Junkao Science Knowledge common mistakes
Junkao Science Knowledge · Understand the traps and how to avoid them.
When asked to identify the manipulated (independent) variable, the candidate names the outcome that was measured, or lists the control group, instead of the factor the experimenter deliberately changed.
Textbook definitions of 'independent' and 'dependent' are memorized as isolated vocabulary, so under time pressure the candidate matches the word 'variable' to whichever quantity is most visible in the scenario rather than tracing who changed what.
What to do instead
Before answering, rewrite the scenario in one sentence of the form 'The experimenter changed ___ and then measured ___.' The first blank is the manipulated variable, the second the responding variable, and any factor held constant is a controlled variable. Practise on 10 short scenarios until the sentence is automatic.
The candidate concludes that a hypothesis is proven correct because the results matched the prediction, rather than saying the data support the hypothesis.
Everyday speech treats 'proven' and 'supported' as synonyms, and school writing often rewards confident conclusions, so the candidate imports that habit into questions about the nature of science.
What to do instead
Adopt a fixed phrase for conclusions: 'The data support the hypothesis' or 'The data do not support the hypothesis.' Reserve 'proven' for mathematical statements. When a question asks what would strengthen a conclusion, answer with replication, larger samples, or controlled variables, not with restating the result.
The candidate reads a value off a graduated cylinder, ruler, or thermometer and reports it without estimating one digit beyond the smallest marked division, or estimates two extra digits.
The rule about significant figures in a measurement is taught once and then buried under calculation practice, so the candidate either ignores it or over-applies it and reports false precision.
What to do instead
Use a two-step check: find the smallest marked interval, then record all certain digits plus exactly one estimated digit. For a cylinder marked every 1 mL, a reading is written as, for example, 24.5 mL, not 24 mL or 24.53 mL. Apply the same rule to rulers and thermometers in practice readings.
The candidate converts between units by moving a decimal point the wrong number of places, for example treating 1 kilogram as 100 grams or 1 kilometer as 100 meters.
Metric prefixes are memorized as a list without their numerical meanings, so 'kilo' and 'centi' become labels rather than multipliers, and the direction of the move is guessed.
What to do instead
Write every prefix as a power of ten before converting: kilo = 10^3, centi = 10^-2, milli = 10^-3. Then set up the conversion as a fraction with the unwanted unit on the bottom so it cancels. Check the answer's plausibility: a kilogram is larger than a gram, so the number of grams must be larger than the number of kilograms.
The candidate balances a chemical equation by changing a subscript in a formula, for example turning H2O into H2O2, instead of placing a coefficient in front of the formula.
The goal is seen as 'make the numbers match', and subscripts are the most visually available numbers to adjust, so the candidate edits the formula without realizing that this changes the substance.
What to do instead
State the rule aloud before balancing: only coefficients change, never subscripts. Balance one element at a time, starting with elements that appear in only one reactant and one product, and leave hydrogen and oxygen for last. Verify by recounting every element on both sides after each coefficient change.
The candidate describes a moving object as having a force acting on it in the direction of motion, saying 'the force keeps it moving forward' even when no forward force is present.
Everyday experience of pushing objects suggests motion requires a continuous push, an Aristotelian intuition that survives instruction because the candidate never contrasts it with the friction-free case.
What to do instead
Apply Newton's first law as a test question: if the object moves at constant velocity, the net force is zero. Draw a free-body diagram and label only real interactions (gravity, normal force, friction, applied force). If no forward interaction exists, no forward force arrow is drawn.
The candidate confuses the amplitude of a wave with its wavelength or frequency, for example claiming that increasing amplitude increases the wave's speed or its pitch.
Diagrams show amplitude and wavelength as vertical and horizontal distances on the same picture, and the candidate memorizes the picture rather than the definitions, so the labels swap under questioning.
What to do instead
Anchor each term to a measurable feature: amplitude is height from the middle line to a crest, wavelength is distance from one crest to the next, frequency is crests passing a point per second. For sound, amplitude maps to loudness and frequency to pitch; for light, amplitude maps to brightness and frequency to color. Test yourself by sketching a wave and labelling all three without looking.
The candidate assumes that a dominant trait is the one that appears most often in a population, or that a dominant allele is somehow stronger or better.
The word 'dominant' carries an everyday meaning of 'most common' or 'most powerful', and the candidate never separates the genetic definition from the colloquial one.
What to do instead
Define dominance precisely: in a heterozygote, the dominant allele's trait is the one expressed. Frequency in a population is a separate question answered by allele counts. When a question gives genotype percentages, calculate phenotype ratios from the genotypes rather than from the word 'dominant'.
The candidate treats an energy pyramid as reversible, claiming that a top predator supports the producers below it, or that energy increases at higher trophic levels.
Food webs are drawn as connected arrows that look symmetric, and the candidate reads the diagram as a network of mutual relationships rather than a directed flow with losses at each step.
What to do instead
Attach a number to each level: roughly 10 percent of energy passes to the next trophic level, with the rest lost as heat and in waste. Trace any arrow in the direction of energy flow, from eaten to eater. If a question asks why top predators are rare, answer with the cumulative energy loss across levels.
The candidate explains seasons by Earth's changing distance from the Sun rather than by the tilt of Earth's axis, and similarly explains day and night as caused by Earth's orbit.
Diagrams of an elliptical orbit exaggerate the eccentricity, and the distance explanation is intuitive and widely repeated outside school, so it competes successfully with the correct tilt model.
What to do instead
Memorize two disconfirming facts and use them as a check: the Northern and Southern Hemispheres have opposite seasons at the same time, and Earth is actually closest to the Sun during Northern winter. Seasons come from axial tilt changing the angle and duration of sunlight; day and night come from rotation on that axis.