64 



THE RESTING AND DIVIDING CELL 



nuclear origin. A cleavage plate through the middle of the cell is 

 secreted by the cytoplasm. This divides the cell into two parts. 

 There is no constriction here as there was in animal cells. 



Cell theory. The illustration (below) shows some of the men 

 who have discovered and made known many interesting facts about 

 animal and plant cells, so that we to-day have come to have four 

 ideas concerning the cellular structure of all organisms. 



1. The cell is the unit of structure of all living plants and animals. 



2. The cell is the unit of all physiological functions of living plants 

 and animals. It is the cell that breathes, digests food, excretes wastes, 

 moves, and performs all the other physiological functions. 



3. The cell embraces all the hereditary qualities of the organism 

 within its nuclear membrane. 



4. Plants and animals may consist of single cells. They always 

 start with a single cell, and in their early stages of development (em- 

 bryo) this cell divides and changes into many cells. 



Questions 



Hall of Fame for biologists who worked on cells 



1. Copy the names and fill in the blank spaces in the above table. 

 Check your results with your answer to question 1 on page 33. 



2. By means of paraffin, soap, clay, or plasticine try to make 

 models of a resting cell and some of the stages of mitosis. 



