The Biological and Biochemical Foundations of Living Systems (Bio/Biochemical) section of the MCAT tests your understanding of the biological processes that keep living systems functioning, from the molecular level all the way up to organ systems.
But knowing the content is only part of the challenge. You’ll also need to apply what you know to unfamiliar scenarios, interpret experiments and data, and reason through how biological and biochemical processes interact. In this guide, I’ll break down what’s tested on the MCAT Bio/Biochem section, the topics you should prioritize, and how to approach the section more strategically.
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The Bio/Biochem section is the third section of the MCAT. You’ll have 95 minutes to answer 59 questions, including both passage-based and discrete questions, on test day. More specifically, the Bio/Biochem section has 10 passages with 44 passage-based questions (4-6 questions per passage) and 15 free-standing questions. This averages out to approximately 1 minute 36 seconds per question. However, if you take into account the amount of time you have to spend reading the passages, you really only have about 1 minute to answer each question.
This is one of the reasons why the MCAT is so difficult. It’s not simply testing your knowledge of the science content and scientific reasoning skills, but it’s also assessing how quickly you can recall the science content and reason through the experimental data presented in the passage to answer the questions. In fact, many students struggle to finish this section on time and often have to rush near the end or even leave some questions unanswered.
Most of this section draws from introductory general biology with lab (65%) and first-semester biochemistry (25%), with a smaller number of questions pulling from general and organic chemistry (5% each). But the section isn’t organized around isolated subjects. You’ll often need to combine concepts from multiple areas and apply them to a biological system, experiment, or unfamiliar scenario.
| MCAT Bio/Biochem | |
| Order on the MCAT | Third section |
| Number of questions | 59 |
| Time | 95 minutes |
| Question format | Passage-based and discrete questions |
| Main subject areas | Biology and biochemistry |
| Score range | 118–132 |
At its core, MCAT Bio/Biochem tests whether you understand how living systems work and how biological processes connect across different levels of organization.
That means you may need to reason about something as small as an amino acid or protein in one question and then think about how an entire organ system maintains homeostasis in another. The AAMC specifically emphasizes processes such as acquiring energy, maintaining a stable internal environment, growing and reproducing, responding to changes in the environment, and adapting.
You’re also expected to understand how cells, tissues, and organ systems work both independently and together. For example, a passage might ask you to connect a change in protein function to a cellular process, then predict how that change affects a larger physiological system.
And this is where the section becomes more than a content test. MCAT questions don’t simply require you recall scientific facts. Instead the AAMC expects you to apply your biological and biochemical knowledge with new information introduced in the passages. These passages are often adapted from scientific journal articles and will describe the experiments performed by the researchers. So while memorizing key concepts matters, you also need to be able to interpret experiments, analyze data, and apply what you know to situations you haven’t seen before.
If you want to excel in the MCAT Bio/Biochem section, I highly recommend joining a basic science research lab. Not only is research experience important for your medical school application but it will also help you immensely on the MCAT. In your biology and biochemistry classes, you’ll learn about some common molecular biology techniques, like polymerase chain reaction (PCR), western blots, and molecular cloning. However, learning what these techniques do is very different from understanding why a researcher would use that technique and what questions that technique can help to answer. That’s the kind of knowledge you can gain by working in a research lab and will give you an advantage in the MCAT Bio/Biochem section.
The AAMC organizes the Bio/Biochem section around three foundational concepts and nine content categories. Rather than treating biology, biochemistry, and chemistry as completely separate subjects, this framework reflects how those disciplines overlap when you’re thinking about living systems.
| Foundational concept | What it covers | Approx. share of Bio/Biochem |
| 1. Biomolecules and the Processes Necessary for Life | Amino acids, proteins, genetics, and metabolism | 55% |
| 2. Cells and Cellular Organization | Cell structure, prokaryotes and viruses, cell division and differentiation | 20% |
| 3. Organ Systems and Homeostasis | Nervous and endocrine regulation, major organ systems, and homeostasis | 25% |
At the center of Foundational Concept 1 is a simple idea: the chemical and structural properties of biomolecules determine the roles they play in cells.
This section carries the most weight, accounting for about 55% of the Bio/Biochem section. The AAMC divides it into four content categories covering proteins and amino acids, genetic information, heredity, and metabolism.
This category focuses on how the structure and chemistry of amino acids determine the structure and function of proteins.
You should be comfortable with:
The AAMC places particular emphasis on the connection between amino acid chemistry, three-dimensional protein structure, and protein function, as well as enzyme catalysis and regulation.
Content Category 1B follows the flow of biological information from DNA to RNA to protein and asks you to understand both the molecules involved and the processes that regulate them.
Key topics include:
You may also see questions that connect these mechanisms to real biological consequences, such as cancer, gene therapy, or changes in protein expression.
This category shifts from how genetic information is used inside a cell to how that information is passed between generations and how genetic variation develops.
You should know:
The key is not just memorizing inheritance patterns. You should also be able to reason through how processes such as mutation, recombination, and selection change genetic diversity within a population.
Content Category 1D focuses on how living systems obtain, store, and use energy.
Major topics include:
For the MCAT, I wouldn’t approach metabolism as simply a collection of isolated pathways to memorize. While it’s true that you do need much of these metabolic pathways memorized ( where each pathway occurs, what goes in and comes out, how it’s regulated, and how it connects to other pathways), you also need to understand the importance of each pathway for the cell and organism as a whole. Being able to answer questions like “why is the pentose-phosphate pathway important)” or “when does ketogenesis occur” are important to ensure that you’re not simply memorizing facts but you truly understand the biochemistry concepts in a way that will help you correctly answer MCAT Bio/Biochem questions.
The AAMC frames this category around the regulated pathways cells use to harvest chemical energy from fuel molecules and power the processes necessary for life.
Foundational Concept 2 accounts for about 20% of the Bio/Biochem section and focuses on how cells are structured, how they maintain the conditions necessary for life, and how groups of specialized cells work together in multicellular organisms.
The AAMC divides this concept into three content categories covering high-yield MCAT biology topics like cellular structure and organization, prokaryotes and viruses, and the processes that allow cells to divide, differentiate, and specialize.
Content Category 2A focuses on how the structures within and around cells allow them to maintain their internal environment, communicate, transport materials, and organize into tissues.
Key topics include:
Pay particular attention to how structure supports function. You may be asked to predict what happens when a membrane protein stops working, an ion gradient changes, or an organelle can no longer perform its normal role.
This category focuses on the structure, physiology, reproduction, and genetics of prokaryotic cells, as well as the structure and life cycles of viruses.
You should be familiar with:
A useful way to study this category is to focus on what makes prokaryotes biologically different from eukaryotic cells. Those distinctions can help you reason through questions about replication, gene transfer, drug targets, and responses to changes in the environment. Furthermore, you should understand how viruses can infect both prokaryotes and eukaryotes, and the viral life cycle.
Content Category 2C looks at how cells reproduce, how the cell cycle is regulated, and how initially similar cells develop into specialized tissues and organs.
Major topics include:
Here again, understanding the sequence of events is only part of what you need. You should also be able to reason through what happens when normal regulation breaks down. For example, you may need to predict how a failure in cell-cycle control could contribute to cancer or how changes in gene expression can alter cell differentiation.
Foundational Concept 3 accounts for about 25% of the Bio/Biochem section and focuses on how tissues and organ systems work together to maintain a stable internal environment.
This is where the section shifts from what happens inside individual cells to how the body coordinates larger physiological processes. The AAMC divides this concept into two main content categories: the nervous and endocrine systems, and the major organ systems that support functions such as circulation, respiration, digestion, movement, reproduction, and immune defense.
Content Category 3A focuses on the two major systems the body uses to coordinate and regulate physiological activity. These are the two high-yield physiology systems tested in the MCAT Bio/Biochem section.
You should be familiar with:
For the MCAT, the important thing is to understand how these systems communicate and regulate one another. You may need to predict how changing a hormone level, receptor, ion gradient, or neural signal affects another part of the physiological pathway.
Content Category 3B covers the major organ systems and how they work together to support homeostasis.
Key systems and topics include:
The MCAT usually expects more than simple anatomy recall. You should be able to connect structure, function, and regulation across multiple systems.
For example, if blood pressure drops, you may need to reason through how the nervous system, endocrine system, kidneys, and cardiovascular system respond together. Thinking in terms of these relationships will prepare you better than memorizing each organ system in isolation.
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The AAMC doesn’t publish an official ranking of individual Bio/Biochem topics by frequency, but its content framework shows how the section is weighed across disciplines and concepts. Foundational Concept 1, which includes proteins, molecular biology, genetics, and metabolism, makes up about 55% of Bio/Biochem questions, so those areas are especially important to understand well.
As you review, make sure you’re especially comfortable with these high-yield areas:
| High-yield area | What to know |
| Amino acids and proteins | Amino acid properties, protein structure, enzyme function, enzyme kinetics, and inhibition |
| Molecular biology | DNA replication, transcription, translation, gene regulation, and mutations |
| Metabolism | Glycolysis, the citric acid cycle, oxidative phosphorylation, gluconeogenesis, and metabolic regulation |
| Cell biology | Membranes, transport, organelles, cell signaling, and the cell cycle |
| Genetics | Mendelian inheritance, meiosis, recombination, mutations, and genetic variation |
| Physiology and homeostasis | Nervous, endocrine, cardiovascular, respiratory, renal, digestive, immune, and reproductive systems |
| Experimental methods and data interpretation | Experimental design, controls, graphs, tables, and common laboratory techniques |
These topics are important not just because of the content itself, but because they often overlap. A question about metabolism, for example, may also require you to understand enzyme regulation, cellular compartments, or how a change in one pathway affects another.
That’s why I wouldn't study Bio/Biochem as a checklist of disconnected facts. The more you understand how these concepts fit together, the easier it becomes to apply them to unfamiliar passages and experiments.
Knowing the content is only part of succeeding on the Bio/Biochem section. The AAMC also tests how well you can apply scientific concepts, reason through unfamiliar problems, evaluate experiments, and interpret data.
Here’s how the section is approximately divided by Scientific Inquiry and Reasoning Skill:
| Skill | Approx. share of Bio/Biochem | What it means for you |
| Knowledge of Scientific Principles | 35% | Recall and apply biological and biochemical concepts |
| Scientific Reasoning and Problem-Solving | 45% | Use scientific principles to make predictions and solve unfamiliar problems |
| Reasoning About the Design and Execution of Research | 10% | Evaluate hypotheses, variables, controls, methods, and experimental design |
| Data-Based and Statistical Reasoning | 10% | Interpret graphs, tables, trends, and basic statistical information |
One important takeaway is that only about 35% of the section is categorized as straightforward knowledge of scientific principles. That doesn’t mean content knowledge matters for only 35% of questions (you’ll still use it throughout the section), but it does explain why memorization alone won’t carry you very far.
You also need to be comfortable applying familiar concepts to unfamiliar biological systems, following the logic of an experiment, and deciding what the data actually support.
Bio/Biochem passages can look intimidating because they often introduce unfamiliar proteins, pathways, experiments, or disease mechanisms. You may also need to work with graphs, tables, figures, or experimental results while bringing in outside content knowledge.
The goal is to identify the biological system being studied, follow the relationships that matter, and determine what information you actually need to answer the questions.
Many Bio/Biochem passages are built around research scenarios. You might see an experiment involving a mutated protein, a signaling pathway, enzyme activity, gene expression, or a change in physiology.
Passages may ask you to combine:
Don’t be surprised if a passage introduces a molecule or pathway you’ve never seen before. The MCAT often gives you enough information to reason through unfamiliar material using concepts you already understand.
When you work through a Bio/Biochem passage, focus on the structure of the problem rather than trying to memorize every detail.
The more comfortable you become with identifying these patterns through practice, the less overwhelming dense Bio/Biochem passages tend to feel.
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A strong Bio/Biochem study plan should balance content review with passage practice. You need enough foundational knowledge to recognize what a question is testing, but you also need to practice applying that knowledge in unfamiliar contexts.
Start by making sure you know the core concepts well enough that you don’t have to relearn them every time they appear in a passage.
Some topics are worth knowing cold, including:
You don’t need to memorize every detail you encounter. Focus instead on the relationships that help you make predictions: what activates or inhibits a process, what goes in and comes out of a pathway, where a process occurs, and what happens when one part of the system changes.
Don’t wait until you’ve finished all of your content review to start doing passages. As you study a topic, work through questions that force you to apply it.
If you’re reviewing enzymes, for example, pair that content with enzyme kinetics passages. If you’re studying genetics, practice questions involving inheritance, mutations, or gene expression.
This helps you learn content in the same way you’ll need to use it on test day.
Because Bio/Biochem frequently uses research scenarios, spend time practicing how to break down experiments.
When reviewing passages, ask yourself:
The goal is to make experimental reasoning feel routine rather than something you have to decode from scratch every time.
Simply knowing that you got a question wrong isn’t enough. Try to identify why you missed it.
A useful way to categorize mistakes is:
Over time, these patterns can show you where your study plan needs to change. If most of your misses are content gaps, you need more review. If you know the material but keep missing experimental questions, more memorization probably isn’t the answer. Instead, you need more practice applying what you know.
Different parts of the MCAT may require different approaches to prep. Whether you need to strengthen your content knowledge, build endurance, or fit more review into your schedule, MedSchoolCoach offers resources to help:
You don’t need to use every study resource available. Focus on the tools that address the areas making the MCAT most challenging for you and that fit naturally into your study plan.
The MCAT is a difficult exam, but with the right prep and understanding of the test’s scope and structure, you can tackle it more confidently. Personalized, one-on-one tutoring can help you master each section, build test-day endurance, and develop strategies that work for you.
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