What is the dormant structure called that forms a thick internal wall in some bacteria?

The dormant structure that forms a thick internal wall in some bacteria is known as an endospore. Endospores are highly resilient structures that develop in response to unfavorable environmental conditions, such as nutrient depletion or extreme temperatures. This allows the bacteria to survive in a dormant state until conditions become favorable again for growth and reproduction.

Endospores have a tough outer coating that protects the genetic material and the cellular machinery of the bacterium from damage caused by harsh environments, including desiccation, heat, and radiation. This unique ability makes endospores essential for the survival of some bacterial species, allowing them to persist for extended periods without water or nutrients. When conditions improve, the endospore can germinate, giving rise to a new bacterial cell.

Other options represent structures with different characteristics and functions. A cyst is a protective structure formed by some protozoans and not specifically bacteria, serving as a means of survival but not with the same complexity as endospores. A sporangium is a structure in fungi that produces spores, and a capsule is a protective layer surrounding some bacteria but does not serve the same purpose as an endospore in terms of dormancy and resilience.