New

Domain Bacteria Class 11 Biology Chapter 1

 

Domain Bacteria Class 11 Biology Chapter 1Domain Bacteria –

(In the Five Kingdom System, bacteria were placed under Kingdom Monera)

General Characteristics:

1. Cell Structure:

- Prokaryotic cells (no true nucleus, no membrane-bound organelles like mitochondria or ER).

- DNA is present in a region called the nucleoid.

- Similar to Archaea in lacking membrane-bound organelles.

2. Cell Wall Composition:

- Made of peptidoglycan (a unique polymer of sugars and amino acids).

- Gives rigidity, shape, and protection.

- Absent in Archaea (they have pseudopeptidoglycan).

3. Genetic Material:

- Single circular DNA molecule, not enclosed in a nucleus.

- DNA lies in the nucleoid region of the cytoplasm.

- No histones (usually).

4. Plasmids:

- Small circular DNA molecules separate from the main chromosome.

- Carry genes for antibiotic resistance, toxin production, etc.

- Can be transferred between bacteria via conjugation.

5. Reproduction:

- Mostly asexual by binary fission.

- One cell divides into two identical daughter cells.

- Some show genetic recombination by transformation, transduction, and conjugation.

6. Nutritional Modes:

a. Autotrophs – Make their own food.

- Photoautotrophs (e.g., Cyanobacteria like Anabaena, Spirulina) use sunlight.

- Chemoautotrophs (e.g., Nitrosomonas) use inorganic compounds.

b. Heterotrophs – Depend on external food.

- Saprophytic (e.g., Bacillus subtilis) – Decompose dead matter.

- Parasitic (e.g., Mycobacterium tuberculosis) – Cause disease.

7. Morphology (Shapes):

- Cocci – Spherical (e.g., Streptococcus pneumoniae)

- Bacilli – Rod-shaped (e.g., Escherichia coli)

- Spirilla – Spiral-shaped (e.g., Spirillum)

- Vibrios – Comma-shaped (e.g., Vibrio cholerae)

8. Arrangement:

- Diplococci – Pairs (e.g., Neisseria)

- Streptococci – Chains (e.g., Streptococcus pyogenes)

- Staphylococci – Clusters (e.g., Staphylococcus aureus)

9. Flagella:

- Whip-like structures used for movement (motility).

- Arrangements:

  - Monotrichous – Single flagellum

  - Lophotrichous – Tuft at one end

  - Peritrichous – All over the surface

10. Pili and Fimbriae:

- Pili – Involved in conjugation (transfer of DNA).

- Fimbriae – Help in attachment to surfaces.

- Found in pathogenic bacteria like Neisseria gonorrhoeae.

11. Respiration:

- Obligate aerobes – Need O₂ (e.g., Mycobacterium)

- Obligate anaerobes – Killed by O₂ (e.g., Clostridium botulinum)

- Facultative anaerobes – With or without O₂ (e.g., E. coli)

- Microaerophiles – Need low O₂ (e.g., Helicobacter pylori)

- Aerotolerant anaerobes – Don’t use O₂ but tolerate it.

- Many perform fermentation in anaerobic conditions.

12. Extremophiles:

- Can survive in extreme conditions:

  - Thermophiles – High temperature (Thermus aquaticus)

  - Halophiles – High salt (Halobacterium)

  - Acidophiles – Low pH (Acidobacterium)

13. Pathogenicity (Disease-Causing Ability):

- Some bacteria cause serious diseases:

  - Mycobacterium tuberculosis – Tuberculosis

  - Treponema pallidum – Syphilis

  - Vibrio cholerae – Cholera

- They produce toxins and virulence factors.

14. Symbiosis (Living Together):

- Mutualism – Both benefit (e.g., Rhizobium in legumes)

- Commensalism – One benefits, other not harmed (e.g., gut bacteria in humans)

- Parasitism – One benefits, other harmed (e.g., pathogenic bacteria)

Examples of Major Bacterial Groups (with Meaning and Role/Disease Caused)

1. Proteobacteria

  • Literal Meaning: From Greek proteo, meaning “first” or “primary,” referring to its diversity.

  • Examples & Roles:

    • Escherichia coli: Found in the gut; some strains cause food poisoning.

    • Rhizobium: Beneficial; fixes nitrogen in root nodules of legumes.

    • Helicobacter pylori: Causes stomach ulcers and can lead to stomach cancer.

2. Firmicutes

  • Literal Meaning: From Latin firmus (strong) and cutis (skin), meaning “thick cell wall.”

  • Examples & Roles:

    • Bacillus subtilis: Non-pathogenic, used in industrial enzyme production.

    • Lactobacillus: Beneficial; helps in yogurt production and gut health.

    • Clostridium botulinum: Produces botulinum toxin; causes botulism (a deadly foodborne illness).

3. Actinobacteria

  • Literal Meaning: From Greek aktis (ray) and bakteria (rod), referring to ray-like branching filaments.

  • Examples & Roles:

    • Streptomyces: Produces antibiotics like streptomycin.

    • Mycobacterium tuberculosis: Causes tuberculosis (TB).

4. Cyanobacteria

  • Literal Meaning: Cyano means blue, and bacteria means rod—"blue-green bacteria."

  • Examples & Roles:

    • Anabaena, Spirulina: Photosynthetic; produce oxygen and fix nitrogen; used as food supplements.

    • Some species can form harmful algal blooms in water bodies.

5. Spirochaetes

  • Literal Meaning: From Greek speira (coil) and chaite (hair), meaning “coiled hair” or spiral-shaped.

  • Examples & Roles:

    • Treponema pallidum: Causes syphilis, a sexually transmitted infection (STI).

6. Acidobacteria

  • Literal Meaning: Acido (acid-loving) + bacteria (rod-shaped) — grow in acidic environments.

  • Examples & Roles:

    • Acidobacterium: Common in acidic soils; plays a role in carbon cycling.

    • Not typically pathogenic to humans.

7. Aquificae

  • Literal Meaning: From Latin aqua (water) and facere (to make), meaning “water makers” – because they live in hot water environments.

  • Examples & Roles:

    • Aquifex pyrophilus: Thermophilic (heat-loving); found in hot springs and hydrothermal vents.

    • Not harmful; important for studying early life forms.

  • Three Domain System of Classification
Tags:

Post a Comment

0 Comments