Chemical and Physical Foundations of Biological Systems — Chem/Phys — asks you to apply chemistry and physics to living systems. It is the section most students find least like their coursework, because the physics and chemistry arrive wrapped in biological context and buried in data.
Test Ninjas Research · Updated September 11, 2026
Chemical and Physical Foundations of Biological 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
General Chemistry
~30%
Biochemistry
~25%
Physics
~25%
Organic Chemistry
~15%
Biology
~5%
Topics that recur
Thermodynamics, kinetics, and chemical equilibrium
Acids, bases, buffers, and titration
Electrochemistry and redox reactions
Atomic structure, periodic trends, and bonding
Fluids, pressure, and flow in biological systems
Circuits, electrostatics, and magnetism
Waves, sound, and geometric optics
Separations, chromatography, and spectroscopy
How to approach it
The data is the question
Most Chem/Phys passages hand you a figure, a table, or an experimental setup and then ask something that depends on reading it correctly. Students who lose points here usually do so by recalling a formula and never checking it against the data in front of them. Read the axes and the units before you read the question stem.
Estimate rather than compute
There is no calculator. Every numerical answer is designed to be reachable by rounding and by tracking orders of magnitude, and the answer choices are usually spread far enough apart that a one-significant-figure estimate picks the right one. If you find yourself doing long division, you have taken a wrong turn.
Units carry the reasoning
When a relationship will not come to mind, dimensional analysis often recovers it. Knowing that pressure is force per area and that power is energy per time resolves a surprising number of questions without the underlying formula.
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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Physics makes up roughly a quarter of the section. It concentrates on fluids, thermodynamics, electrostatics and circuits, waves and sound, and optics — the areas with clear biological and clinical applications. Topics with little bearing on living systems, such as rotational dynamics, receive much less attention.
No. No calculator is permitted on any section of the MCAT. Numerical questions are written so that estimation and rounding get you to the correct answer choice, and a periodic table is available on screen throughout the Chem/Phys section.
There are 59 questions in 95 minutes: 44 attached to 10 passages, and 15 standalone discrete questions. That works out to a little over 1 minute 35 seconds per question including passage reading time.
It is the section students most often name as hardest, largely because it combines four disciplines and demands calculation without a calculator. But difficulty is individual — students coming from a physics or engineering background frequently find CARS far harder than Chem/Phys.