Guided Reading Q s GRQs Lesson 4 Membrane Structure and Function 1 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 kidneys B What if a person has too many in the membranes of their kidney cells Excess water is reabsorbed and body tissues may swell C 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 dehydrating 2 What is meant by the terms fluid mosaic and selective permeability when describing membranes Biologists used the fluid mosaic model to illustrate the structure and function of a plasma membrane Selective permeability in a cellular membrane allows some substances to cross more easily than others 3 Why was the spontaneous formation of membranes such an important step in cell evolution It is an important step because a membrane that encloses a successful assembly of molecules and regulates chemical exchanges with the environment is a basic requirement of life 4 Use the words diffusion and concentration gradient in a sentence Molecules diffuse by diffusion to available spaces and they move down their concentration gradient trying to reach an equilibrium 5 A How does the structure of the membrane relate to its selective permeability Think about 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 protein B What kinds of molecules can freely cross through passive transport without transport proteins Review and define the words polar and nonpolar if you need to Non polar molecules such as o2 and co2 C What kinds of molecules use facilitated diffusion a kind of passive transport that requires transporter proteins Molecules that are polar or charged Ex sugars amino acids ions sometimes water 6 If I give you a 5 sucrose solution and a 10 sucrose solution in which is the water less concentrated 10 sucrose 7 When water moves through a selectively permeable membrane down its concentration gradient this is termed Osmosis 8 Is seawater hypertonic isotonic or hypotonic to drinking water Hypertonic 9 A If a hypotonic solution is put in a selectively permeable membrane and put into a hypertonic solution what will happen to the bag over time Shrink or swell Over time the bag will swell B 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 bag 10 Water is a polar molecule and thus diffuses slowly into cells What type of membrane protein would you expect to find many of in a cell that must be highly permeable to water Aquaporin 11 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 cells In their work shown in Figure 5 7 control frog eggs were compared to frog eggs that carried genetic information to make many aquaporins B What result did they get when they put these two groups of eggs in a hypotonic situation describe Figure 5 7 The experimental eggs exploded in 3 minutes and the controlled eggs had minimal swelling for over an hour C What did it tell them about the function of aquaporins They only allow water to pass through them 12 In our discussion of how cells use glucose as an energy resource we will see that cells are continually bringing glucose in from the blood where the concentration is higher What kind of transport does glucose use Facilitated diffusion 13 How do calcium ions move against their concentration gradient Active transport 14 A Compare and contrast exocytosis and endocytosis Exocytosis Endocytosis cells export bulky materials such as proteins and polysaccharides cells take in large molecules of fluids in B What are the distinctions between phagocytosis and receptor mediated endocytosis Phagocytosis is cellular eating pseudopodia wraps around a particle and engulfs it into a vacuole then the vacuole attaches to a lysosome Receptor mediated endocytosis enables a cell to acquire specific solutes indents to form a pit whose receptor proteins pick up molecules from the extracellular fluid
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