Download clean, printable lists of the most common mistakes students make — so you can fix them before they cost marks.
Each sheet is aligned to its exam board and built from recurring student errors highlighted in examiner reports and mark schemes.
What you get
A topic-by-topic mistakes list with a “do this instead” fix and a quick self-check.
How to use it
Review before past papers, then use the quick checks to catch errors under timed conditions.
Why it works
Many marks are lost on predictable slips: rounding, sign errors, units, and misreading commands.
Coverage by topic
Preview (up to 5 per topic)
14 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| Cell Biology | Saying all organelles are membrane-bound. | Ribosomes and cytoskeleton are NOT membrane-bound. Membrane-bound organelles include: nucleus, ER, Golgi, mitochondria, chloroplasts, lysosomes. | Ribosomes: no membrane. Check which organelles the question specifies. |
| Cell Biology | Confusing mitosis stages — saying chromosomes move to the equator in anaphase. | METAPHASE: chromosomes align at equator (metaphase plate). ANAPHASE: centromeres split, sister chromatids move to poles. | Metaphase = middle. Anaphase = apart (centromeres split, move to poles). |
| Molecular Biology | Saying the codon on mRNA codes directly for protein without mentioning tRNA. | mRNA codon is READ by tRNA anticodon. tRNA carries the corresponding amino acid. Ribosome catalyses peptide bond formation. | mRNA codon → tRNA anticodon → amino acid. Three steps. |
| Molecular Biology | Confusing lagging and leading strand synthesis direction. | DNA polymerase only works 5'→3'. Leading strand: continuous synthesis. Lagging strand: synthesised as Okazaki fragments, joined by DNA ligase. | Lagging: fragments + ligase. Leading: continuous. Both: 5'→3' synthesis. |
| Genetics | Applying Hardy-Weinberg without checking the conditions are met. | H-W equilibrium requires: large population, random mating, no mutation, no migration, no natural selection. State these assumptions in exam answers. | State H-W conditions before applying p² + 2pq + q² = 1. |
| Genetics | Confusing incomplete dominance and codominance. | Incomplete dominance: blend/intermediate phenotype (e.g. pink from red × white). Codominance: BOTH alleles expressed (e.g. MN blood type — both M and N antigens present). | Blend? Incomplete dominance. Both expressed separately? Codominance. |
| Evolution | Saying natural selection acts on genotype. | Natural selection acts on PHENOTYPE (the expressed trait). Genotype is inherited, but only phenotype is 'seen' by the environment. | Selection: acts on phenotype. Inheritance: genotype is passed on. |
| Ecology | Confusing gross production and net production in ecosystems. | Gross production (GP) = total energy fixed by photosynthesis. Net production (NP) = GP − respiration. NP is the energy available to the next trophic level. | NP = GP − R. Consumers use NP, not GP. |
| Ecology | Saying all nitrogen fixation is done by soil bacteria. | Nitrogen fixation is done by: free-living bacteria (Azotobacter), mutualistic bacteria (Rhizobium in legume root nodules), and lightning. Not all are in soil. | List all N-fixers: free-living bacteria, Rhizobium (mutualistic), lightning. |
| Internal Assessment | Writing a research question without an independent and dependent variable. | Research question must specify: what you will CHANGE (IV) and what you will MEASURE (DV). 'How does [IV] affect [DV]?' | Does your RQ name the IV and DV? Both must be measurable. |
| Internal Assessment | Not controlling variables in the methodology. | For every controlled variable, state: WHAT it is, HOW it was controlled, and WHY it needs to be controlled. Three components for full marks. | Controlled variables: what + how + why for each one. |
| Extended Essay | Writing an EE with a question that is too broad. | EE questions must be focused and answerable within 4,000 words. 'What is evolution?' is too broad. 'How does antibiotic resistance evolve in E. coli?' is appropriate. | Can you fully address the question with original analysis in 4,000 words? |
| Paper Skills | Forgetting to use data from graphs in 'describe' questions. | Always quote specific values from the graph when describing trends. 'The rate increases from 20 to 45 units between pH 5 and 7' — not just 'the rate increases'. | Include specific figures, units, and axis values in every description. |
| Paper Skills | Answering 'suggest' questions with only theoretical knowledge. | 'Suggest' means apply knowledge to a novel context. Link the data/situation given to your biological understanding. Do not just regurgitate notes. | Suggest: link what you see in the data to your biological knowledge. Be specific to the context. |