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Endospore Formation and Bacterial Motility Explained – Class 11 Biology Notes

 

Endospore Formation and Bacterial Motility Explained – Class 11 Biology Notes

🔬 Endospore Formation in Bacteria

Many bacteria survive extreme environmental conditions by forming specialized “resting” cells, called endospores (thick-walled dormant structures). These endospores are metabolically inactive and highly resistant to heat, radiation, drying, and chemicals.

👉 The process of endospore formation is called sporulation.

✳️ Steps of Sporulation (Endospore Formation):

  1. When unfavourable conditions arise, the bacterium replicates its DNA (makes a copy).

  2. The cell membrane forms a septum (dividing wall) to isolate the new DNA along with a small portion of cytoplasm.

  3. The cell membrane grows again around this section, enclosing DNA, cytoplasm, and septum.

  4. This results in two membranes surrounding the new DNA and cytoplasm.

  5. The DNA of the original (vegetative) cell disintegrates.

  6. The entire structure dehydrates (loses water).

  7. A new peptidoglycan layer (supportive cell wall material) forms between the membranes.

  8. A tough spore coat develops around the structure.

  9. The vegetative cell breaks, and the endospore is released.

  10. Endospore remains dormant until favourable conditions return.

  11. When conditions are suitable again, the endospore germinates, producing a new vegetative cell.

SPORULATION,ENDOSPORE



🦠 Motility in Bacteria (Types of Bacterial Movement)

Motility refers to the ability of bacteria to move from one place to another, often to find nutrients or escape harmful conditions.

🔹 1. Flagellar Movement

  • Most bacilli and spirilla use flagella (long, whip-like tails) to swim.

  • Movement by flagella is called swarming when many bacteria move together.

  • Counter-clockwise rotation of the flagellum pushes the cell forward.

🔹 2. Twitching or Crawling

  • Uses pili (short hair-like structures) to attach to a solid surface and then retract, pulling the bacteria forward.

🔹 3. Gliding

  • Bacteria secrete a slimy substance that helps them glide smoothly over surfaces.

  • This is similar to twitching, but smoother and less jerky.

🔹 4. Sliding

  • Caused by expansion of the bacterial population as cells divide and push against each other.

🔹 5. Brownian Movement

  • Seen in non-motile bacteria (e.g., Streptococcus).

  • Caused by random collisions of fluid molecules — not true motility.

Navigation in Bacteria

🔹 6. Movement by Axial Filament
  • Found in spirochaetes.

  • Axial filament is a modified flagellum located inside the periplasmic space (between membranes).

  • It enables flexing, spinning, creeping, and swimming.

  • Consists of two sets of flagella-like fibrils, anchored at both ends of the cell.


Axial filament in bacteria


Key Terms Highlighted:

  • Endospore (resting, dormant cell)

  • Sporulation (endospore formation process)

  • Vegetative cell (normal, active bacterial cell)

  • Septum (dividing membrane)

  • Peptidoglycan (cell wall material)

  • Flagella, pili, axial filament

  • Twitching, gliding, swarming, Brownian motion

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