Fungi&Viruses-web-07 - Fungi Overview Although we will...

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Fungi Overview Although we will only spend a few minutes talking about Fungi, I do not want to leave you with the impression that fungi are unimportant. For a human standpoint, fungi are useful as a food source (mushrooms) or something that helps modify food (wine, beer, bread) and they also cause disease. More importantly, fungi are important to the ecology of the earth. They act as decomposers - they breakdown organic materials and recycle chemicals and nutrients into the environment. For example, nearly all plants rely on fungi to provide them with nutrients. Fungi were traditionally classified as plants. The reasoning behind this was two-fold: 1) both plants and fungi are eukaryotes with cell walls, 2) both plants and fungi are relatively immobile. However, there are great many differences between plants and fungi. For example, fungi are heterotrophs that could their food through absorption. Basically, fungi secrete enzymes outside of their cell walls, the enzymes break down food, and the nutrients are absorbed. Of course, most plants are autotrophs, so the mode of nutrient consumption between fungi and plants differs substantially. In the past 10-15 years, molecular phylogenies have help resolved the classification of fungi. The big surprise was the fungi are more closely related to animals than to plants. This finding is recent enough that ten years ago it was common to see basic undergraduate Botany textbooks that include whole sections on Fungi. It would be more appropriate to put a section on Fungi in a Zoology textbook! Extracellular digestion: Fungi are eukaryotic chemoheterotrophs. They get their nutrients from a wide variety of sources, but they all get their nutrients in the same way – via absorption . Absorption is a mechanism by which the fungi have extracellular (or external) digestion. The fungi secrete digestive enzymes outside of their cells. These digestive enzymes degrade large complex molecules - such as cellulose and lignin in plants – into much smaller molecules, such as glucose. These smaller molecules can then be absorbed through the fungal cell wall and be used as a source of nutrition.
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