Transport in plants- Xylem

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  • Transport in plants- Xylem
    • Tissue involved
      • 1) Xylem tissue transports water/ mineral ions in solution. These substances move up the plant from roots to leaves
      • 2) Phloem tissue transports organic e.g sugars both up and down plant
      • 3) Xylem/phloem are mass transport systems- move substances over large distances
      • Xylem vessels- actually transports water and ions. Long, tube like structures formed from lignified cells. No end walls, making uninterrupted tube that allows water to pass up easily
    • Cohesion tension
      • 1) Water evaporates from leaves at top of xylem
      • 2) Creates tension which pulls more water into leaf
      • 3) Water molecules cohesive, when some are pulled into leaf others follow. Whole column of water in xylem from leaves to roots moves upwards
      • 4) Water enters stem through roots
    • Transpiration
      • Evaporation of water from the leaf of a plant
      • 1) Water evaporates from moist cell walls and accumulates in air spaces in leaf
      • 2) When stomata open, moves out of leaf down the concentration gradient (more water inside leaf than in air outside)
    • Factors affecting transpiration rate
      • 1) Light: lighter= faster transpiration (positive correlation between light intensity/TR) Stomata open when its light to let in CO2 for photosynthesis. Dark=stomata closed, little trans
      • 2) Temp: higher temp=faster transpiration. Warm water molecules have higher energy so evaporate from cells faster. Increases conc grad between inside/outside of leaf, making water diffuse faster
      • 3) Humidity: lower humidity= faster transpiration rate (negative correlation). If air around plant dry, conc grad between leaf and air increased- increases transpiration
      • 4) Wind: Windier= faster transpiration. Lots of air movement blows away water molecules from around stomata. Increases conc grad, increases transpiration


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