk flow • Gas exchange • photosynthesis • CO2 in; O2 out • stomates • respiration • O2 in; CO2 out • roots exchange gases within air spaces in soil Why does over-watering kill a plant?

  3. Transport in plants • Physical forces drive transport at different scales • cellular • from environment into plant cells • transport of H2O & solutes into root hairs • short-distance transport • from cell to cell • loading of sugar from photosynthetic leaves into phloem sieve tubes • long-distance transport • transport in xylem & phloem throughout whole plant

  4. Cellular transport • Active transport • solutes are moved into plant cells via active transport • central role of proton pumps • chemiosmosis proton pumps

  5. Short distance (cell-to-cell) transport • Compartmentalized plant cells • cell wall • cell membrane • cytosol • vacuole • Movement from cell to cell • move through cytosol • plasmodesmata junctions connect cytosol of neighboring cells • symplast • move through cell wall • continuum of cell wall connecting cell to cell • apoplast apoplast symplast

  6. Routes from cell to cell • Moving water & solutes between cells • transmembrane route • repeated crossing of plasma membranes • slowest route but offers more control • symplast route • move from cell to cell within cytosol • apoplast route • move through connected cell wall without crossing cell membrane • fastest route but never enter cell

  7. Long distance transport • Bulk flow • movement of fluid driven by pressure • flow in xylem tracheids & vessels • negative pressure • transpiration creates negative pressurepulling xylem sap upwards from roots • flow in phloem sieve tubes • positive pressure • loading of sugar from photosynthetic leaf cells generates high positive pressurepushing phloem sap through tube

  8. Movement of water in plants cells are flaccid plant is wilting • Water relations in plant cells is based on water potential • osmosis through aquaporins • transport proteins • water flows from high potential to low potential cells are turgid

  9. Water & mineral uptake by roots • Mineral uptake by root hairs • dilute solution in soil • active transport pumps • this concentrates solutes (~100x) in root cells • Water uptake by root hairs • flow from high H2O potential to low H2O potential • creates root pressure

  10. Controlling the route of water in root • Endodermis • cell layer surrounding vascular cylinder of root • lined with impervious Casparian strip • forces fluid through selective cell membrane & into symplast • filtered & forced into xylem vessels

  11. Plant TISSUES • Dermal • epidermis (“skin” of plant) • single layer of tightly packed cells that covers & protects plant • Ground • bulk of plant tissue • photosynthetic mesophyll, storage • Vascular • transport system in shoots & roots • xylem & phloem

  12. Plant CELL types in plant tissues • Parenchyma • “typical” plant cells = least specialized • photosynthetic cells, storage cells • tissue of leaves, stem, fruit, storage roots • Collenchyma • unevenly thickened primary walls • support • Sclerenchyma • very thick, “woody” secondary walls • support • rigid cells that can’t elongate • dead at functional maturity

  13. Parenchyma • Parenchyma cells are unspecialized, thin, flexible & carry out many metabolic functions • all other cell types in plants develop from parenchyma

  14. Collenchyma • Collenchyma cells have thicker primary walls & provide support • help support without restraining growth • remain alive in maturity the strings in celery stalks are collenchyma

  15. Sclerenchyma • Thick, rigid cell wall • lignin (wood) • cannot elongate • mostly dead at maturity • Cells for support • xylem vessels • xylem tracheids • fibers • rope fibers • sclereids • nutshells • seed coats • grittiness in pears

  16. Vascular tissue vessel elements • Xylem • move water & minerals up from roots • dead cells at functional maturity • only cell walls remain • need empty pipes to efficiently move H2O • transpirational pull vessel element dead cells Aaaah… Structure–Functionagain! tracheids

  17. Phloem: food-conducting cells • carry sugars & nutrients throughout plant sieve tube companion cell sieve plate plasmodesmata living cells

  18. Phloem • Living cells at functional maturity • cell membrane, cytoplasm • control of diffusion • lose their nucleus, ribosomes & vacuole • more room for specialized transport of liquid food (sucrose) • Cells • sieve tubes • sieve plates — end walls — have pores to facilitate flow of fluid between cells • companion cells • nucleated cells connected to the sieve-tube • help sieve tubes

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