MCAT-Test Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample - Practice Questions

Question 7 (Physical Sciences)

A ski jump is an inclined track from which a ski jumper takes off through the air. After traveling down the track, the skier takes off from a ramp at the bottom of the track. The skier lands farther down on the slope.

Figure 1 shows a ski jump, in which the ramp at the lower end of the track makes an angle of 30° to the horizontal. The track is inclined at an angle of to the horizontal and the slope is inclined at an angle of 45° to the horizontal. A ski jumper is stationary at the top of the track. Once the skier pushes off, she accelerates down the track, and then takes off from the ramp. The vertical height difference between the top of the track and its lowest point is 50 m, and the vertical height difference between the top of the ramp and its lowest point is 10 m.

Figure 1

The distance traveled by the skier between leaving the ski jump ramp and making contact with the slope is called the jump distance. In some cases, in order to increase the jump distance a skier will jump slightly upon leaving the ramp, thereby increasing the vertical velocity. Unless otherwise stated, assume that friction between the skis and the slope is negligible, and ignore the effects of air resistance.

If a skier uses skis of greater surface area, which of the following would occur?

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The normal force of the slope on the skier would increase.
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The normal force of the slope on the skier would decrease.
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The pressure exerted on the slope by the skis would increase.
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The pressure exerted on the slope by the skis would decrease.

Question 8 (Physical Sciences)

Several techniques have been developed to determine the order of a reaction. The rate of a reaction cannot be predicted on the basis of the overall equation, but can be predicted on the basis of the rate-determining step. For instance, the following reaction can be broken down into three steps. A + D → F + G

Step 1

A → B + C(slow)

Step 2

B + D → E + F(fast)

Step 3

E + C → G (fast)

Reaction 1

In this case, the first step in the reaction pathway is the rate-determining step. Therefore, the overall rate of the reaction must equal the rate of the first step, k1 [A] where k1 is the rate constant for the first step. (Rate constants of the different steps are denoted by kx, where x is the step number.)

In some cases, it is desirable to measure the rate of a reaction in relation to only one species. In a second-order reaction, for instance, a large excess of one species is included in the reaction vessel. Since a relatively small amount of this large concentration is reacted, we assume that the concentration essentially remains unchanged. Such a reaction is called a pseudo first-order reaction. A new rate constant, k', is established, equal to the product of the rate constant of the original reaction, k, and the concentration of the species in excess. This approach is often used to analyze enzyme activity.

In some cases, the reaction rate may be dependent on the concentration of a short-lived intermediate. This can happen if the rate-determining step is not the first step. In this case, the concentration of the intermediate must be derived from the equilibrium constant of the preceding step. For redox reactions, the equilibrium can be correlated with the voltage produced by two half-cells by means of the Nernst equation. This equation states that at any given moment:

Equation 1

When

a A + b B → c C + d D

Reaction 2

Note: R = 8.314 J/K·mol; F = 9.6485 × 104 C/mol.)

What is the effect of increasing the concentration of reactants in a voltaic cell?

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The voltage increases, while the spontaneity of the reaction remains the same.
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The spontaneity of the reaction increases, but the voltage remains the same.
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Both the voltage and the spontaneity of the reaction increase.
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The reaction rate increases, but the voltage and spontaneity of the reaction are unchanged.

Reference / correct answer:

Both the voltage and the spontaneity of the reaction increase.

To answer this question, you need to understand the relationship between the concentration of reactants and the spontaneity and voltage of the reaction. First let’s review what is meant by voltage. When a reaction takes place in a voltaic cell, the oxidation reaction at the anode produces excess electrons. Meanwhile, reduction at the cathode uses up electrons. For the reaction to continue, the cathode needs an additional supply of electrons. As a result of the two half-reactions, there is a movement of electrons through the wire from the anode to the cathode. The faster the reaction takes place, the greater the electrical force pushing electrons away from the anode and pulling them toward the cathode will be. This pressure on the electrons is called the electromotive force, or EMF. The electromotive force is measured in volts, and so is also known as the voltage. Don’t confuse the voltage with the current – the voltage is the pressure on the electrons, while the current is the actual movement of electrons through the wire. The current depends not only on the pressure exerted by the EMF, but also on the amount of resistance of the wire. The voltage or electromotive force created by a redox reaction depends on the number of electrons exchanged in the reaction and the rate at which the reaction takes place. If the rate of the reaction changes, then the voltage or potential also changes. If the concentration of reactants is increased, then the reaction will move more quickly to the right, producing more electrons at the anode and using more at the cathode. This increases the voltage. So an increase in the concentration of reactants will increase the voltage. The spontaneity of a reaction is determined by Gibb’s free energy, ∆G. If ∆G is negative, the reaction is spontaneous; if ∆G is positive, the reaction is not spontaneous. There is a direct relationship between the potential of a reaction and its free energy, given by the equation: ∆G = – nFE, where n is the number of moles of electrons transferred in the reaction, F is Faraday’s constant and E is the cell voltage. So what will happen to the value of ∆G if we increase the concentration of the reactants? The reaction will proceed more quickly, increasing the flow of electrons, and therefore increasing the voltage, which in turn will make the value of ∆G more negative. As the value of ∆G becomes more negative, the reaction becomes more spontaneous. So choice C is correct; the increased concentration of reactants increases both the voltage and the spontaneity of the reaction.

Question 9 (Biological Sciences)

Destroying the cerebellum of a cat would cause significant impairment of normal:

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urine formation.
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sense of smell.
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coordinated movement.
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thermoregulation.

Reference / correct answer:

coordinated movement.

To answer this question, you have to be familiar with the functions under the control of the cerebellum. The cerebellum is part of the hindbrain, which is the posterior part of the brain and consists of the pons and the medulla oblongata, in addition to the cerebellum. The cerebellum receives sensory information from the visual and auditory systems, as well as information about the orientation of joints and muscles. In fact, one of the cerebellum’s main functions is hand-eye coordination. It also receives information about the motor signals being initiated by the cerebrum. The cerebellum takes all of this information and integrates it to produce balance and unconscious coordinated movement. Damage to the cerebellum could damage any one of these functions. Total destruction of the cerebellum would eliminate all of them. Therefore, choice C is correct because destruction of a cat’s cerebellum would seriously impair coordinated movement in the cat. Let’s take a look at the other choices. Urine formation, choice A, is the primary function of the kidneys, with a little bit of hormonal regulation to help things out. Choice B, sense of smell, or olfaction, is a function of the cerebrum not the cerebellum. Thermoregulation, choice D, is a function of the hypothalamus, which is a part of the cerebrum.

MCAT-Test – Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample