growing cell faces the problem of making 

 enough of everything to construct two or 

 more daughter cells. And it must divide 

 the proceeds among them in such a way 

 as to produce normal, well-functioning 

 progeny. Most important, it has to endow 

 each daughter cell with a complete set 

 of genetic material. This material is car- 

 ried in large part upon the chromosomes 

 within the nucleus. However, some prop- 

 erties of organisms have been shown to 

 be initiated through genetic determinants 

 that reside in the cytoplasm and these 

 too must be shared.^ 



Varieties of Cell Division 



Nature has found several good solu- 

 tions to the problem of sharing, enabling 

 different methods of cell division to be 

 employed in various types of organisms 



Life Cycle (^g^) 



of the ^' ^^^■^on. The parent cell grows to 



approximately twice its original size and 

 Single Cell then splits into two more or less equal 



daughter cells. Protozoan and animal 

 cells divide in this fashion, simply by 

 pinching off two daughters at the middle 

 and pulling apart the two halves. Bac- 

 terial and plant cells also reproduce by 

 fission but have rigid walls and divide by 

 constructing a cross wall. 



2. Budding. The mother cell forms 

 a little bleb at the surface which grows 



The 



1 See Chapter 6 for a more detailed dis- 

 cussion of these matters. 

 6 



