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MCAT biology and biochemistry: the Bio/Biochem section

Bio/Biochem is the third section: 59 questions in 95 minutes, about 65% introductory biology and 25% first-semester biochemistry, with 5% each of general and organic chemistry. MCAT biochemistry isn’t only here, though. It’s also about 25% of Chem/Phys, which makes it one of the most tested subjects on the exam.

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Updated October 2026 · Written from official sources, listed at the bottom of this page

How much biochemistry is on the MCAT?

The AAMC rounds these to the nearest 5%, and they vary from test to test. Psych/Soc adds a little more biology, about 5%.

SubjectShare of Bio/BiochemShare of Chem/Phys
Introductory biology65%5%
First-semester biochemistry25%25%
General chemistry5%30%
Organic chemistry5%15%
Introductory physics-25%
Chem/Phys →Psych/Soc →

The nine content categories

Foundational Concept 1, on molecules, genetics and metabolism, is about 55% of the section. Concept 2, on cells and organisms, is about 20%, and Concept 3, on organ systems, about 25%.

CategoryWhat the AAMC calls it
1AStructure and function of proteins and their constituent amino acids
1BTransmission of genetic information from the gene to the protein
1CTransmission of heritable information from generation to generation and the processes that increase genetic diversity
1DPrinciples of bioenergetics and fuel molecule metabolism
2AAssemblies of molecules, cells, and groups of cells within single cellular and multicellular organisms
2BThe structure, growth, physiology, and genetics of prokaryotes and viruses
2CProcesses of cell division, differentiation, and specialization
3AStructure and functions of the nervous and endocrine systems and ways in which these systems coordinate the organ systems
3BStructure and integrative functions of the main organ systems

What the biology covers

Proteins and amino acids, genetics from gene to protein and from parent to child, metabolism, cells, bacteria and viruses, cell division, and the organ systems, including the nervous, endocrine and immune systems. The AAMC outline lists the topics inside each category. A periodic table is on screen in this section too.

Where to practice Bio/Biochem

The AAMC’s Biology Question Pack comes in two volumes of 120 questions each, and each Section Bank volume has 100 Bio/Biochem questions. They’re part of the paid bundle.

Official AAMC MCAT prep →

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OverviewMCAT examHow many questionsHow many questions are on the MCAT?Score rangeMCAT score range: highest, lowest and how scoring worksRegistrationMCAT registration: how to sign up, step by stepCostHow much does the MCAT cost?Online testMCAT courses online, but the exam is in personPercentiles and averageAverage MCAT score and percentilesScores for medical schoolGood MCAT scores for medical school: what the AAMC data showsScore releaseMCAT score release: when scores come out and how to checkFormat and lengthHow long is the MCAT? Sections in order, timing and breaksSubjects and topicsWhat subjects are on the MCAT?RequirementsMCAT requirements: who can take it and which classes helpTest datesMCAT test dates for 2027Test day and centersMCAT test day: testing centers, check-in and the rulesAccommodationsMCAT accommodations: extra time, breaks and how to applyCARSMCAT CARS: the Critical Analysis and Reasoning Skills sectionChem/PhysMCAT chemistry and physics: the Chem/Phys sectionPsych/SocMCAT psychology and sociology: the Psych/Soc sectionRetakeCan you retake the MCAT?Official AAMC prepOfficial AAMC MCAT prep: the free tests, the outline and the bundlePractice testFree MCAT practice testWhere to learnMCAT prep: where to studyStudy plannerYour MCAT study plan
Sources: AAMC and 7 more. Checked October 2026.

Rules and fees can change, so check the official site before your test.