Fungi

   General

· Although originally classified as plants because they share some characteristics, fungi have several characteristics that make them different:

i.         Lack chlorophyll so not photosynthetic

                        ii.        Cell wall made of chitin rather than cellulose

                        iii.       Fungi are heterotrophs and absorb food after secretion of enzymes and extracellular digestion while plants are photosynthetic

                        iv.       Fungi reproduce by spores rather than seeds

                        v.         Fungi are composed of filaments called hyphae. Hyphae may be branched. A dense mass of hyphae is called a mycelium.

                        vi.       Hyphae may contain internal crosswalls that divide the hyphae into separate cells. The crosswalls of many species have pores, allowing cytoplasm to flow freely from one cell to the next. Cytoplasmic movement within the hypha provides a means to transport of materials.

· Uses of fungi

i.         Many are harmful and cause decay, rot and spoilage.

                        ii.        Some cause serious plant and animal diseases.

                        iii.       Many are beneficial

                                    (1)       Yeasts are used in the manufacture of bread, wine and beer.

                                    (2)       Production of penicillin.

                                    (3)       Many mushrooms are eaten as food

· Symbiosis

i.         Lichens consist of a mutualistic relationship between fungi and green algae.

                        ii.        Mycorrhizae are associations between fungi and plant roots. The extracellular digestion facilitates absorption of essential nutrients by plant roots.

                        iii.       In both cases, the photosynthetic partner makes food while the fungal partner provides nutrients.

 Nutrition

· Fungi are major decomposers in every ecosystem. They break down matter into simple nutrients that an be used by other organisms.

·  All are heterotrophic. Fungi excrete enzymes into their environment to digest food. They then absorb the nutrients.

·  Most species of fungi are saprotrophic; they decompose dead matter. Many are parasitic and obtain nutrients from living organisms.

·

   Reproduction

· Most fungi reproduce sexually although there are a few examples of those that reproduce asexually. Yeast are a notable exception as they show mostly asexual reproduction.

·  The hyphae of two individuals meet and fuse. The resulting fungus then has cells with two nuclei. The hyphae then produce haploid spores which then grow into new haploid hyphae.

·   The above ground structure that we call a mushroom is actually the reproductive structures. Spores produced in the mushroom are dispersed and grow into new individuals. Spores are non-motile, unlike the gametes of plants and animals.

· Spores are dispersed over great distances by wind, insects, and animals.