Prokaryotic cells lack a true nucleus and membrane-bound organelles, and their DNA is located in a region called the nucleoid

Dimorphic fungi have the unique ability to exist in two distinct morphological forms depending on the temperature of their environment. At environmental or cooler temperatures (usually around 25°C), they grow as filamentous molds, producing hyphae and spores that allow them to survive and reproduce outside a host. At body temperature (37°C), they transition into a yeast form, which is better adapted for survival and pathogenicity within human tissues. This temperature-dependent dimorphism is a key factor in their ability to cause systemic infections. Examples include Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides immitis, all of which demonstrate this adaptive morphological shift.

Gram-negative organisms are characterized by a thin peptidoglycan layer located between the inner cytoplasmic membrane and an outer membrane containing lipopolysaccharide (LPS). The thin peptidoglycan layer is insufficient to retain the crystal violet stain during Gram staining, which is why gram-negative bacteria appear pink after counterstaining with safranin. In contrast, gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet-iodine complex, appearing purple under a microscope. The thin peptidoglycan and outer membrane structure of gram-negative bacteria also contributes to their increased resistance to certain antibiotics compared to gram-positive organisms