Bacteria
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Bacteria are single-celled microorganisms found in nearly every environment on Earth. Key subtopics include:
1. Structure & Classification
Cell Types: Prokaryotic (no nucleus), with cell walls (peptidoglycan in most).
Shapes: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral).
Gram Staining: Classifies bacteria as Gram-positive (thick peptidoglycan) or Gram-negative (thin layer + outer membrane).
2. Reproduction & Growth
Binary Fission: Asexual reproduction by splitting into two identical cells.
Conjugation: Genetic material exchange via pili (horizontal gene transfer).
Growth Phases: Lag, log, stationary, and death phases in culture.
3. Metabolism & Nutrition
Energy Sources:
Autotrophs: Photosynthetic (e.g., cyanobacteria) or chemosynthetic.
Heterotrophs: Feed on organic matter (e.g., E. coli).
Oxygen Requirements: Aerobic (require O₂), anaerobic (thrive without O₂), facultative (adapt to both).
4. Role in Nature & Human Health
Beneficial Roles:
Decomposers in nutrient cycles (nitrogen fixation).
Gut microbiota aiding digestion.
Pathogenic Bacteria: Cause diseases (e.g., Salmonella, Staphylococcus).
5. Antibiotics & Resistance
Mechanisms: Inhibit cell wall synthesis (penicillin), protein production (tetracycline).
Resistance: Mutations or plasmid transfer leading to superbugs (e.g., MRSA).
6. Industrial & Biotech Applications
Used in fermentation (yogurt, antibiotics), bioremediation, and genetic engineering (insulin production).
Bacteria’s adaptability makes them vital to ecosystems, medicine, and industry.