THE CELL AS A UNIT 101 



the business of living almost as effectually as a very complex 

 animal. 



Summary. — This chapter has shown us that the simplest plants 

 and animals are composed of a single cell, but that, nevertheless, 

 they are organisms. Plant cells differ from animal cells in struc- 

 ture and function. But the bacteria and other colorless plants are 

 more like animals than plants, in that they do not make food, 

 but destroy it. Some one-celled organisms, such as Paramecium, 

 are complex in structure, while others, such as bacteria, are very 

 simple. It is probable that bacteria are the lowest forms of life 

 known. 



Problem Questions 



1. Why is a single cell considered an organism? 



2. How do single cells absorb food? Digest food? Are these processes 

 different in plant and animal cells? (Look this up in some good reference 

 books.) 



3. List the characters of a number of plant and animal cells. How are 

 they ahke and how different ? 



Problem and Project References 



Hunter, Laboratory Problems in Civic Biology. American Book Company. 



Calkins, Protozoa. Lemcke and Buechner. 



Hegner, Introduction to Zoology. The Macmillan Company. 



Needham, General Biology. Comstock Publishing Company. 



Needham and Lloyd, Life of Inland Waters. Comstock Publishing Company. 



Sedgwick and Wilson, General Biology. Henry Holt and Company. 



Ward and Whipple, Manual of Freshwater Biology. John Wiley and Sons. 



H. new civ. BIOL. — 8 



