Fungus Chapter 31

What you need to know! The characteristics of fungi Important ecological roles of fungi in mycorrhizal associations, and as decomposers and parasitic pathogens

Introduction

Domain Eukarya Kingdom Fungi Phylum: Myxomycota (slime molds) Phylum: Eumycota (true fungi) class: Phycomycetes class: Glomeromycetes class: Ascomycetes class: Basidiomycetes

Characteristics Fungi are eukaryotes and most are multicellular. Fungi are heterotrophic Animals (not plants) are the closest relatives of fungi.

Role in the Environment Decompose dead organisms (fallen leaves, feces, dead bodies, other organic materials) One of the two major decomposers in the environment: fungi (bacteria is the other) Recycles vital chemical elements back to the environment Some contain enzymes to digest lignin (wood) Most plants depend on mutualistic fungi that help their roots absorb minerals and water from the soil (mycorrhiza) Humans cultivate fungi to eat, produce antibiotics and other drugs, to make bread rise, and to ferment beer and wine.

Symbiosis

Absorption Fungi acquire their nutrients by absorption. Exoenzymes, powerful hydrolytic enzymes secreted by the fungus, digest food outside its body to simpler compounds that the fungus can absorb and use. Some exoenzymes attack the digestive system (toxic to humans) They absorb small organic molecules from the surrounding medium.

Structure Extensive surface area and rapid growth adapt fungi for absorptive nutrition The vegetative bodies of most fungi are constructed of tiny filaments called hyphae that form an interwoven mat called a mycelium.

Structure Fungal mycelia can be huge, but they usually escape notice because they are subterranean. One giant individual Armillaria ostoyae in Oregon is 3.4 miles in diameter and covers 2,200 acres of forest, It is at least 2,400 years old, and weighs hundreds of tons. Fungal hyphae have cell walls. These are built mainly of chitin, a strong but flexible nitrogen-containing polysaccharide, identical to that found in arthropods.

Structure Most fungi are multicellular with hyphae divided into cells by cross walls, or septa. These generally have pores large enough for ribosomes, mitochondria, and even nuclei to flow from cell to cell. Fungi that lack septa (coenocytic fungi) consist of a continuous cytoplasmic mass with hundreds or thousands of nuclei. This results from repeated nuclear division without cytoplasmic division.

Parasitic Fungi Parasitic fungi usually have some hyphae modified as haustoria, nutrient-absorbing hyphal tips that penetrate the tissues of their host. Some fungi even have hyphae adapted for preying on animals.

Planet Earth

Reproduction Fungi reproduce by releasing spores (n) that are produced either sexually or asexually. Distributed by wind, water The nuclei of fungal hyphae and spores of most species are haploid, except for transient diploid stages that form during sexual life cycles. However, some mycelia become genetically heterogeneous –heterokaryotic mycelium- through the fusion of two hyphae that have genetically different nuclei (sordaria) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Reproduction In many fungi with sexual life cycles, karyogamy, fusion of haploid nuclei contributed by two parents (sordaria), occurs well after plasmogamy, cytoplasmic fusion by the two parents. Fig. 31.3

Fungi Review

Phylum: Myxomycophyta (slime molds) Sometimes placed with protists Enormous single cells with thousands of nuclei They swarm together and build fruiting bodies for reproduction using chemical markers

Class: Phycomycetes-Molds Black bread mold Penicillium

Glomeromycetes Symbiotic root fungi -Mycorrhizae Lichens: algae + fungi body

Class: Ascomycota – Sac Fungi Yeast, truffles, sordaria, and ringworm Ergots on wheat – highly toxic Contains Lysergic acid: 40,000 died in 944 in an Epidemic in Europe

Class: Basidiomycota-(mushrooms) Mushrooms, shrooms, shelf fungi, puffballs, etc. May be edible or toxic Depends on the enzymes they have