The phylogenetic analysis of nucleotide sequences for a group of retroviruses has allowed researchers to discover that
there are _____ major types of HIV that originate from one ancestral lentivirus.
a. one
b. two
c. four
d. ten
e. fourteen
b
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Using the tryptophan operon as a model, explain a transcription pause site and the formation of a stem-loop
What will be an ideal response?
Muscle fibers generate maximum force:
A. at intermediate lengths. B. when pulled to long lengths before contraction. C. when contracting at short lengths. D. when the myosin filaments contact the Z discs. E. when the overlap between actin and myosin is minimal.
For which of the following pHs, is the
hydroxide ion concentration greater than the hydrogen ion concentration?
a. 1 b. 3 c. 5 d. 7 e. 9
The accumulation of free oxygen in Earth's atmosphere began with the origin of _____
A) life and respiratory metabolism B) cyanobacteria using photosystem II C) chloroplasts in photosynthetic eukaryotic algae D) land plants