Part of the mycelium is involved in gaining nutrients, the vegetative mycelium, and part in growth and reproduction, the aerial or reproductive mycelium. From the reproductive mycelium, spores are formed. Asexual spores are produced by the aerial mycelium of a single organism, whereas sexual spores are formed by the fusion of cells and nuclei from opposite mating strains. There are many types of spore with names such as chlamydospore and sporangiospore. Examples of moulds include Penicillium, the source of penicillin that was the first antibiotic.
Yeasts are unicellular organisms, normally ovoid or spherical in shape.
Typically, they replicate by budding rather than binary fission. Here, the cytoplasm and dividing nucleus from the parent is initially a continuum with the bud, or daughter yeast, before a new cell wall is deposited to separate the two. In some cells, these buds fail to detach and may form a short chain of cells called a pseudohypha. Although yeasts are single cells and produce smooth bacterial-like colonies on laboratory agar media, unlike bacteria they have a distinct nucleus and are thus eukaryotes. An example of a yeast is Saccharamyces cerevisiae that produces alcohol under anaerobic fermentation.