OCR · A Level · H420
Biology — Keywords & Key Terms — Definitions Glossary (2026)
OCR A Level Biology A (H420)
Topic-by-topic keywords, key terms and definitions for precise exam language—separate from our revision checklists (topic coverage) and formula sheets (equations).
Keywords & Key Terms — definitions
Examiner-style keywords and definitions organised by syllabus topic. Terms are tagged Essential (start here), Core (typical exam standard), and Advanced for harder distinctions — tick each row when you can recall it. Your progress is saved in this browser for this list.
OCR A Level Biology (H420)
OCR A Level Biology (H420)
OCR A Level Biology A (H420)
OCR Biology A (H420) modules: development of practical skills, foundations in biology, exchange and transport, biodiversity/evolution and disease, communication/homeostasis and energy, genetics/evolution and ecosystems — examined across Papers 1–3.
Mark schemes: OCR rewards precise biological terminology — gene, allele, locus, homozygous, heterozygous — and clear logical sequencing in extended responses. Statistical conclusions must compare calculated and critical values with explicit reference to the null hypothesis. Quote figures with units when describing data trends.
Active recall: 0 / 21 terms ticked
| Recalled | Topic | Level | Keyword | Definition |
|---|---|---|---|---|
| Cells, exchange & transport | Essential | Surface area to volume ratio | Falls as organisms get larger, driving the need for specialised exchange surfaces. | |
| Cells, exchange & transport | Core | Fick's law | Rate of diffusion ∝ (surface area × concentration difference) ÷ diffusion distance. | |
| Cells, exchange & transport | Core | Oxygen dissociation curve | Sigmoidal curve showing % saturation of haemoglobin against partial pressure of O₂. | |
| Cells, exchange & transport | Core | Bohr shift | Curve shifts right at higher CO₂ / lower pH, releasing more O₂ to respiring tissues. | |
| Cells, exchange & transport | Advanced | Cooperative binding | Binding of one O₂ to haemoglobin increases affinity for further O₂ molecules. | |
| Communication, homeostasis & energy | Core | Negative feedback | Mechanism that reverses a deviation from a set point to restore equilibrium. | |
| Communication, homeostasis & energy | Core | ATP synthesis | Coupling of electron transport to chemiosmotic phosphorylation of ADP + Pi. | |
| Communication, homeostasis & energy | Core | Photosynthesis — Calvin cycle | Light-independent fixation of CO₂ via RuBisCO into GP, TP and regeneration of RuBP. | |
| Communication, homeostasis & energy | Core | Glycolysis–link–Krebs–ETC | Sequence of respiration stages oxidising glucose to CO₂ and water with ATP yield. | |
| Communication, homeostasis & energy | Advanced | Respiratory quotient | RQ = CO₂ produced ÷ O₂ consumed; indicates the substrate being respired. | |
| Energy flow & ecosystems | Core | Gross primary productivity | Rate at which producers convert light energy to chemical energy in biomass. | |
| Energy flow & ecosystems | Core | Net primary productivity | NPP = GPP − plant respiratory losses; energy available to next trophic level. | |
| Energy flow & ecosystems | Core | Food chain efficiency | Roughly 10% of energy is transferred between successive trophic levels. | |
| Energy flow & ecosystems | Advanced | Simpson's index of diversity | D = 1 − Σ(n/N)²; higher D indicates greater biodiversity in a community. | |
| Energy flow & ecosystems | Core | Nutrient cycling | Movement of carbon and nitrogen through reservoirs via fixation, decomposition and respiration. | |
| Genetics, evolution & statistics | Core | Semi-conservative replication | Each daughter DNA duplex contains one parental and one newly synthesised strand. | |
| Genetics, evolution & statistics | Core | Monohybrid inheritance | Single-gene cross giving a 3:1 phenotypic ratio in F2 from heterozygous parents. | |
| Genetics, evolution & statistics | Core | Dihybrid inheritance | Two-gene cross giving a 9:3:3:1 phenotypic ratio with independent assortment. | |
| Genetics, evolution & statistics | Advanced | Hardy–Weinberg principle | p² + 2pq + q² = 1 predicts allele frequencies in a non-evolving population. | |
| Genetics, evolution & statistics | Core | χ² goodness-of-fit | Tests whether observed counts deviate significantly from those expected by a genetic model. | |
| Genetics, evolution & statistics | Advanced | Spearman's rank rs | Non-parametric correlation coefficient between two ranked variables; range −1 to +1. |
Pair this with our revision checklists, formula sheets hub and past paper finder.
Biology (H420) — Keywords & Key Terms FAQ
- What is on this OCR A Level Biology keywords and key terms list?
- It is a topic-organised glossary of important biology terms with short, exam-style definitions aligned to OCR A Level Biology A (H420) (H420). It is designed for “define”, “state”, “outline” and “explain” questions where precise vocabulary earns marks.
- How should I use this Biology glossary alongside past papers?
- Tick terms when you can recall them without reading the answer, then check your wording against mark schemes. Pair vocabulary practice with past papers for A Level Biology (H420) so you apply terms in context.
- Is this the same as a revision checklist or a formula sheet?
- No. Revision checklists help you track which syllabus topics you have covered and your confidence—separate pages on Tutopiya. Formula sheets summarise equations and quantitative relationships. This page is only a definitions and key-terms glossary for Biology.
- Can I download this Biology keywords and key terms list for free?
- Yes. After a quick free sign-up you can download a UTF-8 CSV (opens in Excel or Google Sheets) or open a print-friendly page and save as PDF. Browsing the list on the page is free.
- Is this Biology list aligned to the H420 specification?
- Topic groupings and wording follow OCR A Level Biology A (H420) for OCR A Level. Always confirm final learning objectives and any regional options in your official specification and recent examiner reports for your exam session.
- Why focus on definitions instead of full notes?
- Mark schemes reward correct technical terms and clear links between ideas. A compact glossary lets you drill the exact language examiners expect for Biology at A Level, separate from longer notes or topic trackers.