Fungal organisms are naturally found in water, soil, and decaying organic matter. Yeasts are a unicellular growth form. The shape is sperical or ellipsoidal while their size is from 3 to 15 micrometer in diameter. Most of these yeasts reproduce by budding, although binary fission is sometimes observed. Molds grow as a multicellular and filamentous colony.
Growth occurs by apical elongation or extension from the tip of the hyphae.
Molds grow on surfaces with some hyphae penetrating deeper which are called vegetative or substrate hyphae. Some species of fungi can grow in both the yeast and mold form dependent upon environmental conditions. Cryptococcus is an example of a yeast like form. Histoplasma is a dimorphic form which makes hyphae at environmental temperatures and yeast cells at body temperature. Candida is a dimorphic species that does the reverse with filamentous form at body temperature and yeast cells in the environment.