BIOLOGY 3B03 Lecture Notes - Lecture 5: Hydraulic Conductivity, Plant Cell, Water Potential
8 Apr 2018
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Recall the use of inhibitors to show that the endodermis offers a barrier to water transport across roots and that respiration (energy) is required or the shoots can wilt. Cut a seedling just above the soil line and the stump will exude sap. Pressure driving sap can be measured and is usually less than 0. 1mpa. With more h2o entering stele the hydrostatic p of the xylem will increase at the base relative to cut end open to atmosphere. Plant has to have lower water potential than soil does, and needs to have more ions in xylem than in cortex. This contributes to driving force that moves water across. At endodermis, it has to go across the membrane. Yes, if the plant is well-watered, fully hydrated, and transpiration is reduced by high humidity. Eg. at night you find dew drops on leaf blades.
