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Lecture notes of 44 pages for the course Genetic at Mcgillu (Cell Cycle)
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BIOL 111Final Study Notes
FUNGI
Phylogeny
- One of 3 major lineages of large, terrestrial eukaryotes
- Few fossils, evolutionary history hard to study
- First fungi (aquatic) 800-1000 mya
- Colonized land 500 mya (before plants)
- Key innovation: how to extract nutrients in a terrestrial env.
Fungi today
- 110,000 named species
- Taxonomy mostly based on reproductive structures & DNA
- From single cells (yeasts) to huge multicellular structures
- Critical to ecosystem functioning
- Wide range of human uses
- Diseases: athlete’s foot, yeast infections, etc
Largest organism in the world: armillaria ostoyae “honey mushroom”
Defining features
1. Structure: single celled or made of filaments. No complex transport systems. Cell walls
(like plants) but contain chitin (more like animals)
2. Nutrition: absorb food directly from surroundings
3. Reproduction: sexual, asexual, diverse
4. Dispersal: spores
Structures
- Yeasts = single cells
- Mycelia made of hyphae: long, thin filaments
o whole fungi made up of hyphae more compact in fruiting body (mushroom)
- yeast vs bacteria: bacteria are prokaryotes (no membrane enclosed nucleus) and fungi are
eukaryotes
- Hyphae usually separated by cross-walls called septa separate the long hyphae into
compartments and allow the passage of whole organelles and even nuclei
- Fungi (mycelia) are called multicellular organism but they are in a slight grey zone b/c
they don’t have fully compartmentalized cells
- Hyphae are incredibly thin 100x thinner than the thinnest plant root: have huge S.A. to
volume ratio b/c it makes them great at absorbing nutrients but mean they loose material
(esp. water ) v easily only live in moist environments
- Septa have large pores that allow passage of nutrients, even nuclei
- Hyphae are 100x thinner than the thinnest plant root
- Fungi occur mostly in moist habitat
,Nutrition
- Implications of structure for nutrition
o Thin hyphae master absorbers
o Need for moisture often symbiotic (can by symbiotic or parasitic)
- Don’t photosynthesize, secrete digestive enzymes externally
o Saprophytes (eat dead things)
o Symbionts
- Novel methods of absorbing nutrients (moving from food source to food source) drove
fungi diversification
- Key in carbon, nitrogen, phosphorus cycles w/o fungi these cycles would function at a
much reduced rate b/c fungi are the main decomposers of complex organic molecules
- Main decomposers of cellulose & lignen (wood) (most abundant molecules on earth)
o Lignen allows plants to support themselves and grow huge
o Fungi allows for decomposition of lignen (wood) b/c they break it down to get at
the cellulose inside for energy
Nutrition implication: ecology
- Famous symbiosis:
- Lichens
o Fungi + algae or cyanobacteria
o 20,000 species
o 6% of earth’s surface
o Potential asymmetry where the algae could be free-living but the fungi cannot
not completely beneficial to both
- Mycorrhizae
o 80% of angiosperms partner with fungi to get nutrients from soil
o Non-existence of mycorrhizae partners can limit plant species distributions
o Introduction of mycorrhizal partners can enable invasion
o Plants can survive without the fungi, but not as well/ don’t grow as quickly
,Reproduction
- Complicated. Many species reproduce in multiple ways, sometimes during both haploid
and diploid phases
- Asexual
o Fragmentation
o Mycelial breaks and both parts form new organisms
o Vegetative spores (conidia) act like sexual spores (small, spread by wind),
produced on equivalent of fruiting body, no recombination (still asexual)
o Produced on conidiophores
- Sexual
o Often only see sexual reproductive structures (mushrooms/fruiting bodies)
o Very dif. From sex in plants or animals
o E.g. ascomycetes & basidiomycetes (incl. almost all the cap mushrooms) form
monophyletic group
o Compatible individuals fuse their mycelia, to initiate sexual cycle
(anastomosis/plasmogamy)
o Two mycelia fuse, and share nuclei dikaryotic (two-nuclei) stage – this stage
can last for decades = not transient but can be a major component of life cycle
o Basidiomycetes: produce mushroom
o Basidia: specialized end cells of mushroom gills (spore bearing)
o Nuclei fuse meiosis spores
o Mushrooms are more like fruit because spores are akin to seeds
*look at reproductive diagrams
Dispersal
- Unlike hyphae, spores tolerate dry conditions
- Important for dispersal
- Small size facilitates airborne dispersal
- Some have ejection mechanisms (e.g. puffballs)
- Some use animal dispersers (e.g. stinkhorns that attract insects to disperse them)
ALGAE
Phylogeny
- Taxonomy of photosynthesizers is messy
- 1735 Linnaeus classification three kingdoms: plants, animals, fungi
- 1969: five kingdoms: plantae, fungi, animalia, Protista (slightly inaccurate – not a
uniform group), monera
- Current eukaryote phylogeny: plantae (incl. land plants), excavates, rhizaria, unikonts
(incl. animals), Chromalveolata
- “protist”: inlc. Huge diversity of organisms, vast majority of eukaryotes
*ability to photosynthesize found widely in the tree of life: plantae, bacteria, etc
- how did it evolve and spread if its found in many different branches?
, Photosynthesize
- First evolved 3 bya
- First organism to photosynthesize was a bacteria cyanobacteria
- How did eukaryotes get photosynthesis?
o All photosynthetic eukaryotes use chloroplasts (bacteria don’t) development of
chloroplasts closely linked to that of photosynthesis
o Photosystem I and photosystem II evolved in bacteria implies there is a
common ancestor
Endosymbiotic Origin of Chloroplasts
Hypothesis: eukaryotic chloroplasts originated when a protist engulfed a cyanobacteria
Support:
- chloroplasts similar to cyanobacteria and behave somewhat independently of cell – don’t
act totally as integrated part of cell
o Replicate by fission, independently of cell division – doesn’t depend on the speed
at which the cell divides – similar to how bacteria divide
o Manufacture some of their own proteins
o Have their own DNA, organized into circular molecule very similar to those in
some cyanobacteria – both in structure and content
o Peptidoglycan in cell wall of some chloroplasts – also found in some
cyanobacteria
o Have (at least) a double membrane – one from the protist and the other from the
original cyanobacteria
- Extant endosymbiotic cyanobacteria live in cells of protists and animals
How did chloroplasts spread to 4/5 major eukaryote lineages?
- All species in plantae have chloroplasts
- Plantae chloroplasts have double membrane
- Chloroplasts and other protist lineages have more than 2 membranes
Hypothesis:
- Endosymbiosis leading to chloroplasts first occurred in common ancestor of plantae
- Ancestor of other groups acquired chloroplasts via secondary endosymbiosis
Secondary endosymbiosis leads to chloroplast with 4 membranes
1. Photosynthetic protist is engulfed by predatory protist
2. Nucleus from photosynthetic protist is lost
3. Organelle has four membranes
Brown algae (phaeophytes)
- Chloroplasts with 4 membranes
- 1500 – 2000 species
- Multicellular marine organisms
- Individual = thallus (no complex vascular system)
- Brownish colour from carotenoid pigment fucoxanthin used in photosynthesis
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