INTRODUCTION 



CHAPTER 32 



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Our studies of the various types of animals 

 have included the subject of nutrition and 

 have prepared us for a general review of 

 the nutritive processes "from amoeba to 

 man." Here we propose to consider (1) 

 what constitutes the food of different types 

 of animals, and of animals in general, (2) 

 how this food is captured and ingested, 

 (3) how it is digested, (4) how it is trans- 

 ported about the body, (5) how it is ab- 

 sorbed, (6) how it is stored or built up into 

 protoplasm, (7) how it is utilized to produce 

 energy before or after being assimilated, and 

 (8) how waste products are eliminated. The 

 processes involved constitute nutrition. The 

 term metabolism may also be applied to 

 these processes, but it is here used in a re- 

 stricted sense for the chemical reactions that 

 take place within the cells. 



Metabolism and 

 Transport in Animals 



Food 



All substances taken into the body that 

 are used to build up protoplasm and to pro- 

 duce energy are foods. The principal foods 

 of animals are organic compounds (carbo- 

 hydrates, fats, and proteins) built up by 

 other organisms, water, inorganic salts, 

 oxygen, and vitamins. Most animals cannot 

 synthesize organic compounds from inor- 

 ganic substances as plants do, but must feed 

 on other living organisms, their remains, or 

 their products. Only certain chlorophyl- 

 bearing protozoans, such as the euglena, can 

 manufacture their food out of inorganic sub- 

 stances; all other animals use plants, or other 

 animals that feed on plants, for their nutri- 

 tive material. 



Photosynthesis 



The manufacture of food by certain proto- 

 zoans and by most plants from inorganic 

 substances is known as photosynthesis (Fig. 

 576). Organisms that are able to carry on 

 photosynthesis contain a green substance, 

 chlorophvl, which is closely related chem- 



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