#16
Date Lecture ______
$ Chapter 36~ Transport in Plants
Transport Overview
$ 1- uptake and loss of water and solutes by individual cells (root cells) $ 2- short-distance transport from cell to cell (sugar loading from leaves to phloem) $ 3- long-distance transport of sap within xylem and phloem in whole plant
Whole Plant Transport
$ 1- Roots absorb water and dissolved minerals from soil $ 2- Water and minerals are transported upward from roots to shoots as xylem sap $ 3- Transpiration, the loss of water from leaves, creates a force that pulls xylem sap upwards $ 4- Leaves exchange CO2 and O2 through stomata $ 5- Sugar is produced by photosynthesis in leaves $ 6- Sugar is transported as phloem sap to roots and other parts of plant $ 7- Roots exchange gases with air spaces of soil (supports cellular respiration in roots)
Cellular Transport
$ Water transport Osmosis; hyper-; hypo-; iso$ Cell wall creates physical pressure: water potential solutes decrease; pressure increase $ Water moves from high to low water potential $ Flaccid (limp, iostonic); $ Plasmolysis (cell loses water in a hypertonic environment; plasma membrane pulls away); $ Turgor pressure (influx of water due to osmosis; hypotonic environment)
Transport within tissues/organs
$ Tonoplast vacuole membrane $ Plasmodesmata (components) cytosolic connection $ Symplast (lateral) route cytoplasmic continuum $ Apoplast route (lateral) continuum of cell walls $ Bulk flow (long distance) movement of a fluid by pressure (xylem)
Transport of Xylem Sap
$ Transpiration: loss of water vapor from leaves pulls water from roots (transpirational pull); cohesion and adhesion of water $ Root pressure: at night (low transpiration), roots cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; guttation
Cohesion of Water
QuickTime and a Cinepak decompressor are needed to see this picture.
Transpirational Control
$ Photosynthesis-Transpiration compromise.... $ Guard cells control the size of the stomata $ Xerophytes (plants adapted to arid environments)~ thick cuticle; small spines for leaves
Translocation of Phloem Sap
$ Translocation: food/phloem transport $ Sugar source: sugar production organ (mature leaves) $ Sugar sink: sugar storage organ (growing roots, tips, stems, fruit) $ 1- loading of sugar into sieve tube at source reduces water potential inside; this causes tube to take up water from surroundings by osmosis $ 2- this absorption of water generates pressure that forces sap to flow alon tube $ 3- pressure gradient in tube is reinforced by unloading of sugar and consequent loss of water from tube at the sink $ 4- xylem then recycles water from sink to source