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.

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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