D 



CHAPTER VII 



THE RESTING 



AND 

 DIVIDING CELL 



When cells divide 



the surface area increases. 



What is the nature of protoplasm? What progress has been made 

 in the building of protoplasm in the laboratory? Are the functions of 

 the cell related to the functions of the organism in any specific way? 



All living things are made of cells. The cell is the unit of struc- 

 ture of the Protozoa. Higher forms of organisms are composed of 

 many cells. It is impossible to discuss the functions of higher 

 organisms without referring to the cell in some detail, for it is 

 really the cells of the organism that perform these functions. Cells 

 vary in shape, size, and structure, but they are all alike in consist- 

 ing of a mass of protoplasm usually containing a nucleus, and 

 always surrounded by a plasma membrane. A plant cell is in- 

 closed in a cell wall which usually consists of cellulose, a form of 

 carbohydrate. Cells are either in a state of division, or, if not 

 actively dividing, are said to be in a state of rest. When in the so- 

 called state of rest, activities other than cell division are being 

 carried on in the cell. 



The nature of the cell and its make up. So complex is the cell 

 and so much has been written about it that there is now a whole 

 branch of biology, cytology, concerned with cell investigations. 



Cytologists differ as to the detailed structure of protoplasm. 

 Some think it is composed of an extremely minute network of fibers, 

 similar in appearance to a sponge, inclosing a liquid. This is 



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