44 



TYPICAL ANIMAL CELL 



Assimilation. The digested protein together with water and 

 absorbed mineral matter are converted into protoplasm by the ac- 

 tivity of the cytoplasm of the 

 living amoeba. This is as- 

 similation. As a result of as- 

 similation, new protoplasm is 

 formed and the animal grows. 

 Respiration. Oxygen from 

 the air in the water may 

 enter through any part of the 

 surface of the amoeba. It 

 meets the digested nutrients 

 in the cytoplasm and oxida- 

 tion takes place, that is, oxy- 

 gen combines with carbon and 

 hydrogen compounds. As a 

 result of oxidation, energy is 

 released. This energy en- 

 ables the amoeba to carry on 

 its functions. Since protein, fat, and sugar contain carbon and 

 hydrogen, carbon dioxide and water are oxidation products. 

 Protein gives rise to nitrogen, sulphur, and phosphorus products, 

 also, one of which, urea, is a nitrogenous waste. The wastes 

 resulting from oxidation are collected in the contractile vacuole. 

 This bursts and expels the wastes through the plasma membrane 

 into the surrounding water. 



Reproduction. When the amoeba reaches a certain maximum 

 size natural to its species, the nucleus divides in two parts and 

 then the entire cell cleaves in two equal parts. This results in the 

 production of two distinct cells each with its own nucleus. This 

 process is called reproduction by fission. 



Irritability. The amoeba is very sensitive to outside stimuli. 

 If it is touched with a pointed object, it draws away. It moves 



A patient investigator watched and described 

 the behavior of an amoeba as it went after a 

 spherical food particle which had rolled away. 

 The drawing shows how the amoeba pursued and 

 engulfed the particle of food. 



