J. A. CAMPBELL Harvey Mudd College Cloremont, California 9171 1
Questions
Q150. T h e rate of t h e O H - catalyzed reaction shown increases by about 1000-fold if a n aqueous solution initialM in both O H - and C H ~ C I C H Z O His ly a t 0°C and frozen a t 0°C. Interpret.
6153. "The addition of a small amount of glycerine t o a thin a n d harsh wine, particularly if i t is over-astringent, has a remarkable smoothing effect" according t o page 96 of "The Science of Wine" by Cedric Austin, American Elsevier. 1968. Suggest a n interpretation or two.
Errata. Professor L. J. Sacks of t h e Christopher Newport
[Pincock, R. E., a n d Kovsky, T. E., J. Amer. Chem. Soc., 88,4455 (1966)l. 6151. Most plants consume oxygen in t h e dark ( u n dergo respiration) h u t many d o so a t a rate which is independent of oxygen concentration down t o a s low a s 1%0 2 i n air. What does this mean about their mechanism of respiration? Q152. Early cell divisions i n a goldfish embryo occur about every 20 min, i n a frog about every hour, i n a mouse every 10-12 hr. Calculate t h e number of cells each might achieve i n 10 hr, i n 100 hr. What d o you deduce from these figures? C a n you suggest a molecular interpretation of t h e difference in rates.
College of the College of William a n d Mary in Virginia points out t h a t t h e answer t o Question 92 should he altered. T h e nitrite-nitrate potential has a n actual voltage of +0.4 v, a n d t h e nitrate-nitrogen potential 0.75 v ( n = 6. not 5 a s shown). H e also e m ~ h a s i z e s .a s should he c o n s t a k l y borne i n mind, t h a t activities (not concentrations) should he used, and t h a t kinetic effects often outweigh thermodynamic effects i n living systems. This column consists of questions (plus possible, hut certainly not uniquely satisfactory, answers) requiring no more than a concurrent first-year, college level coune, a data handbook, and a willingness to apply fundamental chemical ideas to the systems which surround us (or even are inside us). Contributions for possible inclusmn are solicited. Initiated in the Januani. 1972, issue of this Journal.
Answers ' but the concentrations of A150. T remains constant a t OC both reactants in the liquid phase increase as ice freezes out leaving less and less water. A rise in each concentration by 30-fold would lead to a 1M)O-fold increase in rate, assuming second-order kinetics. A151. An overall reaction which is zero-order in one of its reactants must not use that reactant in a rate-determining step. So respiration in plants must involve a step somewhere in the mechanism which is considerably slower than the takeup of Oz from the surroundings. Since many living systems evolved before much atmospheric Oz was available, it is easy tosee why they do not use 0 2 in their rate-determiningsteps. A152. Assuming cells do not die but continue to divide with a constant reproductive doubling period, R we get, starting with 1 cell at t = 0, for the population of cells at time f: Popl = 2"-""". The population of goldfish, frogs, and mice is shown below. Pop at I00 hr I@T108" loz7 lo3' lo0 = 1 103 Pop at
goldfish frogs mice
n 0.33 1.0 11
I0 hr
Clearly the goldfish and frog cannot'eontinue to develop for 100 hours at their initial rate since neither contains the number of cells listed above for 100 hr. The goldfish probably slows
down even before reaching 10 hr, though perhaps not. We also note that the rate of cell division decreases as the animal and it's life history get more complex. Presumably the genes of more complex animals are larger and require longer times for their synthesis and replication, Note that fairly small differences in reproductive doubling period have a marked effect on population because of the exponential relationship.
A153. This advice is, of course, anathema to most wine fanciers, but the chemistry can be studied without ethical judgments on the practice. Glycerine is sweet and this may be a principal effect. It is also able to esterify acids, and it may well be the acids which cause much of the harshness (as suggested by "aver-astringent"). Ethanol could also esterify the acids but the secondary O H of the glycerine may well be more easily esterified than the primary -OH of the ethanol. Glycerine may also increase the viscosity somewhat and change the surface tension so minimizing the "thin" quality.
Volume51. Numbere.
August 7974
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