Fungi
Fungi have been studied systematically for 250 years, although ancient peoples
learned of fermentation (enabled by fungi) thousands of years ago. Scientists
who practice mycology, the study of fungi, are called mycologists. In the early
days of microbiology, mycologists categorized fungi as plants because they
resemble plants in general appearance (they have cell walls) and because both
fungi and plants lack motility (neither can move under its own power).
Today, however, fungi and plants are considered two distinct groups of organ-
isms because plants use chlorophyll to obtain nutrients and fungi do not. Fungi
are heterotrophic: They absorb nutrients from organic matter and organic wastes
(saprophytes) or tissues of other organisms (parasites). Many fungi are multi-
cellular and are called molds. Yeasts are unicellular fungi.
Fungi can be both beneficial and harmful. For example, fungi called mycor-
rhizaeare mutualistic and help roots of plants absorb water and minerals from
the soil. The cellulose and lignin of plants are important food sources for ants;
however, ants are unable to digest them unless fungi first break them down.
Ants are known to cultivate fungi for that purpose. Some fungi are beneficial to
humans as food (mushrooms). They are used in the preparation of food such as
bread and beer (yeast). Fungi are also used to fight off bacterial diseases
(antibiotics).
Some fungi can have a harmful effect because they feed on plants, animals,
and humans, causing plants and animals to decay and spoil as a source of nutri-
ents (rotting food). In humans, fungi cause various diseases such as athlete’s foot.ANATOMY OF FUNGI
The body of a fungus (Fig. 11-1) is referred to as either a soma(meaning
“body”), which is equal to the term “vegetative” in plants, or thallus,which is
also applied to algae and bryophytes (nonflowering plants comprised of mosses
and liverworts). The body of a mold or fleshy fungus consists of long, loosely
packed filaments called hyphae.
Hyphae are divided by cell walls called septa(the singular form is septum). In
most molds the hyphae are divided into one cell units called septate hyphae.
In some fungi, the hyphae have no septa and look like long multinucleated
cells called coenocytic hyphae.Cytoplasm flows or streams throughout the hy-
phae through pores in the septa. Under the right environmental conditions the
hyphae grow to form a filamentous massknown as a mycelium. A fungus can(^168) CHAPTER 11 The Eukar yotes