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BIO153H5 (146)
Chapter 31

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University of Toronto Mississauga
Christoph Richter

Chapter 31 NotesAlong with land plants and animals fungi are one of the major lineages of large multicellular eukaryotes that occupy terrestrial environmentsFungi that absorb nutrients from dead organisms are worlds most important decomposers Without fungi dead tree trunks and branches would pile up on Earths surface while the nutrients bound within them would be unavailable to primary producers Other fungi specialize in absorbing nutrients from living organisms When fungi absorb these nutrients without providing any benefit in return they lower the fitness of their host and act as parasites The vast majority of fungi that live in association with other organisms benefit their hosts they are called mutualists Plants are trading sugar they manufacture for nitrogen or phosphorous atoms that are available from fungiFungi are the master traders and recyclers in terrestrial ecosystems Some fungi release nutrients from dead plants and animals others transfer nutrients they obtain to living plantsBecause they recycle key elements such as carthey transfer key nutrients to plants fungi have a profound influence on productivity and biodiversityFungi that live in close association with plant roots are said to be mycorrhizal Fungi that make their living by digesting dead plant material are called saprophytes Wood grows when stems grow in girth by adding layers of ligninrich vascular tissueWhen trees die fungi are the organisms that break down wood into sugars and other small organic compounds Fungi use these molecules as food When fungi die or are eaten the molecules are passed along to a wide array of other organisms Two basic components of the carbon cycle on land1The fixation of carbon by land plantsmeaning that carbon in atmospheric CO2 is reduced to cellulose lignin and other complex organic compounds in the bodies of plants2The release of CO2 from plants animals and fungi as the result of cellular respirationmeaning the oxidation of glucose and production of the ATP that sustains lifeFungi connect the 2 parts of the cycle for most carbon atomsIf fungi had not evolved the ability to digest lignin cellulose soon after land plants evolved the ability to make these compounds carbon atoms would have been sequestered in wood for millennia instead of being rapidly recycled into glucose molecules and CO2 Terrestrial environments would be radically different than they are today and probably much less productiveOnly about 31 species of fungi cause disease in humansCompared to virus bacteria and protists fungi infections are low in humansFirst antibiotic penicillin isolated from fungusMajor destructive impact that fungi have on people is through food supplyFungi also have important positive impacts on human food supplyMushrooms are consumed in many cultures in the industrialized nations they are used in sauces salads and pizzaThe yeast Saccharomyces cerevisiae was domesticated thousands of years ago today it and other fungi are essential to manufacture of bread soy sauce tofum cheese beer wine whiskey and other products In most cases domesticated fungi are used in conditions where the cells grow via fermentation creating byproducts like CO2 that causes bread to rise and beer and champagne to fizzEnzymes derived from fungi are used to improve the characteristics of foods ranging from fruit juice and candy to meatOnly 2 growth forms occur among fungi1Singlecelled forms called yeasts 2Multicellular filamentous structures called myceliaMost fungi form mycelia and this body type is so fundamental to the absorptive mode of life2Researchers discovered a mycelium growing across 65 km in Oregon This is an area substantially larger than most uni campuses Individuals weight at hundreds of tonnes and its age at thousands of years making it one of the largest and oldest organisms knownMycelia constantly grow in the direction of food sources and die back in areas where food is running out The body shape of a fungus can change almost continuously throughout its lifeIndividual filaments that make up a mycelium live on average only about 5 days The filaments within a mycelium are called hyphae
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