EXERCISE 81 



In the simplest plants and animals the cell surface is at the same time 

 the absorbing area and the excreting area. In higher organisms many 

 of the special surfaces are both absorbing and excreting surfaces for' 

 example, the lining of lungs, the leaves of plants. 



Problem. Is the root of a plant an excreting organ as well as an 

 absorbing organ ? 



What to use. Young seedlings of bean or corn ; two bottles of water ; 

 phenolphthalein solution. 



What to do. In one bottle place a small quantity of phenolphthalein 

 that is colorless ; in the other, enough alkaline (red) phenolphthalein to 

 make the water barely pink. In each bottle insert the roots of a live 

 seedling. Note changes from time to time. 



Record. Tell whether the roots give off any substance, and, if so, 

 whether it is acid or alkaline. 



Questions. 1. Aside from getting rid of waste matter, what use might a secretion of substances 

 by the root be to the plant ? 



2. Compare the output from your lungs with the output, if any, of the roots, using experimental 

 methods. 



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