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Transport213-page7 - • Plant cells have vacuoles to...

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Transport in Plants - 7 Transpiration Plants are especially vulnerable to water loss because they need porous surfaces for gas exchange. To a significant extent, water enters plants through roots, travels through the vascular system and departs through open stomata in leaves. Most water lost from plants is by the process of transpiration, the evaporation of water from the plant through open stomata and other plant surfaces. Transpiration also plays a role in the movement of water throughout the plant, as we shall discuss in a bit. Transpiration loss is significant – a mature maple tree can evaporate more than 50 gallons of water a day. In cornfields, as much as 90% or more of the water absorbed by the roots is lost by transpiration. Naturally, plants have a number of ways to conserve water and minimize transpiration losses: Epidermal cells on above-ground structures have a cuticle layer (cutin) to prevent water loss; the walls of cork cells contain impermeable suberin.
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Unformatted text preview: • Plant cells have vacuoles to accumulate water, and cell walls to help maintain turgor. (This works better at preventing excess water than it does at preventing dehydration.) • Many cells and tissues need not be maintained because they’re dead (saves energy as well as water needed for metabolic functions) • Xeromorphic plants frequently have anatomical adaptations to minimize transpiration loss as well as physiological adaptations such as the CAM metabolism discussed with photosynthesis • Most transpiration loss is through stomata. Guard cells open and close so that water loss by transpiration is minimized when plants can’t use CO 2 for photosynthesis. (The mechanism for stomatal operation will be discussed in a bit.) Even so, taking in sufficient water for metabolic needs and to counter transpiration loss is a challenge that plants must meet and physicists can explain....
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