314 BIOLOGY AND HUMAN LIFE 



MICROBES AND THEIR CONTROL 



1. Microbes (small living things) 



Kinds 



Plant microbes 

 Bacteria 



Bacilli (rod-shaped) 

 Cocci (berry-shaped) 

 Spirilla (spiral-shaped) 

 Animal microbes 

 Protozoa 

 Relation to human affairs 

 Useful 

 Return organic matter to soil and water 

 Part of food series from lowest to highest forms of life 

 Contribute to make air nitrogen usable 

 Injurious 



Spoil food and other organic matter 

 Cause illness in man and other organisms 

 Kill human beings and other organisms 



2. How bacteria live 



Food-getting 

 External digestion ; absorption 

 Assimilation and growth 

 Respiration through cell wall 

 Excretion through cell wall 

 Reproduction 



Simple cell division 



(Spores formed in some species) 



3. Relation of environment to life of bacteria 



Conditions favorable 



Presence of organic matter (food) 



Moisture 



Moderate temperature 



(Darkness) 

 Conditions unfavorable 



Dryness 



Extreme cold (not fatal) 



High temperature 



Sunlight 



Chemical poisons 



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