Osmosis and Oiher Mechanisms - 125 



TEST QU 



1. Define the term osmosis. What is the basis for 

 describing the typical cell as a minute os- 

 motic system? 



2. What is diffusion; how is it energized? 



3. State the general law that governs the direc- 

 tion of diffusion. 



4. Explain why the solute and solvent (in the 

 system shown in Fig. 6-2) continue to diffuse 

 in opposite directions until equilibrium is 

 reached. 



5. Explain why the plasma membrane is typical 

 of semipermeable membranes generally. 



6. Arrange the following substances in an order 

 that will designate their relative speeds in 

 penetrating the plasma membrane: sucrose, 

 oxygen, proteins, sodium chloride, glucose, 

 starch, and ether. 



7. Name three factors that have an important 

 bearing on the capacity of a substance to 

 pass through the plasma membrane. 



8. Assuming that pure water is separated from a 

 protein solution by a membrane that is 

 permeable to water but not to protein, how 

 would the system approach equilibrium? 



9. Assuming that a cell is immersed in pure 

 water, how would the system approach equi- 

 librium? 



10. In addition to the fact that water can trav- 

 erse the plasma membrane more readily than 

 most of the solutes ordinarily present inside 

 and outside the cell, what other factor places 

 the burden of attaining equilibrium mainly 

 upon water? 



11. Explain the respiration of an amoeba (Fig. 

 6-4) on the basis of diffusion. What is the 



ESTIONS 



common law that determines the movement 

 of both the 2 and the C0 2 ? 



12. What is an isotonic solution? Give one spe- 

 cific example. What determines the balanced 

 exchange of water between the cell and such 

 a solution? 



13. A solution that is isotonic to one cell is not 

 necessarily isotonic to another. Explain. 



14. Carefully identify each of the following 

 terms: (a) cytolysis. (b) plasmolysis, (c) crena- 

 tion. (d) deplasmolysis, (e) turgor. 



15. In each of the following cases, what observ- 

 able changes would be expected to occur 

 when the cells are placed in the specified 

 solutions: 



a. an amoeba in a very weak (hypotonic) 

 salt solution 



b. a red blood cell in the same solution 



c. a plant cell in the same solution 



d. a plant cell in a strong (hypertonic) 

 salt solution 



e. a plant cell in a hypertonic glucose 

 solution 



f. a red cell in a hypertonic salt solution 



g. a red cell in a hypertonic glucose so- 

 lution 



h. an amoeba in a hypertonic glucose so- 

 lution 



16. Carefully explain the effects described in 

 parts a, b, c, d, e, and f of Question 15. 



17. Distinguish between active and passive mech- 

 anisms of transport. 



18. Specify three types of active transport mech- 

 anism. To what extent are these mechanisms 

 understood? Explain. 



FURTHER READINGS 



1. "How Things Get into Cells," by H. Holter, 

 in "The Living Cell," special issue of Scien- 

 tific American, September 1961. 



2. Explorations into the Nature of the Living 



Cell, by R. and E. L. Chambers; Cambridge, 

 Mass., 1961. 



Life: an Introduction to Biology, by G. G. 

 Simpson, C. S. Pittendrigh, and L. H. Tiffany; 

 New York, 1957. 



