GMAT Online Practice Questions and Answers

Correct Answer: E

Correct Answer: E

Correct Answer: C

Correct Answer: B

Correct Answer: D

Parasitic wasps propagate by injecting their eggs into a caterpillar that then becomes paralyzed as the eggs inside develop into wasp larvae. The wasp larvae kill the caterpillar host as they feed on it, form cocoons, and finally develop into wasps. In attempting to discover how such wasps detect the presence of the caterpillar hosts that are so critical to the wasps' propagation, researchers have uncovered an intriguing defense mechanism developed by the plants on which the caterpillars feed. When chewed on, many plants release volatile compounds from both damaged and undamaged tissues. When these compounds are toxic to the insects that feed on the plants, they can help defend the plants from such attacks. However, the plants on which the wasps' caterpillar hosts feed have evolved an even more complex defense: the caterpillar-infested plants appear to release volatile chemicals that attract parasitic wasps, which then prey on the caterpillars. Scientists originally suspected that the wasps were attracted by an odor, reminiscent of cut grass, that is released as the caterpillar feeds, but a recent study suggests that a different set of volatile attractants is involved. In this study, when researchers used a razor blade to mimic caterpillar damage on the leaves, only grassy odors were emitted, not the volatile compounds that attracted wasps. However, when oral secretions from the caterpillars were applied to these damaged leaves, the leaves released the wasp attractants several hours later. Further tests revealed that oral secretions placed on the razor-damaged leaves stimulated the release of such attractants, making the plants as attractive to wasps as plants that had suffered actual caterpillar damage. These results suggest that chemicals from the caterpillar must be present for these attractants to be released and that unlike the grassy scent, which emanates only as the caterpillar on the plant, the wasp attractants are produced several hours after the attack and persist for several hours, perhaps days. Researchers have launched additional studies to determine whether the wasps' capacity to prey on caterpillars can be enhanced to the extent that the wasps could be used as a natural pesticide to "police" plants and protect them from crop- destroying caterpillars.

Correct Answer: E

Correct Answer: E

United States Geological Survey scientists have found that a cooling in Pacific Ocean temperatures led to increases in ecologically threatening phytoplankton blooms in San Francisco Bay, California. The declining temperatures took place off the coast of California between 1999 and 2004. The occurrence of these blooms is surprising because such blooms are normally associated with increases in the amount of nutrients, such as nitrogen and phosphorus, entering estuaries from such sources as wastewater treatment plants and agricultural fields. In this case, the bay's phytoplankton blooms occurred during a period of decreasing nutrient concentration and inputs. The scientists discovered the effects of the cold Pacific temperatures by using biological and water-quality data collected over twenty-five years. The colder temperatures caused changes in the types, abundance, and migration patterns of marine life into the San Francisco Bay from coastal ocean waters. For example, marine life, such as fish, shrimp, and crabs, migrated to the warmer waters that are found in the bay. The migrations increased the numbers of predators such as bay shrimp and Dungeness crabs that eat filter feeders, such as clams. Clams can filter large quantities of phytoplankton from the bay's water, which can prevent phytoplankton blooms. With the increase in predators, there was a corresponding decrease in clam populations and an increase in phytoplankton.

Correct Answer: B

Correct Answer: A

Parasitic wasps propagate by injecting their eggs into a caterpillar that then becomes paralyzed as the eggs inside develop into wasp larvae. The wasp larvae kill the caterpillar host as they feed on it, form cocoons, and finally develop into wasps. In attempting to discover how such wasps detect the presence of the caterpillar hosts that are so critical to the wasps' propagation, researchers have uncovered an intriguing defense mechanism developed by the plants on which the caterpillars feed. When chewed on, many plants release volatile compounds from both damaged and undamaged tissues. When these compounds are toxic to the insects that feed on the plants, they can help defend the plants from such attacks. However, the plants on which the wasps' caterpillar hosts feed have evolved an even more complex defense: the caterpillar-infested plants appear to release volatile chemicals that attract parasitic wasps, which then prey on the caterpillars. Scientists originally suspected that the wasps were attracted by an odor, reminiscent of cut grass, that is released as the caterpillar feeds, but a recent study suggests that a different set of volatile attractants is involved. In this study, when researchers used a razor blade to mimic caterpillar damage on the leaves, only grassy odors were emitted, not the volatile compounds that attracted wasps. However, when oral secretions from the caterpillars were applied to these damaged leaves, the leaves released the wasp attractants several hours later. Further tests revealed that oral secretions placed on the razor-damaged leaves stimulated the release of such attractants, making the plants as attractive to wasps as plants that had suffered actual caterpillar damage. These results suggest that chemicals from the caterpillar must be present for these attractants to be released and that unlike the grassy scent, which emanates only as the caterpillar feeds on the plant, the wasp attractants are produced several hours after the attack and persist for several hours, perhaps days. Researchers have launched additional studies to determine whether the wasps' capacity to prey on caterpillars can be enhanced to the extent that the wasps could be used as a natural pesticide to "police" plants and protect them from crop- destroying caterpillars.

Correct Answer: A

Despite overall physiological bilateral symmetry, many species exhibit lateralized biases, i.e., preferences for right- or left-oriented behavior. When approaching prey, for example, some predator species favor their right eye; some prey species respond more quickly when their left eye detects a predator. Similar behavioral asymmetries occur in humans. Most notable is right- and lefthandedness; less notable is the tendency to turn right when entering a room. Paul Farnsworth found that more successful students tended to choose seats near the front, a little to the right. He argued that external factors such as teacher location might have affected this lateral bias. But it is now known that processing differences between the two brain hemispheres can also contribute to behavioral asymmetries. George Karev found that when presented with a movie theater seating diagram, right-handed people were more likely than left-handed people to choose a seat on the right, facing front. But he hypothesized that, since the right hemisphere processes visuospatial and emotional information, the people who chose right- side seats did so because that would put the screen in their left visual field, optimizing information flow to the right hemisphere. Although the right hemisphere is thought to be dominant in processing emotion, some evidence suggests that the left hemisphere plays a role. The valence model proposes that the left and right hemispheres process positive and negative emotion respectively, while the approach-withdrawal model posits that the left hemisphere processes emotion expressed in approach behavior and the right hemisphere processes emotion expressed in withdrawal behavior. Victoria Harms and colleagues suggested that since a paper seating plan was used in the theater-seating studies by Karev and others, the exhibited preference might be due simply to handedness: people choose the same side of the paper as their favored hand. Consequently, the Harms research was designed to study choices in an actual movie theater. Also, hoping to distinguish between various explanations, they studied seating choices for comedies (presumed to contain Positive emotional content), dramas (presumed to contain negative emotional content), and documentaries (presumed to have balanced emotional content). They found significant--though not universal-- preference for seats on the right, facing front, regardless of movie genre and of handedness.