8Chapter 36~ Transport in Plants

Transport Overview 81- uptake and loss of water and solutes by individual cells (root cells) 82- short-distance transport from cell to cell (sugar loading from leaves to phloem) 83- long-distance transport of sap within xylem and phloem in whole plant

Whole Plant Transport 81- Roots absorb water and dissolved minerals from soil 82- Water and minerals are transported upward from roots to shoots as xylem sap 83- Transpiration, the loss of water from leaves, creates a force that pulls xylem sap upwards

Whole Plant Transport 84- Leaves exchange CO2 and O2 through stomata 85- Sugar is produced by photosynthesis in leaves 86- Sugar is transported as phloem sap to roots and other parts of plant 87- Roots exchange gases with air spaces of soil (supports cellular respiration in roots)

Cellular Transport 8Water transport √ Osmosis; hyper-; hypo-; iso- 8Cell wall creates physical pressure: √water potential solutes decrease; pressure increase 8Water moves from high to low water potential

Cellular Transport 8Flaccid (limp, iostonic); 8Plasmolysis (cell loses water in a hypertonic environment; plasma membrane pulls away); 8Turgor pressure (influx of water due to osmosis; hypotonic environment)

Transport within tissues/organs 8Tonoplast vacuole membrane 8Plasmodesmata cytosolic connection between adjoining plant cells

Transport within tissues/organs 8Symplast route (lateral) cytoplasmic continuum 8Apoplast route (lateral) crosses through cell walls and membranes 8Bulk flow (long distance) movement of a fluid by pressure (xylem)

Transport of Xylem Sap 8Transpiration: loss of water vapor from leaves pulls water from roots (transpirational pull) – much like a sucking liquid through a straw; cohesion and adhesion of water help 8Root pressure: at night (low transpiration), roots cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; guttation

Transpirational Control 8Photosynthesis-Transpiration compromise…. 8Guard cells control the size of the stomata 8Xerophytes (plants adapted to arid environments)~ thick cuticle; small spines for leaves

Translocation of Phloem Sap 8Translocation: food/phloem transport 8Sugar source: sugar production organ (mature leaves) 8Sugar sink: sugar storage organ (growing roots, tips, stems, fruit)

Translocation of Phloem Sap 81- loading of sugar into sieve tube at source reduces water potential inside; this causes tube to take up water from surroundings by osmosis; loading of sugar requires energy provided by companion cells 82- this absorption of water generates pressure that forces sap to flow along tube

Translocation of Phloem Sap 83- pressure gradient in tube is reinforced by unloading of sugar and consequent loss of water from tube at the sink 84- xylem then recycles water from sink to source

8Chapter 37 ~ Plant Nutrition

Nutrients 8Essential: required for the plant life cycle 8Macro- (large amounts) carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium 8Micro- (small amounts; cofactors of enzyme action) chlorine, iron, boron, manganese, zinc, copper, molybdenum, nickel 8Deficiency chlorosis (lack of magnesium; chlorophyll production)

Soil 8Determines plant growth & variety (also climate) 8Composition/horizons or layers: 8topsoil (rock particles, living organisms, humus - partially decayed organic material) 8loams (equal amounts of sand, silt, and clay)

Cation exchange 8Clay particles in soil are negatively charged 8Negative ions needed by plant (nitrate, phosphate) are easily removed from the soil 8Positive ions want to cling to the clay 8Cation exchange occurs when hydrogen ions in the soil displace positive ions away from the clay so they can be absorbed by the plant

Nitrogen Fixation 8Atmosphere, 78% N 2 (unsuable by plants) 8N2  ammonium (NH 4 +) or nitrate (NO 3 -) 8Bacteria types: 8Ammonifying (humus decomposition) 8nitrogen-fixing (convert N 2 to a usable form NH3/NH4+ ) 8nitrifying (convert NH 4 + to NO 3 -) 8denitrifying (convert NO 3 - to N 2 ) 8All enzymes needed are in one complex - nitrogenase 8crop rotation helps preserve nitrogen content of soil

Plant symbiosis 8Rhizobium bacteria (found in root nodules in the legume family) 8Mutualistic: legume receives fixed N 2 ; bacteria receives carbohydrates & organic materials

Plant symbiosis 8Mycorrhizae (fungi); modified roots 8Mutualistic: fungus receives sugar; plant receives increased root surface area and increased phosphate uptake

Plant parasitism & predation 8Mistletoe (parasite) 8Epiphytes (live in “air”) 8Carnivorous plants (grow in mineral poor soil, get minerals from bugs they eat)