Next Step Full Length 10, Passage 6, Questions 31-34

Session 103

Together with Bryan Schnedeker of Next Step Test Prep, let’s dive into Passage 6 on Next Step’s full-length 10 which includes nutrition labels, understanding fiber, combustion, and others.

If you didn’t know yet, I also host The Premed Years Podcast, The OldPreMeds Podcast, Specialty Stories, Ask Dr. Gray: Premed Q&A, and some more coming up on the MedEd Media Network. Stay tuned for all of those and subscribe on whatever platform you listen to!

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[01:52] Passage 6

Nutritional facts labels (Figure 1) the percentages supplied for one day of human nutrients provided by one serving of a particular food based on a daily diet of 2,000 nutritional calories. Since 1990, there have been a number of changes to the label guidelines. The purpose was to allow the public to make informed decisions concerning the food they eat.

Table 1 provides thermodynamic information concerning water and changes for some combustion reactions. It should be noted that labeling is based on nutritional calories (nCal), which is equivalent to 1 kCal. Calories (cal) is defined as the heat needed to raise the temperature of 1 gram of water by 1 degree Celsius.

[03:23] Question 32: Read the Label Carefully

Based on the information presented, what is the maximum number of packages of of this product that a person could consume in a day without exceeding the FDA’s recommended caloric intake level?

(So they’re saying here a daily diet of 2,000 nutritional calories and the package says there are 230 calories per serving. But there are 8 servings per package.)

If you have 230 calories and there are 8 servings per package, there’s another 1,840 calories in one package. Therefore, it would only be one package that you could eat without exceeding the calories.

Bryan says that when you look at data from full-length 10, a shockingly large number of students (almost 30%) who take this test actually pick 8 packages as their answer. But the reality is you could only eat 8 servings. So they’re either misreading the label or misreading the question.

Bryan couldn’t emphasize more that the MCAT is a reading test that just so happens to be about science. So READ those questions CAREFULLY.

[06:00] Question 33: Dietary Fiber

Based on the information presented in the passage, how many nutritional calories per serving come from dietary fiber? (So in the label, dietary fiber is 4 grams. And it’s 16% of the daily value.)

  • (A) 0
  • (B) 230
  • (C) 240
  • (D) 320

Bryan explains that the MCAT doesn’t expect you to know much in the way of nutrition. It cares much more about cellular level or molecular level of metabolism. But you should know that carbs is 4 calories per gram of carbohydrate.

Again, based on the passage above, each serving has 230 calories. But you should walk into the test knowing that fiber doesn’t have calories.

Fiber serving is a bulking agent in your stool. The nutrition it provides is actually in the form of maintaining your gut micro bio. It helps maintain your intestinal flora. Aside from eating your fiber, the intestinal flora also make your Vitamin K. So while fiber itself may not be strictly required to keep that human cell alive, fibers are required to keep the human body alive because you need to maintain good intestinal bacteria so they can make your Vitamin K, essential in blood clotting cascade.

So even though fiber doesn’t have any calories, doesn’t mean it’s not a nutrient. In the same way that iron and calcium don’t have any calories but they’re still incredibly important nutrients.

Looking at the statistics on students who have taken this test, most students get this right, probably almost 90% of them. That said, Bryan says this should be a question that is 100% everyone who reads it gets it right because you know that fiber doesn’t have any calories. Or because the serving only has 230 calories. So all these answer choices except for zero are just absurd.

[11:14] Question 34: Propane

How many grams of propane must undergo complete combustion to convert one kilogram of water at 25 degrees Celsius to steam at 100 degrees Celsius?

  • (A) 1 gram
  • (B) 10 grams
  • (C) 51 grams
  • (D) 90 grams

Bryan’s Insights:

This is to remind you that there are some cases where you’ve got to do a whole load of math, whether you like it or not.

Conceptually, this is a question wherein you have to know the framework. So if you have 1kg of water and you have to raise it 75 degrees. So the equation you need to know here is: q = mc(delta T); where heat equals mass x specific gravity x the change in temperature.

The next thing you have to do is to steam at a 100 degrees C. So you have to do a phase change and the equation for this is: m delta H sub L where mass x latent heat.

The heat of vaporization is given in Table 1. Once you add those up, you get some number of Joules. Then go back to Table 1 to see how many is the heat of combustion for propane. And you’d be expected to recognize the name Prop as a 3-carbon (the table doesn’t give this to you; instead, it only has the molecule) So you should find C3H8 and you should recognize that as Propane. Then the delta H is 2219 kJ per mole that gets released by burning it. You would then have to figure out how many moles of propane are needed. The final step is converting moles back to gram by dividing it by the molecular weight.

So there’s a whole bunch of steps there. Heat the water up. Boil the water to steam. Get your Joule total. Go from Joules to Moles. Go from Moles to Grams. And the answer here happens to be 51 grams.

Bryan says this is one of the cases where there’s no cute way to do it, no shortcuts. You really have to pick up that marker and calculate this out. Again, you definitely have to recognize the names of these molecules.

[15:40] About Next Step Test Prep

If you’re in the market for full-length test prep exams, check out Next Step Test Prep and save 10% on any of their full length exam packages. Use the promo code MCATPOD. Also, check out their MCAT course or their one-on-one tutoring.

Links:

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