RESPIRATION, 95 



1). Metabolism^ (b] Respiration.* 



You have found that photosynthesis, the Plant's process of 

 food-making, involves the conversion of working, or kinetic, 

 energy into latent, or potential, energy, with absorption of 

 carbon dioxide and elimination of oxygen. The question now 

 arises as to the conditions of the utilization of this energy. A 



o * 



conspicuous case of its utilization occurs in growth, and hence 

 we may use growth to determine what the gas-exchange in 

 energy-release may be. Since, in its relations to energy, 

 energy-release ^i.e., respiration) is the opposite of photosyn- 

 thesis, we should expect the opposite process of gas-exchange. 



58. Is the gas exchange in energy-release (i.e., Hespiration) 

 the opposite of that in energy-storage (i.e., Photosynthesis) ? 



Answer by Experiments 30, 31. 



EXPERIMENT 30. This may be settled by using germinating seeds 

 and determining (a) whether they will grow without oxygen (which 

 ma)' be removed by chemical means from the chamber in which the 

 seeds are placed), and (/) whether any gas they give off in growing 

 is carbon dioxide (which may be tested by noting whether the gas 

 given oil is absorbed by such an absorbent of carbon dioxide as 

 caustic potash so arranged that it must rise in a tube if it absorbs 

 any gas). Prepare three large U tubes and holders as shown in Fig. 

 21 on the right. In the end of each place ten oat grains soaked over 

 night (to which may be added a small wad of moist cotton or sphag- 

 num to keep them wet, though this is not indispensable), and cork 

 this end air-tight with a fresh rubber stopper. Half-fill each holder, 

 the first with mercury, the second with a solution of caustic potash, 

 the third with concentrated solution of caustic potash and pyrogallic 

 acid/'' Place the open ends of the three tubes in the holders, set 



Respiration is introduced in this place in order that it may be studied alongside 

 of photosynthesis ; for the two processes are popularly confused and misunderstood 

 as to their relations to one another. It would be a more logical arrangement to post- 

 pone the study of respiration until after subsections c, d, and c have been considered,, 

 thus allowing all cases of constructive metabolism to come together, and be followed 

 by destructive metabolism. 



j~ That the seeds are not killed by any influence exerted by the mixture is proven 

 by two facts : first, if the mixture be removed after it has exhausted the oxygen from 

 the tube and be replaced by water, the seeds will germinate, though more slowly than 

 usual ; second, if a bent glass tube be inserted so as to keep the chamber above the 



