Fungi

Fungi (plural: fungi) are a kingdom of eukaryotic organisms—those whose cells contain a nucleus and other membrane-bound compartments. They include yeasts, moulds, and mushrooms. Unlike plants, fungi do not produce food using sunlight. Instead, they secrete enzymes outside their cells to break down organic matter, which they then absorb as nutrition.

The body of most fungi consists of fine filaments called hyphae, which intertwine to form a network known as mycelium. Their cell walls contain chitin, which differs from the cellulose found in plant cell walls. Reproduction occurs through spores, which disperse through air, water, or animals.

Classification and groups

Fungi belong to a branch of life called Opisthokonta, meaning they are evolutionarily closer to animals than to plants. The major groups of note include Ascomycota (fungi that sac their spores), Basidiomycota (which includes most mushrooms), Chytridiomycota, and the earlier Zygomycota. Lower-level classification continues to be revised as new genetic research emerges.

Ecological role

Fungi are the most important decomposers in ecosystems. They break down lignin and cellulose in wood and leaves, returning carbon and nutrients to the soil. Some form a mutual relationship with plant roots called mycorrhiza: the fungus supplies the plant with water and nutrients such as phosphorus, while the plant provides the fungus with sugar. Lichens—found on rocks and trees—are associations of fungus with algae or photosynthesizing bacteria.

Disease and human relations

Some fungi are parasites, causing diseases in crops such as maize, rice, and potatoes, which can affect food production. Humans can suffer from fungal infections, including skin diseases such as those caused by dermatophytes, or internal infections affecting immunocompromised individuals. On the other hand, the yeast Saccharomyces cerevisiae is used in baking and brewing, and Penicillium species yielded penicillin, an antibiotic. Some mushrooms are edible, but others are poisonous; distinguishing them requires expertise.