MCAT Question of the Day

Correct Answer: A. Speed = 6.67 m/s and Velocity = zero

Speed is a scalar quantity involving magnitude only: Speed = distance/time = 400/60 = 6.67 m/s. Velocity is a vector quantity involving both magnitude and direction: Velocity = displacement/time = 0/60 = zero.

Distance traveled is not dependent on a direction, but displacement is. Displacement = distance from the finish to the start, which in this case is zero as the athlete has run around an oval to arrive back at her starting place.

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Correct Answer: C. cellular respiration

In the cell, metabolism is defined as the chemical reactions that occur within the cell to sustain life. Metabolism can further be divided into anabolism (the synthesis of new compounds) and catabolism (breaking down of substances). Answer options A, B, D, and E are all anabolic processes, that require the use of energy to make new compounds. In cellular respiration, glucose is broken down to produce ATP, therefore this is a catabolic process.

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Correct Answer: B. 1/16

F1 generation is the heterozygous offspring of the homozygous parents. F2 generation is the offspring of the heterozygous offspring generation F1. The ratio is 9:3, 3:1 in this generation, meaning that only one of the offspring will have black fur and a long tail.

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Correct Answer: B. Equilibrium favors the products.

In an acid-base equilibrium such as this, the relative strength of an acid can be determined using the magnitude of Ka (or pKa): as Ka increases, the strength of the acid increases; as pKa (inverse log of Ka) decreases, the strength of the acid increases. The equilibrium lies to the left because t-butanol is the weaker acid compared to water. You can also think this way: hydroxide is the weaker base (more stable) compared to t-butoxide because of e- donation of alkyl groups, making the resultant anion less stable (more reactive).

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Correct Answer: D. The amount of salt reabsorbed in the kidneys will increase.

Aldosterone is a hormone released from the adrenal gland. Its presence in the blood helps the kidney’s retain more sodium chloride (NaCl) in the nephrons, thereby desalinating the urine. Glucose regulation is controlled by the pancreas’ release of insulin. Calcium ion levels are controlled by calcitonin and parathyroid hormone. The amount of water retained by the kidneys is controlled by the release of the antidiuretic hormone (ADH) or vasopressin. Aldosterone helps to retain water too, so the amount of water excreted by the body will decrease. Therefore, the correct answer is [D].

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Correct Answer: C. 16 W

When resistors are in parallel, we can find equivalent resistance simply by using the equation:

(1/Req) = (1/R1) + (1/R2) + … + (1/Rn)

In this case, the equivalent resistance is: (1/Req) = (1/12)+(1/12)+(1/12)= 3/12

We find that Req = 4. We then input this into our equation for the power of a circuit

P = IV = V²/R = 8²/4= 16W

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Correct Answer: C. 120^o

An sp²-hybridized carbon has a trigonal planar geometry. This means that the bond angle will be 120^o, so answer choice C is the best choice. An sp-hybridized carbon has a linear geometry, meaning a bond angle of 180^o. Finally, an sp³-hybridized carbon has a tetrahedral geometry with bond angles of 109.5^o.

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Correct Answer: A. Blood is pumped from the ventricles to the arteries.

Systole is the state of contraction of the heart muscles. The heart contracts to pump blood out of the ventricles and into the arteries to move the blood to the body. During diastole or when the heart is resting, blood collects in the chambers of the heart. Arteries carry blood away from the heart and veins carry blood back to the heart. During systole, the blood is being pumped away from the heart, thereby the use of arteries is essential. The only answer option that aligns with the correct function of the heart during systole is [A].

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Correct Answer: D.

Aromatic compounds follow four rules: (1) They are conjugated—there needs to one “p” orbital from each atom in the ring, so each atom must be either sp2 or sp hybridized; 2) They are cyclic: linear systems are not aromatic; 3) They are planar: there is good overlap/interaction between p orbitals; 4) they follow the The Huckel Rule—4n+2 pi electrons in the cyclic conjugated pi system (n = 0, 1, 2, 3 etc.)

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Correct Answer: D. The rate order.

“SN” stands for nucleophilic substitution and the “1” represents the fact that the rate-determining step is unimolecular.

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