Myelination of neurons in the brain is the product of:
A. Schwann cells.
B. oligodendrocytes.
C. astrocytes.
D. both Schwann cells and oligodendrites.
B
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Hemoglobin helps maintain the oxygen pressure gradient by ____
a. carrying oxygen away from the lungs b. carrying carbon dioxide away from the lungs c. releasing oxygen at the lungs d. releasing carbon dioxide at the tissue e. releasing oxygen into the alveoli
For sperm to be able to penetrate the zona pellucida of the egg, enzymes are released from the ________
Fill in the blank(s) with correct word
The largest hole in the ozone layer occurs in the stratospheric layer over
A) the Amazon rainforests.
B) the eastern coast of the United States.
C) the western coast of the United States.
D) Africa and South America.
E) Antarctica.
A plasmid vector and chromosomal DNA are treated separately with the same restriction enzyme. The digested plasmid and chromosomal DNA were incubated together with DNA ligase and transformed into bacteria. Plasmids isolated from some of the colonies do not contain inserted chromosomal DNA. Which of the following could explain this observation?
A. The chromosomal DNA was very short and did not have any restriction sites for the enzyme used. B. The two sticky ends of the plasmid could hybridize back together, recircularizing. C. The two sticky ends of the plasmid could hybridize with two ends of another type of plasmid. D. The two sticky ends of the vector would remain free or unhybridized. E. The two sticky ends of the plasmid could hybridize to both sticky ends of the chromosomal DNA fragments.