A microbiologist is working with two genera of bacteria, A and B, to determine if cells are competent. Strains are grown under optimal conditions, and DNA fragments that carry the gene for green fluorescent protein are added to each culture at 20-minute intervals. Samples from each treatment are plated to nutrient agar and incubated, after which the plates are examined under an ultraviolet lamp. The microbiologist observes that all plates of bacteria B contain colonies that are fluorescent, while for bacteria A only the plates from stationary phase demonstrate fluorescent colonies. What can be concluded from these results?
A. Both bacteria A and bacteria B cells are competent.
B. Competence in bacteria B is dependent on the phase of growth.
C. Competence in bacteria A is constitutively expressed.
D. Neither bacteria A nor bacteria B cells are competent.
Answer: A
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If histones are extracted from DNA, what would remain?
A. DNA only B. DNA and tetranucleosomes C. DNA and chromosomal scaffolding proteins D. degraded segments of DNA
The defining characteristics of the phylum Arthropoda are:
A. jointed legs, ecdysis, and an exoskeleton B. antennae, six legs, and mandibles C. compound eyes, book lungs, and the hemocoel D. Malphigian tubules, ommatidia, and tagmata E. spiracles, cephalothorax, and proboscis
A lab technician is preparing to dispose of a rat and a frog that were euthanized earlier in the day for a scientific study. Although the two animals died at the same time, the rat has rigor mortis while the frog does not yet show any signs of it. What is the best explanation for this time difference in the onset of rigor mortis?
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