fungi. shared characteristics distinctive fungal features – fungi are heterotrophs. – fungi have...
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Shared Characteristics• Distinctive fungal features
– Fungi are heterotrophs.– Fungi have several cell types.– Some fungi have a dikaryon stage.
Two haploid cells coexisting in a single cell (dikaryon) before fusion to form nucleus (diploid)
– Fungi have cell walls that include chitin.– Fungi undergo nuclear mitosis.
In mitosis, nuclear membrane does not breakdown, mitosis occurs in the nucleus
The Body of a Fungus
• Fungi exist mainly in the form of slender filaments (hyphae).
– long chains of cells joined end-to-end divided by cross-walls (septa)
rarely form complete barrier
cytoplasm freely streams in hyphae
– mycelium - mass of connected hyphae
grows through and penetrates substrate
The Body of a Fungus
• Fungi cell walls are formed of polysaccharides and chitin.
– not cellulose like those of plants• Mitosis is unique.
– nuclear envelope does not break down and re-form
spindle apparatus formed within spindle plaques take place of centrioles
How Fungi Reproduce
• Differ from most animals and plants in that each compartment of hypha can contain one, two or more nuclei
– monokaryotic - each compartment has a single nucleus
– dikaryotic - two distinct nuclei within each hyphae compartment
How Fungi Reproduce• Fungi are capable of both sexual and asexual
reproduction.– Fungi reproduce sexually after two hyphae
of opposite mating type fuse. in some fungi fusion two haploid cells
immediately results in diploid cell (2n) basidiomycetes and ascomycetes have
dikaryotic stage (1n + 1n) before parental nuclei fuse to form diploid nucleus
Four Major Groups of Fungi
• Four major groups– Chytridiomycota– Zygomycota– Basidiomycota– Ascomycota
Zygomycota
• includes common bread molds• produces temporarily dormant zygosporangia• sexual reproduction occurs by fusion of
gametangia• asexual reproduction most common
– hyphae produce clumps of erect stalks - sporangiophores
form sporangia
Ascomycota
• Very large group including yeasts, common molds, and morels
• Named for reproductive structure ascus– haploid zygotic nucleus formed within– asci differentiated with ascocarp
• Asexual reproduction takes place in conidia spores at the end of conidiophores.
Ascomycota
• Yeasts– unicellular - most reproduction is asexual
and takes place by cell fission or budding ferment carbohydrates play a leading role in genetic research
Basidiomycota
• Most familiar fungi (mushrooms, toadstools, puffballs, rusts, and smuts)
– named for characteristic sexual reproductive structure, basidium
• Four haploid products of meiosis incorporated into basidiospores
• Mycelium made up of monokaryotic hyphae is called primary mycelium.
– fusion of different mating types forms dikaryotic, secondary mycelium.
Ecology of Fungi
• Mutualistic associations– lichens - fungi and green algae– mycorrhizae - fungi and plant roots
Lichens
• Lichens are symbiotic associations between a fungus and a photosynthetic partner.
– usually ascomycetes Specialized fungal hyphae penetrate
photosynthetic cells and transfer nutrients to fungal partner.
Durable fungus, combined with photosynthetic properties, has enabled lichens to invade harsh climates.
– extremely sensitive to pollutants
Mycorrhizae
• Roots of about 90% of all kinds of vascular plants are involved in mutualistic symbiotic relationships (mycorrhizae).
– arbuscular mycorrhizae - fungal hyphae penetrate outer cells of plant root
most common– ectomycorrhizae - hyphae surround, but
do not penetrate, cell walls of roots