Fungi

FUNGI!

Structure and Function

Fungi are eukaryotic heterotrophs that have cell walls. Except for yeasts, most fungi are multicellular. The cell walls are made of chitin while the main body of multicellular ones are composed of filaments called hyphae. Hyphae are tangled together and compose a thick mass called mycelium. The large surface area of the mycelium is useful in absorbing food because of its large surface area. What one recognizes as a mushroom is actually the fruiting body of the fungus. This is the reproductive structure. Sporangia are the structures on fungi that produce spores. Sporangia are found on sporangiophores which are tips of specalized hyphae.

Reproduction Most fungi reproduce both sexually and asexually. Asexual reproduction takes place when cells of hyphae break off from a fungus and begin to grow on their own. Some fungi also produce spores. Sexual reproduction in fungi usually involves two different mating types. Not male and female, but (+) and (-) because the two types are about the same size. When these two mating types meet, they fuse and after a period of growth and development, they form a diploid zygote that enters meiosis. This produces haploid spores which are capable of growing, by repeated rounds of mitosis, into new organsims.

Classification There are over 100,000 species in the kingdom Fungi. Fungi are classified according to their structure and method of reproduction and they reproduce by methods that are unlike the methods of any other kingdom. There four main groups of Fungi are the common molds, the sac fungi, the club fungi, and the imperfect fungi. Common Molds (Zygomycota) Zygomycetes have life cycles that include zygospores. A zygospore is a resting spore that contains zygotes formed during the sexual phase of the mold's lifestyle. Molds are comprised of two types of hyphae: rhizoids, the root-like anchors, and stolons, the stemlike hyphae. Sac Fungi (Ascomycota) This phylum is named for the ascus, a reproductive structure that contains spores. There are 30,000 species of ascomycetes, making it the largest phylum of fungi. The life cycle of these fungi usually includes asexual and sexual reproduction. This phylum includes microscopic yeast as well as the large fruiting bodies of sac fungi Club Fungi (Basidiomycota) This phylum gets it name from a specialized reproductive structure known as the basidium that resembles a club. Basidia are found on the gills on the underside of the cap of the mushroom. This cap is composed of tightly-packed hyphae on the top and gills on the bottom. these "gills" are actually thin blades of tissue lined with basidia that producebasidiophores. Basidiomycetes undergo one of the most elaborate life cycles in the fungial world. This cycle includes a primary and secondary mycelium, button, fruiting body, and basidial stage. Imperfect Fungi (Deuteromycota) These are fungi that cannot be placed in other phyla because reasearchers have never been able to observe a sexual phase in their life cycles. A majority of the imperfect fungi are very similar to ascomycetes, but some resemble the other phyla. One of the best known imperfect fungi is Penicillium which is the source of the antibiotic penicillin.

Ecology 

Fungi occur in almost every environment on Earth and play very important roles in every ecosystem. Along with bacteria, fungi are the major decomposers in most terrestrial (and some aquatic) ecosystems, and therefore play a critical role in biogeochemical cycles and in many food webs. Many fungi have important symbiotic relationships with organisms from most if not all Kingdoms. These interactions can be mutualistic or antagonistic in nature. Over 90% of all plant species engage in some kind of mycorrhizal relationship with fungi and are dependent upon this relationship for survival. The mycorrhizal symbiosis is ancient, dating to at least 400 million years ago. It often increases the plant's uptake of nutrients. In some mycorrhizal associations, the fungal partners may mediate plant-to-plant transfer of carbohydrates and other nutrients. 