BGCSE Human & Social Biology common mistakes
BGCSE Human & Social Biology · Understand the traps and how to avoid them.
When asked to explain why an enzyme stops working at high temperature, the candidate writes only 'the enzyme is killed' or 'the enzyme dies', treating the enzyme as a living organism rather than describing denaturation of the active site.
Everyday language about heat and death is applied to a molecule, and candidates have memorised 'enzymes are destroyed by heat' without linking it to the shape of the active site and the substrate no longer fitting. The word 'killed' feels sufficient so the explanation stops there.
What to do instead
Train a fixed three-part sentence: heat changes the shape of the active site; the substrate no longer fits to form enzyme-substrate complexes; the enzyme is denatured and the reaction rate falls. Practise rewriting 'killed' answers into this structure for temperature, pH and heavy-metal examples, and insist the word 'denatured' plus 'active site' appears in every answer.
When writing the word equation or balanced equation for aerobic respiration, the candidate writes 'glucose + oxygen -> carbon dioxide + water' but then, in the same answer, claims respiration makes 'energy for the body' as a substance, or writes 'energy' as a product in the equation alongside carbon dioxide and water.
Textbooks say respiration 'releases energy', and candidates collapse the idea of energy transfer into a material product. They also confuse respiration with breathing, so they describe lungs taking in oxygen as the site of the reaction.
What to do instead
Separate the two ideas explicitly in revision: the equation lists only chemical substances (glucose + oxygen -> carbon dioxide + water), and energy is released from the breakdown of glucose, not a substance produced. Have candidates label a diagram with 'site of gas exchange' versus 'site of respiration in mitochondria' and write one sentence distinguishing breathing from respiration.
When explaining how a villus is adapted for absorption, the candidate lists features ('it has villi', 'it is long') without saying what each feature does, or states that villi 'increase the surface area' without linking this to faster diffusion or active transport of digested food into the blood.
Adaptation questions are treated as recall of labels rather than explanation of function. Candidates also mix up the small intestine with the large intestine and forget that glucose and amino acids are absorbed into blood capillaries while fatty acids and glycerol enter lacteals.
What to do instead
Use a two-column table in revision: feature (folded lining, villi, microvilli, thin epithelium, dense capillary network, lacteal) beside its function (large surface area, short diffusion distance, steep concentration gradient maintained by blood flow, fat absorption). Require every exam answer to pair each feature with 'so that...' and to name the vessel or vessel type involved.
When asked about the effect of exercise on heart rate, the candidate answers 'the heart beats faster to pump more blood' and stops, without explaining the chain from increased muscle respiration, raised carbon dioxide, detection by the brain, and increased delivery of oxygen and glucose plus faster removal of carbon dioxide.
The answer feels complete because the observation is correct, but the question asks for explanation. Candidates have memorised the endpoint and not the causal sequence, so they cannot extend the chain under exam pressure.
What to do instead
Practise writing the full causal chain as numbered steps: muscles respire faster; more carbon dioxide produced; detected by receptors and coordinated by the brain; heart rate and stroke volume increase; more oxygen and glucose delivered and more carbon dioxide removed. Then practise condensing the same chain into two sentences for a 3-mark question.
When describing the nephron and urine formation, the candidate says 'the kidney filters the blood and all the useful substances are kept', without naming filtration at the glomerulus under pressure, selective reabsorption of glucose, some salts and water in the tubule, and the role of the loop of Henle or ADH in water balance.
Candidates merge filtration and reabsorption into one vague process because both happen in the kidney and both involve 'keeping the good stuff'. The word 'selective' is often omitted, so the answer implies everything small is reabsorbed.
What to do instead
Draw and label a single nephron repeatedly until the sequence is automatic: glomerulus and Bowman's capsule for ultrafiltration by pressure; tubule for selective reabsorption by diffusion and active transport; collecting duct for water reabsorption controlled by ADH. Then answer one question each on urine composition after sweating, after drinking excess water, and in diabetes, using the same vocabulary.
When explaining negative feedback for temperature or blood glucose, the candidate describes only the correction ('the body sweats to cool down') and omits the detector, the coordination centre and the reversal back to normal, or describes positive feedback by mistake.
The correction is the most memorable part of the loop, so the receptor and control centre are dropped. Candidates also conflate nervous and hormonal control and forget that insulin lowers glucose while glucagon raises it.
What to do instead
Use a standard five-box template for every feedback answer: stimulus, receptor, coordination centre, effector response, return to normal. Fill it for sweating, shivering, vasodilation, vasoconstriction, insulin and glucagon, then write the answer in prose from the boxes. Check every answer ends with the value returning towards the set point.
When describing the menstrual cycle and contraception, the candidate confuses which hormone is produced where and when, for example saying FSH is produced by the ovary or that progesterone triggers ovulation, or states that the pill 'kills sperm'.
Four hormones with overlapping effects are learned as a list rather than as a sequence with sources and targets. The pituitary-ovary loop is abstract, and candidates memorise names without assigning source, target and effect.
What to do instead
Build a timeline diagram from day 1 to day 28 with four rows (FSH, LH, oestrogen, progesterone) showing source and effect, then annotate the same diagram with the points where the pill, condom and IUD act. Rehearse three exam sentences: FSH from the pituitary matures the egg; an LH surge triggers ovulation; progesterone maintains the lining and inhibits FSH and LH.
When answering genetics questions, the candidate writes a Punnett square but does not state the parental genotypes, mixes up genotype and phenotype in the final answer, or gives a ratio without saying what each class is.
The mechanics of the square are taught as the goal, so the surrounding reasoning is skipped. Candidates also use 'gene' and 'allele' interchangeably and forget that a recessive phenotype requires two recessive alleles.
What to do instead
Enforce a four-step written routine: define symbols and parental genotypes; complete the square; list offspring genotypes with counts; convert to a ratio or probability and state the phenotype for each class. Practise with monohybrid crosses including test crosses and sex-linked examples, and mark every answer against the four steps before checking the biology.
When explaining immunity and vaccination, the candidate says 'antibodies kill the pathogen' or 'the vaccine gives you the disease to build strength', without describing antigens on the pathogen surface, lymphocytes producing specific antibodies, memory cells, and the faster secondary response.
Everyday phrases about 'fighting germs' and 'building strength' stand in for the mechanism. Candidates also do not distinguish active from passive immunity, so vaccination and antibody injection are described identically.
What to do instead
Teach a fixed chain: antigen on pathogen surface; specific lymphocyte recognises it; clones divide; antibodies produced and memory cells remain; on second exposure memory cells respond faster and in greater number. Contrast this with ready-made antibodies giving immediate but short-lived protection. Require the words antigen, specific, memory cell and secondary response in every vaccination answer.
When interpreting food chains, pyramids of number or energy flow, the candidate treats the arrow as 'eaten by' in the wrong direction, claims energy is 'used up' or 'destroyed' at each level, or draws a pyramid of numbers that does not match the stated food chain.
Arrows are read as everyday directional arrows rather than as flow of energy, and the law of conservation of energy is not applied, so losses are described as destruction. Candidates also assume pyramids of number are always upright.
What to do instead
Fix the convention with a mnemonic and repeated practice: the arrow points from the organism eaten to the eater and shows energy transfer. For each level, list where energy goes (respiration, heat, excretion, uneaten parts) and state that energy is transferred, not destroyed. Give contrasting examples such as one oak tree supporting many insects to show that number pyramids can be inverted while energy pyramids cannot.