100% Free Test Prep MCAT Practice Test Questions

Question 1

Band theory explains the conductivity of certain solids by stating that the atomic orbitals of the individual atoms

in the solid merge to produce a series of atomic orbitals comprising the entire solid. The closely-spaced energy

levels of the orbitals form bands. The band corresponding to the outermost occupied subshell of the original

atoms is called the valence band. If partially full, as in metals, it serves as a conduction band through which

electrons can move freely. If the valence band is full, then electrons must be raised to a higher band for

conduction to occur. The greater the band gap between the separate valence and conduction bands, the poorer

the material’s conductivity. Figure 1 shows the valence and conduction bands of a semiconductor, which is

intermediate in conductivity between conductors and insulators.

Figure 1

When silicon, a semiconductor with tetrahedral covalent bonds, is heated, a few electrons escape into the

conduction band. Doping the silicon with a few phosphorus atoms provides unbonded electrons that escape

more easily, increasing conductivity. Doping with boron produces holes in the bonding structure, which may be

filled by movement of nearby electrons within the lattice. When a semiconductor in an electric circuit has

excess electrons on one side and holes on the other, electron flow occurs more easily from the side with

excess electrons to the side with holes than in the reverse direction.

Figure 2

How does heat increase the conductivity of a semiconductor?

I) By reducing collisions between moving electrons

II) By breaking covalent bonds

III) By raising electrons to a higher energy level

Section: Physical Sciences

A : I only

B : III only

C : I and III only

D : II and III only

Answer: D

Question 2

…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.

It can be inferred from the passage that geological theories tend to:

Section: Verbal Reasoning

A : exist in the world of science with little controversy.

B : develop over short periods of time after multiple research efforts.

C : be disproved with the next trend in scientific thought.

D : evolve to incorporate the growing body of knowledge derived from geological research.

Answer: D

Question 3

Figure 1

Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain

containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a

greater affinity for than Hb.

A sample of human adult Hb is placed in an 8 M urea solution, resulting in the disruption of noncovalent

interactions. After this procedure, the α chains of Hb are isolated. Which of the four curves most closely

resembles the O2-dissociation curve for the isolated α chains? [Note: Assume that Curve B represents the O2-

dissociation curve for human adult Hb in vivo.]

Section: Biological Sciences

A : Curve A

B : Curve B

C : Curve C

D : Curve D

Answer: D

Question 4

If (sin [0] + cos [180]) = x − 2(sin [90]) and all angles are in degrees, what is x?

Section: Physical Sciences

A : 0

B : −1

C : −2

D : 1

Answer: D

Question 5

One of the most common methods that scientists use to determine the age of fossils is known as carbon

dating. 14C is an unstable isotope of carbon that undergoes beta decay with a half-life of approximately 5,730

years. Beta decay occurs when a neutron in the nucleus decays to form a proton and an electron which is

ejected from the nucleus.

14C is generated in the upper atmosphere when 14N, the most common isotope of nitrogen, is bombarded by

neutrons. This mechanism yields a global production rate of 7.5 kg per year of 14C, which combines with

oxygen in the atmosphere to produce carbon dioxide. Both the production and the decay of 14C occur

simultaneously. This process continues for many half-lives of 14C, until the total amount of 14C approaches a

constant.

A fixed fraction of the carbon ingested by all living organisms will be 14C. Therefore, as long as an organism is

alive, the ratio of 14C to 12C that it contains is constant. After the organism dies, no new 14C is ingested, and

the amount of 14C contained in the organism will decrease by beta decay. The amount of 14C that must have

been present in the organism when it died can be calculated from the amount of 12C present in a fossil. By

comparing the amount of 14C in the fossil to the calculated amount of 14C that was present in the organism

when it died, the age of the fossil can be determined.

If the global production rate of 14C were to increase to 10 kg per year:

Section: Physical Sciences

A : the number of 14C atoms decaying per minute would increase.

B : the number of 14C atoms decaying per minute would decrease.

C : the weight of 14C on the Earth would increase indefinitely

D : the amount of 14C ingested by living organisms would not change.

Answer: A

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