BIOLOGY

Fungi

Concepts/Ideas/Facts:

1. meiosis in fungi is zygotic
2. most fungi spores are propelled ballistically into the air.
3. tropical soils tend to be positively charged and thus hold phosphorous tightly
4. in heavy acid soils the uptake of nitrogen is enhanced by mycorrhizae as well as to increase the tolerance of plants to heavy-metal poisoning.
5. the evolution of mycorrhizal associations may have been a critical step in allowing colonization of land by plants, given the poor soil (or lack of soil) that would have been available during early Earth history.
6. like animals, fungi store food as glycogen
7. rusts and smuts do not form basidiocarps

Definitions:

1. Fungi – non-motile, primarily terrestrial organisms, fungi are decomposers of the biosphere, which return carbon dioxide to the atmosphere and return nitrogenous compounds and other materials to the soil.  Though some fungi are unicellular, most are filamentous.  The cell wall of fungi is composed of the polysaccharide, chitin, the same material found in the exoskeleton of arthropods.  All parts of a fungi are metabolically active and absorption of nutrients is through the tips of the hyphae.  Glycogen is the primary storage polysaccharide in some fungi.  All fungi have cell walls and produce spores.                                           Fungi are rapidly growing, nonphotosynthetic organisms that characteristically from filaments called hyphae, which may either be setate or aseptate.  In most fungi the hyphae are highly branched, forming mycelium.  Parasitic fungi have specialized hypae (hasuteria) by means of which they extract organic carbon from living cells of other organisms.
2. Hyphae – vegetative filaments of fungi
3. Mycelium – mass of hyphae
4. Lichen – symbiotic associations between fungi and either algal or cynobacterial cells
5. Mycorrhizae – mutually beneficial association between vascular plant roots and fungi.  This occurs in 80% of plants.  Mycorrhzae help plants absorb water and nutrients by forming extensive networks of fungal hyphae in the soil, which increases the surface area in the soil available for absorption.  The fungi releases digestive enzymes and they themselves absorb sugars created by the plant during photosynthesis.
6. Mycologist – scientist who studies fungi
7. Chitin – a polysaccharide, the same material found in the exoskeleton of arthropods
8. Haustoria – specialized hyphae of parasitic fungi that absorb nourishment directly from the cells of other organisms.
9. Septate – divided by a cell wall
10. Septa (septum) – cross walls
11. Coenocytic – contained in a common vessel (many nuclei are found in a common cytoplasm).  Refers to filaments without internal cross walls.  Coenocytes contain may nuclei that move through the cytoplasm.
12. Homothallic – self-fertile
13. Heterothallic – require two genetic strains for sexual reproduction
14. Stolons – arching hyphae that form rhizoids wherever their tips come into contact with the substrate.  Hyphae that grow across the surface of a substrate.
15. Rhizoid – specialized branched root-like extensions (hyphae) of fungi and algae that absorb water, food, and nutrients.  They anchor fungi and algae to a substrate and produce digestive enzymes.
16. Sporangia (sporangium) – hollow unicellular or multicellular structure in which spores are produced.  Sporangia are sac-like structures in which the entire contents are converted to spores.
17. Sporangiophores – sturdy erect branchs (hyphae) that arises from a rhizoid, which bears one or more sporangia at their tips.
18. Spore – asexual reproductive cell, usually unicellular, capable of developing into an adult without fusion with another cell.
19. Anamorph – asexual phase of the life cycle of a fungus
20. Telemorph – sexual phase of a the life cycle of a fungus
21. Heterokaryosis – the occurrence of genetically different nuclei together in a common cytoplasm.  Occurs when genetically different nuclei coexist within a hypha.
22. Parasexuality – occurs when genetically distinct haploid nuclei fuse.  Within the resulting diploid nuclei, chromosomes may associate, and recombination occur, and genetically novel haploid nuclei.  This adds to genetic and evolutionary flexibility.
23. Anthracnose – fungal disease of plants which causes lesions and blackening
24. Miso –soy paste produced by fermenting soybeans with a fungus (Aspergillus oryzae)
25. Antobiotics – substances produced by one living organism that inhibit the growth of other living organisms.
26. Aflatoxins- toxic secondary metabolites produced by certain strains of Aspergillus flavus and A. parasiticus.
27. Polyphyletic – organisms that have been derived from more than one source, not of a single line of evolution.
28. Psilocybin – hallucinogenic chemical, similar to mescaline and LSD, found in Psilicybe mushrooms.
29. Heteroecious – an organism that requires two different hosts to complete its life cycle
30. Autoecious – parasites that require only one host
31. Saprobes – fungi that live on organic material from dead organisms.
32. Decomposer – organisms that break down organic materials
33. Homokaryotic – hypha with genetically similar nuclei
34. Conjugation – sexual reproduction in fungi.  Conjugation occurs when two filaments line up next to each other and touch forming a septa near the tip and exchange enclosed haploid (1N) nuclei creating gametangium that contains several nuclei. Gametangia fuse, then the nuclei fuse in pairs forming a diploid zygote (2N). Each pair contains one nucleus from each mating pair.

Fungal Reproduction:

1. Gametangia – reproductive structures that are directly involved in the production of gametes. Gametangia occur where two opposing mating types of hyphae touch (conjugation). The gametangia then fuse forming a diploid zygosprangium.
2. Sporangia – in zygomycete, reproductive structures that are involved in the production of asexual spores.
3. Conidiogenous Cells – in ascomycetes and some basidiomycetes, reproductive structures that are involved in the production of asexual spores.
4. in many fungi, the nuclear envelope does not disintegrate and re-form but is constricted near the midpoint
5. fungi lack centrioles
6. Spindle Pole Bodies – unique structures which appear at the spindle poles
7. Zygosporangium – the fusion of gametangia

Major Groups of Fungi:

Zygomycetes

1. asexual reproduction by means of spores produced in a specialized sporangia borne on the hyphae.
2. live on decaying plant and animal matter in the soil
3. some are parasites of plants, insects and animals
4. most have coenocytic mycelia (haphae)
5. Zygosporangia – the chief characteristic of the division, zygosporangia are thick-walled sexual structures.

Ascomycota (sac fungi) – the distinguishing characteristic of ascomycota is the ascus

1. most of the blue-green, red, and brown molds, as well as the edible truffles and morels
2. except for the unicellular yeast, most are filamentous
3. perforated septate hyphae, which allow the cytoplasm an nuclei to move through the septal pores.
4. do not produce sporangia
5. have ascus and ascospores

Ascomycota

1. Conidia – mostly multinucleated, asexually produce specialized spores
2. Conidiogenous Cells – cells in ascomycota that form conidia which are borne on the tips of the conidiospores
3. Conidiospores – modified tips of hyphae that holds the conidia
4. Ascus (asci) – saclike structure within which haploid ascospores are formed following meiosis.  A specialized cell in which two haploid nuclei fuse to produce a zygote that immediately divides by meiosis
5. Ascospores – a haploid spore produced within an ascus

6. Ascoma (ascomata) – complex tightly interwoven hyphae that produce ascus
7. Ascocarp – reproductive body of an ascomycete formed when heterokaryotic hyphae grow and intertwine
8. Ascogonium – female gametangium
9. Antheridium – male gametangium
10. Hymenium (hymenial layer) – layer of asci
11. Plasmogany – the fusion of two protoplast, the male antheridium and female ascogonium, in ascomycete reproduction.  Occurs when cells from two hyphae with opposing mating types fuse, but only cytoplasmically.  The two nuclei do not fuse, leading to the formation of a dikaryon cell that gives rise to a mycelium consisting of dikaryons.
12. Trichogyne – outgrowth of the ascogonium which allows the antheridium to pass into the ascogonium.
13. Ascogenous Hyphae – hyphae that begin to grow out of the ascogonium upon the entry of the antheridium into the ascogonium, which allows compatible pairs of nuclei to migrate into them.  Two compatible haploid are created by cell division.
14. Dikaryotic – cell division that creates two compatible haploid nuclei in a cell (each compartment having a pair of haploid nuclei)
15. Monokaryotic – cell division that creates one nuclei in a cell
16. Crozier – hook formed at the tip of the dikaryotic hypha
17. Karygamy – in the ascogenous hyphae, the fusion of the two haploid nuclei to form a diploid nucleus (zygote).  Karyogamy (fusion of nuclei) occurs in sporangia and leads to the formation of diploid cells (zygotes) that immediately undergo meiosis to form spores.
18. Yeast – single-celled ascomycetes in which asexual reproduction occurs by budding, a form of conidia formation.  Sexual reproduction occurs by the formation of asci not enclosed in spore-producing bodies.

Life Cycle of Ascomycetes:  germination of ascospores à mycelium à asexual conidiophores à conidia à sexual reproduction à ascus formation on mycelium à multinucleated gametangia (antheridia and ascogonia) à antheridia (male) pass into à ascogonium à plasmogamy fusion of the two prtoplasts à ascogenous hyphae à dikaryotic cells

Deuteromycota (cinidial fungi) (fungi imperfecti) – artificial group of fungi with no known sexual cycle

1. Anamorph – asexual life cycle
2. reproduce only by means of conidia
3. causes ringworm and athlete’s foot

Lichen:

1. Lichen – mutualistic symbiotic associations mostly between ascomycetes (fungus) and certain genera of green algae or cynobacteria.  They get their food from their photosynthetic partners by surrounding their partner with hyphae and penetrating their cells.  A lichen is morphologically and physiologically different from either organism as it exist separately.  In a lichen the fungi brings its photosynthetic partner under control before the characteristics of the lichen appear.  It might be more appropriate to think of the lichen algae/cynobacteria partnership not as mutualism but as a controlled parasitism by the fungi. The ability of lichen to survive under adverse environmental conditions is related to its ability to withstand desiccation and remain dormant when dry.
2. lichen in symbiotic relationship with photosynthetic cynobacteria produce the fixed nitrogen in soil
3. the fungal partner in lichen plays the major role in determining the form of the lichen
4. fungi found in lichen only live in lichen
5. algae and cynobacteria in lichen can live as free-living species outside the lichen
6. Soredia – reproductive special powdery propagules containing both fungi and algae and/or cynobacteria
7. Isidia – reproductive small outgrowths containing both fungal hyphae and algae and/or cynobacteria
8. lichen reproduce by means of fragments, soredia, and isidia
9. extremely slow growth. 0.1 to 10 millimeters per year (some may be 4,500 years old)
10. live in extreme conditions due to their ability to dry out and exist in a state of “suspended animation” where photosynthesis stops.
11. loose and absorb water rapidly.  Lichen can absorb 3 to 35 times its own weight in water is a short time.
12. photosynthesis in lichen reaches its peak when water content is 65% to 90 % of the maximum the organism can hold.
13. lichen obtain organic carbon from the algae or cynobacteria
14. Haustoria – network of fungal hyphae that penetrate the photosynthetic cells of cynobacteria or algae
15. Appressoria – specialized fungal hyphae that lie along the surface of the photosynthetic cells, penetrating them by means of specialized pegs.
16. Lichen Substances (Lichen Acids) – extracellular secondary metabolic substances produced in lichen by lichen forming fungi.
17. Thallus – body of a lichen

Categories of Lichen

1. Crustose – grow as a layer on the surface of rocks or tress
2. Foliose – “leafy” lichen that are loosely attached to the substrate and have thin, leafy thalli (body).
3. Fruticose (two-fold) – “shrubby” lichen with upright growth

Basidiomycota – the distinguishing characteristic of basidiomycota is their production of basidia.

1. Basidiomycota – mushrooms, toadstools, stinkhorns, puffballs, shelf mushrooms, rusts, and smuts.
2. Basidiospores – spore of the basidiomycetes, produced within and borne on a basidium following nuclear fusion and meiosis
3. Basidium (basidia) – specialized reproductive cell of basidiomycetes, often club-shaped, in which nuclear fusion and meiosis occur.  The basidium is produced at the tip of a dikaryotic hyphae and is the structure in which meiosis occurs.  Each basidium produces four basidiospores
4. Basidioma (basidiomata) – a multicellular, fleshy, spore-producing structure, characteristic of the basidiomycetes, within which basidia are formed.  (basidioma – is a mushroom)
5. mycelium are always septate, with the septa that are perforated
6. Dolipore – inflated, barrel-shaped margin of the pore of the septum
7. Parenthesomes – differentiated membrane caps on either side of a dolipore, except in smuts and rusts.
8. Sterigma – a small, minute projection or protuberance of a basidium, bearing a basidiospore
9. Basidiocarp – reproductive body of a basidiomycete.  A mushroom is a basideocarp with a flattened cap attached to a stem called a stalk.
10. Primary Mycelium – homokaryotic (contain one nuceus), septate hyphae
11. Secondary Mycelium – heterokaryotic hyphae (fused hyphae with nuclei from two mating cells)

Structure of a Mushroom

1. Cap (pileus) – top of the mushroom
2. Stalk (stipe) – trunk (stem) of the mushroom
3. Gills – radiating strips of tissue on the lower surface of the cap, which are lined with hymenium.
4. Volva – sheath at the base of the stipe
5. Gleba – convoluted, external hymenium which produces an unpleasant-smelling, sticky mass of spores.

Mycorrhzae:

1. Mycorrhizae – fungus roots that have an intimate mutually beneficial symbiotic relationship between plant roots and fungi.  Mycorrhizae absorb and transport phosphorous and other trace elements from the soil to plant roots while the fungi obtain carbohydrates from the host plant.
1. Endomycorrhizae (vesicular-arbuscular mycorrhizae or V/A mycorrhizae) – most common mycorrhizae occurring in 80% of all vascular plants.  The fungal component is a zygomycete which is not highly host specific.  The fungal hyphae penetrate the cortical cells of the plant root, where they form minute, highly branched, tree-like structures called arbuscules or swellings called vesicles (intermatrical spores).  Exchange between the plant and the fungi occurs in the arbuscules.  Endomycorrhizae are important in the tropics where phosphorous is tightly bound up in the positively charged soil.
2. Ectomycorrhizae – found in trees and shrubs primarily in the temperate regions.  Ectomycorrhizal associations make trees and shrubs more resistant to harsh, cold, dry conditions.  In ectomycorrhizae, the fungus surrounds but does not penetrate living ells in the roots.  The hyphae grow between the cells of the root cortex, forming a structure called the Hartig net, which surrounds many cortical cells.  The Hartig net functions as the interface between the fungus and the plant.  Ectomycorrhical roots often lack root hairs as the hyphae form mycelial strands that extend into the surrounding soil and carry out the function of root hairs.  Ectomycorrhizae are mostly formed with basidiomycetes and some ascomycetes.