🌍 Kingdom Monera: Prokaryotes

Prokaryotic Characteristics

  • Prokaryotic cells: No membrane-bound nucleus or organelles
  • Size: 0.1-600 μm (typically 1-10 μm)
  • Habitat: Thrive in diverse environments worldwide
  • Structure: Single-celled microscopic organisms
  • Cell Wall: Present (except in Mycoplasma)
  • Reproduction: Mostly binary fission
  • Genetic Material: Single circular DNA in nucleoid region

🌟 Fun Fact: Bacteria were among the first life forms on Earth, appearing approximately 3.5 billion years ago!

🔬 Bacterial Shapes & Sizes

⚫

Cocci

Spherical/Oval

0.5-1.0 μm
⎯

Bacilli

Rod-shaped

1-10 μm
🌀

Spiral

Curved/Spring

5-500 μm

Size Range

Type Size Example
Smallest 100-200 nm Mycoplasma
Typical 1-5 μm E. coli
Large 600 μm long Epulopiscium fishelsoni
Average 0.1-600 μm Most bacteria

Arrangement Patterns

  • Diplo-: Pairs (diplococcus, diplobacillus)
  • Strepto-: Chains (streptococcus, streptobacillus)
  • Staphylo-: Clusters (staphylococcus)
  • Tetrad: Groups of four
  • Sarcina: Cubical packets of eight

🏗️ Bacterial Cell Structures

Cell Wall & Envelope

  • Composition: Peptidoglycan (murein)
  • Function: Shape, protection from osmotic lysis
  • Gram Staining: Classifies as Gram+ or Gram-
  • Archaea: No peptidoglycan (proteins/polysaccharides)
  • Mycoplasma: Only bacteria without cell wall

Appendages

Feature Flagella Pili/Fimbriae
Appearance Long, whip-like Short, hair-like
Composition Flagellin protein Pilin protein
Function Locomotion, chemotaxis Attachment, conjugation
Presence Most except cocci Gram-negative bacteria

Internal Structures

  • Nucleoid: Single circular DNA (haploid)
  • Plasmids: Extra-chromosomal DNA (drug resistance)
  • Ribosomes: 70S (smaller than eukaryotic 80S)
  • Mesosomes: Invaginations for respiration/division
  • Storage Granules: Glycogen, sulfur, fat, phosphate
  • Endospores: Dormant, heat-resistant structures

🎨 Gram Staining Classification

Gram-Positive Bacteria

  • Stain: Purple/Blue (retains crystal violet)
  • Cell Wall: Thick peptidoglycan (20-80 nm)
  • Teichoic Acid: Present
  • Lipids: Low (1-4%)
  • Examples: Staphylococcus, Streptococcus, Bacillus, Clostridium

Gram-Negative Bacteria

  • Stain: Pink/Red (takes safranin counterstain)
  • Cell Wall: Thin peptidoglycan + outer membrane
  • Porins: Present in outer membrane
  • Lipopolysaccharides: Present
  • Examples: E. coli, Salmonella, Pseudomonas, Helicobacter

💡 Key Difference: Gram-positive bacteria have a thick peptidoglycan layer without an outer membrane, while Gram-negative bacteria have a thin peptidoglycan layer sandwiched between two membranes!

🌟 Importance of Bacteria

Ecological Importance

  • Decomposers: Break down dead organic matter
  • Nitrogen Fixation: Convert N₂ to usable forms (Rhizobium)
  • Humus Formation: Increase soil fertility
  • Bioremediation: Clean pollutants (oil, heavy metals)
  • Symbiosis: Mutualistic relationships (gut flora)

Economic & Industrial Importance

  • Food Production: Yogurt, cheese, vinegar, pickles
  • Antibiotics: Penicillin, streptomycin, tetracycline
  • Genetic Engineering: Plasmids as vectors
  • Mining: Bioleaching of metals (Acidithiobacillus)
  • Biodegradable Plastics: PHB production
  • Sewage Treatment: Waste degradation

Harmful Effects

  • Human Diseases: Tuberculosis, cholera, pneumonia
  • Plant Diseases: Blight, rot, wilts
  • Food Spoilage: Decomposition of food
  • Material Damage: Wood rot, fabric decay

🛡️ Control of Bacteria

Physical Methods

Method Description Example
Heat Sterilization Dry heat (oxidation) or moist heat (protein coagulation) Autoclave (121°C, 15 psi)
Pasteurization Kills non-spore formers at specific temps Milk: 71°C for 15 sec
Radiation UV (non-ionizing) or Gamma/X-rays (ionizing) UV lamps, food irradiation
Filtration Physical removal through membrane filters 0.2 μm filters for heat-sensitive solutions

Chemical Methods

  • Antiseptics: For living tissues (alcohol, iodine)
  • Disinfectants: For inanimate objects (bleach, phenol)
  • Chemotherapeutics: Systemic treatment (antibiotics)
  • Preservatives: Food preservation (salt, sugar, chemicals)
  • Vaccination: Preventive immunization

🚀 Study Strategies

1

Master Bacterial Shapes

Create flashcards with drawings: Cocci (spheres), Bacilli (rods), Spiral (corkscrews). Memorize arrangements: diplo-, strepto-, staphylo-.

2

Gram Stain Comparison

Make a side-by-side table comparing ALL differences: thickness, composition, stain color, examples, permeability.

3

Structure-Function Relationships

For each structure (flagella, pili, capsule, cell wall, plasmid), learn both structure AND function.

4

Control Methods Mnemonics

“Heat Kills, Cold Slows, Chemicals Stop” – Remember temperature effects and chemical actions.

💡 Quick Memory Tips

Shapes Mnemonic

“CBS Bacteria”: Cocci, Bacilli, Spiral. Add prefixes: Diplo- (pairs), Strepto- (chains), Staphylo- (clusters).

Gram Stain Colors

“Purple Positive, Pink Negative“: Gram+ = Purple, Gram- = Pink. Gram+ has thick peptidoglycan.

Flagella Arrangement

“MAP“: Mono- (one), Amphitrichous (both ends), Peritrichous (all around). Lophotrichous = tuft.

Heat Methods

Dry heat = oxidation (oven), Moist heat = protein coagulation (autoclave). Pasteurization ≠ sterilization.

Bacterial DNA

Nucleoid = main DNA (haploid). Plasmid = extra DNA (drug resistance). Endospore = dormant survival structure.

Ecological Roles

“DNF Bacteria”: Decomposers, Nitrogen fixers, Food producers. Remember bioremediation too!