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HW #36 - AP Biology Period 4#22 Liem Nguyen...

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AP Biology Period – 4 #22 Liem Nguyen 2/20/10 Homework #36 ( 090303 ): Chapter 36 (due Friday 090303 ) Total points: 40 for Attempt on all questions Concept Map: 10 Points Chapter 36: Transport in Vascular Plants Objectives An Overview of Transport Mechanisms in Plants 1. Describe how proton pumps function in transport of materials across plant membranes, using the terms proton gradient, membrane potential, cotransport, and chemiosmosis. Proton pumps: use ATP, remove hydrogen ions out of cell Proton gradient with higher H+ concentration Contributes to membrane potential Cotransport, downhill Application of chemiosmosis Proton pumps use ATP to pump hydrogen ions out of the cell. This results in a proton gradient with a higher H+ concentration. The proton pump also contributes to membrane potential. Plant cells use proton pumps in a mechanism called cotransport, which couples the downhill passage of H+ and the uphill passage of NO 3 - . Proton pumps are also used in chemiosmosis, which features a transmembrane proton gradient. 2. Define osmosis and water potential. Explain how water potential is measured. Passive transport of water through a membrane Combined effects of solute concentration and physical pressure Megapascals (water potential measured) Osmosis is the passive transport of water through a membrane. Water potential is the combined effect of solute concentration and physical pressure. Water potential is measuered in megapascals. 3. Explain how solutes and pressure affect water potential. Dissolved solute molecules Affects direction of osmosis Solutes bind water molecules Adding solutes, lowers water potential Physical pressure/press against The solute potential is proportional to the number of dissolved solute molecules. This is also called osmotic potential because it affects the direction of osmosis. When solutes are added to a solution, they bind water molecules together. Adding solutes can lower the water potential. Pressure potential is the physical pressure acting on a solution. This causes the contents of a plant cell to press against to the cell wall, which is called the
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turgor pressure. 4. 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. Tendency to move from high to low Placed in lower solute concentration, water leaves cell Paced in high solute concentration, water moves into cell Placed in equal solute concentration, pressure is equal Water has the tendency to move in the direction of lower water potential. Because is this, when a plant cell is placed in a lower solute concentration, water will leave the cell, causing the cell to pull away from the wall, or plasmolyze. When a plant cell is placed in a higher solute concentration, water will move into the cell, causing it to be firm and turgid. When a plant cell is placed in the same solute concentration, the pressure is equal.
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