24 VIRUSES, RICKETTSIAE AND BACTERIA 



(5b) Living system that converts simple material to obtain 

 energy. 



CHEMOAUTOTROPHS (attack H 2 S,CH 4 , etc.) 



(5c) Living system that develops PHOTOSYNTHESIS. 



(Note that animals can by chemical means build up C0 2 

 to form carbohydrates.) 



Bacteria and Protozoa 



It is problematical how, if at all, the Bacteria are related 

 to the Protozoa and, if so, which Bacteria gave rise to which 

 Protozoa. 



Grasse (1953) thinks that the Protozoa are in fact monophyletic 

 and derived from the Bacteria. He bases this opinion on the 

 following resemblances between the Protozoa and Bacteria. 



(1) Both have vacuoles. 



(2) Both contain proteins, lipids and carbohydrates. 



(3) Both have mitochondria. 



(4) Certain bacteria have a nucleus and chromosomes. 



(5) A sexual process has been described in some bacteria. 



(6) Both can possess flagella. 



(7) Spore formation occurs in both. 



(8) The membranes around the cell in each case are sometimes 

 morphologically similar. 



These resemblances are rather tenuous and not all apply to any 

 one bacterium. In effect it is difficult to know to what extent the 

 resemblances are real phylogenetic ones and to what extent they 

 have risen by convergence. Thus the bacterial flagellum is very 

 much more simple in structure than the protozoan flagellum. The 

 protozoan flagellum has an inner strand of two rods and an outer 

 ring of nine rods. The bacterial flagellum has just the inner 

 strand of one or two rods. Until we know a great deal more 

 about the electron microscopy of the bacterial and protozoan cells 

 we shall not be in any position to base relationships on morpho- 

 logical similarities. 



The relationship between Bacteria, Protozoa and Metazoa has 

 been discussed by Grasse, who derives the following alternative 

 systems : 



