What is mycelium?

Mycelium is indeed the branching structure that composes the main body of fungi. It consists of a network of hyphae, which are long, thin filamentous cells that spread out in soil, decaying wood, or other substrates. This structure plays a critical role in nutrient absorption and growth, as it penetrates the substrate and breaks down organic material, allowing the fungus to obtain the nutrients it needs.

Understanding mycelium is essential in plant pathology and pest control, as it can be associated with both beneficial and harmful interactions with plants. Mycelium can form symbiotic relationships with plant roots (mycorrhizae), enhancing nutrient uptake for plants, or it can be the structure from which pathogenic fungi emerge, leading to plant diseases. This duality highlights the importance of mycelium in ecosystem health and agricultural practices.

The other options refer to aspects of fungal biology but do not accurately define mycelium. Single cells of fungi refer to yeast cells, spores are reproductive structures, and the fruiting body is typically the structure that produces spores, such as mushrooms, which arise from mycelium but are distinct from it.