The hypothesis of the viral origin of DNA assumes all of the following EXCEPT which one?
a. The main genetic material of cells in the RNA world was DNA.
b. The main genetic material of cells in the RNA world was RNA.
c. Viruses horizontally transferred their DNA genomes to cells.
d. RNA viruses developed DNA as a mechanism to protect their genomes from destruction by cell ribonucleases.
Answer: A
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Why is it necessary to take special safety precautions when using radioactivity?
A. Radioactive substances will ionize cells. B. Radioactive substances have the potential to cause damage to living cells. C. Radioactive substances decay. D. Radioactive substances will perforate plasma membranes.
The establishment of DNA as the genome of the cell may have resulted from the need to store genetic information in a more stable form than RNA
Indicate whether the statement is true or false.
Which statement is true?
a. Breathing rate and depth are completely under voluntary control. b. A person can commit suicide by holding his or her breath. c. The contraction of the diaphragm and muscle of the rib cage are under the control of areas of the brain. d. There are chemoreceptors in the brain that monitor carbon dioxide content in the blood and control breathing. e. The contraction of the diaphragm and muscle of the rib cage are under the control of areas of the brain, and there are chemo-receptors in the brain that monitor carbon dioxide content in the blood and control breathing.
When can ice formation destroy plant cells?
A) as water flows into cells via osmosis as the temperature drops B) as adhesion increases inside xylem tubes C) as jagged ice crystals puncture cell membranes D) as cells are poisoned by dissolved "antifreeze" solutes