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Flashcards in Ch 31 Fungi Deck (42)
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what trait do all fungi share?

they are heterotrophs that absorb their food instead of ingesting it


describe how a saprotrophic fungi obtains nutrients

using chemoheterotrophic extracellular digestion, most often facilitated through the active transport of digested dead or decaying organic matter through endocytosis within the internal mycelium and its constituent hyphae



saprotrophic microscopic fungi



saprotrophic plants or bacterial flora


hypha (pl. hyphae)

in multicellular fungi, tiny filaments which form the body of the organism, constructed as a continuous network of tubular cell walls (composed primarily of the polysaccharide chitin) surrounding the plasma membrane of the cells



An interwoven mass of hyphae that infiltrates the material on which the fungus feeds. The structure of a mycelium maximizes its surface-to-volume ratio, making feeding very efficient. Just 1 cm3 of rich soil may contain as much as 1 km of hyphae with a total surface area of 300 cm2 in contact with the soil. A fungal mycelium grows rapidly, as proteins and other materials synthesized by the fungus move through cytoplasmic streaming to the tips of the extending hyphae. The fungus concentrates its energy and resources on adding hyphal length and thus overall absorptive surface area, rather than on increasing hyphal girth.


a mass of hyphae which extends through a feeding medium is called what?




a long-chain polymer of a n-acetylglucosamine (a derivative of glucose) a characteristic component of the cell walls of fungi, the structure of chitin is comparable to the polysaccharide cellulose, forming crystalline nanofibrils or whiskers in terms of function, it may be compared to the protein keratin (a key structural component of hair and nails).


where is chitin found in the natural world?

a characteristic component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulae of molluscs (an anatomical structure that is used for feeding) , and the beaks and internal shells of cephalopods, including squid and octopuses.


how does chitin assist fungi in the absorption of nutrients?

As a fungus absorbs nutrients from its environment, the concen- trations of those nutrients in its cells increases, causing water to move into the cells by osmosis. The movement of water into fungal cells creates pressure that could cause them to burst if they were not surrounded by a rigid cell wall.


septum (pl. septa)

not possessed in all fungi, septa are dividers in hyphae that contain pores large enough to allow for the passage of ribosomes, mitochondria, and sometimes nuclei to flow from cell to cell


coenocytic fungi

fungi whose hyphae are not divided by septa, a continuous mass of cytoplasm which may contain hundreds or thousands of nuclei, formed by nuclear division without cytokinesis


fungi that do not possess septa in their hyphae are termed what?

coenocytic fungi


what type of fungi possesses cells that divide without cytokinesis?

coenocytic fungi


describe the motility of fungi

Fungi are not motile in the typical sense—they cannot run, swim, or fly in search of food or mates. However, as they grow, fungi can move into new territory, swiftly extending the tips of their hyphae through the cytoplasmic streaming of proteins and other materials synthesized by the fungus.


what are the two most common types of fungal body structures?

Multicellular filaments (hyphae) and single cells (yeasts). Many fungal species can grow as both filaments and yeasts, but even more grow only as filaments; relatively few species grow only as yeasts.


haustorium (pl. haustoria)

specialised hyphae possessed by some fungi that allow nutrient extraction or exchange from host plant cells



a term meaning “fungus roots”, mutually beneficial relationships between fungi possessing haustoria and plant roots.


what is the specialised form of hyphae that allows mycorrhizal fungi to be mutualistic or parasitic?

haustorium (pl. haustoria) specialised hyphae possessed by some fungi that allow nutrient extraction or exchange from host plant cells



As matter decomposes within a medium in which a saprotroph is residing, the saprotroph breaks such matter down into its composites. • Proteins are broken down into their amino acid composites through the breaking of peptide bonds by proteases. • Lipids are broken down into fatty acids and glycerol by lipases. • Starch is broken down into simple disaccharides by amylases. These products are re-absorbed into the hypha through the cell wall via endocytosis and passed on throughout the mycelium complex. This facilitates the passage of such materials throughout the organism and allows for growth and, if necessary, repair.


what are the types of mycorrhizal fungi?

There are two main types of mycorrhizal fungi. • Ectomycorrhizal fungi (from the Greek ektos, out) form sheaths of hyphae over the surface of a root and typically grow into the extracellular spaces of the root cortex • Arbuscular mycorrhizal fungi (from the Latin arbor, tree) extend branching hyphae through the root cell wall and into tubes formed by invagination (pushing inward) of the root cell plasma membrane


What are the respective contributions in a mutualistic mycorrhizal relationship?

Mycorrhizal fungi can improve delivery of phosphate ions and other minerals to plants because the vast mycelial networks of the fungi are more efficient than the plants’ roots at acquiring these minerals from the soil. In exchange, the (autotrophic) plants supply the (heterotrophic) fungi with organic nutrients such as carbohydrates.



haploid cells that form new mycelia (singular mycelium) after germinating


how do fungi generally propagate?

sexually or asexually with many spores



the union of two parent fungal mycelia


explain the "compatibility test" used by some sexually reproducing fungi

Sexual reproduction often begins when hyphae from two mycelia release sexual signal- ing molecules called pheromones. If the mycelia are of dif- ferent mating types, the pheromones from each partner bind to receptors on the other, and the hyphae extend toward the source of the pheromones. When the hyphae meet, they fuse. In species with such a “compatibility test,” this process contributes to genetic variation by preventing hyphae from fusing with other hyphae from the same mycelium or an- other genetically identical mycelium.



In fungal sexual reproduction, after plasmogamy but before karyogamy, parts of the fused mycelium contain coexisting, genetically-distinct but allelically-compatible nuclei and the mycelium is then referred to as heterokaryotic.



A form of heterokaryon in which specifically two genetically-distinct but allelically-compatible nuclei exist in each cell.


how do dikaryons differ from diploids?

As a dikaryotic mycelium grows, the two nuclei in each cell divide in tandem without fusing. Because these cells retain two separate haploid nuclei, they differ from diploid cells, which have pairs of homologous chromosomes within a single nucleus.


what is the difference between a dikaryon and a heterokaryon?

A heterokaryon is a fungal cell which has two or more genetically-distinct but allelically-compatible nuclei, as suggested by this resource, as well as this Wikipedia article. A dikaryon is a fungal cell which has precisely two genetically-distinct but allelically-compatible nuclei, as shown here and here. In this sense, a heterokaryon is a general term, whereas a dikaryon is a specific term. A dikaryon and a trikaryon (although not often seen in literature) are both heterokaryons.