Question 1

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

Accepted Answer

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 energy gained by an ecosystem is eventually lost as heat. C

Question 2

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

Accepted Answer

Answers may vary. A plant virus is associated with the production of striped tulips, which are much admired by tulip fanciers. Agrobacterium tumefaciens causes crown gall tumors on plants. It is applied widely for commercial plant engineering as a natural genetic transformation system. Ophiostoma novo-ulmi, a fungus carried by bark beetles, which bore into the xylem of elm trees, damaging the tree's transport vessels and allow access for fungal spores.

Question 3

What are the benefits and limitations of different environmental sequencing methods? Explain why ribosomal gene sequencing can be used as an initial screen.

Accepted Answer

SSU rRNA gene sequence libraries generated with primers may miss microbes with 16S rRNA sequences very different than known microbes. An advantage of 16S rRNA amplicon sequencing is that we may quickly identify many taxa present in a community, including relatively rare members that do not yield full genomes when large-scale sequencing is performed. SSU rRNA gene similarity is used to define OTUs. Direct metagenome sequencing can identify those organisms not amplified with traditional SSU rRNA gene primers, but also sequences other genes than SSU rRNA. Metagenomes require large amounts of computational analysis and are typically much more expensive than targeted sequencing technologies.

Question 4

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

Accepted Answer

A)   ectomycorrhizae
B)   endomycorrhizae
C)   free-living fungus
D)   lignin decomposer
E)   nitrogen fixer

Question 5

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

Accepted Answer

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

Question 6

Most forest trees require mycorrhizae for growth because

Accepted Answer

A)   forest soils are rich in phosphorous.
B)   mycorrhizae limit toxic metal uptake.
C)   the mycorrhizal form an ammensalic association.
D)   mycorrhizae significantly increase the uptake of nutrients.
E)   forest trees do not have deep roots.

Question 7

Rhizosphere bacteria benefit their host plant by

Accepted Answer

A)   degrading plant lignin.
B)   attracting symbiotic nematodes.
C)   improving water uptake.
D)   producing large amounts of photosynthate.
E)   discouraging growth of plant pathogens.

Question 8

Thousands of species of microbes in the cow ________ ferment and break down plant material to small particles.

Accepted Answer

A)   rumen
B)   stomach
C)   omasum
D)   reticulum
E)   intestine

Question 9

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

Accepted Answer

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

Question 10

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

Accepted Answer

The answer of Define BOD, and explain why it can...

Question 11

How do microbes live if their metabolic process to generate energy has a positive DG?

Accepted Answer

The answer of How do microbes live if their metabolic...

Question 12

Name two factors that differentiate aquatic and terrestrial ecosystems and explain how they affect food cycles in these systems.

Accepted Answer

The answer of Name two factors that differentiate aquatic and...

Question 13

Lakes that have dilute concentrations of nutrients are termed

Accepted Answer

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

Question 14

The term "metagenome" was coined by Jo Handelsman and colleagues in 1998 to refer to

Accepted Answer

A)   shotgun cloning.
B)   screening of libraries for expression of genes.
C)   the DNA sequence obtained directly from a mixture of genomes.
D)   the DNA sequence taken directly from a colony.
E)   all uncultured organisms from a community.

Question 15

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

Accepted Answer

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

Question 16

Culturing methods often detect organisms that may be rare in the environment but prevail when nutrients appear. What are these typically called?

Accepted Answer

A)   weed organisms
B)   protists
C)   rhizobia
D)   OTUs
E)   microbial dark matter

Question 17

Explain the difference between assimilation and dissimilation.

Accepted Answer

The answer of Explain the difference between assimilation and dissimilation....

Question 18

Propose a method to measure biomass production in terms of DNA synthesis. What are the limitations?

Accepted Answer

The answer of Propose a method to measure biomass production...

Question 19

The reactions on the right side of the following table occur only

Accepted Answer

A)   under thermophilic conditions.
B)   under anaerobic conditions.
C)   deep within Earth's crust.
D)   under aerobic conditions.
E)   in the euphotic zone.

Question 20

Describe the steps in sequencing a metagenome.

Accepted Answer

The answer of Describe the steps in sequencing a metagenome....

Exam 21: Microbial Ecology