Question 1

Which of the following best describes the mutualistic relationship in lichens?

Accepted Answer

A fungus and an alga (or cyanobacterium) form a mutualistic relationship where the alga produces organic matter and the fungus provides structure and protection.

Question 2

What is the primary function of leghemoglobin in legume root nodules?

Accepted Answer

To bind free oxygen and protect nitrogenase enzymes from inactivation.

Question 3

Which of the following is a key step in the formation of a root nodule in legumes infected by Rhizobium?

Accepted Answer

Rhizobium secretes Nod factors causing root hair curling, followed by invasion through an infection thread.

Question 4

Which equation correctly represents the nitrogen fixation reaction catalyzed by nitrogenase in root nodules?

Accepted Answer

$$ \mathrm{N_2$ + 8H^+ + 8e^- + 16ATP \rightarrow 2NH_3 + H_2$ + 16ADP + 16P_i} $$

Question 5

Which of the following best explains why nodulated legumes can grow in nitrogen-poor soils where other plants cannot?

Accepted Answer

They form a symbiosis with nitrogen-fixing bacteria that increase available nitrogen in the soil.

Question 6

Which statement about mycorrhizal associations is correct?

Accepted Answer

Endomycorrhizae (arbuscular mycorrhizae) form branched structures inside root cells and are found in over 80% of terrestrial plant species.

Question 7

Which of the following is a real-world application of the Ti plasmid from Agrobacterium tumefaciens?

Accepted Answer

It is used to engineer plants by transferring foreign genes into plant genomes.

Question 8

Which sequence of events correctly describes the transfer of T-DNA from Agrobacterium tumefaciens to a plant cell?

Accepted Answer

VirA activates VirG, VirD nicks the Ti plasmid, VirB forms a conjugation bridge, and VirE assists T-DNA transfer.

Question 9

Which of the following best describes the role of secondary symbionts in insects?

Accepted Answer

They are not required for reproduction, can invade different cells, and must provide a benefit such as nutrition or protection.

Question 10

Leafcutter ants maintain a complex symbiosis involving which of the following interactions?

Accepted Answer

A mutualism with a cultivated fungus and a defensive association with Pseudonocardia bacteria that produce antifungal compounds.

Question 11

Which of the following is the main microbial product assimilated by termites from their gut symbionts?

Accepted Answer

Acetate

Question 12

The mutualistic relationship between Aliivibrio fischeri and the Hawaiian bobtail squid is characterized by which of the following?

Accepted Answer

Aliivibrio fischeri provides light via bioluminescence, camouflaging the squid from predators, and is supplied with nutrients by the squid.

Question 13

Which process controls bioluminescence in Aliivibrio fischeri within the squid light organ?

Accepted Answer

Quorum sensing

Question 14

Which of the following best describes the microbial symbiosis at deep-sea hydrothermal vents?

Accepted Answer

Chemolithotrophic prokaryotes oxidize reduced inorganic compounds and form endosymbiotic relationships with vent invertebrates.

Question 15

Which of the following is a consequence of coral bleaching?

Accepted Answer

Loss of color due to lysis of symbiotic dinoflagellates, often triggered by high temperature and light.

Question 16

Which of the following equations best represents the fermentation of cellulose in the rumen?

Accepted Answer

$$ \mathrm{(C_6H_{10}O_5$)_n + nH_2O \rightarrow nC_6H_{12}O_6$ \rightarrow volatile\ fatty\ acids + CO_2$ + CH_4$} $$

Question 17

What is the main energy source for ruminant animals such as cows, derived from microbial fermentation in the rumen?

Accepted Answer

Volatile fatty acids (e.g., acetate, propionate, butyrate)

Question 18

Which group of bacteria dominates the rumen microbial community?

Accepted Answer

Cellulolytic bacteria

Question 19

Which of the following best explains how Synergistes jonesii protects cattle from mimosine toxicity?

Accepted Answer

It converts toxic 3,4-DHP to nontoxic metabolites via a 2,3-DHP intermediate.

Microbial Symbioses with Microbes, Plants, and Animals

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