B3 - Transpiration

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  • Transpiration
    • Definitions
      • Transpiration
        • evaporation of water from leaves
      • Transpirational Pull
        • continuous movement of water from roots, up the xylem, along the leaves and into the atmosphere (passive process)
    • Factors Affecting Transpiration
      • Light
        • the lighter it is the faster the transpiration rate because the stomata open when it gets light to let in CO2 for photosynthesis. When its dark the stomata are usually closed, so there's little transpiration
      • Temperature
        • the higher the temperature the faster the transpiration rate. Warmer water molecules have more energy so they evaporate from the cells inside the leaf faster
          • This increases concentration gradient between the inside and outside of the leaf making water diffuse out the leaf faster
      • Humidity
        • the lower the humidity, the faster rate of transpiration. If the air around the plant is dry, the concentration gradient between the leaf and air is increased, increasing transpiration
      • Wind
        • the windier it is the faster the rate of transpiration. Lots of air movement blows away water molecules from around the stomata
          • This increases concentration gradient, increasing the rate of transpiration
    • Estimating Transpiration Rate
      • A potometer measures water uptake by a plant
        • It assumes that water uptake by the plant is directly related to water loss by the leaves
          • Cut a shoot underwater to prevent air from entering the xylem and at a slant to increase surface area for water uptake
            • Assemble the potometer in water, so no air can enter


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