Class 11 Biology Notes | Chapter 6: Prokaryotes (FBISE, Best for Exams)

 

Prokaryotes | Best 11th Class Biology Notes | Federal Board 

Chapter 6 : 

Prokaryotes 

6.1 TAXONOMY OF PROKARYOTES

• 1969: R. Whittaker → 5-kingdom system.
• 1988: L. Margulis & K. Schwartz → Prokaryotes in Kingdom Monera.
• 1977: Carl Woese → 3-domain system (Bacteria, Archaea, Eukarya) based on 16S rRNA sequencing.

Mnemonic: BAE → Bacteria, Archaea, Eukarya

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6.2 ARCHAEA

• Unique Features:

  • Cell membrane: Branched-chain hydrocarbons (vs. fatty acids in Bacteria).
  • Cell wall: No peptidoglycan (pseudopeptidoglycan or proteins).
  • rRNA matches Eukaryotes → Evolutionary link.
  • Methanogenesis (unique to Archaea).

• Types:

  1. Methanogens → Produce methane (e.g., Methanobacterium).
  2. Halophiles → High salt (e.g., Halobacterium).
  3. Thermoacidophiles → High heat + acid (e.g., Sulfolobus).

Clinical Correlation: Methanogens in the gut contribute to IBS, flatulence.

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6.3 BACTERIA: ECOLOGY & DIVERSITY

• Structural Adaptations:

  • Flagella → Motility (e.g., E. coli).
  • Pili → Adhesion, conjugation.
  • Endospores → Survival (Bacillus, Clostridium).

• Major Bacterial Groups:

  1. Proteobacteria (Gram-negative, e.g., E. coli, Salmonella).
  2. Cyanobacteria (Photosynthesis, O₂ production).
  3. Spirochetes (Treponema pallidum → Syphilis).
  4. Aquificales (Thermophiles).

Mnemonic: “PC SA” → Pathogenic & Cyanobacteria, Spirochetes, Aquificales

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6.4 STRUCTURE, SHAPE, SIZE

• Cell Wall:

  • Gram-positive: Thick peptidoglycan + teichoic acid.
  • Gram-negative: Thin peptidoglycan + outer membrane (LPS) → Endotoxin (Lipopolysaccharide).

• Shapes:

  1. Cocci → Round (Streptococcus, Staphylococcus).
  2. Bacilli → Rod (E. coli, Bacillus).
  3. Spiral → Corkscrew (Treponema).

• Endospores → Resistant, dormant structures (Bacillus anthracis, Clostridium difficile).

Clinical Correlation: Gram-negative LPS triggers septic shock (TNF-α release).

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6.5 NUTRITION MODES

• Autotrophs:

  1. Photosynthetic (use light, e.g., Cyanobacteria).
  2. Chemoautotrophic (oxidize inorganic compounds, e.g., Nitrosomonas).

• Heterotrophs:

  1. Saprotrophs (decomposers).
  2. Parasites (pathogenic bacteria).

Example: Mycobacterium tuberculosis → Obligate aerobe.

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6.6 GROWTH & REPRODUCTION

• Growth Curve:
  Lag → Log → Stationary → Death

Mnemonic: L-L-S-D (Like LSD trip, bacteria "grow" then "die")

• Reproduction:
  • Binary Fission (rapid, asexual).
  • Genetic Recombination:
    • Conjugation → Plasmid transfer (E. coli, F-plasmid).
    • Transduction → Virus-mediated DNA transfer.
    • Transformation → Uptake of naked DNA (S. pneumoniae).

Clinical Correlation: Antibiotic resistance spreads via conjugation (R-plasmids).

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6.7 IMPORTANCE OF BACTERIA

• Beneficial:

  1. Nitrogen fixation (Rhizobium).
  2. Decomposition (recycling nutrients).
  3. Biotechnology → Insulin production (E. coli, recombinant DNA).

• Harmful:

  1. Diseases → M. tuberculosis (TB), V. cholerae (Cholera).
  2. Food spoilage → Clostridium botulinum (Botulism toxin).

Clinical Note: Bacteroides fragilis is a major anaerobe in gut infections.

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6.8 HUMAN FLORA

• Locations: Skin, gut, vagina.
• Roles:
  • Prevent pathogen colonization.
  • Synthesize vitamins (B, K).

Mnemonic: "E. coli in the colon, Lactobacillus in the vagina"

Clinical Correlation: Antibiotics → Dysbiosis → C. difficile colitis.

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6.9 CONTROL METHODS

• Chemical:

  • Antibiotics (e.g., Penicillin → Inhibits peptidoglycan synthesis).
  • Antiseptics (e.g., Alcohol, Chlorhexidine).

• Physical:

  1. Heat → Pasteurization, Autoclaving (kills spores).
  2. Radiation → UV (DNA damage), Gamma (sterilization).
  3. Filtration → Removes bacteria from fluids (0.22μm pores).

Clinical Correlation: Penicillin ineffective against Mycoplasma (lacks cell wall).

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KEY TABLES

Table 6.1: Eubacteria vs. Archaea

Feature	Eubacteria	Archaea
rRNA sequences	Unique	Match Eukaryotes
Cell wall	Peptidoglycan	No peptidoglycan
Membrane lipids	Unbranched	Branched

Table 6.3: Normal Flora

Organism	Location
E. coli	Colon
Lactobacillus	Vagina, mouth

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Final Notes for Exams

• Gram-negative LPS → Endotoxin → Septic Shock (IL-1, TNF-α).
• S. pneumoniae, H. influenzae, N. meningitidis → Capsule = Virulence (Asplenic patients at risk).
• Anaerobes: Clostridium, Bacteroides, Fusobacterium (Can’t survive O₂).
• Transformation: S. pneumoniae, H. influenzae, Neisseria ("SHiN bacteria").