Nutrition of Green Plant Cells - 171 



lishes an equilibrium in which the inflow of 

 water is balanced by the outflow. Therefore 

 when additional water is formed by metab- 

 olism, the equilibrium is disturbed and the 

 excess water passes to the outside. 



GENERAL SIGNIFICANCE OF HOLOPHYTIC 

 NUTRITION 



The salient points of contrast between 

 holophytic and holozoic nutrition are sum- 

 marized in Table 9-1. The significance of 



small derive their energy from preformed or- 

 ganic foods, by feeding either directly upon 

 the plants, or upon other organisms that di- 

 rectly or indirectly have obtained their or- 

 ganic matter from the plants. In addition to 

 maintaining the supply of organic matter, 

 light energy also maintains our oxygen sup- 

 ply, which would be exhausted in about 2000 

 years if photosynthesis did not occur. Only a 

 small fraction of the sun's radiance happens 

 to fall upon green plants, and only about 3 

 percent of this energy is claimed successfully 



Table 9-1— Holophytic and Holozoic Nutritions Contrasted 



Green Plaitt 



1. Has chlorophyll; can synthesize glucose 



2. Can utilize nitrates and other inorganic 

 salts to synthesize amino acids 



3. Can synthesize all amino acids 



4. Independent of other organisms for or- 

 ganic compounds 



5. Absorbs all food in solution 



6. Does not move about for food; expends 

 less energy; less catabolism 



7. Primary source of energy is light 



8. Metabolism as a whole constructive; that 

 is, increases available organic compounds 

 and increases the reserve of potential 

 energy 



Animal 



1. Has no chlorophyll; cannot synthesize 

 glucose 



2. Cannot utilize nitrates to synthesize amino 

 acids 



3. Cannot synthesize all amino acids 



4. Dependent on other organisms for organic 

 compounds 



5. Ingests solid food 



6. Moves about for food; expends more en- 

 ergy; more catabolism 



7. Only source of energy is organic com- 

 pounds 



8. Metabolism as a whole destructive; that 

 is, decreases available organic compounds 

 and decreases the reserve of potential 

 energy 



these points cannot be overemphasized. The 

 holophytic system, with chlorophyll as a key- 

 stone, enables green plants to tap the tre- 

 mendous fund of energy that radiates upon 

 our earth from the distant sun. This kinetic 

 energy, transformed into the potential energy 

 of a great variety of organic compounds, rep- 

 resents almost the sole energy supply of all 

 varieties of living things. Animals large and 



by photosynthesis. But this small fraction 

 energizes virtually all the manifold processes 

 of life, and this energy is not degraded into 

 heat until it has found expression in the 

 movements and other activities of many liv- 

 ing things. Eventually, however, all the solar 

 energy that strikes the earth becomes trans- 

 formed to heat and is dissipated in the en- 

 vironment (Chap. 10). 



TEST QUESTIONS 



1. Most plants are nonmotile organisms. Ex- 

 plain this observation in terms of the food 

 requirements of plants. 



2. What is the basis for considering that Clo.s- 

 terium, Chlamydomonas, and Spirogyra are 

 all typical plants? 



