ACT® · Science: Interpretation of Data (13-17 items)
Basic Scientific Terminology in a Passage (IOD 302)
A science passage hands you every technical term's meaning in its own text, usually in the opening lines. Your job is to find that homemade definition and plug it into the data, not recall the word from a classroom.
A single unfamiliar word like solute or turbidity can stall a reader even when the rest of the question is just pulling numbers off a table. The fix is built into the passage itself: science writing almost always defines its specialized terms the moment it introduces them, often in the first sentence or two of the introduction. That sentence is a formula in disguise. 'Turbidity index equals particle count per mL divided by 100' is not background color, it is the instruction you apply to every sample in the table that follows.
This is why you are never expected to arrive with outside knowledge of the term. The passage is a closed system: everything needed to answer sits inside it, including the vocabulary. If a word is defined there, that definition is the only one that matters for the rest of the passage, no matter what the word means in an everyday or classroom sense. Treating the definition as temporary and local, rather than hunting for a remembered meaning, is what keeps you fast and correct.
This gets trickier when the passage reuses a word you already know, like resistance, mass, or power, but assigns it a narrower or different meaning than your coursework did. That familiarity can mislead you into answering with the wrong formula in your head. The rule does not change: whatever the passage says the word means, for that passage, is final. This connects directly to reading tables and graphs, since once you have the right definition, interpreting the data columns or axes is pure arithmetic.
Key terms
- Operational definition
- A definition a passage creates for a term, valid only within that passage.
- Turbidity index
- An example passage-defined term equal to particle count per mL divided by 100.
- Net primary productivity
- Gross primary productivity minus respiration, as defined within a given passage.
- Closed system (passage)
- The idea that every fact and definition needed to answer sits inside the passage text.
Watch it explained
- How it worksHow does a science passage define its own vocabulary in its opening lines so you never need outside help?
- Common mistakeWhy isn't a technical term inside a Science passage something you were expected to have memorized?
- Going furtherWhat changes when a passage uses a familiar word like resistance in a sense your class never used?
Check yourself
End of topic.