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Chapter_36_Learning_Objectives - Chapter Learning...

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Chapter Learning Objectives Chapter 36: Resource Acquisition and Transport in Vascular Plants Concept 36.2: Transport occurs by short-distance diffusion or active transport or by long-distance bulk flow Describe how proton pumps function in transport of materials across plant membranes, using the terms proton gradient, membrane potential, cotransport, and chemiosmosis. o In active transport in plant cells, the most important transport proteins are proton pumps , which use energy from ATP to pump protons (H + ) out of the cell. This results in an H + gradient (proton gradient) , with a higher H + concentration outside the cell than inside. The proton gradient across the membrane is a form of potential (store) energy, and the flow of H + back into the cell can be harnessed to do work. The movement of H + out of the cell also makes the inside of the cell negative in charge relative to the outside. (figure 36.6) o This charge separation across the membrane contributes to a voltage called a membrane potential , another form of potential energy that can be harnesses to perform cellular work. This drives active transport for many different solutes (K + by root cells)(figure 36.7a) o In cotransport , a transport protein couples the diffusion of one solute (H + ) with active transport of another (NO 3 - in figure 36.7b). The “coattail” effect of cotransport is also responsible for absorption of neutral solutes, such as the sugar sucrose, by plant cells (figure 36.7c). Define osmosis and water potential. o Osmosis: the diffusion of water across a selectively permeable membrane o Water Potential: the physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure Explain how solutes and pressure affect water potential. o Water Potential equation: Ψ = Ψ s + Ψ P o Where Ψ is the water potential, Ψ S is the solute potential (osmotic potential), and V P is pressure potential. o The solutes bind water molecules, reducing the number of free water molecules and lowering the capacity of the water to move and do work. Thus, adding solutes always lowers water potential, and the Ψ S of a solution is always negative. o Pressure potential is the physical pressure on a solution. Unlike Ψ S , Ψ P , can be positive or negative relative to atmospheric pressure. The water in living cells is usually under positive pressure. Specifically, the cell contents press the plasma membrane against the cell wall, and the cell wall, in turn, presses against the protoplast, producing what is called turgor pressure Explain how the physical properties of plant cells are changed when the plant is placed into solutions that have higher, lower, or the same solute concentration.
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