MCAT-TEST Exam Questions & Answers

For the last two decades many earth scientists have supported the notion that the Mediterranean was once a huge, dry desert, lying 3,000 meters below sea level. This "death valley" was thought to have existed at the end of Miocene time, about 6 to 5.5 million years ago.... ...From a geological point of view, the Mediterranean is a tectonically mobile land-enclosed depression -- small (about 3,000,000 square kilometers) in comparison to the major world oceans...Immediately obvious on all charts is the highly variable topography and relief of both the seafloor and adjacent borderland. The coastline is highly irregular and continental shelves, though generally narrow, are well developed off the major river deltas (Nile, Rhone, Po, and Ebro). Moreover, the deep-sea basins and trenches have distinctive relief, with basin plains ranging in depth from less than 1,000 meters to more than 4,000...Observation that rocks dredged offshore are similar to those on land raised a fundamental concept -- the key to understanding Mediterranean history lies in the adjacent emerged land masses, and vice- versa.... ...Early paleographic reconstructions showed that the once-open communication with the Atlantic deteriorated during the upper Miocene. Water-mass exchange continued for a while in the Rif Strait, but then ceased completely prior to the beginning of the Pliocene.... ...High relief near what is now the Strait of Gibraltar served as a barrier to the exchange of waters with the Atlantic. Exposed to a hot and dry climate, water evaporated and the then-dry basin elicited comparison with a gigantic Death Valley... Microfossil studies suggested that the depth of the Mediterranean basin at these times had been "deep." Estimates suggested a dry seafloor as far as 2,000 meters below ocean level... As a response to suddenly lowered sea level, rivers feeding the Mediterranean and canyons on the now-dry seafloor began a geologically dramatic phase of erosion. Deep, Grand Canyon-like gorges of the Nile and Rhone rivers, presently buried on land, were apparently cut during a great drawdown of water -- when the Mediterranean floor lay exposed 1,000 meters or more below its present level...The sudden flooding through a gigantic waterfall at Gibraltar drowned the exposed basin floor. These falls would have been 1,000 times bigger than Niagara Falls...This flooding event is recorded by the Miocene Pliocene boundary, a time when open marine faunal assemblages were suddenly reintroduced from the Atlantic.... ...Geological theories usually fall at a glacial pace into a sea of controversy, and this one is no exception. Today -- charging that proof for the theory is lacking -- many scientists believe that the Med always contained saltwater, with only the depth of the seafloor and the water being in question... Some of the tenets on which the theory was formulated are, if not defective, very seriously in question. To interpret their findings, a respectable number of geologists studying the surrounding emerged borderland as well as subsea sections indicate that alternative, more comprehensive concepts must be envisioned.... ...It is not realistic to envision the Mediterranean seafloor of about 5 million years ago as a desert at 3,000 meters below present ocean level. Several years ago...the Mediterranean [was compared] to a complex picture- puzzle that comprises numerous intricate pieces, many of which are already in place. A general image is emerging, although gaps in some areas of the picture remain fuzzy and indistinct.

In the context of the passage, the term "emerged land masses" (lines 19-20) refers to: A. regions of land that surround the Mediterranean.

B. barriers that develop into waterfalls.

C. saline-concentrated soil that extracts water from surrounding tributaries.

D. continents that have come to touch one another.

Milk produced initially by the mammary glands contains special lymph-like fluid that is called:

A. amniotic fluid.

B. colostrum.

C. pleural fluid.

D. serum.

Glycogen storage disease type V, also known as GSD-V or McArdle disease, is an autosomal recessive disease that results in the deficiency of myophosphorylase, an isoform of glycogen phosphorylase found in muscle cells. Patients with GSD-V experience severe muscle cramps after strenuous exercise and exercise intolerance.

Physicians may order two histology stains of the patient's muscle tissue in order to aid in the diagnosis (see Figure 1):

(A) A Periodic acid-Schiff (PAS) stain uses periodic acid to detect carbohydrates in tissues. The reaction of the acid with sugar cleaves vicinal diols creating ketone and/or aldehyde fragments, the latter of which then reacts with the Schiff reagent to give a purple color;

(B) A phosphorylase stain identifies the presence of the enzyme using a dark blue color indicator.

Figure 1A. Comparative histochemistry of GSD-V and healthy individual.

PAS stain of muscle tissue shows an accumulation of glycogen in the GSD-V individual (top) compared to the control (bottom). B) Phosphorylase stain of muscle tissue reveals an absence of phosphorylase in the GSD-V individual (top).

Despite initial pain during exercise, many patients with GSD-V have been able to increase their exercise tolerance by engaging in moderate periods of aerobic exercise. Muscle pain and fatigue subsides after a few minutes, a response that

researchers call the "second wind" phenomenon.

Patients who experienced "second wind" typically experienced lowered heart rate and a reported decrease in exercise effort after 7-10 minutes. A similar effect was seen in the same patients after an intravenous infusion of glucose.

Figure 2. Measured heart rates in two GSD-V patients during sustained exercise.

Two subjects were asked to ride stationary bicycles at a steady rate over the course of 40 minutes. The subjects' heart rates were measured continuously, with high and low values coinciding with 7-minute intervals. Glucose was injected

intravenously after 21 minutes. SW = Second Wind.

Adapted from Bhavaraju-Sanka R, Howard J. Jr, Chahin N (2014). SOJ Neurol 1(1), 1-3. and Haller RG, Vissing J. Arch Neurol. 2002;59(9):1395-1402.

Considering the information provided and your knowledge of glucose and fructose, which of the following is MOST likely to be accurate regarding the reaction with periodic acid?

A. The reaction would break the cyclic structures of glucose and fructose, with glucose having an additional fragment per molecule.

B. The reaction would break the cyclic structures of glucose and fructose, each into equal fragments.

C. The reaction would break the cyclic structure of glucose but not fructose.

D. The reaction would neither break the cyclic structure of glucose nor fructose.