Testing and ThinkingForeach of thefollowingstatementsaboutwater,decidewhetherthestatementis 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 of ice.The molecules of liquid water are extensively hydrogen-bondeddto one another.Water does not absorbvisiblelight.Water is odorless andtasteless.Waterhasahighspecificheat（高比热)(h）Water has a high heat of vaporization
1 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
Testing and Thinking(last time)An adulthumanis composed of about 1o13 cells,all ofwhich are derived by cell division from a singlefertilized eggl. Assuming that all cells continue to divide (like bacteria inrich media), how many generations of cell divisions wouldbe required to produce 1013 cells?2. Human cells in culture divide about once per day. Assumingall cells continue to divide at this rate during development.how long would it take to generate an adult organism3. Why is it, do you think, that adult humans take longer todevelop than these calculations might suggest?
2 An adult human is composed of about 1013 cells, all of which are derived by cell division from a single fertilized egg. 1. Assuming that all cells continue to divide (like bacteria in rich media), how many generations of cell divisions would be required to produce 1013 cells? 2. Human cells in culture divide about once per day. Assuming all cells continue to divide at this rate during development, how long would it take to generate an adult organism. 3. Why is it, do you think, that adult humans take longer to develop than these calculations might suggest? Testing and Thinking(last time)
AnswersA. n =43.2allB. If cells divided once per day andcells continued to divide, it would take43.2 days to generate the number ofcells in an adult humanC. Obviously we don't become adults in43 days
3 Answers A. n =43.2 B. If cells divided once per day and all cells continued to divide, it would take 43.2 days to generate the number of cells in an adult human. C. Obviously we don't become adults in 43 days
The simple answer is that all cells don't continueto divide once per day and some cells areprogrammed to die.(apoptosisAs cells differentiate, they generally slow their rateof division, ultimately in the adult dividing justoften enough to replace cells that are lost or die
4 The simple answer is that all cells don’t continue to divide once per day and some cells are programmed to die. （apoptosis） As cells differentiate, they generally slow their rate of division, ultimately in the adult dividing just often enough to replace cells that are lost or die
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