NOTES FOR BIOLOGY 1002

SECTIONS 004, 005, 006

Spring 2006

DR. STEVEN POMARICO

CHAPTER 24

FUNGI

         The Kingdom Fungi consists of organisms that are eukaryotic and mainly multicellular. They are all heterotrophic decomposers that obtain their food by absorption.

While all fungi use absorption to obtain their food, there are three variations with respect to the food type:

         Saprobes - decomposers of dead material (most fungi fall into this group)

         Two types of symbiotes

                   Parasitic - fungi that live on living organisms

                             Dutch elm disease, Corn smut, Athletes foot,

                                       Jock Itch, Yeast infections

                   Mutualistic - fungi live interdependently with photosynthetic organisms

                              Lichens and mycorrhizae

Most members of the Kingdom Fungi have the following characteristics:

         Spores

         Mycelium

         Hyphae (singular hypha)

The general life cycle of fungi involves the production of spores

         We’ve used this term before as a structure which is primarily a “resting state”

For fungi the spore is a haploid cell, which can grow directly into a hyphae

         Mycelium -is the feeding network of a fungus.

This network may be very large but is usually underground or within the surface of a decaying organism.

The mycelium is composed of a woven mesh of hyphae

         Hyphae - the threadlike filaments of a fungus.

These filaments are the building structure of the mycelium. They consist of a tubular cell wall surrounding a plasma membrane and cytoplasm.

There have been over 56,000 fungal species identified and more are added each year.

We will consider four of the major linages of the Kingdom Fungi.

         Zygomycetes - Division Zygomycota

         Sac fungi - Division Ascomycota

         Club fungi - Division Basidiomycota

An additional mixed species group is also part of Kingdom Fungi.

         Imperfect fungi

         Chytrids

The main classification criteria for these groups are the differences in the sexual life cycle.

The Club fungi>

         -named for the “club” shaped: reproductive structure called a basidia (See fig

24.3) which produces basidiospores.

         -usually reproduce sexually (See fig 24.4)

         -the mycelium of this group may grow very large and occasionally produce a                 fairy ring at the circumference.

         -includes the common mushroom and relatives, also shelf fungi, puffballs,                    rusts and smuts

The Zygomycetes>

         -named for the zygospore, which has a thick cell wall. The zygospore is                    produced from the fusion of two different haploid mating types

                             (See fig 24.5).

         -usually only goes through asexual reproduction, involving haploid spores                    which grow directly into sporangia (spore producers). 

         -include Black bread mold and dung fungus

The Sac fungi>

         -named for the sac or ascus (See fig. 24.6), which contains several haploid

ascospores.

         -both sexual and asexual reproduction are common       

-include penicillin fungus (see fig. 20-15), most yeast (good yeast -bread and beer as well as bad yeast - vaginal infections), powder mildew of rye

                              (LSD), Dutch Elm disease and truffles.

The Chytrids>

         -characterized by swimming flagellated spores (similar to water molds).

The Imperfect fungi>

         -named for the apparent complete lack of sexual reproduction in the life cycle.

-includes athlete’s foot fungus, and Bleu cheese fungus

Some important symbiotic relationships involve fungi

Lichens are formed of a symbiotic relationship between a fungal species and either a cyanobacteria or a unicellular photosynthetic eukaryote (See fig 24.8)

This partnership requires very little in the way of external nutrients and can often be found growing on bare rock or dead wood

Lichens are often the first organisms to appear in the primary succession of a community

Mycorrhizae are a symbiotic relationship between fungi and the roots of a plant (see fig 24.9).

The fungi help send the plant water, minerals, and nutrients (especially phosphorus containing compounds). In exchange, the fungus absorbs some of the sugars the plant produces.