Hyphae are the fundamental structural units of fungi. They are long, branching, filamentous structures that collectively form the mycelium. These filaments are typically composed of one or more cells surrounded by a tubular cell wall, facilitating nutrient absorption and growth throughout the substrate.

Plectenchyma is a general term used in mycology to describe the organized, compact masses of fungal hyphae that form the vegetative or reproductive structures of a fungus. Unlike loose mycelium, plectenchyma involves the intertwining and cementing of hyphae to create solid tissues, such as those found in the fruiting bodies of higher fungi or in specialized survival structures like sclerotia.

An appressorium is a specialized, flattened, or swollen hyphal structure that develops at the tip of a germ tube. It functions to attach the fungus to the host surface and generates mechanical pressure or secretes enzymes to facilitate the penetration of the host epidermis, allowing the fungal pathogen to establish an infection within the plant tissues.

In the conidiophore structure of Penicillium, the main stalk branches into smaller structures called metulae. These metulae further support the phialides, which then produce the conidia. This branching pattern is a key morphological feature used in the identification of different Penicillium species.

While some fungi like yeasts are unicellular, the vast majority of fungi are multicellular. They typically grow as a network of thread-like structures called hyphae, which collectively form a mass known as the mycelium. This multicellular body allows for efficient nutrient absorption and reproduction.

Rhizomorphs are thick, rope-like strands of fungal mycelium composed of organized hyphae. These structures allow fungi to transport nutrients over long distances and survive adverse environmental conditions, often found in wood-decaying fungi.

The mycelium of Mucor and related fungi is described as coenocytic, meaning it lacks cross-walls or septa between individual cells. This results in a continuous, multinucleated cytoplasmic mass. The hyphae appear as a fine, white, and highly branched network that spreads rapidly over the substrate, facilitating nutrient absorption and colonization of the environment.

Fungal hyphae grow by extending their tips across or into a nutrient-rich surface known as the substratum. This surface provides the necessary organic matter, moisture, and environmental conditions required for fungal growth. By secreting extracellular enzymes onto the substratum, the fungus breaks down complex organic compounds into simpler molecules, which are then absorbed through the hyphal walls to support metabolic activities.

In many Basidiomycetes, the life cycle begins with the germination of a basidiospore to form a primary mycelium. This mycelium consists of uninucleate cells and is typically haploid. Following plasmogamy between compatible mating types, the primary mycelium transitions into a secondary mycelium, which is dikaryotic (binucleate), marking a distinct phase in the fungal life cycle.

Fungi are classified as absorptive heterotrophs because they secrete extracellular enzymes into their environment to break down complex organic matter into simpler molecules. These nutrients are then absorbed directly through the fungal cell walls. This mode of nutrition distinguishes them from animals, which are ingestive heterotrophs, and autotrophic organisms like plants.