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CHAPTER XLI. 

 PHYSICAL CHEMISTRY OP CELLS. 



Physical chemistry of cells. 



A. Diffusion rates in non-living material. (1) Invert a tube of 

 H 2 O containing a few drops of phenolphthalein in a dish of dilute 

 KOH. Note the rate at which the liquid in the tube turns red. 

 (2) Repeat with a tube of solid agar to which phenolphthalein has 

 been added. (3Hm^4^aatA>^Leolidified ctareh pa^tc in a oolu-??' 

 .tion of IKTrernhttoterraU' uf change uf mkmr. Does the physical " 

 character of the reagents affect the rate of diffusion? fir 



B. Semi-permeable membranes in living cells. (1) Place 

 Spirogyra, Elodoea and Paramecia in a very dilute solution of a*xr 

 neutral red (one drop to a watch glass of water). Describe the 

 phenomena. (2) Try more concentrated solutions. (3) Place living 

 material stained with neutral red in N/40 NaOH, Ba(OH) 2 and 

 NHUOH. Record the time for colour change. Return to H 2 O 

 after colour change has taken place. Is there a return to the 

 original condition? Have any cells been killed? To which solution 



is the material most permeable? (4) Repeat with cells killed by 

 heat or exposure to chloroform. (5) Wash small cubes of beet in 

 running H 2 O to remove the coloured material in broken or injured 

 cells. Heat one half to them to boiling. Compare the rate of 

 diffusion of the red pigment in the boiled and raw cubes. How 

 do you account for this difference in permeability of living and 

 dead cells? (6) Place washed cubes of beet in 1.82% NaCl ( = 0.31 

 molar) which is isotonic with the cell contents. Note result. 

 Explanation? (7) Place similar washed cubes in a salt solution also 

 containing 0.17% CaCl 2 made in the following manner: take a 

 3.64% solution NaCl and add an equal volume of 0.34% CaCl 2 . 

 Explain the result. 



C. Artificial membranes. (1) Float minute crystals of CuSC>4 

 on a 2% solution of K 4 Fe (CN) 6 . Describe results fully. Is there 

 a suggestion of growth? (2) Try the reverse, a crystal of K 4 Fe 



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