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)
31 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| Cell Biology | Saying chloroplasts are found in all plant cells. | Chloroplasts are only in green (photosynthesising) cells — not in root cells or non-green tissues. | Is the cell you're describing green and exposed to light? |
| Cell Biology | Confusing cell membrane with cell wall. | Cell wall = rigid, made of cellulose, plant cells only. Cell membrane = thin, flexible, controls entry/exit, ALL cells. | Which one is selectively permeable? |
| Cell Biology | Saying the nucleus 'controls everything' without explaining how. | The nucleus contains DNA which codes for proteins — proteins carry out cell functions. | Have you linked nucleus → DNA → protein? |
| Cell Biology | Stating mitochondria 'make' energy. | Mitochondria release energy from glucose via aerobic respiration. Energy is not made, it is transferred to ATP. | Did you say 'release' not 'make'? |
| Cell Biology | Drawing an animal cell with a cell wall or vacuole. | Animal cells have: membrane, cytoplasm, nucleus, mitochondria, ribosomes. No cell wall, no chloroplasts, no large vacuole. | Check your diagram — any plant-only features? |
| Transport | Saying water moves from 'low concentration' to 'high concentration' in osmosis. | Water moves from HIGH water potential (dilute) to LOW water potential (concentrated). Use water potential terminology. | Did you use 'water potential' not 'water concentration'? |
| Transport | Confusing osmosis with diffusion. | Osmosis: WATER ONLY through a PARTIALLY PERMEABLE membrane. Diffusion: any molecule, any permeable surface. | Is it water moving through a membrane? → Osmosis. |
| Transport | Saying active transport does not require energy. | Active transport moves molecules AGAINST the concentration gradient and REQUIRES energy (ATP) from respiration. | Does it say 'against gradient'? → needs energy. |
| Transport | Forgetting to mention the concentration gradient direction in diffusion answers. | Always state: moves FROM high TO low concentration gradient. Include the word 'net' movement. | Did you state 'high to low concentration gradient'? |
| Enzymes | Saying enzymes are 'destroyed' by high temperature. | Enzymes are DENATURED — the active site changes shape permanently. They are not destroyed (they still exist as proteins). | Did you say 'denatured' not 'destroyed'? |
| Enzymes | Saying enzymes work on 'any' substrate. | Each enzyme has a specific active site complementary to ONE substrate — this is the basis of enzyme specificity. | Did you mention 'complementary shape' and 'specific'? |
| Enzymes | Confusing optimum temperature with the highest possible temperature. | Optimum = where rate is fastest. Above optimum, rate falls sharply as enzyme denatures. Below optimum, rate is slower (less KE). | Is your graph bell-shaped with a clear peak? |
| Enzymes | Stating pH denatures all enzymes at the same value. | Each enzyme has its own optimum pH — pepsin works best at pH 2; amylase at pH 7. Extremes of pH denature by changing ionic bonds. | Did you name the specific enzyme and its optimum pH? |
| Photosynthesis | Saying plants get food/energy from the soil. | Plants make their own glucose via photosynthesis using CO₂ + H₂O + light energy. Minerals are absorbed from soil but NOT food. | Soil provides minerals (nitrates, magnesium) — NOT glucose or energy. |
| Photosynthesis | Writing the photosynthesis equation the wrong way round. | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy). Reactants: CO₂ and water. Products: glucose and oxygen. | Are CO₂ and water on the LEFT side? |
| Photosynthesis | Saying increasing CO₂ always increases the rate of photosynthesis. | If light or temperature is limiting, increasing CO₂ has no effect. Rate is limited by whichever factor is in shortest supply. | Which factor is limiting? Only that factor's increase matters. |
| Photosynthesis | Confusing chlorophyll with chloroplast. | Chloroplast = organelle. Chlorophyll = green pigment INSIDE the chloroplast. Photosynthesis occurs in the chloroplast. | Chlorophyll is the pigment; chloroplast is the organelle. |
| Respiration | Confusing breathing with respiration. | Breathing = mechanical process of moving air. Respiration = chemical process releasing energy from glucose in cells. | Does the question ask about gas exchange or energy release? |
| Respiration | Writing the aerobic respiration equation without balancing it. | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy/ATP). All 6s must be present. | Count: 6 O₂ in, 6 CO₂ + 6 H₂O out. |
| Respiration | Saying anaerobic respiration produces no energy. | Anaerobic produces LESS ATP than aerobic — but it still releases some energy. In animals: glucose → lactic acid + ATP. | Anaerobic still makes ATP — just less of it. |
| Respiration | Confusing anaerobic products in animals vs yeast. | Animals: glucose → lactic acid + ATP. Yeast/plants: glucose → ethanol + CO₂ + ATP. | Which organism? Animal → lactic acid; yeast → ethanol + CO₂. |
| Genetics | Confusing genotype and phenotype. | Genotype = genetic makeup (e.g. Aa). Phenotype = physical appearance/characteristic (e.g. brown eyes). | Is it the alleles (genotype) or the trait shown (phenotype)? |
| Genetics | Saying dominant allele is always 'better' or more common. | Dominant just means expressed when present. It has nothing to do with frequency or benefit. | Dominant = expressed in heterozygote; nothing else. |
| Genetics | Forgetting to include gametes in genetic cross diagrams. | Always show: parents → gametes → Punnett square → offspring genotypes → offspring phenotypes with ratios. | Did you show the gamete stage above the Punnett square? |
| Genetics | Confusing mitosis and meiosis outcomes. | Mitosis: 2 identical cells, same chromosome number (for growth/repair). Meiosis: 4 different cells, half chromosome number (for gametes). | Gametes? → Meiosis. Growth? → Mitosis. |
| Ecology | Saying the food chain shows energy flow from right to left. | Energy flows LEFT to RIGHT in a food chain: producer → primary consumer → secondary consumer. Arrows show direction of energy transfer. | Arrows point in direction of energy flow. |
| Ecology | Forgetting that only ~10% of energy transfers between trophic levels. | Most energy is lost as heat (respiration), faeces, and uneaten material at each level. Only ~10% passes to the next. | Why are food chains short? → Energy loss at each level. |
| Ecology | Confusing producer with consumer. | Producer = makes own food via photosynthesis (green plant). Consumer = eats other organisms. Primary consumer eats producer. | Does it photosynthesise? → Producer. |
| Ecology | Saying decomposers are consumers. | Decomposers (bacteria, fungi) break down dead organic matter — they are not consumers. They return minerals to the soil. | Does it eat living organisms? → Consumer. Dead matter? → Decomposer. |
| Evolution | Saying organisms 'try' to adapt or 'choose' to evolve. | Natural selection is not directed. Random variation exists → those better adapted survive and reproduce → advantageous alleles increase in frequency. | Never write 'organisms try/decide/need' — selection is random variation + differential survival. |
| Evolution | Confusing adaptation (feature) with natural selection (process). | Adaptation = a feature that improves survival. Natural selection = the process by which adapted organisms survive and pass on alleles. | Is the question asking for a feature or the process? |
A downloadable list of frequent mark-losing Biology errors, paired with a fix and a “quick check” so you can spot the mistake under exam pressure.
It covers common mistakes across the main Cambridge IGCSE Biology topics (cells, movement in/out, enzymes, nutrition, transport, respiration, genetics, ecology).