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SC BIOL 101 - REEC7295_09_TB_chapter07

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Campbell's Biology, 9e (Reece et al.)Chapter 7 Membrane Structure and FunctionMembranes and membrane transport are fundamental to cellular life. The concepts in this chapter require integration of concepts from previous chapters: the nature of water and hydrophobic versus hydrophilic molecules, the properties of lipid molecules and their role in regulating membrane fluidity, and the roles of proteins and carbohydrates in membrane function. The concepts of ion transport and electrochemical gradients across membranes are important foundations for the following chapters on energy metabolism. Finally, the bulk transport phenomena have important clinical significance in the immune system, during invasion by pathogens, and in cell signaling.Multiple-Choice Questions1) Who was/were the first to propose that cell membranes are phospholipid bilayers?A) H. Davson and J. DanielliB) I. LangmuirC) C. OvertonD) S. Singer and G. NicolsonE) E. Gorter and F. GrendelAnswer: ETopic: Concept 7.1Skill: Knowledge/Comprehension2) Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. As a result, these lipid raftsA) are more fluid than the surrounding membrane.B) are more rigid than the surrounding membrane.C) are able to flip from inside to outside.D) detach from the plasma membrane and clog arteries.E) have higher rates of lateral diffusion of lipids and proteins into and out of the lipid rafts.Answer: BTopic: Concept 7.1Skill: Application/Analysis3) Singer and Nicolson's fluid mosaic model of the membrane proposed thatA) membranes are a phospholipid bilayer.B) membranes are a phospholipid bilayer between two layers of hydrophilic proteins.C) membranes are a single layer of phospholipids and proteins.D) membranes consist of protein molecules embedded in a fluid bilayer of phospholipids.E) membranes consist of a mosaic of polysaccharides and proteins.Answer: DTopic: Concept 7.1Skill: Knowledge/Comprehension1Copyright © 2011 Pearson Education, Inc.4) Which of the following types of molecules are the major structural components of the cell membrane?A) phospholipids and celluloseB) nucleic acids and proteinsC) phospholipids and proteinsD) proteins and celluloseE) glycoproteins and cholesterolAnswer: CTopic: Concept 7.1Skill: Knowledge/Comprehension5) When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is thatA) the integral membrane proteins are not strong enough to hold the bilayer together.B) water that is present in the middle of the bilayer freezes and is easily fractured.C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing.D) the carbon-carbon bonds of the phospholipid tails are easily broken.E) the hydrophobic interactions that hold the membrane together are weakest at this point.Answer: ETopic: Concept 7.1Skill: Application/Analysis6) The presence of cholesterol in the plasma membranes of some animalsA) enables the membrane to stay fluid more easily when cell temperature drops.B) enables the animal to remove hydrogen atoms from saturated phospholipids.C) enables the animal to add hydrogen atoms to unsaturated phospholipids.D) makes the membrane less flexible, allowing it to sustain greater pressure from within the cell.E) makes the animal more susceptible to circulatory disorders.Answer: ATopic: Concept 7.1Skill: Knowledge/Comprehension7) According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?A) They can move laterally along the plane of the membrane.B) They frequently flip-flop from one side of the membrane to the other.C) They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane.D) They are free to depart from the membrane and dissolve in the surrounding solution.E) They have hydrophilic tails in the interior of the membrane.Answer: ATopic: Concept 7.1Skill: Knowledge/Comprehension2Copyright © 2011 Pearson Education, Inc.8) Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?A) by increasing the percentage of unsaturated phospholipids in the membraneB) by increasing the percentage of cholesterol molecules in the membraneC) by decreasing the number of hydrophobic proteins in the membraneD) by cotransport of glucose and hydrogenE) by using active transportAnswer: ATopic: Concept 7.1Skill: Knowledge/Comprehension9) In order for a protein to be an integral membrane protein it would have to beA) hydrophilic.B) hydrophobic.C) amphipathic, with at least one hydrophobic region.D) completely covered with phospholipids.E) exposed on only one surface of the membrane.Answer: CTopic: Concept 7.1Skill: Synthesis/Evaluation10) When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane areA) peripheral proteins.B) phospholipids.C) carbohydrates.D) integral proteins.E) cholesterol molecules.Answer: DTopic: Concept 7.1Skill: Application/Analysis11) Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?A) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.B) Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in membranes.C) Unsaturated fatty acids are more polar than saturated fatty acids.D) The double bonds block interaction among the hydrophilic head groups of the lipids.E) The double bonds result in shorter fatty acid tails and thinner membranes.Answer: ATopic: Concept 7.1Skill: Knowledge/Comprehension3Copyright © 2011 Pearson Education, Inc.12) Which of the following is true of integral membrane proteins?A) They lack tertiary structure.B) They are loosely bound to the surface of the bilayer.C) They are usually transmembrane proteins.D) They are not mobile within the bilayer.E) They serve only a structural role in membranes.Answer: CTopic: Concept 7.1Skill: Knowledge/Comprehension13) The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes isA) to facilitate diffusion of molecules down their concentration


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SC BIOL 101 - REEC7295_09_TB_chapter07

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