Question

Difficulty: HardKingdom Monera: Bacteria and Cyanobacteria

Certain rod-shaped bacteria in Kingdom Monera survive extreme environmental stress such as prolonged desiccation, high temperature, and chemical disinfectants by forming specialized dormant cells. Which cellular modification is primarily responsible for the heat resistance and structural stability of these bacterial endospores?

  1. A dehydrated core containing dipicolinic acid complexed with calcium ions surrounded by a thick peptidoglycan cortexAnswer
  2. B
    A rigid outer wall composed of cellulose microfibrils and pectin matrix
  3. C
    An acellular protein capsid shell protecting a naked RNA genome without metabolic organelles
  4. D
    A thick-walled heterocyst engineered for anaerobic nitrogen fixation using nitrogenase enzymes

Answer

A dehydrated core containing dipicolinic acid complexed with calcium ions surrounded by a thick peptidoglycan cortex
The correct answer highlights the presence of calcium dipicolinate and dehydration within a thick peptidoglycan cortex. This specific biochemical makeup protects bacterial DNA and enzymes from denaturation caused by heat, desiccation, and chemical agents during adverse conditions.

Step-by-Step Solution

1
Identify the survival mechanism referred to in the stem.
The dormant resistant structures formed by bacteria under extreme stress are endospores.
Monerans like Bacillus and Clostridium undergo sporulation to form endospores.
2
Analyze the biochemical composition responsible for endospore resistance.
Calcium-dipicolinate (dipicolinic acid complexed with Ca2+Ca^{2+}) reduces water content in the core, stabilizing proteins and DNA against thermal denaturation, while the peptidoglycan cortex provides mechanical resistance.
High dehydration and calcium dipicolinate are key adaptations unique to bacterial endospores.

Key Concept

Bacterial Endospore Structure and Survival Adaptations
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