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14 Cards in this Set
- Front
- Back
For a virus to infect a host cell, the virus
must first adhere to the cell's surface. Viruses accomplish this by fitting specific sites on their surfaces to receptor sites on the surfaces of their host cells in a "lock and key" arrangement. The "lock and key" arrangement between a virus and receptor sites on its host cells is most important in determining the: |
specific type of cell that is normally
infected by the virus. The distinct three-dimensional arrangement of proteins on the viral coat plays a critical role in how viruses recognize their host cells. The protein "key" of each type of virus has a different shape, which fits specific, corresponding "locks" on certain cell surfaces. As a result, the types of cells a particular virus can infect are limited, sometimes to a single species. Cells of different species and different types of cells within a particular organism have distinct specific "locks" on their surfaces. |
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A primary function of gap junctions
between cell membranes is to: |
integrate the metabolic or electrical
activity of a group of cells through permeable channels. Gap junctions are pores that connect the cytoplasm of neighboring cells. The pores permit passage of ions, sugars, and other small molecules, allowing cells to communicate chemically with one another. In this way, the metabolic or electrical activity of cells in specific tissues and organs can be integrated and coordinated. |
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Which of the following best explains why
the catabolism of fats yields about twice as much energy as the catabolism of the same mass of carbohydrates? |
Fats contain a higher proportion
of carbon-hydrogen bonds than carbohydrates do. The energy released from the catabolism of macromolecules, such as fats and carbohydrates, comes from the breaking of bonds. Fats contain long carbon chains with many carbon-hydrogen bonds. The same mass of carbohydrates contains fewer of these types of bonds, so the energy yielded during catabolism is less for carbohydrates than for fats. |
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An important role of histamine in the
humoral response to infection is to: |
signal the presence of an antigen to
other components of the immune system. When damage occurs to tissues, such as from a scratch or by entry of pathogens, the damaged cells release histamine. The histamine triggers capillary dilation and increased capillary permeability, resulting in localized redness and swelling. Phagocytes in the blood, responding to the increased capillary blood flow and permeability, migrate to the site of injury, where they engulf and destroy pathogens. |
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What is the role of helper T cells in the
function of the human immune system? |
to mobilize both the humoral and
cell-mediated responses to antigens. Helper T cells are central components in the human immune system. These cells recognize the presence of antigens in pathogen-consuming macrophages and then stimulate both B cells and other T cells into activity. B cells mobilize against pathogens in the blood and lymph (humoral response), while other T cells target pathogens in infected cells (cell-mediated response). |
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The ability to identify particular loci
associated with a given genetic trait has the greatest implications for which of the following areas of medicine? |
screening for hereditary diseases.
The ability to locate a known gene on a chromosome may provide better methods of screening for hereditary diseases. Once the gene associated with a particular hereditary disease is mapped and the gene's DNA sequence known, DNA can be analyzed for patterns associated with the disease. |
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Variations in phenotypes are sometimes
evident in individuals with abnormal chromosome numbers. Which of the following events accounts for a significant portion of the instances of abnormal chromosome numbers? |
nondisjunction during meiosis.
Nondisjunction occurs when homologous chromosomes fail to move apart during meiosis I or sister chromatids do not separate during meiosis II. This results in a gamete with two copies of a particular chromosome and another gamete with no copies of that chromosome. If the gamete with two copies joins with a normal gamete that has one copy of the chromosome, the offspring will have three copies of the chromosome rather than the normal two copies. An offspring resulting from the joining of the gamete with no copy of the chromosome and a normal gamete will have only one copy of the chromosome in its cells. |
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Which of the following examples best
illustrates the idea that differential gene expression accounts for specialization of cells in multicellular organisms rather than differences among the genes themselves? |
Cells from the mammary gland of
a sheep can provide the genetic material needed to clone a sheep. Research has shown that differences in cells in an organism arise not from genetic differences, but because different types of cells express different portions of the same genetic material. That being the case, a cell from any part of an organism should theoretically contain all of the genetic information necessary to form all parts of the organism. Researchers recently demonstrated this by successfully cloning a sheep using mammary gland cells. Although these cells were specialized in the adult sheep, they were able to provide all the information necessary to produce a sheep. |
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Genetic engineering has the potential to
correct some human genetic diseases in individuals. In gene therapy, a defective gene is replaced or supplemented by using a genetically engineered retrovirus to insert a normal gene in the DNA of some of the patient's cells. This treatment will be most successful if the retrovirus is inserted into cells that: |
continue to divide during the life of
the patient. For gene therapy to be long lasting, the retrovirus carrying the normal gene should be inserted into cells that continue to divide. This will allow the transplanted normal gene to be replicated, increasing the chances that the benefits of the therapy will last for the lifetime of the patient. |
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Which of the following is one
consequence of the fact that natural selection acts on the phenotype of an individual rather than on its genotype? |
Harmful recessive alleles are less
easily removed from a population than dominant alleles that are harmful. A harmful dominant allele is expressed in the phenotype, even in heterozygotes, and is usually removed from the gene pool through natural selection. A recessive allele, however, does not manifest itself unless an individual is homozygous recessive. Heterozygous individuals will not express the harmful trait, so natural selection does not select against them, even though they carry the harmful allele. |
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Researchers studying northern elephant
seals have found a remarkable lack of genetic diversity in the population. In contrast, the southern elephant seal population exhibits a normal amount of genetic variation. Which of the following is the most likely explanation for this difference in the two elephant seal populations? |
The northern elephant seal
population was greatly reduced in the recent past, while the southern elephant seal population was not. The best explanation for the difference in the genetic diversity of the two populations is that the northern elephant seal population went through a recent reduction in size. Such bottlenecks usually result in decreased genetic diversity, because the small surviving population is unlikely to be genetically representative of the original population. |
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A species of finch on an island is divided
into two distinct morphs based on bill size. Finches with large bills eat mostly large, hard-shelled seeds of a particular plant, while finches with small bills eat smaller, softer seeds of a different plant. A smaller number of finches with bills of intermediate size eat both large and small seeds. Which of the following scenarios would be most favorable for sympatric speciation of this finch species? |
Individual finches begin to choose
mates with a bill size similar to their own. In animals, sympatric speciation, the development of separate species from a single species in a given geographic area, results when the random flow of genes in a population is interrupted by non-random mating. The preferential selection of mates based on bill size results in reproductive isolation of parts of the population, which could allow for speciation over time. |
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The effective cycling of nutrients in
an ecosystem depends primarily on maintaining: |
balanced rates of production,
consumption, and decomposition. Effective nutrient cycling depends on balancing the exchange of essential nutrients that move through the bodies of organisms at all trophic levels. If the rate of production, consumption, or decomposition is not balanced with respect to the other processes, recycling in the whole system can be hampered by a deficiency of a single limiting nutrient. For example, if plants remove nitrogen from the soil more quickly than it is returned, the productivity of the entire system can be reduced. This results in reduced consumption and ultimately reduced decomposition. Thus, less nitrogen is returned to the soil. |
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Brown-headed cowbirds are members of
the blackbird family that lay their eggs in other birds' nests. Usually a single egg is laid in the nest of a smaller species. The egg hatches sooner than those of the host species, and after it hatches, the baby cowbird often pushes the other eggs out of the nest. The cowbird is then raised by the foster parents, whom it often dwarfs in size. The relationship between the brownheaded cowbird and its host species is an example of: |
parasitism.
Parasitism is a type of relationship between two different species in which one species benefits at the expense of the other. Parasites usually impair, but do not kill their hosts, since killing their hosts would be detrimental to the parasite. In this example, the cowbirds exploit the nurturing instincts of other birds that are unable to distinguish between their real offspring and the parasite. While the cowbird benefits, the host birds are harmed in that energy and resources are being used to increase the survival chances of organisms that will not pass on the host's genetic information. |