MCAT, Medical exams

Chemical and Physical Foundations of Biological Systems

The first section tests the chemical and physical principles that underlie the mechanisms of living systems, drawing on general chemistry, organic chemistry, introductory physics, and biochemistry. Its content is organized under Foundational Concepts 4 and 5, which cover how organisms move materials and sense their environment and how chemical interactions govern molecular dynamics. Most questions follow passages describing experiments or biological scenarios, with a set of discrete questions mixed in. No calculator is permitted, so estimation and unit reasoning matter as much as the underlying formulas.

Position: 1 of 4 sections
Questions: 59 questions
Time: 95 minutes
Topics covered: 10 topics in this guide

What is covered

Topics inside this section.

These topics describe the scope students most often review for this part of MCAT. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Motion, force, work, and energy in living systems: Kinematics, Newtonian mechanics, work-energy relationships, and equilibrium applied to biological structures. Learn each equation alongside the physical situation that makes it apply, not as an isolated formula.
Fluids, circulation, and gas exchange: Hydrostatics, flow, viscosity, and gas behavior as they govern blood movement and respiration. Practice translating a physiologic description into the fluid relationship it is really testing.
Electrochemistry and electrical circuits: Circuit elements, current and resistance, electrochemical cells, and membrane-potential parallels. Build fluency with the sign conventions, which is where most avoidable errors occur.
Light, sound, and imaging: Wave behavior, optics, and acoustics, including how organisms sense them and how instruments exploit them. Focus on the qualitative relationships that let you predict a direction of change quickly.
Atomic structure and nuclear decay: Subatomic particles, electronic structure, periodic trends, and radioactive decay. Anchor periodic trends to effective nuclear charge so you can rebuild them under pressure.
Water, solutions, and acid-base chemistry: Solubility, ionic equilibria, titration behavior, and buffer systems in aqueous biological environments. Drill buffer and pH reasoning until it takes seconds, because it recurs across passages.
Molecular structure and intermolecular forces: Bonding, geometry, polarity, and the interactions that set physical properties. Use structure-to-property reasoning to answer questions about solubility and boiling behavior without memorized tables.
Separation and purification methods: Chromatography, extraction, distillation, electrophoresis, and spectroscopic identification. These techniques appear as passage machinery constantly, so know what each one separates on.
Structure and reactivity of biologically relevant molecules: Functional groups, stereochemistry, and the organic reactions that matter for biological molecules. Study reactivity patterns and mechanisms rather than long synthetic routes.
Thermodynamics and reaction kinetics: Enthalpy, entropy, free energy, equilibrium, rate laws, and catalysis. Connect the thermodynamic sign conventions to spontaneity questions you can answer without calculation.

Study tips

How to practice Chem/Phys.

Section-specific guidance that follows from how this material is usually tested.

Set up every physics problem in units before numbers; dimensional analysis catches most setup errors when the clock is running.
Study the organic chemistry this section actually samples — separations, spectroscopy, stereochemistry, and functional-group reactivity — rather than full synthesis sequences.
Practice estimation deliberately, since no calculator is allowed; rounding and order-of-magnitude comfort saves minutes across the section.
Work passages rather than isolated problems, because much of the difficulty here is extracting the relevant variable from an unfamiliar experimental setup.

Where this fits

Chemical and Physical Foundations of Biological Systems is 1 of 4 sections in the MCAT guide. Use the full guide to balance it against everything else you have to review.

Back to the MCAT guide Official exam information

Sample Chem/Phys questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
What is the pH of an aqueous solution whose hydrogen ion concentration is 1 x 10^-4 molar?
1. A4
2. B10
3. C-4
4. D0.0001
Show answer
Answer: A. 4
pH is the negative base-ten logarithm of the hydrogen ion concentration, so a concentration of 10^-4 molar gives a pH of 4. The value 10 is the tempting distractor because it is the corresponding pOH, and pH plus pOH equals 14 at 25 degrees Celsius.
Key insight: The exponent is the answer: a hydrogen ion concentration of 10 to the negative n gives a pH of n.
Question 2Foundational
According to Le Chatelier's principle, how does a system at equilibrium respond when additional product is added at constant temperature?
1. AIt shifts toward the reactants
2. BIt shifts toward the products
3. CIt does not shift at all
4. DThe equilibrium constant increases
Show answer
Answer: A. It shifts toward the reactants
Adding product raises the reaction quotient above the equilibrium constant, so the net reaction runs in reverse until the ratio returns to that constant. Saying the equilibrium constant increases is the tempting error, because the constant depends only on temperature and is unchanged by adding or removing a species.
Key insight: Concentration changes move the position of an equilibrium; only temperature changes the equilibrium constant.
Question 3Intermediate
Which principle requires an ideal incompressible fluid to speed up when it flows steadily from a wide tube into a narrower one?
1. ABernoulli's equation
2. BThe continuity equation
3. CPoiseuille's law
4. DPascal's principle
Show answer
Answer: B. The continuity equation
The continuity equation states that the volume flow rate, the product of cross-sectional area and flow speed, is constant along the tube, so a smaller area forces a higher speed. Bernoulli's equation is the tempting distractor because it is the other famous fluid relationship, but it describes how pressure trades off against speed and height once the speeds are known.
Key insight: Continuity gives you the speed change from geometry; Bernoulli then tells you what happens to the pressure.
Question 4Intermediate
Which spectroscopic technique identifies functional groups by the characteristic frequencies at which bonds absorb, such as a broad band near 3300 reciprocal centimeters for a hydroxyl group?
1. AInfrared spectroscopy
2. BNuclear magnetic resonance spectroscopy
3. CMass spectrometry
4. DUltraviolet-visible spectroscopy
Show answer
Answer: A. Infrared spectroscopy
Infrared radiation excites bond stretching and bending, and each functional group absorbs in a characteristic region, which makes the broad hydroxyl stretch near 3300 reciprocal centimeters immediately recognizable. Nuclear magnetic resonance spectroscopy is the tempting distractor, but it reports the chemical environment of nuclei such as hydrogen and carbon and maps the carbon skeleton rather than naming functional groups by absorption band.
Key insight: Infrared spectroscopy answers what functional groups are present; nuclear magnetic resonance answers how the skeleton is connected.
Question 5Advanced
For a reaction with a negative enthalpy change and a positive entropy change, at which temperatures is the reaction spontaneous?
1. AAt all temperatures
2. BOnly at high temperatures
3. COnly at low temperatures
4. DAt no temperature
Show answer
Answer: A. At all temperatures
Gibbs free energy is enthalpy minus temperature times entropy, so a negative enthalpy term and a positive entropy term both push the free energy change negative no matter the temperature. Answering only at high temperatures is the tempting error, since that case applies when enthalpy and entropy changes are both positive and the entropy term must grow large enough to win.
Key insight: Signs decide temperature dependence: matching signs of enthalpy and entropy make spontaneity temperature dependent, while opposing signs give the same verdict at every temperature.

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Chemical and Physical Foundations of Biological Systems