BIO 5 GENERAL
BIOLOGY
1. Kingdom Fungi includes mushrooms, molds, edible fungi,
poisonous fungi, pathogenic fungi, and beneficial fungi such as certain types
of yeast. Those organism included within the Kingdom are commonly called fungi.
The singularly form is fungus. Organisms in the Kingdom fungi are eukaryotes.
This means that the have eukaryotic cells, those with a nucleus and
membrane-bound organelles. Like plant cells, the cells of fungi have cell
walls. However, the cell walls are composed of chitin, not cellulose.
2. Fungi are unlike algae in that they are heterotrophic. This
means that they rely on food from their environment to obtain energy. Fungi,
like animals do not carry out photosynthesis. Unlike animals, fungi do not
ingest (take into their bodies) their food. Fungi release digestive enzymes
into their food and digest it externally. They absorb the food molecules that
result from the external digestion. Fungi are able to effectively digest food
externally because, in all fungi but yeast, the organism consists of long,
thread-like structures called hyphae which surround and grow into the food
source, living or dead. The image shows fungal hyphae ( Septated_hyphae_MC.jpg). These hyphae can grow extremely rapidly. In
24 hours, 0.6 miles of hyphae can be produced.
3. Fungi generally have two stages, the feeding stage and the
fruiting body. The feeding stage consists of hyphae that are involved in
digestion of food. Some fungi eat dead organisms. These fungi are often
beneficial since they contribute to the decomposition of dead organism and the
recycling of organic molecules contained in them. These fungi are called
decomposers. Other fungi utilize living organisms as a food source. These fungi
are parasites. Some of these parasites are disease causing organisms or
pathogens. Fungi cause some human diseases such as swimmers' ear, athlete's
foot, Valley fever, yeast infections, ringworm, and St. Elmo's fire. They also
cause plant diseases such as wheat rust, Dutch elm disease, and potato blight.
The feeding stage of fungi is generally not visible to people since the hyphae
are microscopic and are contained within the food, living or dead. Feeding
stage hyphae are visible only if a huge mass is present.
4. Generally, we notice fungi when a fruiting body is
formed. This is the part of the fungus that produces reproductive cells called
spores. Spores are airborne so the fruiting body grows out of the food source
to allow spore dispersal. It is also the fruiting body that is used to place
fungi into categories: Division, Class, Order, etc.
5. One type of fungus people frequently encounter is the black
bread mold, Rhizopus. This fungus is a member of the zygospore-forming
fungi (Division Zygomycota). The feeding stage of the fungus grows in bread and
other types of food. When the fruiting body forms, the fungus becomes visible
on the surface of the food ( On_a_lemon_MC.jpg). When viewed with microscope, the Rhizopus
consists of rounded, spore-producing structures called sporangia (hyphae_MC.jpg) that are produced on hyphae that extend
upward above the surface of the food, a lemon in the example. When the spores
are mature, they are released into the air ( All_hyphae_MC.jpg). Each sporangium produces thousands of
spores. Each spore, if it lands on suitable food, can produce feeding stage
hyphae.
6. The largest and most diverse group of fungi are the sac
fungi (Division Ascomycota). This group includes edible fungi, such as the
morel ( Ascoma_130.jpg).
It also includes cup fungi ( Scarlet_cup_DK.jpg) which are common in forests. For both of
these examples, the portion of the fungus that is visible is the fruiting body.
In all members of this group, spores are produced in sac-shaped cells. This
image shows a section cup through a cup fungus ( Peziza_section_MC.jpg) and a high magnification of the inner part
of the cup showing the spores within the sac-shaped cell ( Asci_MC.jpg).
5. Two fungi that are sometimes grouped with the sac fungi are
yeast and Penicillium. Yeast is an unusual fungus because it is
unicellular both in the feeding stage (budding_cells_MC.jpg
) and in the fruiting body stage. Penicillium is a fungus that is useful
to people. It is the source of the first antibiotic, penicillin, and it is used
to flavor cheese such as Roquefort, Brie, and Camembert. The image shows a
culture of Penicillium (Culture_MC.jpg ). If the culture is viewed under a
microscope, hyphae that produce spores are visible ( Conidiaphores_MC.jpg). Each of these hyphae produce hundreds of
spores (Conidia_MC.jpg ).
6. The most familiar group of fungi are the club fungi
(Division Basidiomycota). This group includes mushrooms. The visible portion of
the mushroom is the fruiting body. Note the gills on the lower surface of the
mushroom ( mushroom_MC.jpg). It is on the gills that club-shaped cells
that produce spores are located. The image shows a cross section of a mushroom
showing gills ( Gills_MC.jpg).
The second image shows a higher magnification of the gills. Note the spores (Gills_detail_MC.jpg).
7. Other common fungi are members of the club fungi (Division
Basidiomycota). These include shelf fungi ( Conch
MC.jpg),
coral fungi ( coral_fungus.jpg), puffballs ( Puffballs_a_log_MC.jpg), earth stars (Earth_stars_MC.jpg ), and birds nest fungi ( Bird_nest_fungi_MC.jpg).
8. Lichen, while often studied at the same time as fungi, are
really composite organisms that are composed of both a fungus and an alga.
Because of the mutualistic association (one which benefits both parties) of the
two organisms, lichens are able to live in many, sometimes inhospitable
environments. Lichens grow on trees bark ( Lichens_on_bark_lg_MC .jpg), hang from tree branches ( Usnea_on_twig_MC.jpg),
and on soil in cold environments (Reindeer_moss_MC.jpg ). Lichen, for example, are common on trees
in the Sierra Nevada (Lichens_on_tree_bark_MC.jpg).
