MDCAT cheat sheet

Enzymes are biological catalysts that lower activation energy by stabilizing the transition state; they are not consumed and are denatured by extremes of temperature or pH.

DNA replication is semi-conservative: each daughter double helix contains one parental strand and one newly synthesized strand, with A pairing to T and G to C.

Meiosis has two divisions and yields four haploid cells; crossing over occurs between homologous chromosomes during prophase I, and independent assortment occurs at metaphase I.

The resting membrane potential of a typical neuron is about −70 mV, maintained by the Na+/K+ ATPase pump and K+ leak channels, with the inside negative relative to outside.

Hemoglobin is an iron-containing tetramer in red blood cells; it binds oxygen cooperatively in the lungs and releases it in tissues where pH is lower and CO2 is higher.

The Calvin cycle occurs in the chloroplast stroma, uses ATP and NADPH from the light reactions, and fixes CO2 via RuBisCO to produce G3P.

A monohybrid cross between two heterozygotes (Aa × Aa) gives a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio for a completely dominant trait.

The loop of Henle acts as a countercurrent multiplier: the descending limb is water-permeable, the ascending limb transports salts, and the medullary gradient concentrates urine.

Ideal gas law: PV = nRT, where R = 8.314 J mol−1 K−1; at STP (273 K, 1 atm) one mole of ideal gas occupies 22.4 L.

pH = −log[H+]; at 25 °C neutral water has pH 7 and Kw = [H+][OH−] = 1.0 × 10−14.

Le Chatelier’s principle: a system at equilibrium shifts to oppose a change in concentration, pressure, or temperature; catalysts do not shift equilibrium position.

Oxidation is loss of electrons and an increase in oxidation number; reduction is gain of electrons and a decrease in oxidation number.

sp3 hybridization arises from four electron domains and gives tetrahedral geometry with bond angles near 109.5°, as in methane.

Hess’s law: the enthalpy change of a reaction is independent of pathway and equals the sum of enthalpy changes of any sequence of steps.

Colligative properties depend on the number of dissolved particles, not identity: boiling point elevation and freezing point depression increase with particle concentration.

Across a period, atomic radius decreases and ionization energy generally increases; down a group, radius increases and ionization energy decreases.

For constant acceleration: v = u + at, s = ut + ½at², and v² = u² + 2as, where u is initial velocity and a is acceleration.

Newton’s second law: F_net = ma; the acceleration is in the same direction as the net force and inversely proportional to mass.

Work done by a constant force is W = Fd cos θ; kinetic energy is ½mv², and gravitational potential energy near Earth is mgh.

Ohm’s law: V = IR for a conductor at constant temperature; electrical power is P = VI = I²R = V²/R.

Wave equation: v = fλ; wave speed equals frequency times wavelength, and frequency is set by the source.

Thin lens/mirror equation: 1/f = 1/d_o + 1/d_i; magnification m = −d_i/d_o, with sign conventions indicating real or virtual images.

Coulomb’s law: F = k|q1q2|/r²; electric force is proportional to charge product and inversely proportional to the square of separation.

First law of thermodynamics: ΔU = Q − W; change in internal energy equals heat added minus work done by the system.

Subject–verb agreement: the verb agrees with the grammatical subject, ignoring intervening prepositional phrases; singular subjects take singular verbs.

A comma splice joins two independent clauses with only a comma; revise with a semicolon, a coordinating conjunction, or a period.

Affect is usually a verb meaning to influence; effect is usually a noun meaning result, though effect can be a verb meaning to bring about.

In active voice the subject performs the action; in passive voice the subject receives it and the verb uses be + past participle.

A pronoun must agree with its antecedent in number and gender, and its reference should be clear rather than ambiguous.

The main idea of a passage is its central claim; it is often stated in a topic sentence and supported by details rather than being a minor detail.

Dangling modifiers occur when the introductory phrase does not logically describe the subject of the main clause; place the intended noun immediately after the comma.

A conditional 'If A then B' is logically equivalent to its contrapositive 'If not B then not A'; the converse 'If B then A' is not equivalent.

Correlation between two variables does not establish causation; alternative explanations include reverse causation and a common cause.

A necessary condition is required for an outcome: if the outcome occurs, the condition must hold, but the condition alone may not guarantee it.

A sufficient condition guarantees an outcome when present: if the condition holds, the outcome occurs, though other causes may also produce it.

In a valid syllogism, if the premises are true the conclusion must be true; validity concerns form, while soundness also requires true premises.

To weaken a causal argument, identify an alternative cause, show the effect occurred without the cause, or question the reliability of the evidence.

Analogy questions require identifying the precise relationship between the pair, such as part-to-whole, cause-to-effect, or degree, before choosing a match.

Number-series items often use constant differences, ratios, alternating operations, or squares; test the simplest pattern before complex ones.