Fial ]] Flashcards
Fungus overview
Fungi are diverse and widespread
- They are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients
- About 100,000 species of fungi described
- It is estimated there are actually 1.5 million species of fungi
Fungi body structure
- Most fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of organelles
- Coenocytic fungi
lack septa and have a continuous cytoplasmic mass with hundreds or thousands of nuclei
Specialized Hyphae in Mycorrhizal Fungi
haustoria
allows them to penetrate tissues of their host
Sexual Reproduction for fungi
- Plasmogamy
- In most fungi, haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon
- In some fungi, haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic
karyogamy
- Plasmogamy
the union of cytoplasm from two parent mycelia
Karyogamy
nuclear fusion
- During karyogamy, haploid nuclei fuse, producing diploid
cells - Diploid phase is short-lived and undergoes meiosis, producing haploid spores
- The paired processes of karyogamy and meiosis produce genetic variation
Asexual Reproduction
many fungi can reproduce asexually
- Moulds produce haploid spores by mitosis and form
visible mycelia
Other fungi that
reproduce asexually
are yeasts, which are
single cells
- yeasts reproduce
asexually by simple cell
division and pinching of
“bud cells” from a parent cell - Yeasts can reproduce
sexually as well
not as common
haploid
spores are produced by mitosis
- Fungi and animals are more closely related to-
each other than they are to plants or other eukaryotes
- Fungi, animals, and their protistan relatives form-
the opisthokonts clade
Chytrids
(phylum Chytridiomycota)
found in terrestrial, freshwater, and marine habitats
They can be decomposers, parasites, or mutualists
- Chytrids are unique among fungi in having flagellated spores, called zoospores
The zygomycetes
(phylum Zygomycota)
They include fast-growing moulds, parasites, and
commensal symbionts
- Life cycle of black bread mould (Rhizopus stolonifer) is fairly typical of the phylum
- Its hyphae are coenocytic
- Asexual sporangia produce haploid spores
- Fungi exhibit diverse lifestyles
– Decomposers
– Parasites
– Mutualists
- Glomeromycetes
(phylum Glomeromycota)
were once considered zygomycetes
They now classified in a separate clade
- form arbuscular mycorrhizae
Ascomycetes
(phylum Ascomycota)
live in marine, freshwater, and terrestrial habitats
produce sexual spores in saclike asci contained in fruiting bodies called ascocarps
- Commonly called sac fungi
vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels
include plant pathogens, decomposers, and symbionts
reproduce asexually by enormous numbers of asexual spores called conidia
How do conidias (assexual spores) differ from those within the zygomycetes
Conidia are not formed inside sporangia; they are
produced asexually at the tips of specialized hyphae called conidiophores
- Neurospora crassa, a bread mould, is a model organism with a well-studied genome
Basidomycetes
(phylum Basidiomycota)
include mushrooms, puffballs, and shelf fungi, mycorrhizae, and plant parasites
The phylum is defined by a clublike structure called a
basidium, a transient diploid stage in the life cycle
- Basidiomycetes also called club fungi
- Many basidiomycetes are decomposers of wood
- Life cycle of basidiomycete usually includes long-lived
dikaryotic mycelium
In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies
called basidiocarps
Fungi interact with other organisms as-
decomposers, mutualists, and pathogens
Fungi as Decomposers
Fungi are efficient decomposers of organic material including cellulose and lignin
- They perform essential recycling of chemical elements between the living and nonliving world
- Approaches to use fungi in bioremediation projects are
being developed
Fungi as Mutualists
Fungi form mutualistic relationships with plants, algae, cyanobacteria, and animals
- All of these relationships have profound ecological effects
Fungus-Plant Mutualisms
Mycorrhizae are enormously important in natural ecosystems and agriculture
- Plants harbour harmless symbiotic endophytes, fungi that live inside leaves or other plant parts
- Endophytes make toxins that deter herbivores and defend against pathogens
- Most endophytes are ascomycetes
Fungus-Animal Mutualisms
Some fungi share their digestive services with animals
- These fungi help break down plant material in the guts of cows and other grazing mammals
Fungus-Animal Symbioses
Many species of ants use the digestive power of fungi by raising them in “farms”
Lichens
A lichen is a symbiotic association between a
photosynthetic microorganism and a fungus
Millions of photosynthetic cells are held in a mass of fungal hyphae
- The photosynthetic component is green algae or cyanobacteria
- The fungal component is most often an ascomycete
The symbioses are so complete that lichens are given scientific names
- Algae or cyanobacteria occupy an inner layer below the lichen surface
Algae in lichen
The algae provide carbon compounds, cyanobacteria also provide organic nitrogen, and fungi provide the environment for growth
- The fungi of lichens can reproduce sexually and asexually
- Asexual reproduction is by fragmentation or formation of soredia, small clusters of hyphae with embedded algae
Lichens are important pioneers on new rock and soil surfaces
Fungi as Pathogens
About 30% of known fungal species are parasites or
pathogens, mostly on or in plants
- Each year, 10% to 50% of the world’s fruit harvest is lost due to fungi
- Some fungi that attack food crops are toxic to humans
Animals are much less susceptible to-
parasitic fungi than
are plants
- The chytrid Batrachochytrium dendrobatidis might be the
cause of the recent decline in amphibians worldwide
septate hypha
divided by septa,
haploid nuclei
what are haustoria
penitrates tissues of the host
zygotic meiosis
-zygote only diploid state so meiosis to make spores
