When the squid that contain luminescent bacterial symbionts hatch, they do NOT contain a bacterial symbiont. Symbiont transmission in this symbiosis is
A) vertical from parent to offspring.
B) horizontal and involves specific selection of the symbiont from the environment.
C) random and results in various different species being selected as the symbiont.
D) mixed and results in multiple symbiont species colonizing the squid at once.
A species of insect that lives solely on pine sap was found to contain a bacterial symbiont.
Genome sequencing of both the host and the symbiont revealed that the symbiont lacked many genes required for energy production, and the host lacked genes for biosynthesis of several essential amino acids. What is/are the most likely mechanism(s) that caused the loss of these genes?
A) coevolution
B) horizontal gene transfer
C) increased mutation rate
D) horizontal gene transfer and increased mutation rate
Which of the following is NOT true of human gut microbes?
A) The population size is low, but diversity is high.
B) They produce and excrete amino acids.
C) They help catabolize polysaccharides.
D) They are involved in the maturing of the gastrointestinal tract.
Why do obligate symbionts often contain lower G+C content when compared to free-living organisms?
A) Ancestral symbionts had low GC content genomes by chance, and these low GC content genomes are passed onto their progeny.
B) Free-living organisms must have a more stable genome to survive; low G+C content organisms are often selected against in nature.
C) Replicating high G+C content genomes requires several additional enzymes, to break apart the strong triple bonds formed from GC pairs, which are rarely found in symbionts with relatively small genome sizes.
D) Symbionts usually do not have as many DNA repair mechanisms as free-living organisms, and two common spontaneous mutations change GC pairs into AT pairs.
What is the fate of H2 produced within a rumen?
A) It is released via eructation (belching).
B) It is transformed, along with other ions, into inorganic compounds.
C) It is used in acetogenesis.
D) It is used in methanogenesis.
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