Biological and Biochemical Foundations of Living Systems is the most content-dense section on the exam, and the one where systematic review pays off most directly. It spans molecules through organ systems, with biochemistry threaded through almost every passage.
Test Ninjas Research · Updated September 11, 2026
Biological and Biochemical Foundations of Living Systems — at a glance
Attribute
Value
Questions
59
Time
95 minutes
Passages
10
Discrete questions
15
Score range
118–132
What it covers
The AAMC publishes approximate content weightings for each section. They are a guide to where to spend review time rather than a guarantee about any individual test form.
Approximate content weighting
Area
Share of section
Biology
~65%
Biochemistry
~25%
General Chemistry
~5%
Organic Chemistry
~5%
Topics that recur
Amino acids, protein structure, and enzyme kinetics
Metabolism: glycolysis, the citric acid cycle, oxidative phosphorylation
Nucleic acids, replication, transcription, and translation
Genetics, inheritance, and gene regulation
Cell structure, the cell cycle, and signalling
The nervous, endocrine, and circulatory systems
Respiratory, digestive, renal, and reproductive systems
Bio/Biochem passages are usually a described experiment: a hypothesis, a method, and results. The questions ask what the results support, what a change to the method would do, or which control is missing. Reviewing content alone leaves you fluent in the vocabulary and still slow at this, so practise on passages, not flashcards.
Biochemistry is the connective tissue
Biochemistry appears in roughly a quarter of the section by weight, but it turns up inside biology passages far more often than that suggests. Amino acid properties and enzyme regulation in particular are worth knowing cold, because they recur everywhere.
Know the systems as systems
Organ-system questions reward understanding how a perturbation propagates — what happens downstream when a hormone rises or a vessel narrows — rather than isolated recall. Building each system as a causal chain rather than a list of parts is what makes those questions fast.
This section is scored 118–132, exactly like the other three, and contributes equally to your total. Work out what a change here does to your overall score with the MCAT score calculator.
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Biochemistry is roughly a quarter of the Bio/Biochem section and about a quarter of the Chem/Phys section as well, which makes it one of the most heavily represented disciplines on the exam overall. Amino acids, protein structure, enzyme kinetics, and the major metabolic pathways carry most of that weight.
There are 59 questions in 95 minutes: 44 attached to 10 passages and 15 standalone discrete questions, the same structure as Chem/Phys and Psych/Soc.
You need the logic of the major pathways — what goes in, what comes out, where regulation happens, and which steps are reversible — rather than every intermediate. Questions typically test regulation and net yield rather than asking you to recite a sequence.
No. Organic chemistry is about 5% of Bio/Biochem and about 15% of Chem/Phys. The emphasis falls on functional groups, separations and spectroscopy, and the reaction types that appear in biological contexts, rather than on multi-step synthesis.