keycell_membrane_practice_qs - KEY to Cell Membrane...

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KEY to Cell Membrane Practice Questions 1. Rank the following molecules according to the ease with which they can cross a phospholipid bilayer: fructose, water, phosphate, chloride ion, oxygen gas, the amino acid proline Crosses (best to worst): oxygen gas, water, fructose, proline, chloride, phosphate 2. Explain the rationale you used in ranking the molecules in question #1. Oxygen gas is small and nonpolar, water is small but polar, fructose is larger and polar, proline is larger still and polar, chloride is an ion (charged), phosphate is large and an ion 3. The cell membrane is often described as “selectively-permeable”. What is meant by this term? Some materials can cross the membrane freely (such as carbon dioxide and oxygen gases, and nonpolar molecules such as benzene) while others have a very low likelihood of crossing at all (charged and large polar molecules) – thus the membrane, by its amphipathic nature and construction, is selective about what types of materials can permeate (cross). 4. Cells can change the composition of their membranes to adapt to different environmental conditions. What component of the membrane could be changed to help an organism tolerate cold? Heat? (be specific as to the exact component, and how it could be changed) An organism could increase the proportion of unsaturated fatty acid tails in the phospholipid molecules of its membrane to maintain membrane fluidity under cold conditions. To adapt to hotter conditions, an organism could increase the saturated fatty acid content of the phospholipids and / or increase the length of those fatty acids. 5. What is the difference between diffusion and osmosis? Diffusion is a general term describing the tendency of materials to move from high concentration to low due to random kinetic movements (e.g., Brownian motion). Osmosis is a special type of diffusion in which the solvent (water) moves across a membrane from high water concentration (less solute) to low water concentration (more solute) because the movement of the solute across the membrane is restricted. 6. Define the terms hypertonic, hypotonic and isotonic. Hypertonic: A hypertonic solution contains a greater concentration of solute (mol/L) than the solution it is being compared to.
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Hypotonic: A hypotonic solution contains a lower concentration of solute than the solution it is being compared to. Isotonic: A hypertonic solution contains the same molarity of solute as the solution it is being compared to. 7. Use the chart to describe what happens to a cell that has a cell wall, and a cell that lacks one, when placed in these different environments. Hypertonic Hypotonic Isotonic No cell wall Crenation (shriveling) Lysis (bursting) normal Cell wall Plasmolysis (membrane pulling away from cell wall) turgid flaccid 8. Ethanol (the active molecule in alcoholic beverages) is a small, polar, uncharged molecule. Would you predict that this molecule crosses membranes by diffusion slowly or quickly? Explain your reasoning. Ethanol, like the small, uncharged, polar molecule water, can quickly cross cell
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This note was uploaded on 07/03/2009 for the course BIS 64982 taught by Professor Comai during the Spring '09 term at UC Davis.

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keycell_membrane_practice_qs - KEY to Cell Membrane...

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