Basque PAU General Sciences common mistakes
Basque PAU General Sciences · Understand the traps and how to avoid them.
In stoichiometry problems, balancing only the elements that appear obvious and then converting grams to moles with the molar mass of the compound as written rather than the balanced formula, so the limiting-reagent calculation uses the wrong coefficient ratio.
Candidates memorize 'divide by molar mass, then multiply by the coefficient' as a ritual and skip verifying that the equation is balanced and that the coefficient belongs to the species actually being converted.
What to do instead
Adopt a fixed written sequence: write the unbalanced equation, balance it atom-by-atom (leaving H and O last), record the coefficient under each species, then draw an explicit mole-ratio box between the given species and the target before touching numbers. Check the ratio is a ratio of coefficients, not of molar masses.
When asked to design an experiment, stating a hypothesis and a conclusion but omitting the controlled variable, the control group, and the number of replicates, producing a design that cannot distinguish the treatment from confounding factors.
Textbook descriptions of the scientific method are remembered as a linear list (observe, hypothesise, experiment, conclude) without the operational detail examiners reward, and candidates assume the word 'experiment' implies control is understood.
What to do instead
Answer design questions with an explicit four-part template: independent variable and how it is varied; dependent variable and the instrument/units used to measure it; at least three variables held constant with the value chosen; and a negative control plus number of repeats. State how repeats will be used (mean and spread).
Reading a graph's maximum or trend from the plotted line without checking axis units, axis breaks, or whether the x-axis is categorical or continuous, then reporting a rate or slope with the wrong units or an extrapolation beyond the data.
Candidates focus on the shape of the curve and treat the axes as decoration; unit conversion and axis-scale checks are not habitually performed under time pressure.
What to do instead
Before extracting any value, annotate the graph: write the unit of each axis, note any non-zero origin or break, and mark the data range. Compute slopes only between plotted points and attach units as (y-unit)/(x-unit). Explicitly label any statement beyond the last data point as an extrapolation.
Confusing genotype, phenotype and allele frequency when solving genetics crosses, so a monohybrid cross is answered with a 1:1 ratio instead of 3:1, or a test cross is treated as a self-cross.
The vocabulary is learned as synonyms rather than as distinct levels, and Punnett squares are filled mechanically without first writing the parental genotypes and gametes.
What to do instead
Before drawing a Punnett square, write parental genotypes, list the gametes each parent can produce, and state the expected phenotypic ratio in words. Distinguish test cross (cross with homozygous recessive) from self-cross in the first line of the answer, and always report both genotypic and phenotypic ratios.
Calculating work, power or energy without tracking signs and reference frames: treating gravitational potential energy as positive below the reference level, or adding work done by friction as if it increased kinetic energy.
Formulas are applied as arithmetic recipes; the sign conventions and the choice of zero level are rarely written down, and friction is mentally filed as 'a force' rather than as a dissipative one.
What to do instead
At the start of every energy problem, draw the situation, mark the chosen zero of potential energy, and list energy transfers with arrows showing direction (in/out of the system). Use conservation as initial energy plus work done by non-conservative forces equals final energy, and check the sign of the friction term explicitly.
Describing a wave or electrical circuit using the formula alone, mixing up amplitude with wavelength, or confusing series and parallel rules for current and voltage, so a bulb-brightness question is answered from resistance values only.
Symbols look similar and are memorised as a formula sheet; candidates do not connect the physical meaning (amplitude is maximum displacement, wavelength is spatial period) to the graph they are shown.
What to do instead
Anchor each quantity to a feature of the drawn wave or circuit: label amplitude as height from equilibrium, wavelength as crest-to-crest distance, period as time between successive crests. For circuits, write the invariant first (current is the same in series, voltage the same in parallel) and derive brightness from power, not resistance alone.
Answering health and human-body questions with organ names only, without linking structure to function or naming the mechanism (for example, saying 'the kidney filters blood' without mentioning nephrons, filtration, reabsorption and the role of ADH).
Revision focuses on labelling diagrams and memorising lists of organs; the causal chain from structure to function to homeostatic consequence is not rehearsed.
What to do instead
For each system, prepare a three-line chain: structure, function, regulation. Practise answering in the form 'X does Y because Z, and this is controlled by W'. Include one named disorder or failure of regulation per system to demonstrate the mechanism.
In geology and environmental questions, describing a process as a single event rather than a cycle, or omitting the timescale and the driving energy source (for example, explaining the rock cycle or carbon cycle without stating the energy source and the reservoir transfers).
Earth processes are taught as named phenomena (erosion, subduction, photosynthesis) and candidates do not habitually attach timescales or identify reservoirs and fluxes.
What to do instead
Answer with a reservoir-and-flux frame: name the reservoirs, the transfer process, the energy source driving it, and the timescale (seconds for weathering of a slope, millions of years for mountain building). Draw a simple arrow diagram in the margin before writing.
In laboratory questions, describing the procedure without stating safety measures, reagent concentrations, or how the result would be validated, and reporting measurements to more significant figures than the instrument allows.
Practical work is often learned by following a worksheet rather than by justifying each step, so the reasoning behind controls, concentration choices and precision is missing.
What to do instead
Write procedures as numbered steps each containing quantity, instrument and unit. Add a short safety line (hazard, precaution, disposal) and a validation line (repeat, blank, calibration, or comparison with a known value). Round final answers to the precision of the least precise measurement and state the uncertainty.
Treating science-technology-society questions as opinion, giving a one-sided answer that lists benefits without evaluating risks, ethical limits, or the evidence base, and failing to distinguish correlation from causation in a data claim.
These questions feel like general-knowledge prompts, so candidates write persuasive prose instead of structured evaluation, and the correlation/causation distinction is not applied outside statistics topics.
What to do instead
Use a fixed evaluation structure: state the application, give two benefits and two risks with the mechanism for each, name one ethical principle at stake (consent, equity, precaution, animal welfare), and close with what evidence would change your judgement. Whenever a claim links two variables, write one sentence on whether the study design supports causation.