BGCSE BSSE Biology 1428 common mistakes
BGCSE BSSE Biology 1428 · Understand the traps and how to avoid them.
When asked to explain why an enzyme-controlled reaction slows and stops at high temperature, the candidate writes only that the enzyme 'dies' or is 'killed', without stating that the enzyme is a protein whose active site changes shape and that substrate molecules can no longer bind to form enzyme-substrate complexes.
Everyday language treats any loss of function as death, and candidates transfer this wording to molecules. Textbooks stress 'denaturation', but candidates often memorise the label without the mechanism behind it, so the mark-bearing idea of a changed active site is missing.
What to do instead
Practise a three-part answer template for every denaturation question: (1) heat breaks bonds holding the protein's shape; (2) the active site is no longer complementary to the substrate; (3) no enzyme-substrate complexes form, so the rate falls to zero. Apply the same template to extremes of pH.
When describing diffusion or osmosis, the candidate names the process but never states the direction of movement or compares concentrations, writing for example 'water moves by osmosis' instead of 'water moves from a region of higher water potential to a region of lower water potential through a partially permeable membrane'.
Candidates recognise the correct term and believe naming it earns the mark, because in class discussion the term alone often seemed sufficient. Under exam conditions they omit the comparative clause that carries most of the credit.
What to do instead
Build a habit of writing a full sentence with three slots: substance, direction with 'from higher... to lower...', and the membrane or surface involved. Practise converting one-line answers into full sentences for osmosis, diffusion and active transport until the pattern is automatic.
In genetics problems, the candidate writes a cross without defining parental genotypes and gametes, then states a phenotype ratio that does not follow from the cross shown, or mixes up genotype and phenotype labels in the final answer.
Candidates try to reach the ratio by mental shortcut rather than setting out the working. They also confuse the terms genotype and phenotype, and forget that gametes carry only one allele of each gene.
What to do instead
Use a fixed layout every time: define alleles with letters, write parental genotypes, list the gametes each parent produces, draw the grid, then state genotype ratio and phenotype ratio as separate lines. Practise monohybrid crosses until the layout is routine, then extend it to test crosses and sex-linked examples.
When explaining transpiration or the effect of exercise on breathing, the candidate lists several correct facts in a row without linking them as cause and effect, so the answer reads as a list of statements rather than an explanation.
Revision lists encourage recall of isolated facts, and candidates reproduce them in the order memorised rather than following the logical chain the question demands. They do not notice that the command word is 'explain' rather than 'state'.
What to do instead
Underline the command word before writing. For 'explain' questions, draft a numbered chain in the margin first, for example: water evaporates from leaf cells, water potential in leaf falls, water pulled up xylem, stomata open, rate increases with temperature. Then write the chain as connected sentences using 'because', 'so' and 'therefore'.
When asked to describe how the structure of a villus, alveolus or nephron relates to its function, the candidate describes the structure alone and never states the functional benefit, for example 'the villus has many microvilli' without adding that this increases surface area for absorption.
Candidates treat structure and function as two separate topics and answer only the half they recall best. They also assume the examiner will infer the link, not realising that the link is the mark.
What to do instead
Practise writing every structural point as a paired statement: feature plus consequence, using 'which increases...' or 'so that...'. Make a two-column table for each exchange surface with structure on the left and advantage on the right, then write full sentences joining the columns.
In food tests and other practical questions, the candidate gives the reagent but omits the conditions and the expected result, for example 'use Benedict's solution' without stating that the sample is heated in a water bath and that a brick-red precipitate indicates a reducing sugar.
Candidates remember the reagent name as the key fact and treat procedure and colour change as incidental. Practical work seen in class is recalled as a demonstration rather than as a method with controlled conditions.
What to do instead
Learn each food test as a three-line card: reagent, conditions, positive result and negative result. Include the safety or control point where relevant. Test yourself by covering one line and reciting the other two, then write full methods for starch, reducing sugar, protein and lipid tests.
When calculating magnification or actual size from a scale, the candidate substitutes numbers into a formula without converting units, so a measurement in millimetres is divided by a magnification in micrometres, or the answer is given without units.
Candidates focus on the arithmetic and forget that the formula only works when both lengths share the same unit. Unit conversion is treated as a separate topic rather than part of every calculation.
What to do instead
Adopt a routine: write the formula, convert every length to the same unit and show the conversion, substitute, calculate, then write the answer with units and a sensible size check. Practise a set of conversions between millimetres, micrometres and nanometres until they are automatic.
In ecology questions on energy flow, the candidate writes that energy is 'lost' or 'used up' as it passes along a food chain, rather than stating that energy is transferred to the environment as heat during respiration and in uneaten or excreted material, so it is not available to the next trophic level.
The word 'lost' is used loosely in everyday speech, and candidates do not distinguish energy that has left the food chain from energy that has been destroyed. The principle of conservation of energy is not applied to ecological contexts.
What to do instead
Replace 'lost' with a precise phrase every time: 'transferred to the environment as heat', 'lost in faeces and urine', 'not eaten'. Draw a sankey-style diagram of energy transfer through one trophic level and label each output, then write a paragraph explaining why food chains rarely have more than four or five levels.
When explaining homeostasis, the candidate describes only one half of the negative feedback loop, for example stating that insulin lowers blood glucose but not what happens when glucose falls, or omitting the receptor and the corrective response.
Candidates learn the hormone and its effect as a single association and do not picture the loop as a cycle. The word 'negative' is repeated without being unpacked as 'a change is detected and reversed'.
What to do instead
Draw every homeostatic mechanism as a loop with four labelled points: stimulus, receptor, coordinator, effector and response, then an arrow back to normal. Practise with blood glucose, body temperature and water balance, and write the loop out in sentences in both directions.
In questions on classification and evolution, the candidate explains natural selection as an organism 'adapting during its lifetime' or 'choosing' to change, rather than describing variation in a population, differential survival, inheritance of favourable alleles and change in allele frequency over generations.
Everyday phrasing about animals 'adapting' implies intentional change within a lifetime, and candidates do not separate individual acclimatisation from population-level evolutionary change. The mechanism is memorised as a slogan rather than a sequence.
What to do instead
Write natural selection as a fixed five-step sequence: variation exists in the population; a selection pressure acts; individuals with favourable alleles survive and reproduce; alleles are passed to offspring; allele frequencies change over many generations. Apply the same sequence to antibiotic resistance and to a named example such as peppered moths, and explicitly contrast it with lifetime acclimatisation.