no 



THE VEGETATIVE FUNCTIONS OF PLANTS 



thus see that there is a continuous circulation of carbon 

 in nature, known as the carbon cycle (Fig. 71). A com- 

 parison between the two processes is shown in Table II. 



Table II. — Comparison of Respiration and Photosynthesis 



t. Photosynthesis 



Changes inorganic 

 matter into plant- 

 foods (carbohy- 

 drates), which are 

 Assimilated and 

 used by the plant 



To supply energy 

 for work, 

 To repair waste 

 (Nutrition), 

 In the construction 

 of new parts 

 (Development), in- 

 cluding Reproduc- 

 tion. 



Photosynthesis 



I. Takes place only in cells contain- 

 ing chlorophyll. 

 Requires light. 

 CO2 absorbed, O set free. 

 Carbohydrates formed. 

 Plant gains in dry weight. 

 Kinetic energy of sunlight be- 

 comes potential energy. 



All of these proc- 

 esses are depend- 

 ent upon Oxida- 

 tion within the 

 cells. 



This process of 

 oxidation is 



called. . . . 



2. Respiration, 



which involves 

 The taking in of 



oxygen, 

 The oxidizing of 

 oxidizable mat- 

 ter, 



The release of 

 all products of 

 these oxidations. 



Respiration 



1. Takes place in all active cells. 



2. Can proceed in darkness. 



3. O absorbed, CO2 set free. 



4. Carbohydrates consumed. 



5. Plant loses in dry weight. 



6. Potential energy becomes kinetic 

 energy. 



113. Plant and Animal Respiration. — There is probably 

 no erroneous notion about plants more tenaciously held, 

 nor more widespread, than the belief that plant respira- 

 tion is the reverse of animal respiration. This error is 

 due entirely to a confusion of the two processes of respira- 

 tion and photosynthesis. From what has preceded, how- 

 ever, it should now be clear that plants respire in the same 

 way as animals, using up oxygen in the processes of oxida- 

 tion within their tissues, renewing the supply from the 

 surrounding air (or, in anaerobic respiration, from the 

 breaking down of chemical compounds rich in oxygen), and 



