Ch 31 Fungi

Question 1

what trait do all fungi share?

Answer 1

they are heterotrophs that absorb their food instead of ingesting it

Question 2

describe how a saprotrophic fungi obtains nutrients

Answer 2

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

Question 3

saprobe

Answer 3

saprotrophic microscopic fungi

Question 4

saprophyte

Answer 4

saprotrophic plants or bacterial flora

Question 5

hypha (pl. hyphae)

Answer 5

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

Question 6

mycelium

Answer 6

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.

Question 7

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

Answer 7

mycelium

Question 8

chitin

Answer 8

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).

Question 9

where is chitin found in the natural world?

Answer 9

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.

Question 10

how does chitin assist fungi in the absorption of nutrients?

Answer 10

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.

Question 11

septum (pl. septa)

Answer 11

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

Question 12

coenocytic fungi

Answer 12

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

Question 13

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

Answer 13

coenocytic fungi

Question 14

what type of fungi possesses cells that divide without cytokinesis?

Answer 14

coenocytic fungi

Question 15

describe the motility of fungi

Answer 15

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.

Question 16

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

Answer 16

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.

Question 17

haustorium (pl. haustoria)

Answer 17

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

Question 18

mycorrhizae

Answer 18

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

Question 19

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

Answer 19

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

Question 20

saprotroph

Answer 20

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.

Question 21

what are the types of mycorrhizal fungi?

Answer 21

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

Question 22

What are the respective contributions in a mutualistic mycorrhizal relationship?

Answer 22

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.

Question 23

spores

Answer 23

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

Question 24

how do fungi generally propagate?

Answer 24

sexually or asexually with many spores

Question 25

plasmogamy

Answer 25

the union of two parent fungal mycelia

Question 26

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

Answer 26

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.

Question 27

heterokaryon

Answer 27

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.

Question 28

dikaryon

Answer 28

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

Question 29

how do dikaryons differ from diploids?

Answer 29

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.

Question 30

what is the difference between a dikaryon and a heterokaryon?

Answer 30

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.

Question 31

how long between plasmogamy and karyogamy?

Answer 31

Hours, days, or (in some fungi) even centuries may pass between plasmogamy and the next stage in the sexual cycle, karyogamy. During karyogamy, the haploid nuclei contributed by the two parents fuse, producing diploid cells. Zygotes and other transient structures form during karyogamy, the only diploid stage in most fungi. Meiosis then restores the haploid condition, ultimately leading to the formation of genetically diverse spores. Meiosis is a key step in sexual reproduction, so spores produced in this way are sometimes referred to as “sexual spores.”

Question 32

karyogamy

Answer 32

During karyogamy, the haploid nuclei contributed by the two parents fuse, producing diploid cells. Zygotes and other transient structures form during karyogamy, the only diploid stage in most fungi. Meiosis then restores the haploid condition, ultimately leading to the formation of ge- netically diverse spores.

Question 33

roughly how many species of fungi are known to only reproduce asexually?

Answer 33

20,000

Question 34

molds

Answer 34

Many fungi reproduce asexually by growing as filamentous fungi that produce (haploid) spores by mitosis; such species are informally referred to as molds if they form visible mycelia.

Question 35

describe the general life cycle of a fungi that is able to reproduce both sexually and asexually

Answer 35

Question 36

how do molds reproduce?

Answer 36

Molds typically grow rapidly and produce many spores asexually, enabling the fungi to colonize new sources of food. Many species that produce such spores can also reproduce sexually if they happen to contact a member of their species of a different mating type.

Question 37

how do yeasts reproduce?

Answer 37

Instead of producing spores, asexual reproduction in yeasts occurs by ordinary cell division or by the pinching of small “bud cells” off a parent cell (shown). As already mentioned, some fungi that grow as yeasts can also grow as filamentous mycelia.

Question 38

deuteromycetes

Answer 38

Mycologists have traditionally lumped all fungi lacking sexual reproduction into a group called deuteromycetes (from the Greek *deutero*, second, and *mycete*, fungus). Whenever a sexual stage is discovered for a so-called deuteromycete, the species is reclassified in a particular phylum, depending on the type of sexual structures it forms. In addition to searching for sexual stages of such unassigned fungi, mycologists can now use genomic techniques to classify them.

Question 39

nucleariids

Answer 39

Molecular evidence indicates that the nucleariids, a group of single-celled protists, are the closest living relatives of fungi. The three parallel lines leading to the chytrids indicate that this group is paraphyletic

Question 40

breifly describe the ancestor of fungi

Answer 40

The ancestor of fungi was an aquatic, single-celled, flagellated protist. Data from both paleontology and molecular systematics offer insights into the early evolution of fungi. As a result, systematists now recognize that fungi and animals are more closely related to each other than either group is to plants or most other eukaryotes.

Question 41

opisthokonts

Answer 41

name refers to the posterior (opistho-) location of the flagellum in these organisms, DNA sequence data indicate that the fungi, the animals, and their protistan relatives—form a clade called the opisthokonts.