Transport213-page15

Transport213-page15 - Roots actively move nutrient ions...

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Transport in Plants - 15 Other Water Movements Before we leave our discussion of movement of water in plants, let’s look at a few other water phenomena. Imbibition Water can be absorbed rapidly into cells by means other than osmosis. Certain molecules, especially starch and cellulose, “attract” water molecules when they are wet because of surface charges (+ and -). Since water is polar, it is attracted to the surfaces of these molecules, and large amounts of water can be taken into cells in this manner. Imbibition is very important for the process of germination, causing the seeds to swell rapidly with the uptake of water. Imbibition Force of Imbibition Positive Root Pressure and Guttation
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Unformatted text preview: Roots actively move nutrient ions from the soil all of the time, and when transpiration is low, the increasing concentration of ions within the cortex cells creates a water potential gradient for moving water into the roots. This results in a positive pressure. Simple diffusion pressure in roots moves H 2 O upward often forcing the H 2 O to be exuded from vein tips in leaves, a phenomenon called guttation. The special leaf tip cells are called hydathodes. Guttation is limited. Positive root pressure is soon matched by the atmospheric pressure, and in daylight, transpiration rates rapidly exceed any positive pressure generated. Root Pressure Guttation...
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