Mcat Biology Questions

Don’t worry, though. We have you covered. Biology is an important subject on the MCAT, and you’ll see biology in the chemistry/physics, biology/biochemistry, and psychology/sociology sections of the exam. Therefore, you’ll need to be ready to answer bio questions asked in a variety of contexts.

We Break Down Discrete Biology MCAT Questions

This week, we are breaking down discrete biology questions from the MCAT. These questions are taken directly from the Next Step MCAT Full-length Exams.

Everyone knows that biology questions on the MCAT can really test your application and recall of information. But what we’re going to look at today are the more straightforward questions, questions that 80% (or even more) of the students are getting right in the Blueprint MCAT (formerly Next Step Test Prep) system.

These are not necessarily easy questions—they’re only easy if you know the answer. But the point of this is just to illustrate that in the competitive world of MCAT prep, you can’t leave any of these points on the table.

Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points.

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[02:22] MCAT Biology Question #1:

When normal human cells are grown in culture, they will divide a limited number of times, typically 50 rounds of mitosis. After this number is reached, the cells become apoptotic. This cell death is a result of:

• (A) Decreasing number of membrane-bound organelles per cell
• (B) Decreasing number of non-membrane bound organelles per cell
• (C) Decreasing levels of growth hormone
• (D) Chromosomal telomeres shortening after each round of division

[03:07] Bryan’s Insights:

The correct answer is (D), and this is just an important bio/biochem genetic fact that the aging process in cells is due to telomere shortening.

There is actually a lot of interesting science behind the prevention of telomere shortening to hopefully allow us to lengthen our lives. Why can’t we just go in there and make our telomeres longer? Of course, uncontrolled chromosomal alteration and lengthening is what we know as cancer. So you can’t just go in there and muck about with no problems.

[03:57] MCAT Biology Question #2:

A student finishes an experiment involving several bacteria which are highly pathologic in humans. She was to dispose of the agar plates and micropipette tips she used. Which of the following procedures should she carry out?

• (A) Microwave all materials for more than 60 seconds.
• (B) Wipe down on materials with 100% ethanol solution.
• (C) Place all materials in a biohazard bag and autoclave the bag.
• (D) Place all materials under UV light for 90 seconds.

[04:48] Bryan’s Insights:

This is one of the classic lab procedure questions where you have to know the mechanics of life in the lab. This is one of the hallmarks of the new version of the MCAT as opposed to the old version, which was more textbook-based. Basically, a lot of these questions want to assess if you have spent time in the lab recently and you know how it works.

In this case, if you ever have biohazards you need to dispose of, you absolutely have to autoclave it. There is no second-best choice or alternative to it. Every lab in the universe has an autoclave for a reason, and it’s to dispose of biohazards.

Hence, the right answer is (C). Place all the materials in a biohazard bag and autoclave the bag.

[05:36] Biology MCAT Question #3:

In a population of Amish people, the frequency of the recessive autosomal allele for polydactyly is 1.2%. What percent of the population are carriers for this gene?

Bryan’s Insights:

This is actually the hardest one of the set of questions we’re going to look at. A little less than 70% of the students got this right. This is what they call a Hardy-Weinberg Equilibrium. There are a bunch of percentages listed as answers, and we’re told that the recessive allele has a frequency of 1.2%.

Since all of the recessive and all the dominant alleles in the universe have to add up to 100%, that means the frequency of the dominant allele is 98.8%.

The extra bit is remembering what the mathematical term is for the carriers in the Hardy-Weinberg Equation, which is usually expressed like this: p2 + 2pq + q2 = 1 or 100%.

And so to be a carrier, to be a heterozygote, to have both of the genes, that is that term in the middle of the equation, usually written as 2pq, where 2 is just the number two, p as the percentage of dominant, and q as the percentage of recessive.

In this case, the dominant was 98.8% or 0.988, while the recessive was 1.2% or 0.012. With MCAT calculations, you don’t have to go into great detail, so you can just round things off. So 2pq is 2 x 0.988 x 0.012. And that 0.988 can be rounded off to 1. Now the equation becomes 2 x 1 x 1% roughly. In other words, this gives us a total of 2%.

You can ignore all those other decimals and all the fiddly bits and just say, it’s going to be about 2% of carriers. And when you look at the answer choices, they’re really spread out like (A) 0.01%, (B) 1%, (C) 2%, (D) 97%. (There are decimals here, but we’re just going to ignore them.) Since answer choice (C) is the only one that’s anywhere close, a little over 2%, the correct answer is C.

[08:39] When Can You Round Off Calculations on the MCAT?

When to round off calculations on the MCAT entirely depends on how spread out the answer choices are. You will see some physics problems where the answer choices are literally orders of magnitudes apart from each other. In that case, you can afford to round off aggressively.

Here, where the answers were 0.01, 1, 2, and 98, even the two answer choices that were closest together (1 and 2) is a 100% difference. So you can round this off pretty aggressively, too.

[09:30] MCAT Biology Question #4:

Species that are capable of both sexual and asexual reproduction will typically prefer sexual reproduction because it:

• (A) increases the likelihood of each individual offspring surviving.
• (B) increases the likelihood of beneficial mutations
• (C) creates more variation in the next generation
• (D) takes less time to complete

Bryan’s Insights:

The correct answer here is (C). About 10%-15% of students pick (A), but evolution does not work on the level of individuals. Evolution works on the level of whole populations and their likelihood of survival, not one individual necessarily surviving.

When we think about the genetics on the MCAT, it’s not really that you’re getting an ecology question or an evolution question. You simply need to understand the mechanics of that genetic reshuffling that happens during sexual reproduction.

Why would animals go through so much effort like peacocks growing enormous tails and bowerbirds building those huge nests? The point of these enormous metabolic costs animals put into the dance of sexual reproduction is so that the next generation of animals has more variety and is more adaptable to changing environmental conditions. In fact, that variety is so critically important that sexual reproduction strategies are vastly more successful.

Links and Other Resources

MCAT Biology Practice Questions

Prepare for the MCAT Biology section with practice questions

Introduction

MCAT Biology Practice Passage #1

MCAT Biology Practice Passage #2

MCAT Biology Practice Passage #3

MCAT Biology Practice Questions (Standalone)

Introduction

You’ve taken all of your premed classes and are ready to start prepping for the MCAT. You already made a great study schedule, have started content review, and are ready to start taking some more practice problems.

Unlike most tests you’ve taken before in undergrad, the MCAT is an entirely different challenge. The exam is difficult and long, especially if you don’t prepare the right way. As you progress further in your medical training, your method of studying will shift from content review to practice problems. The MCAT is no exception—practice problems will help to significantly improve your score.

Don’t worry, though. We have you covered. Biology is an important subject on the MCAT, and you’ll see biology in the chemistry/physics, biology/biochemistry, and psychology/sociology sections of the exam. Therefore, you’ll need to be ready to answer bio questions asked in a variety of contexts.

Here, we’ll test your biology knowledge using MCAT-style passages written by a 528 scorer. The MCAT relies heavily on repurposing scientific articles and then asking you questions about those articles. As a result, you need to be able to sift through scientific data and answer questions that combine information from the passage with your outside knowledge.

Use the following three biology passages and five standalone questions to test your ability to apply your biology knowledge to real, MCAT-style passages. Each explanation for the passage-based questions will have suggestions for what you should review if you miss a question. Good luck!

MCAT Biology Practice Passage #1

Postoperative acute kidney injury (AKI) is a severe complication after liver transplantation (LT) as its deterioration and magnification can lead to an increase in mortality. Connexin43 (Cx43) mediates direct transmission of intracellular signals between neighboring cells, always considered to be the potent biological basis of organ damage deterioration and magnification.

Researchers obtained donor liver tissues of patients in order to explore the effects of Cx43 on organ damage. Reperfusion is a biological process used to refill blood in AKI. Donor livers displayed more severe lobular distortion with necrosis, apparent edema, hemorrhage, and neutrophil infiltration after reperfusion, compared with donor liver tissues obtained before reperfusion or normal liver tissue (from patients with hepatic hemangioma). After reperfusion, Cx43 mRNA and protein levels were determined as shown in Figure 1.

Autologous orthotopic liver transplantation (AOLT) rats were built by researchers in order to further study AKI. Researchers hypothesized that the change in Cx43 expression might play an important role in AKI following AOLT. Researchers used heptanol, a well-known inhibitor of Cx43 without hepatotoxicity, to alter the function of junctions composed of Cx43. Heptanol had no effects on Cx43 expression in kidneys or livers.

Heptanol or a sham control were injected intravenously into the rats, and the pathological score of kidney cells was determined to analyze disease progression. The results are shown in Figure 2.

Researchers also believe that the RIP1 may be involved in Cx43 function, and they confirmed the interaction of the proteins through co-immunoprecipitation. RIP1 is a typical marker of necroptosis.

_{CREATOR AND ATTRIBUTION PARTY: YUAN, D., LI, X., LUO, C., ET AL. INHIBITION OF GAP JUNCTION COMPOSED OF CX43 PREVENTS AGAINST ACUTE KIDNEY INJURY FOLLOWING LIVER TRANSPLANTATION. CELL DEATH AND DISEASE 10, 767 (2019). THE ARTICLE’S FULL TEXT IS AVAILABLE HERE: https://www.nature.com/articles/s41419-019-1998-y. THE ARTICLE IS NOT COPYRIGHTED BY SHEMMASSIAN ACADEMIC CONSULTING. DISCLAIMER: SHEMMASSIAN ACADEMIC CONSULTING DOES NOT OWN THE PASSAGE PRESENTED HERE. CREATIVE COMMON LICENSE: HTTP://CREATIVECOMMONS.ORG/LICENSES/BY/4.0/. CHANGES WERE MADE TO ORIGINAL ARTICLE TO CREATE AN MCAT-STYLE PASSAGE.}

1. What type of junction does Cx43 most likely form?

B) Tight junction

2. A researcher discovers a new Cx43 inhibitor made of a glycerol backbone and three saturated fatty acid tails. Which of the following describes the path by which the inhibitor enters the cells?

A) The inhibitor is recognized by a specific receptor.

B) The inhibitor is taken up by a non-specific receptor.

C) The inhibitor diffuses through the cell membrane.

D) The inhibitor passes through the cell membrane via a channel.

3. Researchers decide to interrupt the Cx43-RIP1 interaction in the AOLT rat model without using a small molecule inhibitor. Which of the following will most likely disrupt the interaction?

A) SiRNA for RIP1

B) Radiation against heptanol

C) Acetyltransferase specific for β-actin

D) Plasmid producing Cx43

4. Which conclusion about Cx43 regulation is best supported by Figure 1?

A) All expression control occurs at the transcriptional level.

B) All expression control occurs at the translational level.

C) Donor livers have higher levels of Cx43 after reperfusion when compared to normal liver tissue.

D) Normal livers treated with heptanol have lower levels of Cx43 compared to donor livers treated with heptanol.

Answer key for practice passage #1

1. Answer choice A is correct. Cx43 is a connexin protein as stated by the passage, and connexins form gap junctions (choice A is correct).

Review junction types.

2. Answer choice C is correct. The inhibitor described in the question stem is very hydrophobic, and this means it will pass through the membrane via diffusion (choice C is correct).

Review plasma membrane composition and properties.

3. Answer choice A is correct. SiRNAs bind to mRNAs for certain genes and lead to degradation. If the RIP1 mRNA is degraded, Cx43 will no longer be able to interact with RIP1 (choice A is correct). Radiation is highly non-specific and would likely affect other processes (choice B is incorrect). β-actin is not involved in the Cx43-RIP1 interaction based on information from the passage (choice C is incorrect). A plasmid producing Cx43 would likely not be taken up by the rat cells, and an increase in Cx43 expression should not disrupt the interaction (choice D is incorrect).

4. Answer choice C is correct. The graph in Figure 1 shows that donor livers have higher expression levels of Cx43 mRNA when compared to normal liver tissue (choice C is correct). The mRNA expression levels given by the graph and the protein expression levels given by the blot are different, meaning that regulation occurs at both the transcriptional and translational levels (choices A and B are incorrect). Heptanol is not addressed in Figure 1 (choice D is incorrect).

Review transcription versus translation. Practice interpreting experimental data, and make sure to understand the figure completely.