Potato spindle-tuber disease, which causes potatoes to become gnarled and cracked, is caused by an infectious agent consisting of a small circular RNA molecule that totally lacks a protein coat. These infectious agents are thought to exert their effects by interfering with the cell's normal path of gene expression. Such an infectious agent is known as a(n) __________.
A) eviscerion
B) viroid
C) provirous
D) bacteriophage
E) virunette
Ans: B) viroid
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In a PCR reaction, a few seconds at high temperature disrupts the ____ that hold the two strands of DNA together, so
every molecule of DNA unwinds and becomes single-stranded.
a. covalent bonds b. peptide bonds c. hydrogen bonds d. lipoproteins e. DNA ligases
The phospholipid molecule represented in the figure
above a. has a hydrophobic head labeled B and a hydrophilic tail labeled A. b. has a hydrophilic head labeled A and a hydrophobic tail labeled B. c. does not contain a phospholipid. d. contains only a hydrophobic segment. e. contains only a hydrophilic segment.
In the Beadle and Tatum study, it was important that Neurospora was haploid because:a
it is easier to grow haploid molds in the laboratory. b. haploid molds have simpler nutritional requirements than do diploid molds. c. a mutation that arises is not masked by a normal allele on a homologous chromosome. d. haploid Neurospora will always mutate. e. diploid Neurospora will always mutate.
One purpose of the lymphatic system is to:
a. transport nutrients and oxygen. b. returns interstitial fluid to the blood. c. block the transport of blood proteins. d. produce red blood cells. e. deliver carbon dioxide to the heart.