Elsie Item-Writing Academy
About 45 minutes · Academy module: Foundations: Writing MCAT-Style Items
The Elsie Item-Writing Academy is an independent faculty-development resource. It is not affiliated with, endorsed by, or sponsored by the AAMC, NBME, USMLE, LCME, or NRMP. Completion of this module supports faculty-development documentation.
Most MCAT items are passage-based: a passage of text, figures, or data followed by a short set of questions, with a smaller number of standalone discrete items. Every item has four options, lettered A through D. The AAMC describes the exam's reasoning demands in four scientific inquiry and reasoning skill categories: knowledge of scientific concepts and principles; scientific reasoning and problem solving; reasoning about the design and execution of research; and data-based and statistical reasoning. Decide which skill your item targets before you write it, because the skill dictates what the stem must provide. An item about research design needs a described experiment with a genuine design choice in it; an item about data reasoning needs actual data to reason with; a concept item needs a clean, focused question with no camouflage.
Start every item with the tested point: one sentence, written for yourself, stating exactly what the examinee must know or be able to do. Then write the correct answer first, as a complete sentence, before drafting any distractors. This order matters. Authors who write the stem first and hunt for an answer afterward produce the unfocused stems you will diagnose in this module's drills.
Apply the cover-the-options rule: with the options hidden, a well-prepared examinee should be able to state what the question is asking and sketch the answer. If covering the options leaves the examinee guessing what is wanted, the stem is unfinished.
Build four homogeneous options: parallel in grammar, similar in length, and pitched at the same level of detail. Distractors should be plausible, drawn from common student misconceptions or adjacent concepts — never throwaways that no prepared examinee would choose. Never use "all of the above" or "none of the above": the former lets examinees confirm two options and stop thinking, and both can create items with more than one defensible key. Avoid absolute terms like always and never unless the science genuinely supports them; they hand the answer to test-wise examinees. Avoid negative stems such as "which of the following is NOT"; when a negative lead-in is unavoidable, emphasize the negative word so it cannot be missed.
For passage-based items, the item must need the passage. If the question can be answered from general knowledge without reading the passage, it is a discrete item wearing a costume — either rewrite it to require passage reasoning or move it out of the set. Keep notation standard, define every symbol once, and keep the reading level plain: the item tests science, not reading endurance.
(intended key: C)
Stem: An inhibitor raises the Kₘ of an enzyme-catalyzed reaction but does not change Vₘₐₓ. Which of the following is always true of such an inhibitor?
A. It always binds irreversibly to the active site. B. It never affects Vₘₐₓ under any conditions. C. It competes with substrate for binding at the active site. D. All of the above.
"all of the above" option; absolute terms.
"All of the above" lets an examinee confirm any two options and stop reasoning — and here options A and B are trivially false because of "always" and "never," so the item collapses into a vocabulary check on the word "competes." Absolute terms make distractors implausible to test-wise examinees, who eliminate A and B without knowing any enzymology. The rewrite drops the catch-all, removes the absolutes, and replaces the giveaway distractors with plausible near-misses, so the item discriminates on the Kₘ/Vₘₐₓ pattern rather than on test-taking savvy.
— cold-solve verified: 2/2 (solvers chose C, C)
Stem: A researcher measures the initial rate of an enzyme-catalyzed reaction at several substrate concentrations, with and without a small-molecule inhibitor. In the presence of the inhibitor, the apparent Kₘ increases while Vₘₐₓ is unchanged. Which statement best describes the inhibitor?
A. It binds irreversibly to the enzyme's active site. B. It binds the enzyme–substrate complex more tightly than it binds the free enzyme. C. It competes with substrate for binding at the active site. D. It decreases the activation energy of the catalyzed reaction.
Key: C
Increased Kₘ with unchanged Vₘₐₓ is the signature of competitive inhibition: the inhibitor competes for the active site, so more substrate overcomes it (Vₘₐₓ recoverable) but apparent affinity falls (Kₘ rises). Option A is wrong because irreversible inhibition lowers Vₘₐₓ. Option B describes uncompetitive inhibition, which lowers Kₘ. Option D confuses inhibitors with catalysts. Both independent cold solvers selected C and named no other defensible option.
(intended key: D)
Stem: A galvanic cell is built from Zn(s) | Zn²⁺ (1 M) and Cu(s) | Cu²⁺ (1 M) half-cells. E°(Zn²⁺/Zn) = −0.76 V; E°(Cu²⁺/Cu) = +0.34 V. Which of the following statements about the cell is correct?
A. Zinc is reduced at the cathode. B. Electrons flow from copper to zinc through the external circuit. C. The cell reaction is nonspontaneous under standard conditions. D. The standard cell potential is +1.10 V.
unfocused stem.
"Which of the following statements is correct" is not a question — it is four mini-questions wearing a stem. Cover the options and the examinee cannot say what is being asked: cathode identity? electron flow? spontaneity? cell potential? Each option tests a different fact, so the item has no single tested point. The rewrite gives the stem one focused task (compute the standard cell potential) and makes every option a numeric answer to that task. One stem, one question, one skill.
— cold-solve verified: 2/2 (solvers chose D, D)
Stem: A galvanic cell is constructed from a Zn(s) | Zn²⁺ (1 M) half-cell and a Cu(s) | Cu²⁺ (1 M) half-cell. The standard reduction potentials are E° = −0.76 V for Zn²⁺/Zn and E° = +0.34 V for Cu²⁺/Cu. What is the standard cell potential?
A. −1.10 V B. −0.42 V C. +0.42 V D. +1.10 V
Key: D
Copper has the more positive reduction potential, so Cu²⁺ is reduced (cathode) and Zn is oxidized (anode): E°cell = E°cathode − E°anode = (+0.34) − (−0.76) = +1.10 V. Option A flips the sign; B and C come from adding or misassigning the half-cell potentials. Both independent cold solvers selected D and named no other defensible option.
(intended key: A)
Stem: During the absolute refractory period, the neuron:
A. is absolutely unable to fire another action potential no matter how strong the stimulus B. can fire if the stimulus is strong enough C. releases extra neurotransmitter to make up for lost time D. grows a new segment of axon to restore excitability
grammatical cueing; implausible distractors.
Two flaws compound here. First, "absolutely" in option A echoes "absolute refractory period" in the stem — a word-match cue that rewards reading rather than reasoning. Second, options C and D are implausible: no prepared examinee would choose them, so the item is effectively a two-option coin flip between A and B. The rewrite removes the echo and replaces the throwaways with near-misses drawn from the adjacent concept (the relative refractory period), so every option must be evaluated on content.
— cold-solve verified: 2/2 (solvers chose B, B)
Stem: During the absolute refractory period of a neuronal action potential, which statement is true?
A. A second action potential can be triggered by an unusually strong stimulus. B. Voltage-gated Na⁺ channels are inactivated and cannot reopen. C. The membrane is hyperpolarized below its resting potential. D. Neurotransmitter release from the presynaptic terminal is increased.
Key: B
During the absolute refractory period, voltage-gated Na⁺ channels are in the inactivated state and cannot reopen regardless of stimulus strength — that inactivation is what makes the period absolute. Options A and C describe the relative refractory period (strong stimuli can fire; the membrane is hyperpolarized). Option D is unrelated to refractoriness. Both independent cold solvers selected B and named no other defensible option.
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