- (Topic 3)
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?

Correct Answer:C

- (Topic 3)
Experimental magazine essays are quite in vogue, but many of the characteristic that now seem innovative will doubtless look (1) _____ in thirty years" time; a vaunted self- consciousness will look affected, a fractured style, far from appearing (ii) _____ will appear (lii) _____ instead.

Correct Answer:CDE

- (Topic 3)
One reason researchers have long believed that Mars never enjoyed an extensive period of warm and wet climate is that much of the surface not covered by wind-borne dust appears to be composed of unweathered material. If water flowed for an extended period, researchers reasoned, it should have altered and weathered the volcanic minerals, creating clays or other oxidized, hydrated phases (minerals that incorporate water molecules in their crystal structure).
It turns out. though, that the scientists were not looking closely enough. New high- resolution mapping data and close-up surface studies have revealed clays and other hydrated minerals in many regions The clay deposits are scattered all over, in ancient volcanic surfaces and heavily cratered highland regions, some of which have apparently been exposed by erosion only recently.
Consider each of the choices separately and select all that apply.
The passage indicates which of the following about the clay deposits an Mars?

Correct Answer:ABC

- (Topic 3)
In 1995 the United States National Park Service reintroduced wolves into Yellowstone National Park, from which they had been eliminated decades before by overhunting. Biologists hoped the reintroduction would return the park's mix of animals to a more natural state. After the wolves* disappearance, the population of their onetime prey, the elk. had burgeoned. Subsequently, new tree growth declined as multiplying elk browsed young trees, denuding certain areas of the park. Following the wolves" return, the elk population declined and young trees rebounded. Most scientists attribute the vegetation changes to the wolves" return. However. Patton observes that Yellowstone has not had a harsh winter since wolf numbers reached high levels and suggests that elk may not have needed to resort to trees for food.
If the view attributed to the majority of scientists is correct, which of the following must be true?

Correct Answer:C

- (Topic 3)
Although the claim that no one knows what dark matter is remains parallel assertion that dark matter has not been detected.

Correct Answer:CE

- (Topic 3)
The landmasses that we see on Earth today have moved around the globe, smashing together and splitting apart several times over the past 3 billion years. These cycles of (i) _____ and (ii) _____ have affected Earth's crust and underlying mantle, its atmosphere and climate, and the life ii supports.

Correct Answer:CE