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Applied Biology - Week 6 - Lecture 1 (Fungi are heterotrophs that feed by…
Applied Biology - Week 6 - Lecture 1
Fungi are heterotrophs that feed by absorption
despite their diversity, they share key traits
absorb nutrients form outside the body
Use enzymes to break down a large variety of complex molecules into smaller organic compounds
master of external absorptions
Versatility of these enzymes contributes to fungi's ecological success
breakdown plant material, animal material, other synthetic materials = jet fuel
Fungi exhibits diverse lifestyles
decomposers
parasites
mutualists
Body structures
most common structures are multi cellular filaments ans single cells (yeast)
Grow as filaments or yeast
Morphology enhances their ability to absorb nutrients
consist as hyphae = threads of fungi
high surface area to volume ratio
can be branched
fanning structure
Specialised hyphae in Mycorrhizal = unique fungi have specialised hyphae called haustoria that allow them to penetrate the tissues of their host
Cell walls are made of chitin instead of cellulose
Mycelium = mass of hyphae
most hyphae are divided into cells by septa
Coenocytic = no cross walls separating = free ranging nuclei, no one cell one nucleus
Ectomycorrhizal fungi = form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex
Arbuscular mycorrhizal fungi = extend hyphae through the cells walls of the root cells and into tubes formed by invagination of the root cell mebrane.
Mycorrhizae = mutually beneficial relationship between fungi and plant roots
Mycorrhizal fungi deliver phosphate ions and minerals to plants
Most vascular plants have mycorrihizae
Fungi produce spores through sexual or asexual life cycles
Fungi propagate themselves by producing vast numbers of spores either sexual or asexual plant cycles
Sexual Reproduction
nuclei are usually haploid with the exception of transient diploid stages during sexual life cycles
Requires fusion of hyphae from different mating types
Uses sexual signalling molecules called pheromones to communicate their mating type
Plasmogamy is the union of cytoplasm form two parent mycelia
haploid nuclei from each parent do not fuse right away; they coexist in the mycelium called a heterokaryon
Haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic
A long time may pass before the occurrence of nuclear fusion
during karyogamy, the haploid nuclei fuse, producing haploid spores
paired processes of karyogamy and meiosis produce genetic variation
Asexual Reproduction
Many fungi can reproduce asexually
moulds produce haploid spores by mitosis and from visible mycelia
yeast = instead or producing spores, yeast reproduce asexually by simple cell division and the pinching of "bud cells" from a parent cell
Some fungi can grow as yeasts and as filamentous mycelia
Many moulds and yeast have no known sexual stage
fungi are re classified once their sexual stage is discovered
The ancestor of fungi was as aquatic, single-celled flagellated protist
Fungi and animals are more closely related to each other then they are to plats or other eukaryotes
Fungi, animals and their protistan relatives form the opisthokonts
DNA evidence suggest that
Fungi are most closely related to unicellular nucleariids
Animals are most closely related to unicellular choanoflagellates
Multicellularity arose separately in animals and fungi
Oldest fossil of fungi are only 460 million years old
Are Microsporidia Fungi?
Microsporidia are unicellular parasites of animals and protists
They are tiny organelles derived from mitochondria but not conventional
Molecular comparison indicate they are fungi or are closely related to fungi
The move to land
Fungi were among the earliest colonisers of land and formed mutualistic relationships with early land plants
Fungi have radiated into a diverse set of lineages
Molecular analyses have helped clarify evolutionary relationships among fungal groups, although area of uncertainty remain
Chytrids
found in freshwater and terrestrial habitats
decomposers, parasites or mutualists
evidence supports that chytrids diverged early in fungal evolution
Have flagellated spores called zoospores
Zygomycetes
exhibit great diversity
include fast growing moulds, parasites and commensal symbionts
Coenocytic
Asexual sporangia produce haploid spores
Glomeromycetes
Form arbuscular mycorrhizae
Ascomycetes
produce sexual spores in saclike asci contained in ascocarps
Live in marine, freshwater and terrestrial
are commonly called sac fungi
vary in size and complexity from unicellular yeasts to elaboarate
Basidiomycetes
include mushrooms, puffballs and shelf fungi, plat parasites
clublike structure
transient diploid stage in the life cycle
decomposers of wood
can produce "fairy rings"
Fungi play key roles in nutrient cycling, ecological interactions and human welfare
Decomposers
efficent decomposers
organic material including cellulose and lignin
perform essential recycling of chemical elements
also used in bio remediation prjoects
Mutualists
with plants, algae, cyanobacteria and animals
profound ecological effects
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
Animal symbiosis
share digestive services
help breakdown plant material in guts if animals
Lichens = symbiotic association between a photosunthetic microorganism and a fungus
held together by hyphae
photosynthtic component = cynobacteria
fungal component = ascomycete
Algae and cynobacteria occupy an inner layer below the lichen surface
Pathogens
30% of fungal species
attack food crops are toxic to humans
Ascomycete
animals are less susceptible to parasitic fungi
mycosis
Practical uses
humans eat it
production of antibiotics
Mushrooms
diverse and widespread
Essential for well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients
100,000 species have been identified
Actually 1.5 million species of fungi
