Introduction of bacteria: classification, Reproduction and Importance

 Introduction to bacteria:

    Bacteria are unicellular organisms; they are prokaryotic in nature. Prokaryote derived from Greek word "Pro" means "before" and "Karuon" means "nut". This term is used as "before nucleus". They have no true nucleus and don not have membrane-bound organelles.
They are classified into two main domains eubacteria(eu means true; true bacteria) and archaeobacteria(archeao means ancient; ancient bacteria). It is thought that archaeobacteria were the first living organisms on earth and may be the ancestor of earliest organisms.

Occurrence:

    Bacteria are widespread organisms and found in every environment. They are found in soil, air, water, oil, organic matter, hot springs and even in the body of animal(in saliva and intestine) and plant.

Classification of bacteria:

      Bacteria can be classified in many ways. Such as according to shape, mode of nutrition, cell wall and respiration.

Shapes of bacteria:

    There are three shapes of bacteria. 
  • Rod shape bacteria are called bacilli. They are further divided into bacillus, diplobacillus and streptobacillus. When a cell is single is called bacillus, when there are two cell in the form of one pair is called diplobacillus and when they form a long chain are called streptobacillus.

  • Spherical shaped bacteria are called cocci. If this sphere is single called cocci, in the form of pair is diplococci, a straight chain of more than two is streptococci, if four cocci are in the form of two planes is called tetrad, three planes of division of eight cocci is sarcina and if many cocci are random arranged then it is called staphylococci.
  • Helical-shaped bacteria is called spirilla. Comma-shaped rod is called vibrio, a thick rigid spiral is spirillum and thin flexible spiral is called spirochete
  • Mode of nutrition:

         There are two types of bacteria according to mode of nutrition.
    • Some bacteria are heterotrophic, it means they cannot prepare their own food. Heterotrophic bacteria further categorize into saprophytic bacteria and parasitic bacteria. Saprophytic bacteria get their food from dead organic matter by absorption. These bacteria with fungi called decomposer because they convert complex organic matter into simple matter. Parasitic bacteria get nutrition from their host. They absorb nutrients from the body of host.
    •  Some bacteria are autotrophic, it means they can prepare their own food. Autotrophic bacteria are further categorize into photosynthetic bacteria and chemosynthetic bacteria. Photosynthetic bacteria prepare their food through photosynthesis and use CO₂ and H₂S instead of water. Chemosynthetic bacteria prepare food through certain chemical(ammonia, nitrite, methane etc)and covert into organic matter without using light.

    Respiration:

        There are four types of bacteria according to need of oxygen.
    • Anaerobic bacteria no need of oxygen for growth and reproduction.
    • Aerobic bacteria cannot survive without oxygen.
    • Microaerophilic bacteria need a low concentration of oxygen. 
    • Facultative bacteria can survive in both environment; in the presence or absence of oxygen.

    Cell wall:

        Cell wall is a rigid structure. It is outermost boundary of cell in plants, fungi and some bacteria. It maintain structure and shape of cell. Bacteria are divide into two categories through a process of staining. It was develop by a bacteriologist Hans Christian Gram.
    • Gram-positive bacteria which have a thick peptidoglycan cell wall and appear purple after staining.
    • Gram-negative bacteria give pink color after staining and having cell wall.

    Flagella:

        Flagella(single: flagellum) are thin, hair like structure, which is originate from basal body. It is come out through cell wall or cell membrane. Flagella is made of protein flagellin and many other materials. It help in movement of organism. It is found in many organisms such as green algae, euglena, mosses, slime mold and bacteria. Pattern and number of flagella also categories bacteria.
    • Bacteria without flagella is called atrichous.
    • With single flagella is called monotrichous.
    •  If tuft of flagella present on one pole is called lophotrichous.
    • When tuft of flagella present at two poles called amphitrichous.
    • If flagella is surround to whole cell is called peritrichous
       

    Growth and reproduction in bacteria:

        Bacteria have no special reproductive system as higher animals, they only can asexually reproduce. For their reproduction, they use binary fission. In this type of reproduction firstly cell enlarge in size, chromosome duplicate and cell wall grows inward the cell. Then cell is separated and a new individual grow and develop. The daughter cell repeat this process and increase their population number. However some bacteria exchange genetic material through transformation, conjugation and transduction        

    Importance of bacteria:

        Bacteria have great importance in ecology and medical.

    Ecological importance:

       Bacteria are decomposer when related to fungi. They decompose dead organic matter into simple substances and have a crucial role in ecological cycles such as nitrogen, sulfur and carbon.

    Medical importance:

        Bacteria are important in study of evolution and also in genetic transfer. They are use in antibiotics, vaccine and antiseptics.      

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