PROTOPLASM AND CELL 45 



first part of the list. A few of them are usually given as constitut- 

 ing approximately the following percentages of protoplasm: oxy- 

 gen 65 per cent, carbon 18 per cent, hydrogen 10 per cent, nitrogen 

 3 per cent, calcium 2 per cent, phosphorus 1 per cent, and all others 

 making up the remaining 1 per cent. These elements are found 

 combined to form compounds. The organic compounds include car- 

 bohydrates, fats, proteins, and also enzymes. The inorganic com- 

 pounds consist of several inorganic salts and water. 



The carbohydrates, which include starches and sugars, are com- 

 pounds of carbon, oxygen, and hydrogen. The proportion of the 

 hydrogen to oxygen in the molecule is the same as found in water, 

 two to one. The principal carbohydrate found in protoplasm is the 

 monosaccharid, or simple sugar, glucose, whose formula is CpHigOe- 

 This is actually built into some parts of the cell, but its chief func- 

 tion is to furnish the most available source of energy by its ready 

 oxidation. When a molecule of glucose is burned, the potential 

 energy is released as kinetic or mechanical energy, and there are 

 formed six molecules of water (HgO) and six molecules of carbon 

 dioxide (CO2). Glucose is converted to a starchlike substance, 

 glycogen, for storage in the various animal tissues. This substance 

 must be reconverted to glucose before it is available . for production 

 of energy. 



Fats, like carbohydrates, are composed of carbon, hydrogen, and 

 oxygen but in more complex molecular arrangement. There is much 

 more carbon and hydrogen with less oxygen, which allows the fats 

 to combine with more oxygen in oxidation and therefore release more 

 energy. Fat is extremely well adapted as a form of material for 

 storage, since weight by weight it contains more potential energy 

 than any of the organic group. Such common substances as lard, 

 butter, tallow, whale blubber, and cottonseed oil are good examples. 

 Fats serve a double function in protoplasm : constitution of a part 

 of the structure of the cell and the storage of food. 



Proteins constitute the bulk of the foundation or framework of 

 the cellular structure and are the most abundant organic constituents. 

 They are composed of carbon, hydrogen, oxygen, and nitrogen, with 

 the frequent addition of traces of sulphur, phosphorus, magnesium, 

 and iron. All of the proteins have large molecules, each being com- 

 posed of thousands of atoms ; as an illustration, take hemoglobin of 

 the red blood corpuscles with its formula C7i2Hii3oN2i40245FeS2. Pre- 



