Two sample questions from the Medical College Admission Test (MCAT)

I’ve said many, many times that BIO 181 (General Biology for Majors at Arizona public colleges and universities) just scratches the surface of what we know. I also point out that the material in the class will support upper division (300 and 400-level) study at the universities. The primary goal of the course is to educate those who wish to establish professional lives in biological sciences and (or) medicine, not to assign grades.

Here I present evidence for these statements. Below I post 2 sample MCAT questions (from the Association of American Medical Colleges website). Please read these carefully. Look for references to material taught in BIO 181 (Na⁺ and K⁺ gradients, energy metabolism, glycolysis, bar graphs, error bars, scientific reasoning). But also compare the level of understanding required to answer these questions effortlessly and accurately to the level of BIO 181. Also remember, these are just a tiny sampling of the test to get into medical school.

It’s not about grades. It’s about knowledge and skills. If you master those, the grades will take care of themselves.

Sample MCAT Questions:

Passage:

The myocellular transmembrane Na⁺ gradient is important for proper cellular function. During septic shock, disruption of Na⁺ homeostasis often occurs and leads to decreased membrane potential and increased intracellular Na⁺. It has been found that failure of cellular energy metabolism is a common symptom in septic patients who do not respond to therapeutics. Because normal intracellular levels of Na⁺ are maintained by the Na⁺K⁺ ATPase, it is important to understand how metabolic energy production is linked to cation transport.

Researchers are interested in whether the energy used for ion transport is derived from glycolysis or oxidative phosphorylation. This information would provide a better understanding of myocellular damage that occurs during critical illness. Experiments were conducted to evaluate the effects of glycolytic inhibition on cellular Na⁺ and K⁺ concentrations and lactate production in rat skeletal myocytes.

Rat skeletal muscle fibers were extracted and incubated in normal media (control), glucose-free media (G(–)), and glucose-free media with various concentrations of the glycolytic inhibitor iodoacetate (IAA). IAA directly prevents the formation of 1,3-bisphosphoglycerate. After one hour in the media, the muscle tissues were assayed for intracellular Na⁺ and K⁺ content and lactate production. Cellular viability was determined by measuring the amount of lactate dehydrogenase (LDH) released, as LDH release is an indicator of cell death. The results are displayed in Figure 1.

Figure 1 Effects of glycolytic inhibition on intracellular Na⁺ and K⁺ content and lactate production with cellular viability measured by LDH release. (Note: The * indicates p < 0.05 versus control.)

The researchers also examined the effect disruption of oxidative phosphorylation had on Na⁺ and K⁺ content. Inhibition of oxidative phosphorylation was caused by carbonyl-cyanide m-chlorophenylhydrazone (CCCP), an ionophore that allows protons to move freely through membranes. No correlation between Na⁺ and K⁺ content and oxidative phosphorylation was found.

Adapted from: Okamoto K, Wang W, Rounds J, Chambers EA, Jacobs DO. ATP from glycolysis is required for normal sodium homeostasis in resting fast-twitch rodent skeletal muscle. The American Journal of Physiology-Endocrinology and Metabolism. 2001 Sept;281(3):E479-88.

Questions:

1. The researchers chose a concentration of 0.3 mM IAA as the working concentration for any additional studies instead of 1 mM or 2 mM. What is the likely reason for this?

A) The lower concentration of IAA gave the largest Na⁺ response.

B) Higher concentrations induced significant cytotoxicity.

C) The solubility of IAA was not high enough.

D) The researchers were trying to mimic control conditions as closely as possible.

 

2. The information in the passage suggests that glycolysis:

A) is important for maintaining normal Na⁺ and K⁺ levels in skeletal muscle.

B) facilitates membrane permeability in skeletal muscle.

C) impedes the function of the Na⁺ and K⁺ ATPase in skeletal muscle.

D) is regulated by the Na⁺ and K⁺ ATPase in skeletal muscle.