Plant Transport - Plant Transport Moving Liquids Without a...

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Plant Transport: Moving Liquids Without a Mechanical Pump Plants take up and transport water and solutes long distances and against the force of gravity How Far? Largest gymnosperm ( Sequoia sempervirens ), angiosperm ( Eucalyptus regnans ) > 110m How much? Maple tree 15m tall, has 177, 000 leaves, total area 675 m 2 (~1.5 basketball courts) Needs to transport 220 liters water/ hr (50 gallon drum = 189 l) ( At rest, your heart pumps about 250 l blood/hr )
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Selective Permeability of Membranes: A Review The selective permeability of a plant cell’s plasma membrane controls the movement of solutes into and out of the cell Specific transport proteins enable plant cells to maintain an internal environment different from their surroundings Water flow (osmosis) follows solute transport
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The Central Role of Proton Pumps Proton pumps in plant cells Create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work Contribute to a voltage known as a membrane potential CYTOPLASM EXTRACELLULAR FLUID ATP H + H + H + H + H + H + H + H + Proton pump generates membrane potential and H + gradient. + + + + +
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Solute transport across membranes Plant cells use energy stored in the proton gradient and membrane potential to drive the transport of many different solutes + CYTOPLASM EXTRACELLULAR FLUID Cations ( , for example) are driven into the cell by the membrane potential. Transport protein K + K + K + K + K + K + K + K + + + Membrane potential and cation uptake + +
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Solute transport across membranes In the mechanism called co-transport, a transport protein couples the passage of one solute to the passage of another H + H + H + H + H + H + H + H + H + H + H + H + NO 3 3 + + + + + + NO 3 Co-transport of anions H+ of through a Co-transporter. Cell accumulates anions ( , for example) by coupling their transport to the inward diffusion
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H + H + H + H + H + H + H + H + H + H + S S Plant cells can also accumulate a neutral solute, such as sucrose ( ), by Co-transporting down the steep proton gradient. S H + + + + + + H + H + S + Co-transport of a neutral solute Solute transport across membranes The “coattail” effect of co-transport is also responsible for the uptake of the sugar sucrose by plant cells
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Effects of Differences in Water Potential To survive plants must balance water uptake & loss. Osmosis determines the net uptake or water loss by a cell and is affected by solute conc. and pressure Water potential (Ψ) is a measurement that combines the effects of solute concentration and pressure and determines the direction of movement of water Water flows from regions of high water potential to regions of low water potential The solute potential (Ψs) of a solution is proportional to the number of dissolved molecules Pressure potential (Ψp) is the physical pressure on a solution Ψ = Ψs + Ψp
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This note was uploaded on 05/23/2011 for the course BIOLOGY 1520 taught by Professor Davidgarton during the Fall '09 term at Georgia Tech.

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Plant Transport - Plant Transport Moving Liquids Without a...

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