Which of the following represents a double-blind study?
A. The test group knows whether they are receiving a placebo or the actual treatment, and so do the researchers.
B. The test group knows whether they are receiving a placebo or the actual treatment, but the researchers do not know until all the data are collected.
C. The test group does not know whether they are receiving a placebo or the actual treatment, but the researchers do.
D. Neither the test group nor the researchers know whether the test group is receiving a placebo or the actual treatment until all the data are collected.
Answer: D
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What percentage of oxygen in the air is typically extracted by the mammalian lung?
A. less than 25% B. 26–50% C. 51–75% D. 76–90% E. 91–100%
The chemical reaction in Figure 47-2 occurs in the:a
stomach as the result of secretions from the pancreas. b. small intestine as the result of secretions from the pancreas. c. large intestine as the result of secretions from the small intestine. d. stomach as the result of secretions from the stomach. e. small intestine as the result of secretions from the liver.
Endosymbiosis is an evolutionary theory that explains the origin of eukaryotes and suggests a specific order in which this might have occurred. Ancestral cells engulfed and then began to use the metabolic processes of the smaller cells
Based on shared core processes and features, which statement most accurately describes the order, the theory and the evolutionary implications for all organisms within domain Eukarya? A) Ancestral heterotrophic eukaryotes most likely engulfed both a heterotrophic and an autotrophic prokaryote, whereas ancestral photosynthetic eukaryotes probably provided the host cell for the first mitochondria. Over time, natural selection favored these relationships and these cells became ancestors of all eukaryotes. B) All ancestral eukaryotes would have most likely consumed a nucleus-like prokaryote that eventually became the eukaryotic nucleus. These new eukaryotic cells would have had an advantage over prokaryotic cells by acquiring a nuclear command center for regulating cellular activities. C) As carbon dioxide levels were increasing over time, natural selection would have favored organisms that acquired a photosynthetic prokaryote to convert carbon dioxide into sugars. These would have likely been the first eukaryotic cells. At which point, these ancestral cells engulfed mitochondria-like prokaryotes that would have provided an even greater advantage for cells in this environment. D) As Earth was becoming more aerobic, mitochondria would have provided an advantage to host cells by converting "toxic" oxygen into energy for heterotrophic cells. Since mitochondria are found in all eukaryotes, these combinations likely evolved first. Photosynthetic eukaryotes probably acquired an autotrophic prokaryote, which developed an advantageous symbiotic relationship with the host cell.
The spindle fibers are produced by the
A) nucleus. B) chromosomes. C) centrioles. D) chromatin.