Testing and ThinkingGorter and Grendel's classic conclusion that the plasmamembrane of the human erythrocyte consists of a lipid bilayerwas based on the following observations:the lipids that they extracted with acetone(丙酮）from 4.74×1091erythrocytes formed a monolayer 0.89 m?in area when spreadout on a water surface;andthe surface area of one erythrocyte was about 1o0μm?according to their measurements.Show from these data how they came to the conclusion that thea)erythrocyte membrane is a bilayerWe now know that the surface area of a human erythrocyte isbabout145um2.Explain how Gorter and Grendel could have come to the rightconclusion when one of their measurementswas only abouttwo-thirds of the correct value
1 Testing and Thinking 1. Gorter and Grendel's classic conclusion that the plasma membrane of the human erythrocyte consists of a lipid bilayer was based on the following observations: (i) the lipids that they extracted with acetone(丙酮 ) from 4.74 ×109 erythrocytes formed a monolayer 0.89 m2 in area when spread out on a water surface; and (ii) the surface area of one erythrocyte was about 100μm2 ， according to their measurements. (a) Show from these data how they came to the conclusion that the erythrocyte membrane is a bilayer. (b) We now know that the surface area of a human erythrocyte is about 145μm2 . Explain how Gorter and Grendel could have come to the right conclusion when one of their measurements was only about two-thirds of the correct value
Testingand ThinkingForeach of thefollowingstatementsaboutwater,decide whetherthestatementis true and describes a property that makes watera desirablecomponentof cells (T);istrue but describes a propertythathas nobearing on water as a cellularconstituent (X); oris false(F).Foreachtrue statement, indicate a possible benefit to living organisms.Water is a polar molecule and hence an excellent solvent for polaracompounds.(b) Water can be formed by the reduction of molecular oxygen (O,)The density of wateris lessthan the density oficeThe molecules of liquid water are extensively hydrogen-bondedd氢键to one another.Water does not absorbvisiblelight.Water is odorless andtasteless.Waterhasahighspecificheat（高比热)(h）Water has a high heat of vaporization
2 Testing and Thinking For each of the following statements about water, decide whether the statement is true and describes a property that makes water a desirable component of cells (T); is true but describes a property that has no bearing on water as a cellular constituent (X); or is false (F). For each true statement, indicate a possible benefit to living organisms. (a) Water is a polar molecule and hence an excellent solvent for polar compounds. (b) Water can be formed by the reduction of molecular oxygen (02 ). (c) The density of water is less than the density of ice. (d) The molecules of liquid water are extensively hydrogen-bonded to one another. (e) Water does not absorb visible light. (f) Water is odorless and tasteless. (g) Water has a high specific heat (高比热). (h) Water has a high heat of vaporization. 氢键
Answers(a)T; living organisms are essentially aqueous solutions containingmanykinds of molecules, most of which are polar and hencereadily solublein water.(b)T;oxygen is theultimateelectron acceptorin cellularrespiration, with wateras the product.(c)F;the density oficeis less than that of water,thereby ensuringthat ice will float on the surface of a body of water.(d)T;this property explains the high specific heat and highheatofvaporization and hencethe capacity of water to "buffercellsand organisms against temperature changes
3 Answers (a)T; living organisms are essentially aqueous solutions containing many kinds of molecules, most of which are polar and hence readily soluble in water. (b) T; oxygen is the ultimate electron acceptor in cellular respiration, with water as the product. (c) F; the density of ice is less than that of water, thereby ensuring that ice will float on the surface of a body of water. (d) T; this property explains the high specific heat and high heat of vaporization and hence the capacity of water to “buffer" cells and organisms against temperature changes
续(e)T;this property of water allows lightto penetrate readily, such thatsubmerged photosynthetic organisms (or parts of organisms) canreceive sunlight.(f) X; the lack of odor or taste is probably not a strategic advantagetomostorganisms.(g)T; high specific heat means that much heat is required to increasethetemperature,which effectivelywbufferscells and organismsagainst temperature changes in response to changes in temperature ofthe environment.(h)T;high heat of vaporization means that much heat is required toconvert waterfrom a liquid to a gas,which means that organisms canbe effectively cooled by evaporation of perspiration or other forms ofliquid water from the skin or other surface of the organism.排汗
4 续 (e) T; this property of water allows light to penetrate readily, such that submerged photosynthetic organisms (or parts of organisms) can receive sunlight. (f) X; the lack of odor or taste is probably not a strategic advantage to most organisms. (g) T; high specific heat means that much heat is required to increase the temperature, which effectively “buffers" cells and organisms against temperature changes in response to changes in temperature of the environment. (h) T; high heat of vaporization means that much heat is required to convert water from a liquid to a gas, which means that organisms can be effectively cooled by evaporation of perspiration or other forms of liquid water from the skin or other surface of the organism. 排汗
第三章细质膜与跨膜运输Chapter 3 Plasma Membrane and Transport AcrossMembranes
5 第三章 细胞质膜与跨膜运输 Chapter 3 Plasma Membrane and Transport Across Membranes