Which structure is a dormant, thick-walled, non-reproductive form produced by certain bacteria in response to nutrient limitation?

• A. Endospore
• B. Capsule
• C. Flagella
• D. Pili

Answer: (A)

The concept being tested is the formation of an endospore, a dormant, thick-walled structure made by certain bacteria when nutrients are scarce. Endospores form during sporulation, a developmental program in some Gram-positive bacteria such as Bacillus and Clostridium, inside a mother cell. This form is not for reproduction; instead it is a highly durable survival unit. Its coat and cortex, plus low water content and protective compounds like dipicolinic acid in the core, give extreme resistance to heat, desiccation, chemicals, and radiation, letting the organism endure harsh conditions until the environment becomes favorable again. When nutrients return, the endospore can germinate back into a normal, metabolically active cell. In contrast, a capsule is a sticky protective layer for adherence and evading phagocytosis, a flagellum provides motility, and pili are for attachment or DNA transfer—none of which are dormant, thick-walled survival forms produced specifically in response to nutrient limitation.