- (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.
The primary purpose of the passage is to
Correct Answer:
A
CORRECT TEXT - (Topic 2)
The units digit of 7 is v. and the units digit of 
What is the value of the product xy
Solution:
xy= 54
Does this meet the goal?
Correct Answer:
A
- (Topic 2)
Exhibit.
For what number of pets per household is the total number of households the least?
Correct Answer:
A
- (Topic 3)
Like paleontologists who interpret timescales from fossil evidence, we infer the history of star formation in the Milks' Way galaxy from the heavy-element composition of its stars. According to the big bang theory of the origin of the universe, the first gas clouds—and the first generation of stars formed from them—were composed of pure hydrogen and helium; most heavier elements— iron and calcium, for example—came later, created by explosions of supernovas, massive stars in their death thaws. Loaded with heavy elements, material ejected from supernovas enriched the interstellar gas clouds from which the next generation of stars formed, the level of heavy elements increasing with succeeding generations. Because most stars live for many billions of years and because the Milky Way is thus composed of multiple stellar generations, comparing the number of stars of low heavy-element abundance with those of high heavy-element abundance enables astronomers to untangle the history of star formation in the Milky Way.
The passage implies that if a star contains calcium, then the
Correct Answer:
A
CORRECT TEXT - (Topic 2)
Pumping at a constant rate, a certain gasoline pump can fill an empty 50-gallon tank in 2 minutes. If the pump pumped gasoline into the 50-gallon tank at the constant rate for 1.5 minutes and the tank had 10 gallons of gasoline in it when the pump began pumping, what percent of the volume of the 50-gallon tank was filled with gasoline at the end of the 1.5 minutes?
Solution:
% 95s
Does this meet the goal?
Correct Answer:
A