CHAPTER VI 

 THE CELL 



We have now become acquainted with two simple 

 living organisms, Amceba and Protococcus, with their 

 structure, behaviour and life histories ; and we have 

 seen that the " vital functions " which they exhibit are 

 expressions of the activity of the protoplasm of which 

 their bodies are composed, and that these same " vital 

 functions " are exhibited by all living organisms, however 

 large and complex, however different in structure and 

 appearance — ^by trees and human beings, just as by 

 Protococcus and Amoeba. But we have also seen that 

 the exact ways in which the various functions are 

 performed by the organism as a whole varies with its 

 structure, and before we can understand these variations 

 in any detail we must become acquainted with the 

 organisation and variations of the unit of which organic 

 structure is built up — the cell. 



Unicellular and Multicellular Organisms. Differen- 

 tiation and Divisi(»i of Labour. Tissues. — We have 

 already seen that the whole body of an amoeba is a 

 unit of living protoplasm consisting of cytoplasm and 

 nucleus : the same is true of Protococcus, which has, 

 however, a special green protoplasmic body called the 

 chloroplast within the cell which enables the organism 

 to make carbohydrate out of carbon dioxide and water, 

 and also a non-living cell wall of cellulose (a complex 



carbohydrate) which is formed by the protoplasm. 



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