Living Plants and Animals Contrasted 105 



"to 



a carbohydrate, is also present in certain unicellular animals (protozoa) 

 and even in certain members (such as tunicates) of the highest phylum 

 of animals. Certain animal cells may secrete hard, rigid intercellular 

 materials. A few animal cells may even possess a cell wall. When water 

 is removed from cells by plasmolysis (plaz -mol' i sis) (Gr. plasma, form; 

 lysis, loosing), the entire animal cell shrinks, while the plasma membrane 

 usually shrinks away from the cell wall in plants. 



CHLOROPHYLL AND PHOTOSYNTHESIS 



Plants usually possess green chlorophyll by means of which carbon 

 dioxide and water, in the presence of energy-supplying light, are com- 

 bined into carbohydrate foods by the process of photosynthesis. Certain 

 plants such as the fungi (molds, bacteria, yeasts, mushrooms, etc.) lack 

 chlorophyll and must depend upon outside sources for their nutrition. 

 Chlorophyll-bearing plants have the ability to convert kinetic energy 

 derived from the sunlight into potential energy which is stored in the 

 plant. True animals do not possess chlorophyll, although a few border- 

 line organisms (Euglena, Volvox [Figs. 173, 174], etc.) may. Hence, in 

 general, animals are dependent upon plants either directly (herbivorous 

 animals) or indirectly (carnivorous animals) for their nutrition. Animals 

 have the ability to change the potential (stored) energy of foods into 

 other types of energy, including kinetic, which can be used for movement 

 and other purposes. The various methods of securing nutrition in plants 

 and animals will be considered in more detail in later chapters. 



GROWTH 



In plants and animals, growth consists of an increase in the number 

 of cells, an increase in size without an increase in the number of cells, 

 or a combination of the two. Plants might be considered as possessing 

 unlimited growth in which the ratio ai nonliving tissues to living tissues 

 gradually increases until the greater part of the plant body may be 

 composed of dead tissues. The older, dead tissues usually remain in 

 plants for support and are constantly increasing over a period of time, 

 while young growing tissues are constantly forming. In most plants, 

 active, embryonic tissues continue growing over long periods of time, as 

 in tips of stems and roots. In plants, the maximum size for a certain 

 species is quite variable and depends greatly upon external environ- 

 mental conditions. 



Animals might be considered as having rather limited growth, in 

 which the mature individual reaches a certain size and characteristic 



