The correct answer is Uracil. Uracil is one of the four nitrogenous bases found in RNA. The other three nitrogenous bases in RNA are also found in DNA, but uracil is not found in DNA.
Nitrogenous base that occurs in RNA
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The correct answer is Uracil. Uracil is one of the four nitrogenous bases found in RNA. The other three nitrogenous bases in RNA are also found in DNA, but uracil is not found in DNA.
Nitrogenous base that occurs in RNA but not in DNA
(A) Deoxyribose
(B) Ribose
(C) Uracil
(D) Cytosine
(E) Thymine
The correct answer is cytosine. The only base that is always found in equal quantities with guanine is its complement, cytosine (recall that the nitrogenous bases in DNA pair, A with T and C with G.)
A nitrogenous base that occurs in DNA in equal quantities with guanine
(A) Deoxyribose
(B) Ribose
(C) Uracil
(D) Cytosine
(E) Thymine
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The correct answer is succession. Within a given area, the vegetation changes over time, tending towards the climax type of vegetation for that particular area. (Repeated disturbances, of course, interrupt this process, and may in effect reset the clock, so that succession begins anew.)
The change in plant types inhabiting an area over time, resulting in a climax community
(A) Succession
(B) Dispersion
(C) Fertilization
(D) Speciation
(E) Mutation
The correct answer is speciation. Recall that the functional definition of a species is a group of organisms that can interbreed with each other but do not interbreed with others. The inability to interbreed after long separation is a sign that speciation has occurred; the two populations now represent two different species.
The inability of two populations to interbreed after being separated by a barrier for a long period of time
(A) Succession
(B) Dispersion
(C) Fertilization
(D) Speciation
(E) Mutation
The correct answer is succession. This is a specific example of succession, the gradual filling in of a wetland to become a meadow or a forest.
Plants growing in and around a pond eventually filling in the pond and changing it to a terrestrial habitat
(A) Succession
(B) Dispersion
(C) Fertilization
(D) Speciation
(E) Mutation
The correct answer is Producers (e.g., grasses). Organisms that comprise the greatest biomass in a terrestrial food chain are the producers. Net productivity (photosynthesis minus respiration) creates biomass.
Organisms that comprise the greatest mass of living substance (biomass) in a terrestrial food chain
(A) Decomposers (e.g., bacteria)
(B) Producers (e.g., grasses)
(C) Primary consumers (e.g., mice)
(D) Secondary consumers (e.g., snakes)
(E) Tertiary consumers (e.g., hawks)
The correct answer is Decomposers (e.g., bacteria). Of the list of organisms given, decomposer bacteria are the only ones that can covert nitrogen-containing organic molecules into ammonia. Ammonia, which is a form of nitrogen-containing molecule, is subsequently converted to nitrate that plants can use to synthesize new organic compounds with nitrifying bacteria.
Organisms that convert nitrogen-containing organic molecules into nitrates
(A) Decomposers (e.g., bacteria)
(B) Producers (e.g., grasses)
(C) Primary consumers (e.g., mice)
(D) Secondary consumers (e.g., snakes)
(E) Tertiary consumers (e.g., hawks)
The correct answer is 7.4. The question gives you the information that blood is slightly basic. 10.6 is very basic (recall that pH is a logarithmic scale), 7.0 is neutral, 6.4 is slightly acid, and of course 4.6 is the most acid of the five choices.
The pH of human blood is slightly basic. Which of the following is most likely to be the pH of human blood?
(A)
(B)
(C)
(D)
(E)
The correct answer is a stable dominance hierarchy, (A). Ritualized combat, such as that found in many wild animal populations, leads to a stable hierarchy; generally one individual is acknowledged to be dominant, and true combat is avoided. This benefits both the winner and the loser, as neither faces death or serious injury in a mock battle.
In animals, ritualized contests with little risk of serious injury or death to participants within the species lead to
(A) a stable dominance hierarchy
(B) biological altruism
(C) adaptive radiation
(D) instinctive behavior
(E) a broader habitat
The correct answer is natural selection, (B). Favorable traits increase in a population over time because the organisms bearing those favorable traits have some advantage over other members of the population, and thus leave more surviving offspring than do individuals without the trait. This is sometimes called "survival of the fittest" but it is important to realize that survival alone is only part of the equation; the gene frequency is most influenced by the differential reproductive success of these survivors (that is, by the fact that individuals with the trait leave more offspring than individuals without the favorable trait).
Lamarck, (while a very important man in his time, and one who struggled to come up with an explanation that made sense) has been shown to have been wrong about the inheritance of acquired characteristics, so choice (A) is clearly wrong. Adaptive radiation involves the spread of organisms into open niches and subsequent speciation, so (C) is not a correct choice. Genetic recombination is part of sexual reproduction, whether or not gene frequencies are changing, so (D) is not a correct choice. And finally, segregation of alleles does not explain a change in gene frequency over time. Choice (E) is not correct.
Which of the following correctly explains how a favorable genetic trait can increase in frequency in a population?
(A) Lamarck's principle
(B) Natural selection
(C) Adaptive radiation
(D) Genetic recombination
(E) Segregation of alleles
The correct answer is decomposition, (E). Decomposition breaks down organic material such as sewage. Succession of vegetation types (A) does not explain this process. Eutrophication (B) might well result from the dumping of sewage into a body of water, but does not explain the observation that the stream is free from pollutants a few miles downstream. Evaporation (C ) would result in the loss of water from the stream but not the loss of pollutants. Photosynthesis (D) takes place in aquatic plants and algae, sometimes using the products of decomposition, but it does not result in the breakdown of organic material.
A stream is free of pollutants within a few miles downstream of a point at which a small amount of sewage is being dumped into it. This is most likely the result of
(A) succession
(B) eutrophication
(C) evaporation
(D) photosynthesis
(E) decomposition
The correct answer is that it lowers the pH in ponds and limits the survival of many organisms (A). Choice (B) correctly identifies the lower pH, but incorrectly couples it with water temperature. Choices (C) and (D) incorrectly state that acid rain will raise the pH. Choice (E) suggests that somehow carbon dioxide will removed from the air when acid rain is formed. Carbon dioxide within bodies of water is at equilibrium with carbon dioxide in the air.
As rain mixes with chemicals such as sulfur dioxide in the air, acid rain is produced. This may result in
(A) lowering the pH in ponds, thus limiting the survival of many organisms
(B) lowering the pH in ponds, thus affecting water temperature
(C) raising the pH in ponds, thus encouraging the growth of organisms
(D) raising the pH in ponds, thus limiting animal development
(E) depleting atmospheric carbon dioxide available for photosynthesis
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