Are Yeasts Fungi?
Are yeasts Fungi?
Yes, the 700 known yeasts really are fungi, although their colonies often look more like those of bacteria.
Most fungi explore their surroundings by producing miles of fine, branching filaments called hyphae, but most yeasts have become more or less unicellular, with rounded cells. This is often an adaptation to living in a liquid medium of high osmotic pressure. This usually means media with a high sugar content, such as is found in the nectaries of flowers or on the surface of fruits, where if they present the least possible surface area (as close to spherical as possible), it makes it easier for them to control the movement of dissolved substances in and out of their cells.
The cells of most yeasts can be regarded as asexual propagules, and they produce more of the same by a variety of methods similar to those found in moulds.
Some yeasts are related to ascomycetes, others to basidiomycetes, and even zygomycetes sometimes take on a yeast-like appearance.
Some yeasts make hyphae as well as unicells, and some are even exclusively hyphal, being recognizable as yeasts only by biochemical characters.
Yeasts are, of course, among the most important fungi, because they raise bread, ferment sugars to make beer, wine, and spirits, and represent a concentrated food and a source of B vitamins.
A few yeasts cause serious diseases of people.
For some pictures of yeasts, go to Chapter 6.
A more detailed account can be found in Chapter 6 of the book The Fifth Kingdom