Which of the following organisms is known to have no cell wall?

Mycoplasma is the correct answer because this genus of bacteria is unique among prokaryotes in that it completely lacks a cell wall. Instead, Mycoplasma species have a simple cell membrane structure that allows them to maintain their shape and integrity. The absence of a cell wall is significant because it makes these organisms resistant to antibiotics that target cell wall synthesis, such as penicillin. This characteristic also contributes to their ability to adapt to various environments and host organisms.

In contrast, the other organisms listed have distinct cell wall structures. Chlamydia, while it has a modified cell wall, still retains some form of it. Rickettsia possess cell walls that are similar to those of gram-negative bacteria, and Treponema, known for causing syphilis, has a cell wall composed of peptidoglycan along with additional components. Understanding these differences is important in bacteriology as it impacts how these bacteria respond to treatment and their ecological roles.