bacteria types and explanation new edit.

🔹 Definition

Bacteria are microscopic, single-celled organisms that belong to the domain Prokaryota. They lack a true nucleus and membrane-bound organelles. Their DNA is found in a circular chromosome within the cytoplasm.


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🔹 General Characteristics

Size: Usually 0.2 – 2.0 µm in dia...

🔹 Definition

Bacteria are microscopic, single-celled organisms that belong to the domain Prokaryota. They lack a true nucleus and membrane-bound organelles. Their DNA is found in a circular chromosome within the cytoplasm.


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🔹 General Characteristics

Size: Usually 0.2 – 2.0 µm in diameter.

Shape: Common forms are

Coccus (spherical)

Bacillus (rod-shaped)

Spirillum (spiral)

Vibrio (comma-shaped)


Structure: Surrounded by a rigid cell wall, may have capsule, flagella (for movement), or pili (for attachment).

Reproduction: Asexual by binary fission.

Genetic Material: Single circular DNA molecule; may have plasmids (extra DNA).



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🔹 Classification

1. By Gram Staining

Gram-positive: Thick peptidoglycan wall, stain purple (e.g., Staphylococcus, Bacillus).

Gram-negative: Thin wall + outer membrane, stain pink/red (e.g., E. coli, Salmonella).



2. By Oxygen Requirement

Aerobic: Need oxygen (Pseudomonas).

Anaerobic: Grow without oxygen (Clostridium).

Facultative anaerobes: Can grow with or without oxygen (E. coli).



3. By Nutrition

Autotrophic: Make their own food (photosynthetic or chemosynthetic).

Heterotrophic: Depend on organic matter (saprophytic, parasitic, symbiotic).





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🔹 Structure of a Typical Bacterial Cell

Cell wall: Provides shape and protection.

Cell membrane: Controls entry/exit of substances.

Cytoplasm: Contains ribosomes and enzymes.

Nucleoid: Region containing DNA.

Ribosomes: Sites of protein synthesis.

Flagella: For motility.

Capsule/slime layer: Prevents desiccation and helps in virulence.

Pili/Fimbriae: Help in attachment and conjugation.



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🔹 Reproduction and Growth

Binary fission: Parent cell divides into two identical daughter cells.

Generation time: Time required for a population to double (varies from minutes to hours).

Growth phases in culture:

1. Lag phase: Adaptation period


2. Log (Exponential) phase: Rapid division


3. Stationary phase: Growth = Death


4. Death phase: Nutrients exhausted





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🔹 Genetic Exchange in Bacteria

1. Conjugation: Transfer of plasmid DNA through a pilus.


2. Transformation: Uptake of free DNA from environment.


3. Transduction: Transfer of DNA via bacteriophages (viruses that infect bacteria).




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🔹 Beneficial Roles

Decomposition: Break down dead organic matter.

Nitrogen fixation: Rhizobium in root nodules converts nitrogen gas to ammonia.

Food industry: Fermentation (yogurt, cheese, vinegar).

Medicine: Antibiotic and vitamin production.

Biotechnology: Gene cloning, insulin production.

Waste treatment: Biodegradation and sewage treatment.