Fungi Flashcards
Fungi
monophyletic group of eukaryotic heterotrophs closely related to animals
- cells contain nucleus, mitochondria, complex system of internal membrane
- fungal cells do not have chloroplasts or chlorophyll
- lineage that led to fungi + animals is thought to have diverged from the future-plants lineage during the Proterozoic Eon
- believed to diverge from future-animals lineage near end-Proterozoic
- FUNGI ARE MORE CLOSELY RELATED TO ANIMALS THAN PLANTS
- common ancestor of all fungi was likely fungi, flagellated, and single-celled
- the evolutionary relationship between some groups of fungi are not yet resolved
Shared Adaptations/Traits in Fungi
- different species of fungi can be mutualistic, parasitic, or serve as decomposers
- fungi can be multicellular or unicellular and have a wide range of body plans
- all fungi have: heterotrophic eukaryotes, cell walls made up of chitin, and external digestion systems
Heterotrophic Eukaryotes
all fungi must use existing organic compounds as a source of carbon
Chitin Cell Walls
the cell wall provides structural strength to the fungal body
- chitin is a tough polysaccharide that is also a major component of exoskeletons in other organisms
External Digestion
all fungi externally digest food - they excrete digestive enzymes outside of their bodies, and the digested nutrients are then absorbed from the external environment
- fungi do not have internal digestive tracts
Morphology
most fungi are multicellular but some are unicellular; some can switch between the two states depending on environmental conditions
Unicellular Fungi
reproduce via BUDDING, and the new bud separates from the parent cell to form 2 separate, individual cells
Multicellular Fungi
have cells that work together in a body structure called MYCELIUM (plural: mycelia)
- composed of branches of cells (HYPHAE)
- produces reproductive units (SPORES) directly or through a FRUITING BODY
Hyphae
long, branching filamentous thread-like structures that look like roots
- composed of individual cells connected end-to-end in a long branching thread
- depending on the species, they can grow on the surface, in soil or decaying material, or on living tissue
- excrete digestive enzymes into the environment and absorb nutrients released by digestion
Spores/Fruiting Body
the morphology of the reproductive stage varies across fungal species
- some are visible as mushroom fruiting bodies (mushrooms is the only above ground fruiting body and underground hyphae)
- in other fungi, the reproductive stage is microscopic
LIFE CYCLE
some fungi reproduce only asexually but some can reproduce both asexually and sexually via the HAPLONTIC LIFE CYCLE
- the multicellular stage is haploid, and the diploid stage (the fertilized egg) exists as a single cell before undergoing meiosis to produce haploid spores
- in both sexual + asexual reproduction, fungi produce spores that disperse from the parent organism by floating on the wind or attaching to an animal
- the large # of spores released increases the likelihood of landing in an environment that will support growth
Vegetative Growth (Asexual Reproduction)
the mycelium (the fungal body composed of hyphae) is HAPLOID; the mycelium germinates via mitosis from a haploid spores
- the haploid mycelium can continue to grow via mitosis or reproducing asexually via BUDDING, FRAGMENTATION, or by PRODUCING ITS OWN HAPLOID SPORES
Asexual: Budding
controlled growth of a new cell on the side of an existing cell, which detaches
Asexual: Fragmentation
breaking into smaller pieces where each piece can continue growing as an independent organism
Asexual: Producing Spores
a fungi can produce its own haploid spores via mitosis which disperse and grow a new haploid mycelia
- spores produced via mitosis are genetically identical to the parent (ASEXUAL REPRODUCTION!)
Sexual Reproduction
results from the fusing of cells from two mycelia followed by the production of spores by meiosis
THE PROCESS:
1. Plasmogamy + Heterokaryotic Stage
2. Karyogamy
3. Meiosis
4. Germination
Sexual: Plasmogamy + Heterokaryotic Stage
to initiate sexual reproduction, haploid cells from two different mycelium fuse together, sharing their cytoplasm (PLASMOGAMY)
- their nuclei DO NOT FURE and remain independent in a structure that is “HETEROKARYOTIC”
- depending on the species, the heterokaryon grows into a fruiting body or remains microscopic
Sexual: Karyogamy
at this stage, 2 nuclei within a heterokaryotic cell fuse to form a diploid nucleus
- this stage does not grow any new cells or tissue
Sexual: Meiosis
the diploid nucleus undergoes meiosis to produce 4 haploid spores (these spores are a product of sexual reproduction as a result form the meiotic cell division of a diploid cell)
Sexual: Germination
the meiotically produced spores are dispersed by wind or animal to a new environment, where they can germinate into a new mycelium + enter a new cycle of growth (sexual or asexual)
Common Fungal Metabolism Traits
Because of their varied metabolic pathways (listed below) humans use fungi for applications like producing food, antibiotics, medicine, and tools in bioremediation:
1. External Digestion
2. Decomposers
3. Mutualists
4. Parasites
5. Predators
Decomposers
most fungi are decomposers - they derive nutrients from decaying/dead organic material
- fungal decomposers are also called SAPROPHYTIC FUNGI
- fungal digestive enzymes break down insoluble polysaccharides (cellulose + lignin) into absorbable glucose molecules
- fungi decompose matter to release larger, vital elements such as nitrogen and phosphorus
- within decomposers, these nutrients would remain fixed within dead organisms and unavailable for living things
Mutualists
some fungi form mutualistic relationships with plants, where fungi trade water and nutrients for exchange for plant sugars
- MYCORRHIZAL FUNGI (~80-90% of plants rely on them for growth)
Parasites
some fungi are parasitic, infecting either plants or animals
Predators
in environments pour in NITROGEN, some fungi act as predators, trapping small animals like nematodes via a constricting ring within their hyphae that functions as a noose
Symbiosis
the ecological interaction between two organisms that live together
Mutualistic Symbiosis
a symbiotic relationship in which both members of the association benefit
- fungi form these associations with many organisms like cyanobacteria, algae, plants, and animals
Plants + Fungi
- ~80-90% of plants form mutualistic relationships with fungi via their ROOTS (EX: mycorrhizal fungi) to exposes them to more nutrients, nitrogen, and water from decaying organisms in the soil
- in exchange, plants supply the products of photosynthesis (sugars) to fuel the metabolism of fungus
Plants + Fungi History
- in EARLY-PALEOZOIC, there way very little soil and most land on Earth was rock; the combined action of early fungi secreting digestive enzymes coupled with erosion slowly created SOIL (plants needed this soil in the future)
- First land plants were Bryophytes, where early fungal associations with these plants helped provide water + nutrients as these plants lacked TRUE ROOTS
- Seedless Vascular Plants that had true roots had selective advantage over bryophytes because they could anchor and extract water. These roots allowed a greater surface area of contact with fungal partners and more mutualistic exchange
- Over time, these interactions led to the evolution of present day mycorrhizae
