J. A. CAMPBELL Harvey Mudd College Cloremont, California 9171 1
Questions
Q117. Dezincification of brasses occurs rapidly in waters having a high concentration of both 0 2 and COa. Write possible equations to show the effect of each. Ql18. It is well-known that most seeds regardless of orientation send their first root "down" and first stem "up." Suggest a molecular mechanism for these growth phenomenon. Q119. Automobile batteries (ordinarily delivering 6 or 12 V) are often rated in ampere hours of operating capability. How many kg of PhSOn must he in a lead storage battery to provide for a 100 A-hr rating" Q120. Plant cell walls are typically composed of very long microfibrils of crystalline carbohydrate embedded parallel to the cell surface and roughly perpendicular to direction of growth in an amorphous carbohydrate (e.g., cellulose) matrix, much as Fiberglass consists of oriented silicate fibers surrounded by amorphous plastic. Both have great strength per unit weight. Current theory suggests that cell growth, mainly elongation, results from the slow yielding of the cell wall to the intracellular pressure of about 6 a t m [Guillard, R., p. 529 and Green, P. B., p. 625, in "Physiology and Biochemistry of Algae," (Editor: Lewin, R. A.,) Academic Press, New York, 19621. Suggest a source of the pressure and why growth is mainly by elongation into a tubular structure.
Q121. Suggest a molecular mechanism active in allowing "permanent press" fabrics. The most common treating agents for cellulosic fabrics are dimethylols of structural formula
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Suggest its mode of interaction with cellulose. Q122. L. Sokoloff, R. Mangold, e t al [J. Clin. Inuest., 34, 1092, 1101 (1955)) have shown that cerebral oxygen consumption is remarkably uniform over the range of consciousness from sleep to severe intellectual activity. How then can "thinking" he such hard work and require increased oxygen uptake in humans? This column consists of questions (plus possible. but certainly not uniquely satisfactory, answers) requiring no more than a concurrent first-year, college level course, 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 inclusion are solicited. Initiated in the January 1972 issue of this Journal.
Answers A117. Brass contams Cu and Zn, ihe Zn being more readily oxidized causing dezincification.
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FormationofH+:2(COzi,,, H 2 0 , ~=, H i a q , + H C 0 3 1 n q , l Oxidation of Zn: Zn,,, 3 0 2 , a q , 2H,,,,,+ = Zn,,,,Z+ + Hz0,1
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AIIR. Gravity (including forces in a centrifuge) affects cell growth in seeds such that root cells tend to elongate and add new cells down, stem cells to elongate and add new cells up. Possibly the root hormones or enzymes which catalyze root eell growth are concentrated by gravity at the bottom of their cells, while the reverse is true for stem cells. I t is quite possible that one of the genetic distinctions between these two types of cells is the sedimentation property of the growth regulator (whieh could be either a n inhibitor or stimulator, of course). It is interesting to note that these "commands" are not all powerful ones. Both roots and stems can grow around obstacles (like rocks) if the distances involved are not too great. However, either will stop growing if they would have to "violate" their genetic instructions far long. A119. 100 ( a m p X h r ) X 60 (min/hrl x 60 (sec/min) = 3.6 x I'd5 coulombs, or a m p x see 13.6 x 105 icoulombs1196.500 lcoulomhslmolesafchareel x
Half of this P b S 0 4 must be an each set of plates behre the cell is charged.
AIYO. Osmosis of H 2 0 from dilute aqueous media surrounding the cell into the more concentrated cell medium (maintained by active pumping of salts and some larger molecules) should easily generate 6 atm pressure. Elongation upward would be expected since the upper cell wall is not constrained by cells below or to the side and should push out more readily. If the cells are growing in a liquid medium, hydrostatic pressure is less at the t a p encouraging eell extension there. A121. Permanent press means strong permanent bonds hetween adjacent fabric fibers. T h e dimethylols can form ether linkages with cellulose (similar to those holding the long cellulase fibers in their chains) and thus assure "permanent" interchain orientation. A122. Brain activity requires a n almost constant rate of energy generation. Since thinking often involves extraordinary heat generation, it must involve physiological reactions outside the brain. If you observe yourself when you are thinking hard (a difficult thing to do since a mild hifurcation of your "person" must occur), you will observe tenseness in many muscles, often twitching and other overt activity, all requiring generation of work and heat, hence tiring. Far example, a tense muscle, even if doing no external work, is doing work since tenseness is maintained first by one set of fibers then another with the first set relaxing. This alternate tensing and relaxation of individual fibers involves heat generation. There is evidence that some of this muscle activity may actually be involved in the thinking process, not just be a result of "tenseness." Thinking about serving a tennis hall, for example, may actually activate the appropriate muscles minimally as you think throurh the total orocess. Volume 50, Number 12, December 1973 / 847
