INTRODUCTION TO PROKARYOTES AND EUKARYOTES::


Classification of Microorganisms:


(a) Acellular organisms: These are the microorganisms that have neither cells nor cell membrane. They are composed of few genes which are protected by protein coat. Outside of the host they acts as dead but inside host they are alive and reproduce. Example: Viruses. 

 (b) Cellular organisms: These are the microorganisms which have definite cell structures. Based on the cellular structure they are further divided into prokaryotic and eukaryotic. Prokaryotics are cells without nucleus and have no membrane bond organelles. They are less complex in structures. Examples: Bacteria and Archaeac.

A. Bacteria: 

 1. They are prokaryotic and unicellular 

 2. The size is 1/1000 the volume of a typical eukaryotic cell. 

 3. Mainly two groups of bacteria are: 
 (a) Archaeobacteria: Ancient bacteria. 
 (b) Eubacteria: True bacteria. 

 4. They are in various shapes likely bacillus (rod), coccus (spherical), spirillum (spiral), vibrio (curved rod). 

 5. They are motile or non-motile. 

 6. They obtain their energy from sun as well as from organic and inorganic molecules, and as per that they are classified as: Photosynthetic autotrophs (use energy from the sun to produce their own carbohydrates for energy), Chemosynthetic autotrophs (process inorganic molecules for energy (example: sulfur or iron) and heterotrophs (depend on outside sources of organic molecules (example: carbohydrates or sugars) for energy. 

 7. Optimum temperature: −20o C to 110o C (freezing is 0o C and boiling is 100degree C).  

 B. Algae: 

 1. They are eukaryotic, unicellular or multicellular. 
 2. They are microscopic and macroscopic in size. 
 3. They are motile or non-motile. 
 4. They obtain their energy from photosynthetic autotrophs.

C. Fungi: 

 1. They are eukaryotic. 
 2. They are unicellular or multicellular (yeasts are unicellular, molds are multicellular). 
 3. They are non-motile. 
 4. They obtain their energy from outside source of organic molecules. 
 5. They acts as scavengers, they live off dead matter and thus, decompose it. 

 D. Protozoa: 

 1. They are eukaryotic. 
 2. They are unicellular. 
 3. They are motile or non-motile. 
 4. They obtain energy from outside source of organic molecules.  

E. Viruses: 

 1. They are acellular and obligate intracellular parasites. 
 2. Structure of a virus: A piece of nucleic acid (RNA or DNA) enclosed by a protein coat (capsid); possess no nucleus, organelles, cell membrane, or cytoplasm. 
 3. Size - 1/10 to 1/1000 the size of an ordinary bacterial cell. 
 4. They are non-motile.  

Differences between Eukaryotic and Prokaryotic cells  

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