transport in plants

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  • Created by: lskitty
  • Created on: 14-04-16 19:56
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  • Transport in plants
    • Xylem
      • Function: transporting water and mineral ions
      • Adaptions
        • Continuous- no end walls
        • Lignified- waterproof and provides strength
        • Narrow - increases adhesion
        • Pits - holes in lignin through water can pass
        • Dead - no cytoplasm not restrcited
      • Tension - water pulled by transpiration and down by gravity/ water moves along pressure gradient
      • Adhesion - water to xylem walls
      • Cohesion - formation of H bonds between water molecules
      • Root pressure - salts actively pumped into xylem lowers water potential, drawing in water by osmosis
    • Translocation
      • Energy-requiring process transporting assimilates, especially sucrose, between sources  and sinks
      • Mass flow - the bulk movement of substances due to differences in hydrostatic pressure
        • Evidence for
          • Aphids mouthparts- sap flows up quicker near leaves
          • Remove ring of bark, analyse fluid from bulge, has high conc. of assimilates than ring below
          • Metabolic inhibitor in phloem - evidence ATP used
        • Evidence against
          • Sugar travels to different sinks
          • Sieve plates would create barrier
    • Transpiration
      • Measure using potometer
        • Record starting position of bubble and distance moved in time
        • Cut stem at slant as increases SA
        • Cut shoot underwater to stop air entering
        • Dry leaves
      • Factors
        • External
          • Distribution of stomata
          • Leaf SA
          • Waxy cuticle thickness
        • Internal
          • Temperature
          • Humidity
          • Light
          • Wind
      • Consequence of gaseous exchange needed for photosynthesis
      • The evaporation of water from the aerial parts of a plant
    • Xerophytes
      • Curled leaves
      • Adapted to living in dry climates
      • Shrunken/ reduced number of stomata
      • Thick waxy cuticle
      • Untitled
      • Hairs trap moist air
    • Phloem
      • Companion cells
        • Metabolically active
        • Large nucleus, mitochondria, rough ER
      • Sieve tube elements
        • joined end to end
        • No nucleus, thin cytoplasm and few organelles
      • Transports solutes
    • Need for transport systems
      • Multicellular small SA:volume ratio
      • Cells deep plant would not get all nutrients and substances
      • Direct diffusion too slow
    • Water uptake by roots
      • Symplast pathway
        • Through cytoplasm via plasmodesmata
      • Apoplast pathway
        • Through cellulose cell wall
          • Blocked by casparian stip so takes symplast route
      • Vacuolar pathway
        • Through the vacuole

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