Which of the following statements regarding the development of AIDS following infection with HIV is incorrect?
A. Antibodies to HIV antigens formed in response to HIV infection appear within a few weeks of infection and remain high through latency and AIDS.
B. CD4 T cells are present in low numbers in an uninfected individual, but become elevated upon HIV infection, and ultimately fall to very low numbers (<200 cells/ml) as the infection progresses to AIDS.
C. An HIV-positive individual in the latency phase can be distinguished from an uninfected individual by the presence of antibodies to HIV antigens in their blood.
D. Viral antigens can be detected at high levels in the blood within days following infection, then their numbers fall dramatically during a latent period and rise again when AIDS symptoms occur.
Answer: B
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A ________ mutation is one that causes premature termination of the synthesis of the protein product.
A. nonsense B. silent C. missense D. None of the choices are correct.
In response to global climate change, it is likely that some plant species will survive while others will go extinct. All of the following are explanations of this pattern except:
A. greenhouse gases are toxic, so increasing levels of these gases will cause some plants to go extinct. B. plants differ in their abilities to respond physiologically to persistent environmental change, and some will survive increased temperatures. C. temperatures may increase more rapidly than some species can adapt, which will lead to their extinction. D. some plants are able to migrate more effectively than others and can move into areas with more favorable conditions for survival. E. All of the answer options are correct explanations for the predicted pattern.
Four of the five answers listed below are types of complex tissue. Select the exception
a. phloem b. xylem c. epidermis d. parenchyma e. periderm
The presence of circular DNA in mitochondria and chloroplasts suggests that these organelles evolved from ____
a. bacteria b. nuclei c. single celled eukaryotes d. anaerobic microorganisms e. archaea