MCAT Question of the Day

Correct Answer: A. mitochondria and peroxisomes.

Beta oxidation occurs in the peroxisomes in plant and yeast cells. In contrast, this vital reaction takes place in mitochondria and peroxisomes in mammalian cells. Peroxisomes are equipped with the appropriate enzymes that can facilitate the break down of very long fatty acid molecules.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: C. Rolling backwards on an even floor.

Friction is the cause of the heated wheels. The heat energy produce by friction is the work done by frictional forces.

Because the distance and the surfaces are the same, all we need to focus on is the normal force. Normal force is the equal but opposite force a body, generally it’s weight, applies to the contacting surface. On any incline only a fraction of the weight, Wa, is applied to the inclined surface. Assuming the acceleration of his rolls is not directly into the ramp, you will have the greatest friction on a flat surface. This is apparent when we tend to see objects sliding on ramps and not as much on the floor.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: B. V = IR

At a first glance, one might think that none of these equations deal with heat. It is important to recall that heat is energy. Immediately one can rule out answer choices A and C, as they do not deal with energy. Taking a deeper look into equation D we can see Einstein’s famous equation states that the energy is equal to some constant squared. We can try to relate that with heat, by asking if heat is proportion to a single constant. We know that this is not true by 1.) ice melts at different rates depending on the temperature and 2.) chocolate and ice melt at different rates at the same temperature. We have parameterized heat based on ambient temperature as well as by the individual material. The remaining solution is choice B.
Lets confirm this be taking a further look into choice B. Ohm’s law says that the potential is directly related to the current by a resistance. This can be rearranged to have the current indirectly related to the potential through resistance, or directly related to the potential through the conductance, g.

The current is a charge rate, Q/t. If we replace charge with heat, we can obtain the thermal conduction formula. With the charge rate becoming a heat rate, the conductance becoming a heat conductance, and the potential difference becoming the temperature drop.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: A. H3N⁺-CH2-COO^–

Recall that you can use isoelectric point (PI) to predict an amino acid’s charge at any given pH. Specifically, if PI < pH, then this means that pH is high -- which means that [H+] is low, and charge is negative. Likewise, if PI > pH, then this means that pH is lower — which means [H+] is high and charge is positive. In this case, PI = pH, which means that charge is zero (the amino acid is neutral). Thus, the answer is A since this is the amino acid where both charges cancel each other out, leaving a neutral zwitterion glycine.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: A. (CH3CH2)3CF; SN1

This is an example of a SN1 reaction where first step is Br (good leaving group) dissociates to produces a carbocation (stabilized by the polar protic solvent, water). The tertiary carbocation intermediate is very stable, especially in the highly polar protic solvent water. The carbocation then combines with the strong nucleophile, the the F- ion. (the original substituent (Br) must be a better leaving group than the nucleophile (F-) in order for the reaction to occur). C and D are wrong because this is not an elimination reaction. B is wrong because this is not an SN2 reaction, due to the highly hindered substrate, and the type of solvent used in the reaction (SN2 reactions favor polar aprotic solvents, not polar protic solvents).

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: C. frequency of homozygote BB is q² .

This question requires just a simple understanding of the According to the Hardy-Weinberg equation, (p+q)²=1, , or rather: and p² + 2pq + q² = 1.
If we have a gene with two alleles, A and B, and its frequencies are p and q, then we can know that the frequencies of the genotypes are as follows, by plugging into our Hardy Weinberg equation:
predicted frequency of homozygote AA = p²
predicted frequency of homozygote BB = q²
predicted frequency of heterozygote AB = 2pq.
The only answer choice that fits this solution is answer choice C.
Looking at the other answers, A is incorrect because it is an inaccurate representation of the Hardy Weinberg equation. Answer B is also incorrect because if one assumes that a gene has only two alleles, then then the frequency of p+q combined has to be 100%, or rather p + q = 1.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: A. 2 billion W/m²

We know that the ratio of photons to rod cells is 1:1. With that we can compute the required amount of photons needed by multiplying the total amount of rod cells for 2 eyes, with the percentage required to blind. The required amount of photons are distributed across an entire retina. This will give a photon density of 10 billion per meter squared.

Each photon has a power of P. Intensity is power over area, or power times particle density.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: A. R * C * ln(6/5) * s

You can answer this question quickly by dimensional analysis. The natural log is dimensionless yielding us 2 set of 2 choices. We are looking for time, units of seconds. One electrical value that contains seconds is current.

This leaves answers A and B. You should know with a discharging capacitor at time RC = Tc the value of the discharged capacitor is 37% (e^-1) its initial value. 0.37 != (25/30) leaving answer choice A.
For those who would like to remember the discharge formula its:

All you would need to do is plug in the values and rearrange until you arrive at answer choice A.
300 volts or proportionally 0.4 A/kg is a good estimate of how much charge is needed to restart the heart. You can calculate a lower 10 ohms resistance for the heart, from the required current and voltage.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: B. 10 m/s

First apply the flow equation: A1v1 = A2v2, where A2 and v2 are the cross section and velocity of the top surface of the water:

A1v1 = A2v2
v1*pi* (1 * 10^-2 m)² = v2*pi*(2m²)

v1 = 4m²/ (1 * 10^-4 m²) * v2
Solving for v1 gives us v1 = (4 * 10⁴ m²/s) v2

Though this does not give us an exact answer yet, it DOES give us important info! That is the velocity of the top surface of the water (v2) is insignificant compared to the velocity of the water coming out of the hole (v1). This allows us to set v2 = 0 in our second equation, Bernoulli’s equation:
p1 + pgy1 + (1/2)pv1² = p2 +pgy2 + (1/2)pv2²
Not only can we set v2 = 0, but we can also recognize that in a 5 meter-high column of water, the pressure at the bottom (p2) and bottom (p1) will be essentially the same, due to the fact that the additional pressure added by 5 meters of water is insignificant compared with the atmospheric pressure at the top (p1). Thus, the pressure terms can also be neglected, and the Bernoulli equation simplifies to give us:

pgy1 + (1/2)pv1² = pgy2
v1² = 2g(y2 – y1)
Solving for v1 gives:

v1 = Sqrt(2(10m/s²)*5m)) = 10 m/s, or answer B.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: B. 9 m/s

The water will exit at a velocity which is proportional to the height it has fallen, according to the equation v = sqrt(2gh). This can be derived from the basic equation for velocity and displacement, v2 = 2a * s, where a is acceleration, and s is displacement (or in this case height). Thus, the height the water has fallen in this problem is 4 meters, and v = 8.85m/s, which we round up to 9.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.