Chapter 9 Kingdom Fungi

Chapter 9 : Kingdom Fungi. Total worldwide of 100,000 species, fungi are mainly saprophytes (decomposers that absorb organic molecules from dead organisms). Fungi secrete enzymes that digest organic materials outside the body, then absorb the small molecules that are produced. The cell wall is made of chitin. Fungi consist of thread-like hyphae that form a connected network : a mycelium Fig 19-1A. Sexual reproduction : the cytoplasm of two cells join in plasmogamy, later the two nuclei join in karyogamy. Fungi reproduce using spores.Fungi can infect people with weak immune systems. Infections. On the other hand they are a good source of antibiotics: New. Other medical products from fungi include cyclosporin which is given to transplant recipients to lower their immune system. Also statin drugs that reduce the risk of heart attack are obtained from fungi. Both of these drugs have sales of over $1 billion a year. Phylum Zygomycota 1000 species. Reproduce by forming a single zygospore that can resist harsh environments. Hyphae are coenocytic (nuclei are not separated from each other by cell membrane or cell wall). Mainly saprophytes, but some form mycorrhizae in plant roots, which helps the plant obtain nutrients. Examples : Rhizopus causes bread mold. The black "dust" on the surface of infected food is the zygospores of this fungus. Fig 19.3 Rhizopus oligosporous is used in making tofu and tempeh. Arthrobotrys grows through the soil and kills nematode worms. Nematodes damage plant roots and so having this fungus in the soil improves crop yields. Video Pilobolus artillery fungus. It grows mainly on dung. It shoots its spores several feet away from dung. The spores that land in grass are eaten by animals and survive through the digestive system and start growing in the animal's dung. Video Phylum Ascomycota 60,000 species. They form 8 ascospores in a long cell called an ascus. Fig 19.7. Many are mutualistic with algae, forming lichens. Fig 19.36. Lichens grow on rocks or trees (they are photosynthetic), and are important sources of food in cold climates (reindeer eat mainly lichen). They are also very sensitive to air pollution, so several cities regularly survey lichens to sample the air quality. Lichens can also survive the harsh conditions of space. Examples : Claviceps purpurea causes ergot disease in crops, particularly rye. If the infected seeds are eaten, toxins from the fungus cause the disease St. Anthonys fire in humans. Penicillium used in making antibiotics, blue cheese and salami. Several fungi produce antibiotics, because bacteria are often decomposers and therefore compete with fungi for food. Saccharomyces is yeast. Used in baking and brewing (Note: this is different from the "yeast" that causes infections). Tuber melanosporum truffles are edible and very expensive. They are collected using pigs, or dogs, to locate the fungus which is often buried deep in the leaf litter. Truffles and crime! Phylum Basidiomycota 30,000 species, mainly saprophytes. Form 4 basidiospores in a club shaped basidium. Fig 19.18. Examples : Agaricus the common mushroom. Growing mushrooms Phallus or stinkhorn. Sometimes found growing in mulch. The spores are dispersed by flies attracted to the smell of rotting meat. Puccinia graminis causes wheat rust. It overwinters in barberry (genus Berberis) where it produces spores in a cup-shaped aecium. Aecium. In the spring and summer spores infect wheat, and spread from uredia that burst through the leaf. Uredia. Armillaria is the largest living fungus, with a single individual able to cover several acres (underground), and live for over 1,000 years! Giant fungus Amanita fly agaric is hallucinogenic and was used by Vikings! It has a red cap with white spots - the typical "mushroom" you see in illustrations. Fly agaric Smuts, such as Ustilago infect corn. Smuts are a problem to farmers in this country, but in parts of Mexico people like the taste of the infected corn. Smut Phylum Deuteromycota (Imperfect Fungi) Artificial group : no sexual reproduction has been observed. This is often a temporary category, until a fungus is studied in more detail. Examples : dermatophytes cause athlete's foot Aspergillus : used for making soy sauce, and saki. It is also a source of citric acid for soft drinks, which has a huge commercial value (look at the ingredients list on your soft drink!). Peanuts infected with Aspergillus contain aflatoxins that cause liver cancer, particularly in Africa and Asia. Liver cancer