Final answer:
The filamentous structures that make up the vegetative feeding part of the fungus are called hyphae, which collectively form a complex network known as the mycelium, serving multiple vital functions for growth and survival.
Step-by-step explanation:
Fungi have feeding structures made up of filaments; these filaments together compose the mycelium.
The fundamental nature of fungi lies in their vegetative structures, which are highly consistent across the kingdom. These structures are composed of hyphae, which are thread-like filaments that penetrate and explore the environment to absorb nutrients. Hyphae can grow from the tip, branch out, and even fuse with other hyphae, thus forming a complex and dynamic network known as a mycelium. This network serves as the digestive system for fungi, breaking down and absorbing food, and transporting nutrients to various parts of the organism, including the reproductive structures when applicable. Unlike the cells in animal or plant tissues, the hyphae in a mycelium lack specialization, resulting in a colonial organism rather than a truly multicellular one. In certain fungi, such as the bread molds, the hyphae are coenocytic, meaning they possess multiple nuclei within a shared cytoplasm, without cellular partitioning. This large surface area and the intricate network of hyphae make the mycelium an efficient structure for nutrient absorption from the diverse substrates in which fungi thrive.