BCS Written General Science & Tech common mistakes
BCS Written General Science & Tech · Understand the traps and how to avoid them.
Defining a physics quantity by its formula alone (for example calling momentum 'mass times velocity') without stating what it physically measures, its SI unit, and whether it is a vector or scalar.
Candidates memorise equations from guides and can plug in numbers, but written exams ask for conceptual explanations, so a formula-only answer reads as recall without understanding and earns partial marks at best.
What to do instead
For every quantity you revise, write a three-part card: physical meaning in one sentence, SI unit with symbol, and vector/scalar with direction convention. Practise explaining each aloud in 20-30 words without using the formula.
Balancing chemical equations by adjusting subscripts inside formulae (turning H2O into H2O2) or by changing product identities to force atoms to match.
Under time pressure, candidates treat the equation as an arithmetic puzzle and reach for the fastest visual fix, forgetting that subscripts define the substance and only coefficients may change.
What to do instead
Adopt a fixed procedure: list each element with reactant and product counts, balance metals first, then non-metals, then hydrogen, then oxygen, and finish by re-checking every atom. Redo five equations where you deliberately write the wrong subscript first and correct it, to feel the error.
Describing cell division or inheritance using only labels ('mitosis makes two cells', 'dominant gene wins') with no account of chromosome behaviour, allele combinations, or resulting ratios.
Biology is often revised as vocabulary lists, so candidates can name terms but cannot narrate a process or predict outcomes, which is exactly what structured written questions require.
What to do instead
Draw the process from memory on blank paper: chromosome replication, pairing, separation, and daughter cell chromosome number for mitosis versus meiosis. Then work three monohybrid crosses to a Punnett square and state genotype and phenotype ratios explicitly.
Answering public health questions with individual lifestyle advice only ('eat well, exercise, see a doctor') and omitting prevention levels, surveillance, or the roles of different agencies.
Candidates conflate health education with public health and default to personal advice, missing the population-level framing that earns marks in policy-oriented questions.
What to do instead
Build an answer skeleton with three tiers: primary, secondary and tertiary prevention, each with one concrete measure. Add one sentence naming who acts (household, health worker, local government, national agency) so every answer spans individual and system levels.
Confusing memory and storage, or bits and bytes, in numerical answers, for example stating that a 1 GB file fits comfortably in 512 MB of RAM or that ROM is wiped on power loss.
Everyday usage blurs these terms, and candidates learn definitions without ever converting units or tracing what happens to data during execution, so errors surface only in applied questions.
What to do instead
Memorise the ladder 8 bits = 1 byte, 1024 bytes = 1 KB upward, then solve five conversion problems by hand. Write a one-paragraph trace of a program load: storage, then RAM, then CPU registers and cache, noting which are volatile.
Describing an emerging technology such as AI, blockchain, or 5G purely with hype adjectives ('smart', 'fast', 'secure') without stating the underlying principle, one real application, and one limitation or risk.
Candidates absorb headlines rather than mechanisms, and under exam pressure they pad with enthusiasm instead of substance, which examiners penalise as unsupported assertion.
What to do instead
Prepare a three-line template per technology: how it works in plain language, one concrete use case with a named sector, and one limitation (cost, bias, energy use, regulation). Rehearse until you can deliver it in about 40 words.
Presenting a conclusion as certain after describing an experiment, without stating sample size, controls, or possible confounding variables, and without distinguishing correlation from causation.
Textbook experiments are taught as finished results, so candidates never practise critiquing evidence and unconsciously copy the confident tone of a summary rather than the caution of a researcher.
What to do instead
End every experimental answer with a two-sentence evaluation: what was controlled, and what alternative explanation remains. Practise with a short scenario, naming one confounder and one way to test for it, and always label observed association as association until a mechanism is shown.
Treating environmental issues as purely technical, proposing a device or treatment plant while ignoring policy instruments, cost, monitoring, and who enforces the rule.
Science syllabi emphasise mechanisms, so candidates answer pollution questions with chemistry or biology alone and omit the governance layer that science-policy questions explicitly reward.
What to do instead
For each issue (air pollution, plastic waste, groundwater depletion), prepare a two-column plan: technical measures and policy measures (standards, subsidies, fines, monitoring, public disclosure). Write one integrated paragraph linking a technology to the regulation that would make it effective.
Mismanaging answer structure: writing one long undifferentiated paragraph, skipping the directive verb, or spending disproportionate time on a low-mark part and leaving a high-mark part blank.
Candidates rehearse content but never rehearse the paper, so they discover timing and structure problems for the first time in the exam hall and default to stream-of-consciousness writing.
What to do instead
Do two full timed mock papers. Before writing, underline the directive verb (describe, explain, compare, evaluate) and allocate minutes proportional to marks. Answer in labelled parts or short paragraphs, and leave a two-line plan at the top of each answer.
Using vague quantitative language ('a lot of energy', 'very small', 'much faster') where a number, unit, or order of magnitude is expected, or giving a numeric result with no unit.
Candidates fear being wrong on numbers, so they hedge with adjectives, and because they rarely practise estimation they have no feel for plausible magnitudes.
What to do instead
Learn ten anchor values (speed of light, speed of sound in air, body temperature, typical household voltage, boiling point at altitude) and attach units to every number you write. Practise Fermi estimates to one significant figure and state assumptions openly rather than avoiding the calculation.