Which type of bacteria is unique for lacking a cell wall?

Mycoplasma is the unique type of bacteria that is characterized by a complete lack of a cell wall. Instead of the typical rigid structure that defines most bacterial cells, mycoplasma have a flexible membrane composed primarily of lipids and proteins. This unique feature allows them to maintain a range of shapes and gives them the ability to survive in various environments.

In contrast, bacillus, cocci, and spirilla are all categories of bacteria that possess a cell wall, which is fundamental for their structure and protection. The cell wall provides rigidity and defines the shape of these bacteria, whether they are rod-shaped (bacillus), spherical (cocci), or spiral (spirilla). Mycoplasma, due to their absence of a cell wall, are also intrinsically resistant to antibiotics that target cell wall synthesis, which is a critical point of differentiation from these other bacterial classifications.