General Biology 101
Chapter Outlines
Starr & Taggert
10th edition
Chapter 24:
Fungi
Intro – Ode to the fungus among us.
Symbiosis – species living together and closely interacting.
Mutualistic interactions include:
1) Lichens – fungus and photosynthetic organisms, e.g. cyanobacteria.
Some have the ability to resist attacks from predators/grazers and some can make antibiotics against bacteria.
Metabolic products from lichens help enrich soil or make new soil.
Lichens are also indicators of poor air quality.
2) Mycorrhiza – (plural mycorrhizae) association of fungi and tree roots.
Fungus contribute the ability to take up important nutrients from the environment e.g. phosphorous and roots contribute some sugars to fungus.
This is a “trade off” relationship.
Some fungi are decomposers i.e. they break down organic compounds in their environment.
Fungi consume nutrients by “extra-cellular digestion and absorption.” This means essentially that they secrete enzymes from their cells and digest it outside their body. After the substances are broken down they then get absorbed.
Section 24.1 – Characteristics of Fungi
1) Heterotrophic
2) Saprobic – take nutrients from non-living organic matter and cause its decay.
3) Some are parasitic
4) 56,000 known species
Zygomycetes (some molds)
Ascomycota – sac fungi
Basidomycota – club fungi
Chytrids (some water molds)
“Imperfect” fungi
Key features of fungal life cycle
- Reproduce asexually often
- Can reproduce sexually as well.
- Form spores (reproductive cells that germinate after dispersal)
- Mycelium – branches of filaments made of hyphae, with interconnecting cytoplasm.
Section 24.2
Club Fungi – include the mushrooms, shelf fungi, coral fungi and puffballs.
Perhaps the most familiar group.
Features some members that are:
- Deomposers
- Symbionts with tree roots
- Destroy crops e.g. rusts and smuts
- Highly toxic e.g. Death cap mushrooms
Ø Note: the honey mushroom or Armillaria ostoyae of Oregon may be the largest mushroom, occupying over 2000 acres, to an average depth of 3 feet. It is the LARGEST known organism. This form can actually kill trees.
Example of fungal life cycle:
Mushrooms (reproductive bodies above ground)
These may have gills that make:
à Spores – that disperse and germinate and give rise to:
à Haploid mycelium – which spreads, where the cytoplasm of two compatible strains may fuse and make a:
à Dikaryotic mycelium (mushroom forms).
Nuclei fuse and become a:
à Zygote > meiosis > haploid spores.
…..the process then repeats.
Section 24.3
A fungus can make either sexual or asexual spores (or both) depending upon resources such as nutrients and environmental conditions. Usually dispersed by air currents.
I. In zygomycetes”
Parasitic species can feed on insects.
Can be molds on bread.
Can reproduce sexually – to make a diploid zygote
Zygospore – a thick-walled sexual spore enclosed in a thin, clear covering, makes a spore sac called a sporangium. Asexual spores are found in the sporangium perched on a stalk.
II. Producers of Ascospores
Ascospores are sac-shaped cells, the structure is called an ascus (pl is asci).
Hyphae can become interwoven and form cups, globes and flask shaped objects e.g. morels and yeast.
Well known ascospores
Aspergillus – makes citric acid used in soft drinks and ferments soy beans for soy sauce.
Penicillium – flavor some forms of cheeses.
Many food spoiling forms are conidial stage of multi-celled sac fungi.
Saccharomyces cerevisiae is the yeast that leavens bread.
Also important for wine and beer making.
III. Imperfect fungi
These fungi do not have recognizable spores and are awaiting further classification work, but in this group is a predatory species that hunts soil nematodes (a type of worm).
Section 24.4
The Symbionts Revisited
I. Lichens
A mix of fungi intertwined with one or more photosynthetic species.
Mycobiont - Fungal part
Photobiont – Photosynthetic part (usually green algae or cyanobacteria).
There are 13,500 known types of lichens
Nearly half incorporate a sac fungi.
Usually the fungus is the largest component (in terms of size/volume).
Sometimes more than one fungus may be present.
II. Mycorrhizae
Associations of fungus with young tree roots.
Without this association plants don’t grow as well.
Ectomycorrhizae – a dense net of fungal hyphae around living cells in roots but they do not penetrate the roots.
Endomycorrhizae – fungal hyphae that associate with and penetrate plant cells.
Wild mushroom populations are declining; it is currently thought that the decline is due to increasing air pollution. If fungi are not successful does that mean the forest plants i.e. young saplings will also not be successful?
Section 24.5
Table 24.1 Gives a list of some of the pathogenic or toxic fungi forms.
Examples of fungi that can cause harm to humans include:
- Athletes foot – Epidermophyton floccosum
- Mildew (such as on crops and flowers)
- Histoplasmosis (a lung infection)
- Sinus, ear and lung infections
- Ergotism that infects rye plants – Claviceps purpurea
- Chestnut blight