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 or RESPIRATION AND PHOTOSYNTHESIS 



Photosynthesis 



i.' Takes place only in cells contain- 

 ing chlorophyll. 



2. Requires light. 



3. CO 2 absorbed, O set free. 



4. Carbohydrates formed. 



5. Plant gains in dry weight. 



6. Kinetic energy of sunlight be- 

 comes potential energy. 



Respiration 



1. Takes place in all active cells. 



2. Can proceed in darkness. 



3. O absorbed, C0 2 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 



