Fungi are characterized by their eukaryotic cell structure, meaning they have a true nucleus and membrane-bound organelles, distinguishing them from prokaryotes. A key diagnostic feature is their cell wall composed of chitin, unlike bacteria which have peptidoglycan walls. This chitinous cell wall provides mechanical strength and is a target for antifungal agents. Recognizing this structural difference is crucial in clinical settings, as it guides the choice of appropriate antimicrobial therapy and surgical management of fungal infections.

Reference: Robbins Basic Pathology, Kumar Vinay, 10th Edition.