Question 1

Which statement is a correct interpretation of the data in the previous tables?

Accepted Answer

As a cylinder's dimensions increase, its surface area increases at a greater rate than its volume due to the linear and squared terms in the surface area formula compared to the cubic term in the volume formula.

Question 2

-Both axes of the graph are linear. Thus, the shape of the line plotted on this graph most accurately depicts the

Accepted Answer

The volume of a cylinder increases linearly with its length, L, when the radius is constant, resulting in a straight line on a linear graph.

Question 3

A researcher took water in which a Jl population had been thriving, filtered the water to remove all bacterial cells, and then applied the water to the skins of adult amphibians to see if there would subsequently be a reduced infection rate by Bd when frog skins were inoculated with Bd. For which of the following hypotheses is the procedure described a potential test?

Accepted Answer

The procedure described tests the hypothesis that a toxin secreted by Jl cells kills Bd cells. Since the water was filtered to remove all bacterial cells, leaving only substances that could have been secreted by Jl, applying this water tests whether something from Jl (like a toxin) can reduce Bd infection without the physical presence of Jl cells.

Question 4

Which of the following microsporidian features are shared with many other fungi?
1)chitinous cell wall
2)two haploid nuclei per cell
3)polar filament
4)chemoheterotrophy

Accepted Answer

Microsporidia share a chitinous cell wall, chemoheterotrophy, and two haploid nuclei per cell with many other fungi.

Question 5

Which of the following are protists, the organisms thought to share the closest ancestor with the chytrids?

Accepted Answer

Nucleariids are protists that are thought to share the closest ancestor with the chytrids. This is based on molecular and morphological evidence.

Question 6

Sexual reproduction has not been observed in Bd. If its morphology and genetics did not identify it as a chytridiomycete, then to which fungal group would Bd be assigned?

Accepted Answer

Deuteromycetes, also known as Fungi Imperfecti, is the group where fungi that do not have an observed sexual reproduction cycle are traditionally classified. Since sexual reproduction has not been observed in Bd (Batrachochytrium dendrobatidis) and if its morphology and genetics did not identify it as a chytridiomycete, it would be classified under deuteromycetes based on the absence of a known sexual reproduction cycle.

Question 7

When adult amphibian skin harbors populations of the bacterium, Janthinobacterium lividum (Jl), chytrid infection seems to be inhibited. Which of the following represents the best experimental design for conclusively determining whether this inhibition is real?

Accepted Answer

This experimental design allows for direct comparison of the rate of infection between the two populations, one with Jl and one without. It also controls for individual variation in susceptibility to the chytrid infection. Choice A does not allow for comparison to uninfected control amphibians, so it would be difficult to determine whether the Jl is actually protective against the chytrid infection. Choice B only assesses recovery from infection, which could be influenced by factors other than Jl. Choice D introduces a confounding variable of dose, making it difficult to determine whether any differences in survival frequency are due to the presence of Jl or the level of inoculation.

Question 8

The fact that infection by Bd causes lethargy in many infected amphibians can have what effect on efforts to accurately census the numbers of dead or dying amphibians at a particular time, in a particular habitat?

Accepted Answer

A and B are plausible because lethargic, infected amphibians may hide or be more susceptible to predation, both of which could lead to underestimation of their numbers. C is not plausible because lethargy would likely make infected amphibians less observable, not more.

Question 9

The lifestyle of microsporidians is most similar to that of

Accepted Answer

Microsporidians are obligate intracellular parasites that lack mitochondria and rely on their host's machinery for energy production, similar to viruses.

Question 10

For several decades now, amphibian species worldwide have been in decline. A significant proportion of the decline seems to be due to the spread of the chytrid fungus, Batrachochytrium dendrobatidis (Bd). Chytrid sporangia reside within the epidermal cells of infected animals, animals that consequently show areas of sloughed skin. They can also be lethargic, which is expressed through failure to hide and failure to flee. The infection cycle typically takes four to five days, at the end of which zoospores are released from sporangia into the environment. In some amphibian species, mortality rates approach 100%; other species seem able to survive the infection.
-The chytrid sporangia reside within the amphibian epidermal cells. Consequently, which term(s)apply to Bd?
1)ectosymbionts
2)parasites
3)commensals
4)pathogens
5)endosymbionts

Accepted Answer

Bd is a parasite because it lives off the amphibian, causing harm, and a pathogen because it causes disease. It's an endosymbiont because it resides within the cells of the host.

Question 11

Sexual reproduction has not been observed in Bd. A Bd sporangium initially contains a single, haploid cell. Which of the following processes must be involved in generating the multiple zoospores eventually produced by each sporangium?
1)S phase
2)cytokinesis
3)mitosis
4)meiosis

Accepted Answer

To generate multiple zoospores from a single haploid cell, the cell must first replicate its DNA (S phase), then divide its nucleus (mitosis), and finally undergo cytokinesis to split into multiple cells. Meiosis is not involved since the process starts from a haploid cell and sexual reproduction has not been observed.

Question 12

If infection primarily involves the outermost layers of adult amphibian skin, and if the chytrids use the skin as their sole source of nutrition, then which term best applies to the chytrids?

Accepted Answer

Chytrids that infect amphibian skin and use it as their sole source of nutrition are aerobic chemoheterotrophs. This is because they require oxygen for their metabolic processes (aerobic) and they obtain their energy by consuming organic substances (chemoheterotroph), such as the skin of amphibians.

Question 13

If Bd cannot grow properly at temperatures above 28°C (82°F), then, assuming the amphibians can survive, in which time or place should the chytrid infection proceed most rapidly?
1)cooler months
2)warmer months
3)lower altitudes
4)higher altitudes

Accepted Answer

Bd (Batrachochytrium dendrobatidis), the fungus causing chytrid infection in amphibians, thrives in cooler temperatures and struggles at temperatures above 28°C. Cooler months and higher altitudes typically have lower temperatures, providing a more suitable environment for Bd to grow and infect amphibians.

Question 14

Surface area represents the area available for exchange with the environment, whereas volume represents the cytoplasm which requires nutrients and from which waste products (usually toxic)must be removed. Which of the following should provide the most favorable conditions for effective exchange?

Accepted Answer

The answer of Surface area represents the area available for...

Question 15

For several decades now, amphibian species worldwide have been in decline. A significant proportion of the decline seems to be due to the spread of the chytrid fungus, Batrachochytrium dendrobatidis (Bd). Chytrid sporangia reside within the epidermal cells of infected animals, animals that consequently show areas of sloughed skin. They can also be lethargic, which is expressed through failure to hide and failure to flee. The infection cycle typically takes four to five days, at the end of which zoospores are released from sporangia into the environment. In some amphibian species, mortality rates approach 100%; other species seem able to survive the infection.
-Apart from direct amphibian-to-amphibian contact, what is the most likely means by which the zoospores spread from one free-living amphibian to another?

Accepted Answer

Zoospores have flagella that they use to swim and move from one amphibian to another in the surrounding water or on moist surfaces. The other options (A, C, D, E) are not relevant modes of Bd dispersal.

Question 16

Some fungi can exist either as unicellular yeasts or as filamentous hyphae. Which of these forms would be most favorable in an environment where nutrients are limited?

Accepted Answer

A longer filamentous hypha would be most favorable in an environment where nutrients are limited because it can extend into the environment to access more resources, increasing the fungus's ability to absorb nutrients over a larger area.

Question 17

Please refer to the following information to answer the next few questions.
Diploid nuclei of the ascomycete, Neurospora crassa, contain 14 chromosomes. A single diploid cell in an ascus will undergo one round of meiosis, followed in each of the daughter cells by one round of mitosis, producing a total of eight ascospores.
-Each of the eight ascospores present at the end of mitosis has the same chromosome number and DNA content (ng)as each of the four cells at the end of meiosis. What must have occurred in each spore between the round of meiosis and the round of mitosis?

Accepted Answer

Each spore must have undergone DNA replication (S phase) before entering mitosis to maintain the same chromosome number and DNA content as the cells at the end of meiosis. Double fertilization, crossing over, nondisjunction, and autopolyploidy would have altered the chromosome number or DNA content, resulting in different spores.

Question 18

What makes it risky to rely on the presence of chitin in adult amphibian skin as the sole positive test for the presence of chytrids?

Accepted Answer

Both options A and B are correct. Other mycoses can complicate the interpretation of the presence of chitin, and the presence of arthropod ectoparasites can also lead to a positive test for chitin in the skin. However, option C is not a valid explanation because bacterial infections do not produce chitin.

Question 19

Recent genetic studies of the structure of microsporidian genomes, as well as the sequences of their tubulin genes and the gene for RNA polymerase II, indicate that microsporidians are closely related to the fungi. Microsporidians lack flagella, centrioles, peroxisomes, and mitochondria (although they do have degenerate mitochondria, called mitosomes). They have the smallest genome of any eukaryote, and it is a genome that changes quickly. The genome is contained within two haploid nuclei. All microsporidians are obligate intracellular parasites. They use a unique organelle called a polar filament to gain access to the cells of their hosts. One species causes chronic diarrhea in AIDS patients. Another parasitizes Anopheles gambiae, the mosquito that transmits a fatal form of malaria to humans.
-Given the eukaryotic structures they lack, it should be expected that microsporidians also lack

Accepted Answer

The answer of Recent genetic studies of the structure of...

Question 20

Unicellular yeasts can be represented as spheres, whereas filamentous hyphae more closely resemble cylinders. As these two geometric figures increase in size, their surface area-to-volume ratios change. The following tables demonstrate how this ratio changes, first for spheres, and second for cylinders. For the cylinder, girth (i.e., radius, r) will remain constant, whereas length, L, will increase. Note the formulas below the respective tables.
A sphere's change in surface area and volume with increasing radius, r
  
Area of a Sphere = 4r² Volume of a Sphere = 4/3r³
A cylinder's change in surface area and volume with increasing length, L
  
Area of a Cylinder = 2(r²) + 2rL Volume of a Cylinder = r²ᴸ
-As a direct result of increasing surface area in both yeasts and filamentous hyphae, which cell structures/materials must also increase?
1)amount of chitin
2)number of nuclei
3)amount of plasma membrane
4)number of mitochondria
5)amount of peptidoglycan

Accepted Answer

As the surface area of the cell increases, there is a greater need for structural support, which is provided by the cell wall. Yeasts and filamentous hyphae both have chitin in their cell walls, which must increase in amount as the surface area increases. Additionally, the plasma membrane must also increase in amount to cover the larger surface area. Therefore, the correct choices are 1 and 3. The other choices are not directly related to surface area increase.

Quiz 31: Fungi

Which statement is a correct interpretation of the data in the previous tables?

-Both axes of the graph are linear. Thus, the shape of the line plotted on this graph most accurately depicts the

Which of the following microsporidian features are shared with many other fungi? 1) chitinous cell wall 2) two haploid nuclei per cell 3) polar filament 4) chemoheterotrophy

Which of the following are protists, the organisms thought to share the closest ancestor with the chytrids?

Sexual reproduction has not been observed in Bd. If its morphology and genetics did not identify it as a chytridiomycete, then to which fungal group would Bd be assigned?

When adult amphibian skin harbors populations of the bacterium, Janthinobacterium lividum (Jl) , chytrid infection seems to be inhibited. Which of the following represents the best experimental design for conclusively determining whether this inhibition is real?

The fact that infection by Bd causes lethargy in many infected amphibians can have what effect on efforts to accurately census the numbers of dead or dying amphibians at a particular time, in a particular habitat?

The lifestyle of microsporidians is most similar to that of

Sexual reproduction has not been observed in Bd. A Bd sporangium initially contains a single, haploid cell. Which of the following processes must be involved in generating the multiple zoospores eventually produced by each sporangium? 1) S phase 2) cytokinesis 3) mitosis 4) meiosis

If infection primarily involves the outermost layers of adult amphibian skin, and if the chytrids use the skin as their sole source of nutrition, then which term best applies to the chytrids?

If Bd cannot grow properly at temperatures above 28°C (82°F) , then, assuming the amphibians can survive, in which time or place should the chytrid infection proceed most rapidly? 1) cooler months 2) warmer months 3) lower altitudes 4) higher altitudes

Surface area represents the area available for exchange with the environment, whereas volume represents the cytoplasm which requires nutrients and from which waste products (usually toxic) must be removed. Which of the following should provide the most favorable conditions for effective exchange?

Some fungi can exist either as unicellular yeasts or as filamentous hyphae. Which of these forms would be most favorable in an environment where nutrients are limited?

What makes it risky to rely on the presence of chitin in adult amphibian skin as the sole positive test for the presence of chytrids?