98 - The Cell 



d. microscopic visibility 



e. detectability with the ultramicroscope 



f. capacity to reflect or diffract light waves 



g. thermal movements, including Brown- 

 ian movement 



39. Briefly explain how the polarity of a mole- 

 cule is related to its degree of hydration and 

 its "effective size." 



40. Mention three polar and two nonpolar com- 

 pounds present in protoplasm. 



41. Distinguish between emulsions, suspensions, 

 and solutions; give an example in each case. 



42. Explain why phase reversal is possible in 

 emulsion but not in suspensions. 



43. Define the terms: (a) adsorption; (b) emul- 

 sifying agent; and (c) stable emulsion. Ex- 

 plain how these terms are interrelated. 



44. Differentiate between a sol and a gel, using 

 a gelatin "solution" to exemplify the discus- 

 sion. 



45. How does a gelatin gel differ from actomyosin 

 and other "protoplasmic gels"? 

 Explain the relation between gelation and 

 the contractility of protoplasm. 



46. 



FURTHER READINGS 



Dynamic Aspects of Biochemistry, 3d ed., by 



E. Baldwin; New York, 1957. 



Unresting Cells, by R. W. Gerard; New York, 



1949. 



Tlie Cell, vol. 2, Cells and Their Component 



Parts, ed. by J. Brachet and A. E. Mirsky; 



New York and London, 1961. 



Cellular Physiology and Biochemistry, by 



W. D. McElroy; Englewood Cliffs, N. J., 



1961. 



