Questions 10-13 on Next Step Test Prep’s full-length 10 are the first set of discrete questions that we’re going to cover during this full-length breakdown. Take a look!
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[02:25] Passage vs. Discrete
Bryan explains that in all the science sections, all have the same compositions with 15 discrete questions given in four little chunks of 3-4 questions each. The test always ends on a chunk of discrete, independent (no passage) questions. And then the other three chunks are sprinkled throughout where in every two or three passages, you will get a little break. You won’t have to read a passage and you just get some independent questions.
[03:14] Stationary Charge
Question 10: A stationary charge lies to the right of a current carrying loop of wire as depicted in the figure below (Please see the handouts). While the current is flowing, the charge will:
- (A) Accelerate out of the page
- (B) Move out of the page at a constant speed
- (C) Accelerate into the page
- (D) Remain motionless
The current is actually going clockwise with a positive charge. Bryan explains there’s a couple of components underlying this question. First, flowing charge or current makes some magnetic field. So you have this magnetic field being generated and you have this charge hanging out over on the side. The question is once the magnetic field is present, what does the charge do?
Students need to remember the equation F = QVB sin theta.
But the questions says that the charge is stationary. So based on the equation, there is no velocity. So there’s no force. Hence, the magnetic field doesn’t actually push on the charge at all. Then you have to remember Newton’s second law, which is F = ma. No force, no acceleration. This means it doesn’t start moving. It doesn’t slow down. It doesn’t change direction. So the right answer is D.
[06:15] An Issue of Spontaneity
Question 11: While solving a chemistry problem, a student uses the equation Delta G = negative NFE to determine that Delta G is negative 179kJ/mol. Which of the following must be true:
- The reaction is spontaneous.
- The reaction is exothermic.
III. The reaction increases entropy.
- (A) I only
- (B) II only
- (C) I and II
- (D) I, II, and III
It’s an important fact to remember that the sign of Delta G is really the definition of spontaneity – so things like breaking apart ATP. They have negative Delta Gs. They are exergonic or spontaneous. What you don’t want to confuse is exo and endothermic or increase or decrease of entropy which is Delta H and Delta S respectively. So we end up with answer choice (A) I only.
[07:58] Phosphoric Acids
Question 12: Which of the following phosphate ions is amphiprotic?
- (A) PO43 minus
- (B) HPO42 minus
- (C) P2O74 minus
- (D) H3PO4
By amphi, that means it can go either way or has both. In the case of amphiprotic, it means you can accept the proton or you can give one out. So you can do both.
If amphiprotic requires that you could give one out, B and D could give out because they have one Hydrogen. But could you take one?
It could take one and come up to negative one, or it could give one and go down to negative 3. So it can be a switch hitter, whereas H3PO4, you can’t another proton because phosphate is full now. Phosphate only has room to take three protons.
Bryan adds that students should be very comfortable and very familiar with phosphoric acid because it plays a key role in nucleic acids. He hints that the new MCAT biochemistry component really likes phosphoric acid.
[10:30] Bernoulli’s Principle
Question 13: Which of the following statements are true:
- Blood velocity and pressure are higher in the arteries than in the capillaries.
- Blood vessels do not follow Bernoulli’s principle if viscosity of blood is taken into account.
III. For an incompressible fluid undergoing a laminar flow through a pipe, with both narrow and wide sections, the fluid velocity is higher in the narrow areas than in the wide areas.
- For an incompressible fluid undergoing a laminar flow through a pipe, with both narrow and wide sections, the fluid pressure is higher in the narrow areas than in the wide areas.
- (A) I only
- (B) I and III
- (C) II and IV only
- (D) I, II, and III
A common strategy is to answer the easy Roman numerals, where when you read it, you recognize it’s wrong right away. So you can do the process of elimination this way. However you do it, do the easy thing first.
Based on the physiology, I is true. So the answer choice C is out since it didn’t have Roman numeral I.
Looking at Roman numeral II, you have to remember that Bernoulli’s principle is one of these idealized, abstract physics descriptions. So II is just a true statement about how we apply Bernoulli’s principle on the MCAT. It’s an idealized equation for laminar flow. But if you take viscosity into account, then it doesn’t work anymore. So II is also true. And you don’t even need to go over III and IV here.
[14:00] More Tips about Roman Numerals
Again, follow some simple steps. Read the question. Try to eliminate some and without doing more work than you need to, you would already get to the answer. Do the Roman numerals that seem easier for you. In this case, Bryan just picked I and II because they were shorter than III and IV. But whichever one you knew right away is the one you should go to.
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