Free Admission Tests GRE Practice Exam with Questions & Answers | Set: 8

Instances of "galactic cannibalism"—mergers in which large galaxies completely consume smaller ones—may be fairly common. Tidal forces produced by the Milky Way's powerful gravity, for example, appear to be dismantling and engulfing a dwarf galaxy in the constellation Sagittarius, producing large clumps and streamers of stars connecting the two galaxies. Astronomers have also observed two dense clusters of stars and gas at the heart of the Andromeda galaxy, an apparent "double nucleus" that may contain the remnant of a cannibalized dwarf galaxy. But this Twin-lobed appearance could also be created by two parts of a single nucleus bisected by a lane of dust. Scientists believe that only about 25 percent of such apparent double nuclei actually represent galactic cannibalism. Many of the rest result from the illusion of proximity that occurs when objects at different distances appear along the same line of sight: others consist of debris from galactic "collisions." in which one galaxy has passed through another without merging, causing waves of new star formation.

According to the passage, a true double nucleus may be produced by the

Recent research has questioned the long-standing view of pearly mussels as exclusively suspension feeders (animals that strain suspended particles from water) that subsist on phytoplankton (mostly algae). Early studies of mussel feeding were based on analyses of gut contents, a method that has three weaknesses. First, material in mucus-bound gut contents is difficult to identify and quantify. Second, material found in the gut may pass undigested out of the mussel, not contributing to its nutrition. Finally, examination of gut contents offers limited insight into the mechanisms and behaviors by which mussels acquire food. Modem studies suggest that pearly mussels feed on more than just algae and may use other means than suspension feeding. Pedal feeding (sweeping up edible material with a muscular structure called the foot) has been observed in juvenile pearly mussels.

Besides the phytoplankton pearly mussels capture from the water column, their guts also contain small animals, protozoans, and detritus (nonliving particulate organic material). Recent studies show that mussels can capture and assimilate bacteria as well, a potentially important source of food in many fresh waters. Another potential source of food for mussels is dissolved organic matter. Early studies showing that pearly mussels could take up simple organic compounds were largely discounted because such labile (unstable) compounds are rarely abundant in nature. Nevertheless, recent work on other bivalves suggests that dissolved organic matter may be a significant source of nutrition.

Of this complex mix of materials that pearly mussels acquire, what is actually required and assimilated? Stable-isotope analyses of mussels taken from nature and of captive-reared mussels are beginning to offer some insight into this question. Nichols and Garling showed that pearly mussels in a small river were omnivorous, subsisting mainly on particles less than 2S micrometers in diameter, including algae, detritus, and bacteria. Bacterially derived carbon was apparently the primary source of soft-tissue carbon. However, bacteria alone cannot support mussel growth, because they lack the necessary long-chain fatty acids and sterols and are deficient in some amino acids. Bacteria may supplement other food resources, provide growth factors, or be the primary food In habitats such as headwater streams, where phytoplankton is scarce. Juvenile mussels have been most successfully reared m the laboratory on diets containing algae high in polyunsaturated fatty acids. Thus, it appears that the pearly mussel diet in nature may consist of algae, bacteria, detritus, and small animals and that at least some algae and bacteria may be required as a source of essential biochemicals.

Which of the following can be inferred about the "recent research?

The movie has a surfeit of inscrutable characters and tortuous subplots, so it is no surprise that viewers leaving the recent screening appeared_________-

Until 1992. microprocessor types were identified by number, and for a long time they were considered so _________that manufacturers would share design specifications for them.

The poet Paul Laurence Dunbar (1872-1906) was the premier Black writer of poetry that used the dialect of rural African Americans of the southern United States. Although Dunbar's works were both popular with readers and acclaimed by literary critics during his lifetime, after the First World War a radical shift occurred, at least in critical opinion of his poetry, and twentieth-century critical evaluation of his work has been generally negative. Some critics attacked his work on social grounds for failing to challenge plantation stereotypes of African Americans. Other critics, such as the poet James Weldon Johnson, argued from aesthetic grounds that dialect poetry in general was too limited as an artistic medium, and capable of producing only two effects: pathos and humor. The negative critical trend only began to reverse itself in the 1970s, when scholars began to emphasize the importance of mythic, psychological, and historical dimensions of Dunbar's works, focusing on the interior and exterior realities of African American life after the Civil War.

Which of the following can be inferred from the passage concerning scholars' use of mythic, psychological, and historical considerations in evaluating Dunbar's works?

What accounts for the low-lying. Hat surface of Mars's north? On Earth's surface, higher- and lower-lying areas have different types of onest: one. thin and dense, is pulled toward Earth's center more strongly by gravity, and the planet's water naturally comes to sit over it. creating oceans. The processes that generate this oceanic crust drive plate tectonics.

Is Mars's north similarly characterized by a sort of crust different from other areas of the planet? Some researchers do see signs of tectonic activity surrounding the northern basin that suggest that it was created through the formation of new crust, like ocean basins on Earth. However. McGill points to northern bedrock structures that predate the features said to mark the start of the tectonic process. McGill instead believes that through some novel mechanism the ancient surface sank to its current depth as a single unit. This would explain why features around the basin's edge. which would have formed as the surface dropped, seem to be younger than structures at its floor.

The third possibility is that the northern lowlands result from impacts. Some researchers suggest they formed as a series of big overlapping impact craters. Others, arguing that the odds against such a pattern of impacts are large, postulate a single event—the impact of an object bigger than any asteroid the solar system now contains.

The passage implies that McGill points to certain "northern bedrock Structures? in order to

Female Australian Dunaiothhps [small, sap-sucking insects] create tent-like structures on the surface of leaves to protect themselves and their eggs and larvae from desiccation in the arid Australian climate. Bono and Crespi compared survival and reproduction of thrips that founded structures alone with those in groups of two or more individuals. They found that although per capita egg production fell with increasing group size, foundresses were more likely to survive and lay eggs in groups than when alone. Several studies of other species of nest-building insects have concluded that foundress associations are beneficial to all parties. It is likely that the relative success of groups is at least in part accounted for by a reduction of energy use in the modification of a shared nest.

The author mentions "desiccation" primarily to

Nature's Metropolis was Cronon's effort to show that the idea of a boundary between natural and unnatural is profoundly_________. that neither the city of Chicago nor its hinterland can be understood independently of the other.

People who come to believe false rumors often do so quite (i)_________in the sense mat their new belief

(ii)_________their existing knowledge. This problem is especially acute on the Internet. Rumors often arise and gain

traction because they fit with, and support, the prior convictions of those who accept them.

The public has not reacted favorably to the majority of the policies adopted by the present government. If. however, the electoral landslide by which the government achieved power five years ago was. as is often claimed, a mandate for more conservative policies, then the public response to most of the government's policies would have been favorable.

If the statements in the passage are true, which of the following must also be true on the basis of them?