35 - 35 Transport in Plants or Plant Plumbing 35 Transport...

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35 Transport in Plants or Plant Plumbing
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35 Transport in Plants How Do Plant Cells Take Up Water and Solutes? How Are Water and Minerals Transported in the Xylem? How Do Stomata Control the Loss of Water and the Uptake of CO 2 ? How Are Substances Translocated in the Phloem?
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35.1 How Do Plant Cells Take Up Water and Solutes? Terrestrial plants obtain water and mineral nutrients from the soil. Water is essential for transporting solutes upward and downward, for cooling the plant, and for internal pressure that supports the plant. Plants lose large quantities of water to evaporation.
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Figure 35.1 The Pathways of Water and Solutes in the Plant
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35.1 How Do Plant Cells Take Up Water and Solutes? Osmosis: movement of water through a membrane in accordance with the laws of diffusion. Osmosis is passive : no input of energy is required.
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35.1 How Do Plant Cells Take Up Water and Solutes? The greater the solute concentration of a solution, the greater the tendency for water to move into it from another solution of lower solute concentration. Water always moves from a solution of low solute concentration to one of higher solute concentration.
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35.1 How Do Plant Cells Take Up Water and Solutes? For osmosis to occur, two solutions must be separated by a selectively permeable membrane; permeable to water, but not to the solute. Plants have rigid cell walls. As water enters a cell due to its negative solute potential, entry of more water is resisted by an opposing pressure potential (turgor pressure).
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35.1 How Do Plant Cells Take Up Water and Solutes? Water enters plant cells until the pressure exactly balances the solute potential. At this point the cell is turgid : it has significant positive pressure potential.
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35.1 How Do Plant Cells Take Up Water and Solutes? Osmosis is extremely important to plants. Physical structure is maintained by the positive pressure potential. If this is lost, the plant wilts . Over long distances in xylem and phloem, flow of water and dissolved solutes is driven by a gradient of pressure potential.
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CPS Question Water a. Moves through biological membranes by simple diffusion b. Would flow into a cell suspended in an isotonic solution c. Would flow into a cell suspended in a hypotonic solution d. Would flow into a cell suspended in a hypertonic solution e. Does not move across membranes
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TONICITY
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35.1 How Do Plant Cells Take Up Water and Solutes? Aquaporins - membrane channel proteins that water can pass through rapidly. Abundance in plasma membrane and tonoplast (vacuole membrane) depends on cell’s need to obtain or retain water. Rate of water movement can be regulated but direction of movement can not.
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35.1 How Do Plant Cells Take Up Water and Solutes? Mineral ions cannot pass membranes
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This note was uploaded on 04/22/2008 for the course BIOLOGY 020.152 taught by Professor Pearlman during the Spring '08 term at Johns Hopkins.

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