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)
19 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| Cell Structure | Describing the cell surface membrane as a solid layer. | The membrane is FLUID — phospholipids and proteins move laterally. This is the basis of the fluid-mosaic model (Singer & Nicolson). | Fluid-mosaic: fluid phospholipid bilayer + mosaic of proteins. |
| Cell Structure | Confusing rough and smooth ER function. | Rough ER: ribosomes on surface, synthesises and transports proteins. Smooth ER: no ribosomes, synthesises lipids and steroids. | Ribosomes present? Rough ER → proteins. No ribosomes? Smooth ER → lipids. |
| Biological Molecules | Saying DNA is double-stranded so it has two backbones and two sets of bases. | Two antiparallel strands, each with a sugar-phosphate backbone. Bases project inward and pair by hydrogen bonds: A-T (2H-bonds), G-C (3H-bonds). | A pairs with T (2 H-bonds). G pairs with C (3 H-bonds). Antiparallel. |
| Biological Molecules | Confusing the roles of ATP hydrolysis and ATP synthesis. | ATP → ADP + Pi releases energy (hydrolysis). ADP + Pi → ATP stores energy (phosphorylation). Condensation reaction builds ATP. | Energy release: ATP hydrolysis. Energy storage: ATP synthesis/phosphorylation. |
| Enzymes | Saying competitive inhibitors permanently block the active site. | Competitive inhibitors are REVERSIBLE — they compete with substrate for the active site. Adding more substrate can overcome inhibition. Vmax unchanged. | Competitive: reversible, same shape as substrate, increasing [S] overcomes. Vmax same, Km increases. |
| Enzymes | Saying non-competitive inhibitors attach to the active site. | Non-competitive inhibitors bind to an ALLOSTERIC site (not the active site), causing a conformational change that reduces enzyme activity. | Non-competitive: allosteric site, Vmax decreases, Km unchanged. |
| Transport | Saying co-transport requires direct use of ATP. | Co-transport is INDIRECTLY dependent on ATP. A Na⁺/K⁺ pump (using ATP) creates a Na⁺ gradient; glucose rides this gradient into the cell. | Co-transport: uses Na⁺ gradient (maintained by active transport) — not ATP directly. |
| Genetics | Confusing transcription and translation locations. | Transcription: nucleus — DNA → mRNA. Translation: ribosomes (cytoplasm/RER) — mRNA → polypeptide. Different locations. | Transcription = nucleus. Translation = ribosome. |
| Genetics | Saying the genetic code is ambiguous. | The genetic code is NON-AMBIGUOUS — each codon codes for ONE amino acid only. It IS degenerate (multiple codons can code for same amino acid). | Non-ambiguous: one codon = one amino acid. Degenerate: one amino acid may have multiple codons. |
| Genetics | Drawing a Hardy-Weinberg Punnett square with wrong allele frequency inputs. | p + q = 1. p² + 2pq + q² = 1. p = frequency of dominant allele, q = recessive. Usually find q from q² (homozygous recessive frequency). | Start with q² (easiest to identify from phenotype), then find q, then p. |
| Respiration | Placing the Krebs cycle in the mitochondrial matrix but the electron transport chain on the outer membrane. | Krebs cycle: matrix. Electron transport chain (ETC): inner mitochondrial membrane. Protons accumulate in intermembrane space. | Matrix: Krebs. Inner membrane: ETC. Intermembrane space: proton gradient. |
| Respiration | Stating glycolysis requires oxygen. | Glycolysis is ANAEROBIC — it occurs in the cytoplasm and produces 2 ATP and 2 pyruvate without requiring oxygen. | Glycolysis: cytoplasm, no oxygen needed, always occurs (aerobic or anaerobic). |
| Photosynthesis | Saying the light-independent reaction occurs in the dark. | The light-independent (Calvin) cycle requires products of the light-dependent stage (ATP + NADPH). It CAN occur in light — it just doesn't directly need light. | 'Light-independent' means light not directly required — not that it occurs in darkness. |
| Photosynthesis | Confusing cyclic and non-cyclic photophosphorylation. | Non-cyclic: involves PSI and PSII, produces ATP + NADPH + O₂. Cyclic: PSI only, produces only ATP, no NADPH or O₂. Cyclic supplements ATP. | Non-cyclic: O₂ produced, NADPH made. Cyclic: no O₂, no NADPH, just ATP. |
| Homeostasis | Saying the hypothalamus produces ADH. | ADH is PRODUCED by the hypothalamus but RELEASED by the posterior pituitary gland. The distinction matters in exam answers. | Produced: hypothalamus. Released: posterior pituitary. Two different locations. |
| Homeostasis | Confusing vasodilation and vasoconstriction effects on temperature. | Vasodilation: blood vessels near skin widen → more heat lost → body cools. Vasoconstriction: vessels narrow → less heat lost → body warms. | Vasodilate = cool down (more blood to skin). Vasoconstrict = warm up (less blood to skin). |
| Immunity | Confusing B lymphocytes and T lymphocytes roles. | B cells: produce antibodies (humoral immunity). T cells: cell-mediated immunity — helper T cells activate B cells; cytotoxic T cells kill infected cells. | B cells = antibodies. T cells = cell-mediated (kill/activate). |
| Immunity | Saying antibodies destroy antigens. | Antibodies BIND to antigens, forming antigen-antibody complexes. This labels the pathogen for destruction by phagocytes — antibodies do not destroy directly. | Antibodies: bind → label for phagocytosis/agglutination. They don't kill directly. |
| Ecology | Confusing net primary productivity (NPP) and gross primary productivity (GPP). | GPP = total photosynthesis rate. NPP = GPP − plant respiration. NPP is the energy available to consumers. | NPP = GPP − R. Consumers can only access NPP, not GPP. |