Question 1

Suzanne Simard and colleagues knew that the same mycorrhizal fungal species could colonise multiple types of trees. They wondered if the same fungal individual would colonise different trees, forming an underground network that potentially could transport carbon and nutrients from one tree to another (S. Simard et al. 1997. Net transfer of carbon between mycorrhizal tree species in the field. Nature 388:579-82).
Pots containing seedlings of three different tree species were set up and grown under natural conditions for three years (Fig.A). Two of the three species (Douglas fir, birch) could form ectomycorrhizal connections with the same fungal species, but the third species (cedar) could not form an ectomycorrhizal connection with the fungal species. In some of the pots, the researchers placed airtight bags over the Douglas fir and birch seedlings and injected carbon dioxide made from carbon-13 into the bags with the Douglas fir and carbon dioxide made from carbon-14 into the bags with the birch. (13C and 14C are different isotopes of carbon that can be detected and measured by researchers.) As the seedlings photosynthesised, the carbon dioxide was converted into sugars that could be tracked and measured by the researchers. The researchers measured whether the sugars in each plant contained only the carbon isotope that was in the air of their plastic bag or also the carbon isotope from the air around the other plant.

Figure A
-Referring to Simard et al. (1997), which design element is the control in this experiment and why?

Accepted Answer

A)   the bags over the seedlings to contain the different types of carbon dioxide
B)   the fact that all the seedlings are different species
C)   the cedar seedling, because it is not bagged
D)   the cedar seedling, because it does not form ectomycorrhizal connections with the tested fungus D

Question 2

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

A)   The hyphae secrete antibiotics, which increases the ability of the infected human to tolerate the fungus.
B)   The fungal conversion from yeast to hyphal morphology allows such fast growth that the body's defences are at least temporarily overwhelmed.
C)   Defensive cells of humans cannot detect foreign cells that are covered with cell walls composed of cellulose.
D)   Given that most fungal pathogens attack plants, human defences are simply not adapted to seek out and destroy fungi. B

Question 3

The closest relatives of fungi are thought to be the

Accepted Answer

A)   animals.
B)   vascular plants.
C)   mosses.
D)   slime moulds. A

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

A)   demonstrate that their laboratory culture conditions allowed all potential mutualists to grow
B)   determine how much each potential mutualist contributed to cell wall degradation
C)   better mimic the conditions of the rumen
D)   demonstrate that the various potential mutualists did not compete with each other

Question 5

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

A)   by wind-blown spores
B)   by flagella
C)   by cilia
D)   by hyphae

Question 6

Arrange the following in order from largest to smallest, assuming that they all come from the same fungus.

Accepted Answer

A)   mycelium, gill, basidiocarp, basidium, basidiospore
B)   gill, basidiocarp, mycelium, basidium, basidiospore
C)   gill, basidiocarp, basidiospore, basidium, mycelium
D)   mycelium, basidiocarp, gill, basidium, basidiospore

Question 7

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

A)   All tree species are susceptible to Heterobasidion.
B)   Heterobasidion strains are equally lethal to all tree species.
C)   Heterobasidion reduces mortality of some species.
D)   Tree species vary in their susceptibility to Heterobasidion.

Question 8

In most fungi, karyogamy does not immediately follow plasmogamy, which consequently ________.

Accepted Answer

A)   means that sexual reproduction can occur in specialised structures
B)   results in multiple diploid nuclei per cell
C)   allows fungi to reproduce asexually most of the time
D)   results in heterokaryotic or dikaryotic cells

Question 9

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

A)   The organism saves energy during cell division because fewer DNA bases must be duplicated.
B)   It is more difficult for viruses to insert themselves into a compact genome.
C)   There is less genetic variation that can lead to mutation.
D)   The spores will be small and thus travel a greater distance.

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. 
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

A)   tree stump
B)   deceased animal
C)   fire pit
D)   cement-capped well

Question 11

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. 
Which location is nearest to basidiocarps?

Accepted Answer

A)   A
B)   B
C)   C
D)   D

Question 12

Fungi produce many compounds that humans are able to use medically. How can you account for these compounds?

Accepted Answer

A)   Humans used artificial selection to develop fungi that produced specific compounds.
B)   The presence of the compounds in the fungi were accidentally produced and have no function.
C)   The compounds probably provide a benefit to the fungi.
D)   The compounds are produced as a result of sexual reproduction and recombination.

Question 13

In the United States and Canada, bats use one of two strategies to survive winter. They either migrate south, or they hibernate. Recently, those that hibernate seem to have come under attack by a fungus, Geomyces destructans (Gd). Many infected bats have a delicate, white filamentous mat on their muzzles, which is referred to as white-nose syndrome (WNS). The fungus invades the bat tissues, causes discomfort, and awakens the bat from its hibernation. The bat fidgets and wastes calories, using up its stored fat. The bat then behaves abnormally, leaving its cave during daytime in winter to search for food. Their food, primarily insects, is scarce during the winter, and the bats ultimately starve to death. Since 2006, it is estimated that over six million bats have perished from WNS.
-The Gd mat on the fur of the bats should be expected to consist of ________.

Accepted Answer

A)   hyphae
B)   haustoria
C)   yeasts
D)   basidia

Question 14

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

A)   Inoculate uninfected amphibians with Jl, and determine whether the amphibians continue to remain uninfected by chytrids.
B)   Inoculate infected amphibians with Jl and determine whether the amphibians recover from infection by chytrids.
C)   Take infected amphibians and assign them to two populations. Leave one population alone; inoculate the other with Jl. Measure the rate at which infection proceeds in both populations.
D)   Take infected amphibians and assign them to two populations. Inoculate one population with a high dose of Jl; inoculate the other with a low dose of Jl. Measure the survival frequency in both populations.

Question 15

Chitin is a long-chain polymer derived from glucose. It strengthens cell walls of fungi and the outer covering (exoskeleton) of arthropods (including crabs, shrimps, and insects). The presence of chitin in these groups is likely due to ________.

Accepted Answer

A)   secondary endoparasitism
B)   horizontal gene transfer
C)   paraphyletic evolution
D)   convergent evolution

Question 16

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

Accepted Answer

A)   morphology
B)   hyphae structure
C)   DNA sequence
D)   life cycle

Question 17

After cytokinesis occurs in budding yeasts, the daughter cell has a ________.

Accepted Answer

A)   similar nucleus and more cytoplasm than the mother cell
B)   smaller nucleus and less cytoplasm than the mother cell
C)   larger nucleus and less cytoplasm than the mother cell
D)   similar nucleus and less cytoplasm than the mother cell

Question 18

The multicellular condition of animals and fungi seems to have arisen ________.

Accepted Answer

A)   due to common ancestry
B)   by convergent evolution
C)   by inheritance of acquired traits
D)   by serial endosymbioses

Question 19

A fungal spore germinates, giving rise to a mycelium that grows outward into the soil surrounding the site where the spore originally landed. Which of the following accounts for the fungal movement, as described here?

Accepted Answer

A)   karyogamy
B)   mycelial flagella
C)   breezes distributing spores
D)   cytoplasmic streaming in hyphae

Question 20

The ascomycete Brachiola gambiae parasitises the mosquito Anopheles gambiae. Adult female mosquitoes must take blood meals for their eggs to develop, and it is while they take blood that they transmit malarial parasites to humans. Male mosquitoes drink flower nectar. If humans are to safely and effectively use Brachiola gambiae as a biological control to reduce human deaths from malaria, then which of the following statements should be correct?

Accepted Answer

A)   The ascomycete should not be harmful to other insects and must be harmful to male mosquitoes, but not to female mosquitoes.
B)   The ascomycete should kill the mosquitoes before the malarial parasite they carry reaches maturity and should not be harmful to other insects.
C)   The ascomycete should not be harmful to other insects and should infect mosquito larvae, rather than mosquito adults.
D)   The ascomycete should infect mosquito larvae, rather than mosquito adults, and the subsequent decline in anopheline mosquitoes should not significantly disrupt human food resources.

Exam 31: Fungi