Fungi

Section 18-2

What is a Fungus?

They are heterotrophic eukaryotes with a cell wall

They obtain food by extracellular digestion and absorption Enzymes are released to break down

food particles outside their bodies Digested molecules are then

absorbed

What is a Fungus? Most are multicellular (except yeast) Can be parasitic or decomposers They look more like plants, but are

technically more like animals: They have cell walls like plants, but the cell

wall is made of chitin not cellulose (chitin is found in the exoskeletons of insects)

They store energy as the starch glycogen, like animals and are heterotrophic

Characteristics of Fungi Evolved around 430 million years ago All multicellular fungi have the same

basic structure: Hypha (pl. hyphae) – a threadlike filament

whose cells have varying numbers of nuclei Mycelium – mass of hyphae that grows into

the food source (this is the part that secretes the enzymes for digestion)

Fruiting body – the reproductive part of the fungus that produces spores

Reproduction in Fungi

Can be asexual: Some produce spores Some reproduce by fragmentation of

hyphae

Reproduction in Fungi

Can be sexual: There are two mating types - +

hyphae and – hyphae When opposite hyphae meet, some of

their filaments fuse Their nuclei then fuse, undergo

meiosis, and produce spores

Types of Fungi

Phylum Zygomycota (called zygomycetes) Also called bread molds or common

molds Reproduction has two phases, one

asexual and one sexual An example is Rhizopus stolonifer

(black mold)

Types of Fungi

Phylum Ascomycota (called ascomycetes) Also called sac fungi 30,000+ species of mildews, molds,

and yeasts Examples include truffles, baker’s

yeast

Types of Fungi

Phylum Basidiomycota (called basidiomycetes) Fruiting bodies form mushrooms

(above ground) Many are delicious, some can be

poisonous

Types of Fungi

Phylum Deuteromycota (called deuteromycetes) Also called “imperfect” fungi because

scientists have never been able to identify the sexual stage of their life cycle

Example is Penicillium, which is used to make the antibiotic penicillin; also the fungus that causes athlete’s foot

Lichens Look like moss, usually seen growing on

tree trunks or rocks Not actually a single organism – represents

a symbiotic partnership between a fungus and some photosynthetic organism, like a bacterium or algae

The autotroph performs photosynthesis, which provides nourishment for the fungus

The fungus provides the autotroph with water and minerals that it removes from the rock or the tree