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UNC-Chapel Hill BIOL 101 - Membrane Structure and Function

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Guided Reading Q’s (GRQs) – Lesson 4Membrane Structure and Function1. A.)The chapter opener discusses aquaporins. What is the function of these proteins?They help with water balance. They are vital to the proper function of your kidneysB.)What if a person has too many in the membranes of their kidney cells?Excess water is reabsorbed and body tissues may swellC.)What if a person has too few in the membranes of their kidney cells?Those people must drink at least 20 liters of water a day to keep from dehydrating2.What is meant by the terms “fluid mosaic” and “selective permeability” whendescribing membranes?Biologists used the fluid mosaic model to illustrate the structure and function of aplasma membrane. Selective permeability in a cellular membrane allowssome substances to cross more easily than others3. Why was the spontaneous formation of membranes such an important step in cellevolution?It is an important step because a membrane that encloses a successful assembly of molecules andregulates chemical exchanges with the environment is a basic requirement of life4.Use the words diffusion and concentration gradient in a sentence.Molecules diffuse by diffusion to available spaces, and they move down their concentrationgradient trying to reach an equilibrium5. A.)How does the structure of the membrane relate to its selective permeability? (Thinkabout the chemical properties of the inner core of the bi-layer.)The hydrophobic bilayer allows non polar molecules to enter easily. The hydrophilic heads do not permit polar molecules to come in so easily so they might have to enter by a transporter proteinB.)What kinds of molecules can freely cross through passive transport withouttransport proteins? (Review and define the words polar and nonpolar if you need to!)Non polar molecules such as o2 and co2C.)What kinds of molecules use facilitated diffusion (a kind of passive transport thatrequires transporter proteins)?Molecules that are polar or charged Ex. sugars, amino acids, ions, sometimes water6.If I give you a 5% sucrose solution and a 10% sucrose solution, in which is the waterless concentrated?10% sucrose7.When water moves through a selectively permeable membrane down its concentrationgradient this is termed ______________.Osmosis8.Is seawater hypertonic, isotonic, or hypotonic to drinking water?Hypertonic9.A.)If a hypotonic solution is put in a selectively permeable membrane and put into ahypertonic solution, what will happen to the bag over time? (Shrink or swell?)Over time the bag will swellB.)Why?Because red blood cells in a hypotonic solution swell because of water.C.)Where is the water more concentrated?The water is more concentrated in the selectively permeable bag10.Water is a polar molecule and thus diffuses slowly into cells. What type of membraneprotein would you expect to find many of in a cell that must be highly permeable towater?Aquaporin11.Scientific Thinking in Module 5.7: Sometimes discovery is accidental.A.)What type of cell did Dr. Agre’s team accidentally discover aquaporins in?Frog cellsIn their work, shown in Figure 5.7 control frog eggs were compared to frog eggs thatcarried genetic information to make many aquaporins. B.)What result did they get when they put these two groups of eggs in a hypotonicsituation (describe Figure 5.7).The experimental eggs exploded in 3 minutes and the controlled eggs had minimal swellingfor over an hourC.)What did it tell them about the function of aquaporins?They only allow water to pass through them12.In our discussion of how cells use glucose as an energy resource, we will see that cellsare continually bringing glucose in from the blood where the concentration is higher.What kind of transport does glucose use? Facilitated diffusion13.How do calcium ions move against their concentration gradient?Active transport14.A.)Compare and contrast exocytosis and endocytosis.Exocytosis Endocytosiscells export bulky materials suchas proteins and polysaccharidescells take in large molecules offluids inB.)What are the distinctions between phagocytosis and receptor-mediated endocytosis?- Phagocytosis is cellular eating, pseudopodia wraps around a particle and engulfs it into avacuole, then the vacuole attaches to a lysosome. - Receptor-mediated endocytosis enables a cell to acquire specific solutes indents to form apit whose receptor proteins pick up molecules from the extracellular

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