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):
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When unfavourable conditions arise, the bacterium replicates its DNA (makes a copy).
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The cell membrane forms a septum (dividing wall) to isolate the new DNA along with a small portion of cytoplasm.
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The cell membrane grows again around this section, enclosing DNA, cytoplasm, and septum.
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This results in two membranes surrounding the new DNA and cytoplasm.
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The DNA of the original (vegetative) cell disintegrates.
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The entire structure dehydrates (loses water).
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A new peptidoglycan layer (supportive cell wall material) forms between the membranes.
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A tough spore coat develops around the structure.
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The vegetative cell breaks, and the endospore is released.
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Endospore remains dormant until favourable conditions return.
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When conditions are suitable again, the endospore germinates, producing a new vegetative cell.
🦠 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
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Most bacilli and spirilla use flagella (long, whip-like tails) to swim.
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Movement by flagella is called swarming when many bacteria move together.
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Counter-clockwise rotation of the flagellum pushes the cell forward.
🔹 2. Twitching or Crawling
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Uses pili (short hair-like structures) to attach to a solid surface and then retract, pulling the bacteria forward.
🔹 3. Gliding
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Bacteria secrete a slimy substance that helps them glide smoothly over surfaces.
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This is similar to twitching, but smoother and less jerky.
🔹 4. Sliding
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Caused by expansion of the bacterial population as cells divide and push against each other.
🔹 5. Brownian Movement
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Seen in non-motile bacteria (e.g., Streptococcus).
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Caused by random collisions of fluid molecules — not true motility.

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Found in spirochaetes.
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Axial filament is a modified flagellum located inside the periplasmic space (between membranes).
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It enables flexing, spinning, creeping, and swimming.
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Consists of two sets of flagella-like fibrils, anchored at both ends of the cell.
✅ Key Terms Highlighted:
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Endospore (resting, dormant cell)
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Sporulation (endospore formation process)
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Vegetative cell (normal, active bacterial cell)
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Septum (dividing membrane)
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Peptidoglycan (cell wall material)
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Flagella, pili, axial filament
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Twitching, gliding, swarming, Brownian motion
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