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).