Deck 21: Microbial Ecology

Question 1

Metagonomics is one of the newer techniques in microbial ecology. It is useful for obtaining data in:

A) diversity of microbes within habitats and over time
B) metabolic flux through trophic levels
C) interactions among organisms
D) community gene expression and function
E) ultrastructure of newly discovered bacteria

Answer 1

A

Question 2

Cryptogamic "soils" are found in dry, hot deserts. Which of the following is NOT true of cryptogamic crusts?

A) They develop very slowly.
B) They are made of lichens, mosses, and other algae and fungi.
C) They are quite resilient and not easily killed.
D) They play a vital role in protecting seeds for germination.
E) They help to prevent erosion in desert ecosystems.

Answer 2

C

Question 3

The relationship among endosymbiotic microbes in the termite gut that results in complex metabolic fluxes with a negative $\Delta$ G, and that would NOT happen for individual members is called:

A) mutualism
B) parasitism
C) exothermic association
D) predation
E) syntrophy

Answer 3

syntrophy

Question 4

Synechococcus, a cyanobacterium, is a free-living marine organism that fixes CO₂ into biomass while producing molecular oxygen utilized by swarms of heterotrophic bacteria. Its biomass provides food for protists and predators. What is the niche of this organism?

A) phototroph in the open ocean
B) base of the food chain
C) nitrogen assimilation for the ocean environment
D) all of the above
E) none of the above

Question 5

The algal and fungal interaction within a lichen would best be described as:

A) mutualism
B) synergism
C) commensalism
D) amensalism
E) parasitism

Question 6

Synechococcus, a cyanobacterium, is a free-living marine organism that fixes CO₂ into biomass while producing molecular oxygen utilized by swarms of heterotrophic bacteria. Which of the following is the most likely habitat of this bacterium?

A) euphotic zone of the pelagic environment
B) the benthos
C) the littoral zone
D) lake sediments
E) aphotic zone

Question 7

The oceans cover __________ of the Earth's surface.

A) 25%
B) more than two-thirds
C) more than 90 %
D) about 10%
E) 50%

Question 8

Which of the following is NOT true regarding food webs in ecosystems?

A) primary producers assimilate minerals into biomass
B) primary producers absorb energy from outside the ecosystem
C) grazers convert 10% of carbon back to carbon dioxide
D) consumers convert 90% of biomass carbon to atmospheric CO₂
E) all biomass is recycled and eventually converted to heat

Question 9

In wetlands, Beggiatoa bacteria oxidize H₂S for energy. Removal of H₂S enables growth of other microbes for which H₂S is toxic. However, Beggiatoa derives no benefit from these microbes. This interaction is an example of:

A) syntrophy
B) mutualism
C) commensalism
D) amensalism
E) synergism

Question 10

Compared to eutrophic lakes, the biochemical oxygen demand (BOD) of oligotrophic lakes is:

A) low
B) same
C) high
D) unpredictable
E) extremely high

Question 11

Which of the following is true about lichens in the boreal forests?

A) They cover the majority of the ground.
B) They are a major food source for caribou in the winter.
C) They are used for medicine.
D) They are used to dye cloth.
E) All of the above.

Question 12

Which of the following is NOT part of the cryptogamic crust community?

A) heterotrophic bacteria
B) mosses
C) lichens
D) nonlichenous algae
E) nonlichenous fungi

Question 13

Which of the following are major consumers of the bulk of biomass in the ocean?

A) multicellular organisms
B) fish and tube worms
C) protists and viruses
D) heterotrophic bacteria
E) fungi

Question 14

The availability of oxygen and other electron acceptors is the most important determinant of the types of metabolisms in a habitat. Which of the following is NOT true about anaerobic environments?

A) They have slower rates of assimilation compared to aerobic habitats.
B) Their rates of dissimilation are slower compared to aerobic environments.
C) Microbes sometimes use minerals such as NOto oxidize organic compounds.
D) Anaerobic microbial communities far exceed that of the oxygenated biosphere.
E) Respiration of organic compounds is highly dissimilatory, reducing them to CO₂.

Question 15

Various populations of species in their habitats or environment are best described as a(n):

A) niche
B) ecosystem
C) biosphere
D) biomass
E) microbial environment

Question 16

Which of the following techniques will be useful in studying the molecular basis of a specific mutualistic interaction between a microbe and a plant?

A) metagenomics
B) fluorescence microscopy
C) metatranscriptome analysis
D) gene expression analysis
E) B and D

Question 17

Lichens consist of an intimate mutualistic symbiosis between a fungus, an alga, and/or cyanobacteria. What is the primary role of the cyanobacteria in this association?

A) protection of the symbionts
B) production of photosynthate
C) decomposition of toxic compounds
D) recycling of waste products
E) degradation of lignin

Question 18

The usual habitat of Vibrio cholerae, the causative agent of cholera is/are:

A) ocean water
B) freshwater lakes
C) both marine and fresh water
D) sewage
E) littoral zone

Question 19

The salt concentration of marine water is about 3.5%. Which of the following is NOT a major ion in seawater?

A) Na+
B) Cl^-
C) Br^-
D) Cu²⁺
E) I^-

Question 20

Climatic changes that adversely impact planktonic phototropic bacteria in the oceans will directly alter the function of which trophic level(s)?

A) the largest biomass producers
B) marine invertebrates
C) the protist grazers
D) the predators
E) marine consumers

Question 21

The __________ region of an oligotrophic lake is about 10 meters below the surface.

A) neutron
B) benthic
C) epilimnion
D) hypolimnion
E) none of the above

Question 22

Which of the following is responsible for the characteristic odor of soil?

A) Vibrio sp.
B) Bacillus sp.
C) Streptomyces sp.
D) Staphylococcus sp.
E) Pseudomonas sp.

Question 23

All of the following may be found among the benthic microbes EXCEPT:

A) barophiles
B) psychrophiles
C) thermophiles
D) phototrophs
E) methanogens

Question 24

Lithotrophic bacteria found in between crystals of solid bedrock as deep as 3 km below Earth's surface are specifically called:

A) endophytes
B) symbionts
C) endoliths
D) decomposers
E) saprophytes

Question 25

In the Legume-Rhizobium symbiosis, nitrogen fixation is carried out in nodules by:

A) bacteroids that lack cell wall
B) intact rhizobia in the plant cortex
C) plant cells in the presence of symbiotic bacteria
D) bacteroids in oxygen-rich nodules
E) photosynthetic bacteroids in plants

Question 26

The best description for the microbial communities in the cold-seep ecosystem is:

A) thermophilic
B) psychrotrophic
C) barophilic thermophiles
D) barophilic psychrophiles
E) barophilic psychrotrophs

Question 27

Lakes that have low concentrations of organic nutrients are termed:

A) eutrophic
B) syntrophic
C) aphotic
D) oligotrophic
E) atrophic

Question 28

A graduate student filtered a liter of seawater using a Millipore filter membrane of 2 $\mu$ m pore size. Which of the following is true about his filtrate?

A) It is sterile.
B) Microplanktons are present.
C) Contains picoplanktons.
D) The filtrate contains nanoplanktons.
E) None of the above.

Question 29

The vast majority of microbes in the ocean are:

A) psychrophiles
B) thermophiles
C) mesophiles
D) acidophiles
E) osmophiles

Question 30

All planktonic microbes are:

A) motile
B) smaller than 200 $\mu$ m in size
C) prokaryotes
D) primary producers
E) unicellular

Question 31

Which of the following plays an important role in keeping the water column clear enough for the penetration of light?

A) algae
B) bacteria
C) fish
D) invertebrates
E) viruses

Question 32

The depth of the photic zone in the coastal shelf of marine habitats is

A) 100-200 m
B) 10-20 m
C) about 1 m
D) about 0.1 m
E) about 2 m

Question 33

In which of the following ways do rhizosphere bacteria benefit their host plant?

A) degrade plant lignin
B) attract symbiotic nematodes
C) improve water uptake
D) produce large amounts of photosynthate
E) discourage growth of plant pathogens

Question 34

Eutrophic lakes typically support ten times the microbial concentrations of an oligotrophic lake. Which of the following statements are NOT true of eutrophic lakes?

A) Biochemical oxygen demand is high.
B) Population of consumer aquatic animals is high.
C) Nitrogen and phosphorous levels are usually high.
D) Photosynthetic activities are altered.
E) Algal bloom is a common characteristic.

Question 35

Which category has the largest microbes?

A) viruses
B) femtoplankton
C) picoplankton
D) nanoplankton
E) microplankton

Question 36

Which region of marine habitat refers to the microscopic interface between water and air?

A) pelagic zone
B) neuston
C) euphotic zone
D) aphotic zone
E) benthic zone

Question 37

Which of the following refers to the oxygenated zone of a lake?

A) neuston
B) epilimnion
C) thermocline
D) hypolimnion
E) benthos

Question 38

The high biological oxygen demand (BOD) that accompanies algal bloom in eutrophic lakes increases the span of the __________ zone.

A) oxygenic epilimnion
B) anoxic hypolimnion
C) coastal shelf
D) anoxic benthic
E) oxygenic neuston

Question 39

Which class of extremophile would you expect to find within rock crystals down to a depth of 3 km?

A) acidophile
B) barophile
C) endolith
D) halophile
E) oligotroph

Question 40

Which of the following techniques is most appropriate for rapid detection and differentiation of specific classes of microbes in a drop of seawater?

A) metagenomics
B) viable plate count
C) DNA and RNA sequencing
D) fluorescent microscopy
E) radiography

Question 41

Fungi play a much larger and significant role in the decomposition of terrestrial biomass than they do in marine ecosystems. Why?

A) Fungi do not thrive in a marine environment.
B) Fungi out-compete bacteria in terrestrial habitats.
C) Fungi can degrade lignin to form humus.
D) Fungi decompose leghemoglobin rapidly.
E) Fungi degrade human waste faster than bacteria.

Question 42

The net biomass of a population does not indicate productivity within an ecosystem. Explain.

Question 43

Describe the interaction of Vibrio cholerae with copepods. How can saris help decrease the incidence of cholera in Bangladesh?

Question 44

Lignin decomposition forms:

A) arbuscules
B) detritus
C) fruiting bodies
D) humus
E) rhizopus

Question 45

Bacteroids remain sequestered within a sac of plant-derived membrane known as the:

A) flavonoid
B) infection thread
C) Nod factor
D) nucleosome
E) symbiosome

Question 46

How can one measure biomass production in terms of DNA replication? What are the limitations?

Question 47

What percent of forest trees require mycorrhizae for growth?

A) 10%
B) 25%
C) 50%
D) 75%
E) 90%

Question 48

Define cryptogamic crust and explain its vital role in desert ecosystems.

Question 49

Which term represents the region of soil directly in contact with the root surface?

A) stele
B) cortex
C) root cap
D) rhizoplane
E) rhizosphere

Question 50

Where would you expect to find the highest density of heterotrophic populations in the lake ecosystem? Why?

Question 51

Feeding cattle grain generates high rumen acidity, selecting for acid-resistant pathogens such as:

A) Sulfolobus sp.
B) E. coli O157:H7
C) Halobacterium NRC-1
D) fuselloviruses
E) Helicobacter pylori

Question 52

Which of the following organisms forms a specific mutualistic association with legumes?

A) rhizobia
B) agrobacteria
C) E. coli
D) morels
E) truffles

Question 53

As much as 90% of forest trees require mycorrhizae for growth, suggesting that:

A) forest soils are rich in phosphorous
B) mycorrhizae are found everywhere
C) the plant-mycorrhizal association is ammensalic
D) mycorrhizae significantly increase the uptake of nutrients
E) forest trees do not have deep roots

Question 54

Explain how viruses select for increased diversity of microbial plankton in the oceans.

Question 55

Which of the following do NOT require endosymbiotic bacteria to digest plant material such as cellulose?

A) termites
B) cattle
C) gorillas
D) humans
E) all of the above require endosymbiotic bacteria

Question 56

Compare and contrast the photic zones of pelagic and fresh-water lake ecosystems.

Question 57

Vascular abuscular mycorrhizae (VAM) are an example of which of the following?

A) ectosymbiont
B) endosymbiont
C) free-living fungus
D) lignin decomposer
E) nitrogen fixer

Question 58

Explain how the benthic interface between the ocean floor and water can act as a charged battery to generate electricity.

Question 59

One of the most important ecological roles of the Florida Everglades is that:

A) it is home to beautiful birds
B) it filters most of the water supply for Floridians
C) many bacteria reside in it
D) nutrient can easily be leached to the lakes
E) tourists come to see it in large numbers

Question 60

What does it mean when one says that a particular fluorescent dye intercalates into DNA? Provide an example of how epifluorescence has been used.

Question 61

What is one major way that wetlands such as the Everglades benefit human communities?

Question 62

What are endoliths and what do they feed on inside rocks?

Question 63

Describe haustorial parasitism.

Question 64

In any environment, pathogens are always outnumbered by the vast community of neutral or helpful microbes. Describe some beneficial as well as devastating incidences of plant pathogens.

Question 65

Define BOD, which can be used to measure the pollution level of lakes. Describe how effluents carrying high levels of nutrients can cause eutrophication.

Question 66

Explain how endoliths derive energy inside bedrock where there is no sunlight.

Question 67

What is coral bleaching? What is its possible cause?

Question 68

Why is it important to restrict the protein content of cattle feed?

Question 69

What is responsible for the high species-species specificity of the Legume-Rhizobium symbiosis?

Question 70

How would a high cereal or grain diet for cattle affect the growth of pathogens like E. coli?

Question 71

Describe the technique pioneered by Robert Hungate, of the University of California at Davis, to study anaerobic microbiology of the rumen. What types of questions can be answered with this technique?