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Living organisms on our planet are divided into
different kingdoms. Until fifty years ago, only two major kingdoms were
recognized, the Plant Kingdom and Animal Kingdom. After a half-century
of studies on the morphology, physiology, biochemistry, ultrastructure,
and molecular nature of organisms, several kingdoms are now recognized.
Many current biology books recognize 5 basic kingdoms of living
organisms, the Monera (bacteria), Protoctista (protozoa),
Plantae (plants), Animalia (animals) and Mycota (fungi). In 1988,
scientists on three different continents discovered independently, using
rDNA, that the fungi emerged very early from the animal kingdom not from
plants as was traditionally assumed. We will look at how the fungi
differ from four other kingdoms currently recognized.
The kingdoms of organisms are further divided into the following
categories:
Kingdom
Phyla or Divisions
Classes
Orders
Families
Genera
Species
The
scientific name of a species is a binomial, consisting of
the generic name and the species name. Thus, the common mushroom is Agaricus
bisporus; (Agaricus = the generic name and bisporus =
the species name).
Fungi
differ from bacteria (the
Kingdom Monera) in that
bacteria do not have organized nuclei or other membrane-bound organelles
(i.e., they are prokaryotes).
Bacterial cell walls do not contain chitin and glucans (Fig. 1-16).
Fig.
1-16. A dividing bacterium with developing cell wall.
Some
bacteria, like all fungi, are heterotrophic
(they can not manufacture their own food). Other bacteria, the
Cyanobacteria, or what once were called the blue-green
algae, have chlorophyll and are able to manufacture their food (autotrophic).
They are the common green “scum” on bodies of water.
Bacteria may be spiraled, cylindric, or globose.
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Fungi differ from the Protozoa (Kingdom Protoctista)
in that protozoan groups are haploid or diploid, heterotrophic or
autotrophic, most engulf their food (phagocytosis),
and when flagellate, they have two or more flagella (01-34). This
large kingdom contains about 35 phyla, three of which are very similar
to fungi because their thalli
(structures without roots, stems, or leaves) and zoospores
resemble those of fungi, and they live in the same habitats with fungi.
Current molecular studies suggest that this large group of phyla
probably represents a number of different kingdoms.
Fungi differ from the Stamenopilids (Kingdom Stamenopila), a group that looks morphologically very similar to fungi, in that
Stamenopilids reproduce by means of biflagellate
zoospores with a long whiplash
flagellum and a shorter tinsel
flagellum. Their vegetative mycelioid phase is
diploid, i.e. having a 2N
number of chromosomes within the nucleus, and their walls are
composed of cellulose and glucans. They have oogamous
sexual reproduction and a pattern of steroid synthesis similar to
plants. One large class of Stamenopilids, the Oomycetes,
has been placed until recent years among the fungi and will be
considered in more detail when we look at fungal-like organisms. Although they look like fungi, they differ in having
biflagellate zoospores, diploid mycelium, cellulose in their walls, and
sexually produced oospores.
Unlike fungi, plants (Kingdom Plantae) are composed of diploid cells (except the gametes in pollen
and ovules), their cell walls contain cellulose and pectin (plus
other compounds), and they are autotrophic
(i.e. they can manufacture their own food through the process of
photosynthesis). Plants range from one-celled algae to
multicelled giant redwoods, and include mosses, liverworts,
ferns, and seed plants. Seed plants include small
herbaceous ones to large palms, pines, oaks, and others.
Lichens are organisms that have fungi and algae growing together in a
mutual relationship.
Fungi differ from animals (Kingdom Animalia)
in that the cells of animals are without walls, the body cells are
diploid (only gametes are haploid), and animals engulf their food (and
boy, do some of us engulf our food!). Animals may be cellular, or larger multicelled like the corals and
snails, worms and fish, turtles and frogs,
or birds and mammals.
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