PROTOPLASM 13 



Three types of these unicellular Fungi are noted, namely, the 

 spherical cocci, the rod-shaped bacilli, and the spiral spirilla. 

 The Bacteria and all Fungi absorb their food materials in soluble 

 form through the cell wall. Enzymes are secreted in many in- 

 stances which act upon solid nutrient materials and render them 

 soluble. Certain noteworthy groups of Bacteria are (a) the Decay 

 Bacteria, which are almost omnipresent, (b) the Nitrogen-fixing 

 Bacteria, which live on the roots of various plants and are charac- 

 terized by their ability to 'fix' the free nitrogen of the air and thus 

 make it available for the use of green plants, (c) the Disease- 

 producing, or Pathogenic, Bacteria, which attack the tissues of 

 living plants and animals and cause many of our worst diseases. 



Yeast. The Yeasts, like the Bacteria, are widely distributed, 

 unicellular Fungi with very simple structural features. Each 

 Yeast plant consists of a microscopic, egg-shaped cell with a well- 

 defined cell wall and a poorly defined nucleus. Yeast finds a 

 particularly favorable environment in fruit juices containing sugar 

 and protein material in solution. The respiratory function of the 

 Yeast cell centers in the disintegration of the sugar molecule with 

 the resulting formation of alcohol and carbon dioxide, and this is 

 accomplished by a characteristic enzyme, zymase. 



Molds. There are a whole host of filamentous fungus forms, 

 the Molds, which attack and thrive on a great variety of materials. 

 They are able, as in the case of the common Bread Mold, to secrete 

 an enzyme which renders the foodstuffs soluble so that they can be 

 taken into the organism. In some cases the plant body is an 

 undivided, multinucleate mass of protoplasm, thus lacking a defi- 

 nite cellular organization. In other groups the plant body of 

 the Mold is definitely multicellular. 



3. Growth and Reproduction 



It is evident from the earlier discussion that two antagonistic 

 life processes are in synchronous operation in a living cell. On 

 the one hand there is the tearing down of the complex compounds 

 with the resultant liberation of energy and the formation of 

 metabolic wastes ; on the other, there is a rebuilding through the 

 utilization of the incoming nutritive materials. If the katabolic 

 processes are greater, the death of the cell will eventually result. 

 If the sum total of the anabolic processes are greater, the growth 

 of the cell will occur. The growth of a living organism is by the 



