Animal Cells and Their Nutrition - 127 



Table 7-1— Principal Food Substances— Sources and Uses in Organisms 



Food Substanc 



Oxygen 



Water 



Carbon dioxide. 



Salts 



Proteins 



Carbohydrates . . 



Fats (lipids) . 



Vitamins 



Principal Uses in the Organism 



Essential for oxidation of organic com- 

 pounds in both plants and animals; 

 oxidative metabolism important as a 

 source of energy 



An essential structural component in 

 all protoplasm and body fluids; par- 

 ticipates in many metabolic reac- 

 tions; used by green plants for the 

 synthesis of glucose 



Used mainly by green plants as a source 

 of carbon in the synthesis of glucose 

 and other organic compounds. Ani- 

 mals, however, possess a limited 

 ability to "fix" CO, (p. 152) 



Essential components in all protoplasm 

 and body fluids. Take part in many 

 metabolic reactions. Ions determine 

 the electrical conductivity and mem- 

 brane potential in cells generally 



Animals derive their essential amino 

 acids from protein foods; whereas 

 plants can synthesize all their amino 

 acids. Animals also obtain some en- 

 ergy from protein foods 



Animals utilize carbohydrates in syn- 

 thesizing essential protoplasmic com- 

 pounds; plants synthesize these com- 

 pounds from CO, and H 2 0. Carbo- 

 hydrates yield energy on oxidation, 

 in both plant and animal cells 



Animals require fatty foods for synthe- 

 sis of essential compounds; plants 

 derive these compounds indirectly 

 from C0 2 and HoO. Fats yield energy 

 (on oxidation) in animals and (to a 

 limited extent) in plants 



Essential structural components in the 

 protoplasm. Generally serve as co- 

 enzymes or prosthetic constituents 

 in various intracellular enzymes 



Usual Source 



Present in the atmosphere and 

 (in solution) in the waters of 

 the earth; liberated by green 

 plants 



Abundant in the environment as 

 soil water, lake water, etc.; 

 present in virtually all natural 

 foods 



Abundant in the environment as 

 a component of the atmos- 

 phere and (dissolved) natural 

 waters; plants diminish, ani- 

 mals replenish the carbon di- 

 oxide of the environment 



Abundant in the environment as 

 components of the soil, and as 

 solutes in natural waters; pres- 

 ent in almost all natural foods 



Protein parts and remnants of 

 other organisms. Ultimate ori- 

 gin mainly from the plants 



Ultimate origin mainly from 

 plants 



Ultimate origin mainly from 

 plants 



Synthesized by plants (see Chap. 

 18) 



