Question 1

Which of the following characteristics would be most helpful in distinguishing among different species of fungi?

Accepted Answer

While characteristics such as morphology, hyphae structure, and life cycle can provide some information in distinguishing among different species of fungi, DNA sequence is the most reliable and accurate method for identifying and differentiating between fungal species. DNA sequencing allows for the comparison of genetic information and can reveal subtle differences that may not be visible through other methods.

Question 2

The figure depicts the outline of a large fairy ring that has appeared overnight in an open paddock, as viewed from above. The fairy ring represents the furthest advance of this mycelium through the soil. Locations A-D are all 0.5 metres below the soil surface. 
At which location should one find the lowest concentration of fungal enzymes, assuming that the enzymes do not diffuse far from their source and that no other fungi are present in this habitat?

Accepted Answer

The answer of The figure depicts the outline of a...

Question 3

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. If a single, diploid G2 nucleus in an ascus contains 400 nanograms (ng) of DNA, then a single ascospore nucleus of this species should contain how much DNA (ng), carried on how many chromosomes?

Accepted Answer

In meiosis, the diploid number of chromosomes (2n) is halved to the haploid number (n). In this case, the diploid number is 14, so the haploid number is 7. Each round of mitosis produces two daughter cells, each with the same number of chromosomes as the parent cell. Therefore, after one round of meiosis and one round of mitosis, each ascospore nucleus will contain 7 chromosomes.The amount of DNA in a cell is proportional to the number of chromosomes. Therefore, if a single diploid G2 nucleus contains 400 ng of DNA, then a single ascospore nucleus will contain 400 ng / 2 = 200 ng of DNA.

Question 4

Along with bacteria and protozoa, some chytrid fungi live in the digestive tracts of cattle and aid in the digestion of plant matter; thus, all three groups represent potential mutualists with cattle. In an experiment designed to test how much of a contribution to cell wall digestion was made by fungi in one part of the stomach (rumen), Lee et al. fed grain to cattle and then removed samples of the rumen contents. They took these samples to the laboratory and experimentally treated them with various chemicals to produce fractions that contained (A) only fungi, (B) only bacteria, (C) only protozoa, and (D) all of the potential mutualists. They then measured the percent of the cell wall that was degraded (see the figure). 
Degradation rates of cell walls extracted from Orchard grass by the monoculture system to assess the relative contributions of digestion by bacterial (square), protozoan (triangle), and fungal (diamond) systems, and all components (closed circle) as a control. The lowercase letters above the spots indicate statistical significance; mean values with different letters are significantly different (P < 0.05).
-Which of the following reasons provides the best explanation for the use of a control that contained all potential mutualists? Comparison to a fraction that contained all potential mutualists allowed the researchers to ________.

Accepted Answer

The control that contained all potential mutualists allowed the researchers to determine how much each potential mutualist contributed to cell wall degradation by comparing it to the fractions that contained only fungi, bacteria, or protozoa.

Question 5

Rose-picker's disease is caused by the yeast Sporothrix schenkii (S. schenkii). The yeast grows on the exteriors of rose-bush thorns. If a human gets pricked by such a thorn, the yeasts can be introduced under the skin. The yeasts then assume a hyphal morphology and grow along the interiors of lymphatic vessels until they reach a lymph node. This often results in the accumulation of pus in the lymph node, which subsequently ulcerates through the skin surface and then drains.
Suppose that S. schenkii had initially been classified as a deuteromycete. Asci were later discovered in the pus that oozed from an ulcerated lymph node, and the spores therein germinated, giving rise to S. schenkii yeasts. Which of these statements make sense on the basis of this information?

Accepted Answer

The answer of Rose-picker's disease is caused by the yeast...

Question 6

The figure depicts the outline of a large fairy ring that has appeared overnight in an open paddock, as viewed from above. The fairy ring represents the furthest advance of this mycelium through the soil. Locations A-D are all 0.5 metres below the soil surface. 
In which of the following human mycoses should one expect to find a growth pattern most similar to that of the mycelium that produced the fairy ring?

Accepted Answer

The fairy ring in the open paddock is a classic growth pattern of a fungal mycelium, which appears as a circular ring of mushrooms or grass that grows outward from the center. This growth pattern is similar to that of dermatophyte fungi that cause skin mycoses, which often produce circular or annular lesions. Coccidiomycosis, systemic Candida infections, and infections of lymphatic vessels do not typically exhibit this type of growth pattern.

Question 7

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. However, when adult amphibian skin harbours populations of the bacterium Janthinobacterium lividum (Jl), chytrid infection seems to be inhibited.
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 tests whether a toxin secreted by Jl, which would remain in the filtered water, can inhibit Bd infection.

Question 8

The figure depicts the outline of a large fairy ring that has appeared overnight in an open paddock, as viewed from above. The fairy ring represents the furthest advance of this mycelium through the soil. Locations A-D are all 0.5 metres below the soil surface. 
If the fungus that produced the fairy ring can also produce arbuscules, then which of the following is most likely to be buried at location "C"?

Accepted Answer

The answer of The figure depicts the outline of a...

Question 9

Along with bacteria and protozoa, some chytrid fungi live in the digestive tracts of cattle and aid in the digestion of plant matter; thus, all three groups represent potential mutualists with cattle. In an experiment designed to test how much of a contribution to cell wall digestion was made by fungi in one part of the stomach (rumen), Lee et al. fed grain to cattle and then removed samples of the rumen contents. They took these samples to the laboratory and experimentally treated them with various chemicals to produce fractions that contained (A) only fungi, (B) only bacteria, (C) only protozoa, and (D) all of the potential mutualists. They then measured the percent of the cell wall that was degraded (see the figure). 
Degradation rates of cell walls extracted from Orchard grass by the monoculture system to assess the relative contributions of digestion by bacterial (square), protozoan (triangle), and fungal (diamond) systems, and all components (closed circle) as a control. The lowercase letters above the spots indicate statistical significance; mean values with different letters are significantly different (P < 0.05).
-Predict the results if the researchers had used a control that contained no potential mutualists (negative control).

Accepted Answer

The negative control would have very little cell wall degradation because it would lack the potential mutualists (bacteria, protozoa, and fungi) that are known to aid in the digestion of plant matter in the rumen.

Question 10

The figure depicts the outline of a large fairy ring that has appeared overnight in an open paddock, as viewed from above. The fairy ring represents the furthest advance of this mycelium through the soil. Locations A-D are all 0.5 metres below the soil surface. 
Assume that all four locations are 0.5 metres above the surface. On a breezy day with prevailing winds blowing from left to right, where should one expect to find the highest concentration of free basidiospores in an air sample?

Accepted Answer

The answer of The figure depicts the outline of a...

Question 11

A billionaire buys a sterile volcanic island that recently emerged from the sea. To speed the arrival of conditions necessary for plant growth, the billionaire might be advised to aerially sow what over the island?

Accepted Answer

The answer of A billionaire buys a sterile volcanic island...

Question 12

Heterobasidion is a basidiomycete that contributes to mortality of trees. Kuhlman isolated 23 strains of Heterobasidion and applied them to 16 seedlings of 10 different tree species. Partial results of this experiment are shown in the table. (From Kuhlman, E. G. 1970. Seedling inoculations with Fomes annosus show variation in virulence and in host susceptibility. Phytopathology 60:1743-1746. https://www.apsnet.org/publications/phytopathology/backissues/Documents/1970Articles/Phyto60n12_1743.PDF)
% mortality of five host species from five Heterobasidion isolates
$$\begin{array} { | l | l | l | l | l | l | } 
\hline & \text { Isolate } & \text { Isolate } & \text { Isolate } & \text { Isolate } & \text { Isolate } \
\hline \text { Host } & 63 & 117 & 195 & 126 & 118 \
\hline \text { Slash Pine } & 50 & 69 & 94 & 100 & 94 \
\hline \text { Shortleaf Pine } & 75 & 56 & 94 & 94 & 100 \
\hline \text { Red Cedar } & 38 & 32 & 19 & 50 & 25 \
\hline \text { Yellow-Poplar } &0 & 0 & 6 & 6 & 6 \
\hline \text { Sycamore } & 0 & 0 & 0 & 0 & 6 \
\hline
\end{array}$$
-Which of the following conclusions can best be drawn from these results?

Accepted Answer

The data shows variability in mortality rates among different tree species and isolates, indicating that Heterobasidion strains vary in their effect on tree species.

Question 13

Rose-picker's disease is caused by the yeast Sporothrix schenkii (S. schenkii). The yeast grows on the exteriors of rose-bush thorns. If a human gets pricked by such a thorn, the yeasts can be introduced under the skin. The yeasts then assume a hyphal morphology and grow along the interiors of lymphatic vessels until they reach a lymph node. This often results in the accumulation of pus in the lymph node, which subsequently ulcerates through the skin surface and then drains.
Humans have immune systems in which lymph nodes are important, because many white blood cells (phagocytes and lymphocytes) reside there. Given that a successful infection by S. schenkii damages lymph nodes themselves, which of the following is most probable?

Accepted Answer

The conversion of the yeast into the hyphal morphology results in their growth along the interiors of lymphatic vessels, which can overwhelm the body's defences at least temporarily, leading to a successful infection. Options A, C, and D are not relevant to the given information.

Question 14

Along with bacteria and protozoa, some chytrid fungi live in the digestive tracts of cattle and aid in the digestion of plant matter; thus, all three groups represent potential mutualists with cattle. In an experiment designed to test how much of a contribution to cell wall digestion was made by fungi in one part of the stomach (rumen), Lee et al. fed grain to cattle and then removed samples of the rumen contents. They took these samples to the laboratory and experimentally treated them with various chemicals to produce fractions that contained (A) only fungi, (B) only bacteria, (C) only protozoa, and (D) all of the potential mutualists. They then measured the percent of the cell wall that was degraded (see the figure). 
Degradation rates of cell walls extracted from Orchard grass by the monoculture system to assess the relative contributions of digestion by bacterial (square), protozoan (triangle), and fungal (diamond) systems, and all components (closed circle) as a control. The lowercase letters above the spots indicate statistical significance; mean values with different letters are significantly different (P < 0.05).
Which of the following conclusions can be drawn correctly from the data?

Accepted Answer

The answer of Along with bacteria and protozoa, some chytrid...

Question 15

Orchid seeds are tiny, with virtually no endosperm and with miniscule cotyledons. If such seeds are deposited in a dark, moist environment, then which of the following represents the most likely means by which fungi might assist in seed germination, given what the seeds lack?

Accepted Answer

Since the orchid seeds lack endosperm and have small cotyledons, they would be unable to germinate and grow without organic nutrients. Fungi can assist in this process by providing the embryos with some of the organic nutrients that they have absorbed through their mycelia. This relationship between orchid seeds and fungi is an example of mycorrhizal symbiosis. Options A, B, and D are unlikely since they do not address the specific needs of the orchid seeds.

Question 16

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

Accepted Answer

This design includes a control group and allows for comparison between infected amphibians with and without Jl, directly testing the effect of Jl on chytrid infection progression.

Question 17

The Neurospora genome is quite compact, lacking many of the noncoding DNA sequences that occur in humans and many other eukaryotes. Which of the following are probable benefits of the compactness of the genome?

Accepted Answer

Compact genomes require less energy for DNA duplication during cell division, which is an advantage in terms of metabolic efficiency.

Question 18

Heterobasidion is a basidiomycete that contributes to mortality of trees. Kuhlman isolated 23 strains of Heterobasidion and applied them to 16 seedlings of 10 different tree species. Partial results of this experiment are shown in the table. (From Kuhlman, E. G. 1970. Seedling inoculations with Fomes annosus show variation in virulence and in host susceptibility. Phytopathology 60:1743-1746. https://www.apsnet.org/publications/phytopathology/backissues/Documents/1970Articles/Phyto60n12_1743.PDF)
% mortality of five host species from five Heterobasidion isolates
$$\begin{array} { | l | l | l | l | l | l | } 
\hline & \text { Isolate } & \text { Isolate } & \text { Isolate } & \text { Isolate } & \text { Isolate } \
\hline \text { Host } & 63 & 117 & 195 & 126 & 118 \
\hline \text { Slash Pine } & 50 & 69 & 94 & 100 & 94 \
\hline \text { Shortleaf Pine } & 75 & 56 & 94 & 94 & 100 \
\hline \text { Red Cedar } & 38 & 32 & 19 & 50 & 25 \
\hline \text { Yellow-Poplar } &0 & 0 & 6 & 6 & 6 \
\hline \text { Sycamore } & 0 & 0 & 0 & 0 & 6 \
\hline
\end{array}$$
-Which of the following conclusions can best be drawn from these results?

Accepted Answer

The data shows varying percentages of mortality among different tree species when exposed to different Heterobasidion isolates, indicating that tree species have different levels of susceptibility to the pathogen.

Question 19

If haustoria from the fungal partner were to appear within the photosynthetic partner of a lichen, and if the growth rate of the photosynthetic partner consequently slowed substantially, then this would support the claim that ________.

Accepted Answer

The appearance of haustoria from the fungal partner within the photosynthetic partner, leading to a substantial slowing of the growth rate of the photosynthetic partner, would suggest that the mutualistic relationship between the two partners is not purely beneficial for both parties. This is because the fungal partner is potentially benefiting at the expense of the photosynthetic partner. This supports the claim that lichens are not purely mutualistic relationships.

Question 20

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

The zoospores are motile and have flagella, which enables them to actively swim through water and infect other amphibians. Wind-blown spores (A), cilia (C), and hyphae (D) are not associated with the spread of chytrid in amphibians.

Quiz 31: Fungi

Which of the following characteristics would be most helpful in distinguishing among different species of fungi?

A billionaire buys a sterile volcanic island that recently emerged from the sea. To speed the arrival of conditions necessary for plant growth, the billionaire might be advised to aerially sow what over the island?

Orchid seeds are tiny, with virtually no endosperm and with miniscule cotyledons. If such seeds are deposited in a dark, moist environment, then which of the following represents the most likely means by which fungi might assist in seed germination, given what the seeds lack?

The Neurospora genome is quite compact, lacking many of the noncoding DNA sequences that occur in humans and many other eukaryotes. Which of the following are probable benefits of the compactness of the genome?

If haustoria from the fungal partner were to appear within the photosynthetic partner of a lichen, and if the growth rate of the photosynthetic partner consequently slowed substantially, then this would support the claim that ________.