Biology is the heart of medical science, so it's no surprise that MCAT Biology questions make up the majority of the exam's contents. It's therefore crucial to do well in the Biology and Biochemical Foundations of Living Systems (BBFLS) section, and a big part of getting a good MCAT score is learning how to tackle questions on biology and biology-related subfields during your preparation for the test.  

This blog serves as an ultimate guide to understanding the BBFLS section of the MCAT, and will show you how to succeed in this challenging part of the test. We’ll also take a look at several sample MCAT biology questions and provide expert breakdowns of the answers. 


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Why is Biology so important? 

The importance of having a broad yet detailed knowledge of biological sciences for the MCAT cannot be overstated. The definition of biology as "the study of living things and their vital processes" explains why. Medicine in almost every respect is oriented around the diagnosis, treatment, and management of phenomena affecting these vital systems, and so those involved in the field must be able to navigate the vast array of knowledge underpinning this task. Examining the four sections of the test, it's immediately apparent that various modalities of biology and biochemistry plays a part in all sections save MCAT CARS. As such, it's not only vital to develop your knowledge of biology for the BBFLS section, but for each of the other science-based sections as well. Think of Biology as both the skeleton and the connective tissue of medical science—our understanding of the latter is heavily rooted in the former. Before you sit down to study for your exam, do not forget to research which disciplines are covered in each section and how long the MCAT is.  

Additionally, biology and its many subfields comprise a massive portion of the USMLE Step-1 examination as well. Of course, each exam tests different dimensions of biology: the MCAT tests what you've learned as an undergraduate while the USMLE exams test what you've learned in medical school. Nonetheless, many medical school admissions committees view applicants' MCAT scores, and BBFLS scores in particular, as a possible predictor of future success in licensing exams. Showing that you're able to navigate challenging material on Biology and Biochemistry is therefore a big asset for your medical school application

What's Tested in the MCAT Biology and Biochemistry Section? 

The Biology and Biochemical Foundations of Living Systems section is the central—though as we’ve noted already, not the only—part of the test that incorporates concepts taught at university during introductory-level biology and chemistry courses, as well as first-semester biochemistry courses. The BBFLS section contains approximately 65% introductory biology questions, 25% first-semester biochemistry questions, 5% general chemistry questions, and 5% organic chemistry questions. Each of these disciplines will be tested in conjunction with your scientific inquiry and reasoning skills. 

The biology and biochemistry section covers the following foundational concepts: 

For a detailed list of subtopics included within these three foundational concepts, check out the AAMC’s guide to what’s on the MCAT exam, and specifically the pdf on the BBFLS section. Here’s an overview of the main subtopics included in this section of the MCAT: 

 

To excel in the BBFLS section, you’ll not only need a solid knowledge base in each of these content areas but also the ability to “activate” this foundational knowledge with scientific inquiry and reasoning skills. Understanding how to apply your knowledge of biology and biochemistry to solve complex problems is the key to a great score on this section. However, this complex problem-solving also plays a part in every section utilizing applications of biology, such as the MCAT psychology section. 

What’s the Structure of the MCAT Biology and Biochemistry Section? 

When you take the MCAT, the Biological and Biochemical Foundations of Living Systems section is the third out of four sections that you will complete and follows the longest optional break, which is 30 minutes in duration. By this point, you’ll have already made it through two demanding MCAT sections—you’re halfway done! 

In this third section, you will have 95 minutes to answer 59 questions. Out of these 59 questions, 44 are passage-based. You’ll be presented with 10 passages about biology and biochemistry topics and asked 4-7 passage-based questions after each passage. In addition to testing your content knowledge, the MCAT—both here and in other sections—tests your ability to pull relevant information from passages and a deep understanding of the mechanisms behind the facts you have learned. As an applicant to medical school, you must show proficiency in these subject areas and ability to apply this proficiency using your critical thinking and reasoning skills. 

Check Out Our Video on the MCAT Biology Section for More Tips

  

There will also be 15 stand-alone questions dispersed between passages. Each question in this section will address one or more of the 4 skills outlined by the AAMC: knowledge of scientific concepts and principles, scientific reasoning and problem-solving, reasoning about the design and execution of research, and data-based and statistical reasoning. 

How to Prepare for the MCAT Biology and Biochemistry Section 

Most students are intimidated by the expansive volume of information involved in review for the MCAT, and the BBFLS section most of all. If you're wondering when to start studying for the MCAT, you should assess how much knowledge you have retained from your introductory university classes.  

Wondering how your practice MCAT results stack up? Check out our video on MCAT Scores here

  

Tips For Answering Biology and Biochemistry Questions on the MCAT 

Now that we've discussed general and long-term strategies for studying and preparation, let's get into the nitty-gritty on just how to approach the BBFLS section as you begin grinding through your practice questions. 

Tip #1: Understand the Skill/s Being Tested 

When you read an MCAT question—whether in practice or on test day—you should begin by identifying the question type by what skill it's testing. The AAMC lists four skills that are tested throughout the test: 

[graphic describing these 4 skills] 

By determining exactly which of these skills is being tested, you can better orient yourself as you retrieve relevant information. For instance, if a question seems to be asking you to explain or elaborate some aspect of research design, you can narrow down your focus and not bother considering answers about concrete knowledge of scientific concepts. You don’t need to waste ten minutes straining to recall every stage of the Krebs cycle in order to answer a question about measuring glucose levels in a fermentation experiment. Understand that while the MCAT is a broad and extensive test, it does have structures that repeat throughout, and being able to identify these can not only improve the quality of your response but also how quickly you’re able to commit to it and move on to the next question. 

Tip #2: Mimic the Resources Available on Test Day 

You will not have access to a calculator during the MCAT. However, you will have access to a periodic table of elements throughout the test. It is important that you complete practice questions under conditions that will mimic those of test day as you prepare. If you won’t have a calculator during the MCAT, don’t practice with a calculator! If you will be given a periodic table, be sure to understand how to use it to your full advantage. It will be most helpful to complete your practice with the identical version of the periodic table that you will have on test day, which provides the name, atomic mass, and atomic number of each element; this version of the periodic table can be found on the AAMC website. During the actual test, you’ll also be given a noteboard booklet of laminated graph paper and a non-permanent marker to use for writing notes and equations. If these tools are unfamiliar to you, we recommend obtaining similar materials during your preparation so it’s not such a stark shift on test day. Feeling frustrated by hitherto alien writing implements on such an important and grueling day of testing is totally avoidable. Give yourself time to acclimate to the known elements of your test-taking environment, and you’ll be much more able to adapt to any totally unforeseen circumstances like weird ambient sounds or lighting. 

Tip #3: Be Ready for Data & Experiments 

The AAMC incorporates biology and biochemistry experiments into the MCAT, which means that you can't just practice vocabulary: come test day, you must be able to apply your knowledge to experiment-style questions. Be sure to review key experimental techniques, such as gel electrophoresis and polymerase chain reaction. As you complete practice passages, get into the habit of determining the independent and dependent variable for the experiment, as well as necessary controls. When completing the biology and biochemistry section of the MCAT, you should not spend too much time on a graph or figure within a passage, unless a question specifically asks about it. However, as you practice, you'll want to sharpen your analysis skills in the event that you need them. How can you ensure that you get enough practice interpreting data and graphs? Once you finish a practice passage, take some time to return to any graphs or figures and review them to fully understand the information presented. This practice will ensure efficiency during the test day time-crunch. 

Tip #4: Build Your Confidence 

Confidence is a key factor in both improving your score and performing well on test day. In addition to the Biological and Biochemical Foundations of Living Systems section, biology will also be assessed in the Chemical and Physical Foundations of Biological Systems section and the Psychological, Social, and Biological Foundations of Behavior section. In chemistry and physics, you will be asked how chemical and physical factors interact with biology. In psychology and sociology, you will need to understand how biological factors can impact behavior. Neither of these MCAT sections are focused on biology, but you'll find that biology is a major theme that runs through the entire exam. Don’t underestimate the power of confidence in your biology knowledge base and in your test taking strategies!  

Confidence promotes a consistent pace as you move through passages and helps to prevent second-guessing on answer choices. If there is a particular biology or biochemistry topic that has been challenging for you in the past, tackle it head-on during your MCAT preparations. Delve deep into the topic repeatedly until you feel comfortable and confident with it. This will prevent negative past experiences from derailing your confidence on test day. As you approach your exam, remind yourself that you have worked extremely hard to prepare for the MCAT and that this will surely be reflected in your score.  

Another way to build confidence is to teach the concepts to a friend. You know you've mastered the material when you can successfully teach someone else. Try this whenever possible, especially with topics in biology and biochemistry that you found initially challenging. Did your temporary student understand it? If so, you probably have it down! There's also the tried-and-true method of creating flashcards with key questions on one side and answers on the other. These are easy to make and incredibly helpful to check your knowledge on any given topic. Keep in mind that lots of companies sell flashcards, but it’s far more effective to make them yourself as it allows for active learning during their construction as well as when you're studying with them. Additionally, you can tailor these to your specific strengths and weaknesses, making more for your blind spots and fewer for those areas you know inside and out.  

Sample MCAT biology and biochemistry questions

Give it a try! Below you will find several Biological and Biochemical Foundations of Living Systems sample questions to test your skills for this section of the MCAT:

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.

Sample 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.

3. If the effects of IAA treatment in nerve cells are the same as those observed in myocytes, which feature of an action potential would be most affected by IAA treatment?

A) Initiation of depolarization

B) Rising phase of depolarization

C) Falling phase to undershoot

D) Return to resting potential

Sample Discrete Questions

4. How is the basal layer of the epidermis and the innermost lining of the small intestine similar?

A) Both are non-dividing tissues.

B) Both are derived from ectoderm.

C) Both are composed of squamous cells.

D) The cells of both are connected by tight junctions.

5. Starting with the translation initiation codon, the following sequence encodes a polypeptide of how many amino acids?

5'-CUGCCAAUGUGCUAAUCGCGGGGG-3'

A) 2

B) 3

C) 6

D) 8

6. Sodium dodecyl sulfate (SDS) contains a 12-carbon tail attached to a sulfate group and is used in denaturing gel electrophoresis of proteins. Numerous SDS molecules will bind to the exposed hydrophobic regions of denatured proteins. The use of SDS in this experiment allows for the separation of proteins by:

A) charge

B) molecular weight

C) shape

D) solubility

7. In the figure, the three curves represent hemoglobin oxygen binding at three different pH values, pH 7.2, pH 7.4, and pH 7.6.

What conclusion can be drawn from these data about the oxygen binding of hemoglobin at different pH values?

A) Low pH favors the high affinity oxygen binding state.

B) Low pH favors the low affinity oxygen binding state.

C) Oxygen affinity is independent of pH.

D) Oxygen binding is non-cooperative at low pH.

Answers to sample 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.

The correct answer is B.

Rationale: This question requires you to apply your knowledge of cytotoxicity and cell lysis to the experimental design described in the passage. You must understand that an experiment with IAA levels cytotoxic to cells would not lend itself to understanding the role of glycolysis in establishing ion concentration gradients. When compared to control conditions, under cytotoxic IAA levels the membrane integrity of cells will be compromised leading to cell lysis. Therefore, the researchers chose a concentration of 0.3 mM IAA as the working concentration for their experiments to reduce the chance of cell lysis.

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.

The correct answer is A.

Rationale: For this question, you must apply your understanding of glycolysis to the data shown in Figure 1. The data reveals that an increase in concentration of IAA results in a higher Na+ to K+ concentration ratio when compared to the control sample. This increase must be correlated with the role of IAA in disruption of glycolysis. This finding is further supported by reduced lactate production at higher concentrations of IAA, which is shown in Figure 1. This is because IAA prevents the formation of NADH, which is used in pyruvate reduction to lactate. The combination of the proposed role of IAA and the results from Figure 1 should lead you to the conclusion that glycolysis is important to the Na+K+ ATPase and, therefore, important to the maintenance of the concentration ratio of Na+ to K+ in skeletal muscle.

3. If the effects of IAA treatment in nerve cells are the same as those observed in myocytes, which feature of an action potential would be most affected by IAA treatment?

A) Initiation of depolarization

B) Rising phase of depolarization

C) Falling phase to undershoot

D) Return to resting potential

The correct answer is D.

Rationale: This question necessitates that you draw on your knowledge of Na+K+ ATPase’s role in recovery of nerve cell resting potential after an action potential. Typically, repolarization of a nerve cell will overshoot the resting potential, making it more negative, a state known as hyperpolarization. Na+K+ ATPase works to restore the initial balance of ions in the cell (the resting potential) after hyperpolarization, by using the hydrolysis of ATP to move Na+ out of the cell, and K+ into the cell, against their concentration gradients. Based on the information within the passage, you are asked to reason about the effect of IAA treatment and how glycolysis inhibition by IAA will affect cellular concentration of ATP. Based on these two lines of reasoning, you can propose a hypothesis about which portion of an action potential would be affected by IAA treatment.

4. How is the basal layer of the epidermis and the innermost lining of the small intestine similar?

A) Both are nondividing tissues.

B) Both are derived from ectoderm.

C) Both are composed of squamous cells.

D) The cells of both are connected by tight junctions.

The correct answer is D.

Rationale: This question tests your knowledge of how molecules, cells, and groups of cells are assembled within organisms. You are asked to recall the structural and embryological characteristics of two tissues and must relate them to one another. To answer this question correctly, you must identify a similarity between the basal layer of the epidermis and the innermost lining of the small intestine. Option D is the only option that identifies a correct similarity, which is that the cells of both the epidermis and the innermost lining of the small intestine are connected by tight junctions.

5. Starting with the translation initiation codon, the following sequence encodes a polypeptide of how many amino acids?

5'-CUGCCAAUGUGCUAAUCGCGGGGG-3'

A) 2

B) 3

C) 6

D) 8

The correct answer is A.

Rationale: This is a scientific reasoning question, in which you must use your knowledge about transmission of genetic information to solve a problem. You are told that the sequence contains codons and you can see that the sequence includes U, or uracil; Uracil is a base found in RNA, but not DNA, so you can deduce that you are looking at a sequence of RNA. The cell reads RNA sequences three bases at a time, with each group of three bases constituting a codon that will code for one amino acid. You must recall the sequence for the start codon, AUG, and that there are three stop codons in the genetic code: UAG, UAA, and UGA. In this sequence, the stop codon UAA appears two codons after the start codon, so you can conclude that the polypeptide generated from this RNA sequence will be comprised of only two amino acids.

6. Sodium dodecyl sulfate (SDS) contains a 12-carbon tail attached to a sulfate group and is used in denaturing gel electrophoresis of proteins. Numerous SDS molecules will bind to the exposed hydrophobic regions of denatured proteins. The use of SDS in this experiment allows for the separation of proteins by:

A) charge

B) molecular weight

C) shape

D) solubility

The correct answer is B.

Rationale: In this question, you must reason about the design and execution of research. You are also asked to recall knowledge about protein structure and function, as well as how gel electrophoresis works. In this technique, SDS detergent binds to proteins uniformly coating them in a negative charge and denaturing them, removing any three-dimensional shape. When a current is applied to the gel, the SDS-coated proteins migrate through the gel and towards the positively charged electrode. Proteins of lower molecular weight travel faster through the gel than those with greater molecular weight as smaller proteins have an easier time moving through the pores of the gel matrix. Based on this understanding, you can determine that, through this technique, proteins will be separated only by their molecular weight.

7. In the figure, the three curves represent hemoglobin oxygen binding at three different pH values, pH 7.2, pH 7.4, and pH 7.6.

What conclusion can be drawn from these data about the oxygen binding of hemoglobin at different pH values?

A) Low pH favors the high affinity oxygen binding state.

B) Low pH favors the low affinity oxygen binding state.

C) Oxygen affinity is independent of pH.

D) Oxygen binding is non-cooperative at low pH.

The correct answer is B.

Rationale: This is a data-based statistical reasoning question that again draws on your knowledge of protein structure and function. You are asked to explain the oxygen binding property of hemoglobin using the graph provided. You must evaluate and compare the hemoglobin oxygen binding data, or percent saturation of blood with O2, for each pH value to determine the relationship between pH and hemoglobin oxygen affinity. This approach will allow you to conclude that the lower the pH, the lower the affinity of hemoglobin for oxygen.

Conclusion

It is important to appreciate that the Biological and Biochemical Foundations of Living Systems section of the MCAT is an important piece of your medical school application. The BBFLS section spans a wide range of academic disciplines that form the framework for your medical school studies and for your success as a physician. The MCAT is viewed as a strong predictor of student success, so get ready to delve into studying and to demonstrate to admissions committees that you really know your stuff! 

FAQs

1. What if I encounter a very difficult passage within the biology and biochemistry section of the MCAT?

Firstly, should you encounter a difficult passage on the MCAT, no matter what the section, try not to panic! Start by reading the passage to obtain a general understanding. Go through the passage one paragraph at a time, pausing after each paragraph to ask yourself what the paragraph was about. At the end of the passage, link these ideas together into an overall understanding of the whole passage. Ask yourself what the central thesis of the passage was. Remember, wrong answers do not count against you; thus, for difficult passages and challenging questions, it is important to put your best foot forward and to answer every question, even if you need to make an educated guess. 

2. What is a good score on the biology and biochemistry section of the MCAT? How will I know I am ready to take the MCAT?

The biology and biochemistry section of the MCAT is scored on a scale of 118-132, with the median score set at 125. By focusing on a “good” score that will just get you in to medical school you may not reach your full potential. Instead, aim for the best score that you can achieve on this MCAT section, and every section, to maximize your medical school options. To gauge if you are ready to take the MCAT, take a look at your diagnostic MCAT score and the scores you have been earning more recently on your full-length practice exams. Has the improvement in your scores leveled off? Continue to study as long as your scores continue to improve; take the MCAT once your scores stabilize and you consistently achieve your desired score range at least 3 times in a row. 

3. What was the mean score for the biology and biochemistry section of the MCAT last cycle?

Last cycle’s matriculating medical school students earned a mean score of 128.1 on the Biological and Biochemical Foundations of Living Systems section of the MCAT, which translates to a percentile rank in the 83rd percentile. Therefore, on average, matriculating students earned a score on this section that was the same or better than 83% of all students. For a look at mean scores and percentile ranks for the other MCAT sections, take a look at our blog How Hard is the MCAT?. After you take the MCAT, determine the median MCAT scores for previous admissions cycles at your medical schools of interest; look at individual section scores as well as the median total score. As you build your school list, include several programs where your MCAT scores give you a realistic chance of acceptance. 

4. I am only having trouble with the biology and biochemistry section of the MCAT and I am doing well on the other sections. Does that matter?

Each medical school interprets your MCAT scores differently and some may even put an emphasis on particular sections. In general, most medical schools will view balanced scores more favorably than imbalanced scores. It is important to aim for your best score in each section. This consistency will show your ability to think critically in many different content areas, a skill that medical schools value. It is also important to remember that each section makes up ¼ of your overall MCAT score! 

5. How can I strengthen my skills in reading and interpreting graphs and figures within passages?

Depending on where you are in your academic career, getting involved in a research lab is a great way to strengthen your skills in reading and interpreting graphs for experiment-based passages. Obtaining research experience will enhance other aspects of your medical school application as well. If you're applying for research positions, have a look at our research assistant cover letter blog to help maximize your odds at securing a valuable research position. Another option is to start a journal club with friends that are also studying for the MCAT. Read a scientific article from a peer-reviewed journal each week, then meet to discuss your thoughts. Practice explaining graphs and figures out loud to the journal club, then ask club members if they understood your explanation. 

6. Is there specific coursework that I should take to prepare for the biology concepts on the MCAT?

The biology content on the MCAT spans a wide variety of topics from molecular biology, cell biology, microbiology, and genetics, to the physiology of organ systems. While introductory biology courses include these topics, depending on your program they may not cover them in great detail. By taking more advanced biology courses, you will increase your depth of understanding of these topics, which will give you an advantage on tougher MCAT questions. These advanced courses are not required, but can certainly help. If your budget allows, you can enroll in an MCAT prep course as a part of your MCAT study plan or you can check if your university offers any free MCAT preparation. If you are a non-traditional medical school applicant, your coursework may not have included these typical medical school prerequisites. If you find yourself in this situation, leave yourself ample time to complete a thorough study plan for the MCAT. You can study biology and biochemistry content on your own, but you may also benefit from taking additional university courses or pursuing a postbaccalaureate program designed to get you up to speed with the knowledge base you will need for the MCAT. 

7. How can I minimize test day stress?

To minimize stress on the day of your MCAT, you must start well before the morning of your MCAT exam. In the week leading up to your MCAT, you should not take any more full-length practice exams. These exams are long and require a great deal of focus, and you need to start saving your energy for the big day. You have dedicated a lot of hard work to studying up to this point, and now it is time to relax. Resist the temptation to spend the day before the exam frantically trying to review all of your notes or cramming last-minute information into your head: this is not an effective strategy to improve your MCAT score! Make sure you prepare everything for test day the night before, so you are not scrambling as you run out the door in the morning. On test day, be sure to take the optional breaks to give yourself some time to decompress in between MCAT sections.  

To your success,

Your friends at BeMo

BeMo Academic Consulting

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