These International A Level (IAL) Biology WBI11–WBI16 topics consistently produce the lowest scores. Prioritise these in your revision.
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Sex-linked inheritance — distinguishing 'allele' from 'gene' for haemophilia and colour blindness
Examiners report: 'Examiners expected there to be confusion between the terms allele and gene as this is a difficult concept for candidates studying biology at this level. Marks were also lost by candidates who did not make it clear which alleles had to be present for a male to have haemophilia or a female to have haemophilia. Some candidates thought that females could only be carriers and not have the disease.'
Affects: Unit 1
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Roles of organelles in protein synthesis — separating ribosomes, RER and Golgi
ER notes: 'It was disappointing that many candidates could not separate the role of the rough endoplasmic reticulum from the role of the Golgi apparatus. A significant number of responses referred to the role of the wrong organelle. Where candidates did refer to the role of the RER they frequently lost marks due to incorrect terminology or carelessness, for example referring to transcription instead of translation or the synthesis of lipids instead of proteins.'
Affects: Unit 2
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Surface area to volume ratio applied to gas exchange and diffusion
Reports note: 'On the whole, candidates could list two factors that affect the rate of diffusion. The commonest error was to write surface area to volume ratio, an expression that they have learnt without really appreciating its significance or its application.'
Affects: Unit 1
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The command word 'evaluate' on practical data
ER: 'This question proved very demanding for most candidates. This is almost certainly, at least in part, as a consequence of their lack of understanding of the command word evaluate. However, it is not just this. Candidates fell into three groups. Those who understood what they were required to do, although never managed to do it more than twice or occasionally three times. Those who seemed to begin to understand the requirements, but merely stated problems with the investigation without actually explaining why they were problems.'
Affects: Unit 3
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Microbiology — log calculations and counting methods (turbidimetry vs dilution plating)
ER: 'The mathematical ability of candidates overall has noticeably improved since 2020. The last time a question involving logs was asked, the number of candidates scoring full marks was limited.' Examiner tip: 'Don't take log of logs.' Candidates also confuse turbidimetry (counts living + dead, uses colorimeter) with dilution plating / haemocytometer with exclusion dye (counts living only).
Affects: Unit 4
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Natural selection — distinguishing selection pressure from cause of mutation
Examiner tip: 'Selection pressures do not cause mutations. Mutations occur and the selection pressure results in the survival of the organism with the advantageous mutation.' This same misconception recurs across antibiotic-resistance and pesticide-resistance questions.
Affects: Unit 4
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Synapse function and SSRI / neurotoxin mode of action
ER: 'Several candidates wrote about dopamine throughout their entire response; this gained no credit.' For tetrodotoxin: 'Key here is the command word explain. Candidates who merely describe the pattern from the graphs cannot gain full marks.' Candidates must explain the binding to voltage-gated sodium channels, not just describe the graph.
Affects: Unit 5
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Drawing lines of best fit and selecting graph axes correctly
ER: 'A good number of candidates struggled with drawing an appropriate line of best fit on this graph.' And: 'A line of best fit should follow the direction of the slope, should have as many points on one side as on the other, or as close as possible to that, and the points should be a balanced distance from the line.' Common errors include curved lines when straight is required, lines that don't balance points above/below, and unlabelled axes.
Affects: Unit 3
