Which structure allows bacteria to survive harsh environmental conditions?

Question

BlackTom AI · Accepted Answer

Endospores (spores) are dormant, highly resistant structures that allow certain bacteria to survive extreme environmental stress, so the correct answer is b. Spore.

1. Relevant knowledge points and concepts
- Endospore (spore): a specialized, dormant cell formed by some Gram-positive bacteria (e.g., Bacillus, Clostridium) that is extremely resistant to heat, radiation, desiccation, chemicals, and nutrient deprivation. Key protective features include a dehydrated core, thick cortex and proteinaceous coat, calcium-dipicolinate, and small acid‑soluble spore proteins (SASPs) that protect DNA.
- Plasmid: a small, circular, extrachromosomal piece of DNA that often carries genes (e.g., antibiotic resistance) but does not confer extreme environmental resistance.
- Pili (fimbriae): hair-like protein appendages used for attachment or conjugation (gene transfer), not long-term survival under harsh conditions.
- Capsule: an external polysaccharide layer that helps immune evasion and prevents desiccation to some extent but does not provide the extreme durability of an endospore.

2. Step-by-step reasoning
- Identify the survival requirement: surviving harsh environmental conditions (heat, desiccation, chemicals, radiation).
- Compare structures: plasmids alter genetics, pili mediate attachment/conjugation, capsule offers moderate protection versus host defenses. Only endospores are specifically adapted for extreme dormancy and resistance.
- Mechanistic support: spores enter metabolic dormancy, sequester and protect DNA (SASPs), dehydrate the core and incorporate calcium-dipicolinate to stabilize proteins and DNA, and build multiple protective layers (cortex and coat). These features directly explain survival under extremes.

3. Intermediate steps / supporting facts
- Examples: Bacillus anthracis spores survive years in soil; Clostridium botulinum spores withstand cooking temperatures unless properly treated. These empirical observations align with the spore’s protective mechanisms.

4. Why the correct answer is correct
- Only spores are specialized for long-term survival under harsh abiotic conditions; their structural and biochemical adaptations make them uniquely effective.

5. Why other options are incorrect (brief)
- a. Plasmid: genetic element, not a protective dormant structure.
- c. Pili: used for attachment/conjugation, not environmental dormancy.
- d. Capsule: provides some protection from desiccation and immune response but not the extreme resistance of spores.

Conclusion: The best choice is b. Spore, which matches the provided correct answer.

Which structure allows bacteria to survive harsh environmental conditions?单项选择题

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