Yeasts are unicellular organisms, reproducing by budding and division; molds are multicellular organisms growing in filaments called hyphae, forming mycelium and reproducing by conidia and spores. Both yeasts and molds have sexual and asexual reproduction. Rare fungi have other forms (cysts, spherulas). Fungi have a rigid cell wall with mannans, glucans and chitin in it, and with ergosterol in the cell membrane.