BW Abitur Biology Bilingual EN common mistakes
BW Abitur Biology Bilingual EN · Understand the traps and how to avoid them.
When explaining membrane transport, the candidate labels any protein-mediated movement as 'active transport' and does not check whether ATP is hydrolysed or whether the solute moves down or against its electrochemical gradient.
Textbook diagrams show carrier proteins in both passive facilitated diffusion and active transport, so the visual cue 'protein channel' gets mapped onto 'active transport' without checking the energy criterion. Under time pressure the candidate matches the picture rather than applying the definition.
What to do instead
Before naming a transport type, write three checks in the margin: direction relative to the gradient, energy source (ATP, ion gradient, none), and whether the protein is a channel or a carrier. Only call it active transport if the answer to 'energy input required?' is yes; otherwise use facilitated diffusion. Practise with the Na+/K+ pump, GLUT transporters and aquaporins side by side.
In enzyme kinetics questions, the candidate reads a substrate-concentration curve and states that the reaction rate keeps rising linearly at high substrate concentration, or claims Vmax increases when enzyme concentration is unchanged.
The candidate confuses the initial steep section of a Michaelis-Menten curve with the whole curve, and treats Vmax as a property of the substrate rather than of the amount of enzyme present.
What to do instead
Always identify the plateau first: at saturation all active sites are occupied, so rate is limited by turnover number, not substrate. State explicitly that Vmax is proportional to enzyme concentration and that Km is a constant for the enzyme-substrate pair. Sketch the curve, mark Vmax and Km (Km = substrate at half Vmax), then answer.
When describing the light-dependent reactions, the candidate says 'ATP and NADPH are produced by photosystem II' and omits that water is the electron donor, that oxygen is released at photosystem II, and that a proton gradient across the thylakoid membrane drives ATP synthase.
The two photosystems are taught as a single 'light reaction' block, so candidates collapse the Z-scheme into one step and lose the spatial detail of the thylakoid membrane.
What to do instead
Rehearse the linear electron transport chain as a sequence with locations: water splitting at PSII (lumen side), electron flow via plastoquinone and cytochrome complex, proton pumping into the lumen, PSI re-excitation, NADP+ reduction in the stroma, ATP synthesis via the proton gradient. Draw the membrane with lumen and stroma labelled and place each step.
In genetics problems, the candidate writes a Punnett square for a dihybrid cross but ignores linkage, or assumes independent assortment for genes on the same chromosome without checking the recombination data given.
Mendel's third law is over-learned as a default, and candidates do not test whether observed offspring ratios deviate significantly from 9:3:3:1.
What to do instead
Before solving, check the given ratios: a significant excess of parental combinations and deficit of recombinants indicates linkage. Then use recombination frequency as a map distance (1% recombination = 1 map unit). For testcross data, count recombinants and divide by total offspring.
When explaining an action potential, the candidate says 'sodium channels open and the membrane depolarises' but does not distinguish voltage-gated channel states (closed, open, inactivated), and explains the refractory period as 'the pump working harder' rather than as channel inactivation and K+ efflux.
Summary diagrams show only open and closed states, so inactivation and the resulting unidirectional propagation are not part of the candidate's mental model.
What to do instead
Learn the four phases as channel states: resting (K+ leak, Na+ channels closed), depolarisation (Na+ channels open), repolarisation (Na+ inactivated, K+ channels open), hyperpolarisation (K+ channels slow to close). Explain the absolute refractory period by Na+ channel inactivation, not by pump activity; the pump restores gradients over a longer timescale.
When describing synaptic transmission, the candidate treats excitatory and inhibitory synapses as differing only in neurotransmitter identity, and does not explain how the same neurotransmitter can excite or inhibit depending on receptor type and ion conductance.
Neurotransmitters are memorised as 'excitatory' or 'inhibitory' labels, so receptor identity and the resulting ion flow (Na+ vs Cl-) are skipped.
What to do instead
Anchor each synapse to the receptor and the ion: ligand-gated Na+ channels depolarise (EPSP), ligand-gated Cl- channels hyperpolarise (IPSP). Use acetylcholine at the neuromuscular junction (nicotinic, Na+) and GABA-A (Cl-) as contrasting examples. Explain summation of EPSPs and IPSPs at the axon hillock as the decision point.
In evolution questions, the candidate explains natural selection as 'organisms adapt because they need to' or describes a population changing because individuals change during their lifetime, rather than describing differential reproductive success of existing heritable variation.
Everyday language uses 'adapt' for individual adjustment, and this teleological phrasing carries into exam answers, which then fail the criterion of variation, heritability and differential fitness.
What to do instead
Use a fixed three-part sentence structure: (1) variation exists in the population, (2) the variation is heritable, (3) differential survival/reproduction changes allele frequencies across generations. Explicitly state that individual organisms do not evolve; populations do. Flag and rewrite any sentence containing 'in order to' or 'needs to'.
When interpreting ecological data on population growth or predator-prey dynamics, the candidate reads a logistic curve as exponential and ignores density-dependent factors, or claims carrying capacity K is fixed regardless of environmental change.
The exponential equation is more familiar and easier to calculate, so candidates apply it to any growth curve without checking whether the growth rate declines as population size rises.
What to do instead
Check the shape first: constant per-capita growth = exponential; declining per-capita growth with a plateau = logistic. Identify density-dependent factors (food, disease, predation) explicitly, and state that K is set by environmental conditions and can shift with season, habitat or human impact.
In immunology answers, the candidate describes 'antibodies killing pathogens' and conflates the primary and secondary immune response, missing that the secondary response is faster, larger and dominated by memory B and T cells.
Antibodies are described in media as the immune system's weapon, so their actual effector functions (neutralisation, opsonisation, complement activation) are replaced by a vague 'killing'.
What to do instead
State antibody function precisely: binding and neutralisation, opsonisation for phagocytosis, complement activation, agglutination. Contrast primary and secondary response with a graph: lag phase, IgM then IgG, and the memory-cell-driven rapid high-titre secondary peak. Link this to vaccination and booster doses.
In scientific-practice items, the candidate describes a method or conclusion without identifying the controlled variable, the sample size, or a plausible confound, and writes 'the results prove' instead of 'the results support'.
Candidates treat experimental description as a recall task rather than an evaluation task, and school practicals often lack explicit discussion of controls and error.
What to do instead
Use a fixed evaluation checklist for every experiment: independent variable, dependent variable, at least two controlled variables, sample size and repeats, control group, and one alternative explanation. Then phrase conclusions as 'support/are consistent with', and state the limitation that prevents a causal claim.