AQA · International A Level · HL/SL
Biology — Keywords & Key Terms — Definitions Glossary (2026)
IB Diploma Programme Biology (HL/SL)
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.
IB Diploma Programme Biology (HL/SL)
IB Diploma Programme Biology (HL/SL)
IB Diploma Programme Biology (HL/SL)
Topics follow the IB DP Biology syllabus (first assessment 2025). HL students cover all topics plus AHL content; SL students cover core topics only. Check your specification for HL-only material.
Mark schemes: IB mark schemes award marks for precise biological vocabulary, correct use of units, and linked chains of reasoning. Internal Assessments (IA) are marked on Personal Engagement, Exploration, Analysis, Evaluation and Communication.
Active recall: 0 / 63 terms ticked
| Recalled | Topic | Level | Keyword | Definition |
|---|---|---|---|---|
| Cell Biology | Essential | Cell | The basic structural and functional unit of all living organisms. | |
| Cell Biology | Essential | Prokaryote | Cell without a membrane-bound nucleus; includes bacteria and archaea. | |
| Cell Biology | Essential | Eukaryote | Cell with a membrane-bound nucleus; includes animals, plants, fungi and protists. | |
| Cell Biology | Core | Cell membrane | Partially permeable phospholipid bilayer controlling movement of substances into and out of the cell. | |
| Cell Biology | Core | Nucleus | Membrane-bound organelle containing DNA; controls cell activities and protein synthesis. | |
| Cell Biology | Core | Mitochondria | Double-membrane organelle; site of aerobic cell respiration and ATP production. | |
| Cell Biology | Core | Chloroplast | Double-membrane organelle in plant cells containing chlorophyll; site of photosynthesis. | |
| Cell Biology | Core | Ribosome | Site of protein synthesis; reads mRNA to assemble amino acids. | |
| Cell Biology | Core | Endoplasmic reticulum (ER) | Network of membranes: rough ER (with ribosomes, protein synthesis), smooth ER (lipid/steroid synthesis). | |
| Cell Biology | Core | Golgi apparatus | Modifies, sorts and packages proteins for secretion or intracellular use. | |
| Cell Biology | Core | Lysosome | Contains digestive enzymes; breaks down waste materials and cellular debris. | |
| Cell Biology | Core | Vacuole | Large, fluid-filled organelle in plant cells maintaining turgor pressure. | |
| Cell Biology | Core | Cell wall | Rigid structure surrounding plant, fungal and bacterial cells; provides support and shape. | |
| Cell Biology | Advanced | Stem cell | Undifferentiated cell capable of dividing and differentiating into specialised cell types. | |
| Cell Biology | Advanced | Totipotent | Stem cell capable of differentiating into any cell type, including extra-embryonic tissues. | |
| Cell Biology | Advanced | Pluripotent | Stem cell capable of differentiating into most cell types but not extra-embryonic tissues. | |
| Molecular Biology | Essential | Monomer | Small repeating molecule that joins with others to form a polymer. | |
| Molecular Biology | Essential | Polymer | Large molecule formed by joining many monomers together. | |
| Molecular Biology | Core | Monosaccharide | Single sugar unit; e.g. glucose, fructose, galactose. | |
| Molecular Biology | Core | Disaccharide | Two monosaccharides joined by a glycosidic bond; e.g. maltose, sucrose, lactose. | |
| Molecular Biology | Core | Polysaccharide | Many monosaccharides joined by glycosidic bonds; e.g. starch, glycogen, cellulose. | |
| Molecular Biology | Core | Amino acid | Monomer of proteins; contains amino group (–NH₂), carboxyl group (–COOH) and R group. | |
| Molecular Biology | Core | Peptide bond | Covalent bond formed between amino acids during condensation reactions. | |
| Molecular Biology | Core | Primary structure | Sequence of amino acids in a polypeptide chain. | |
| Molecular Biology | Core | Secondary structure | Local folding of polypeptide into α-helix or β-pleated sheet held by hydrogen bonds. | |
| Molecular Biology | Core | Tertiary structure | 3D folding of polypeptide held by ionic, hydrogen, disulfide bonds and hydrophobic interactions. | |
| Molecular Biology | Core | Quaternary structure | Two or more polypeptide chains associated together. | |
| Molecular Biology | Essential | DNA | Deoxyribonucleic acid; double-stranded helix carrying genetic information. | |
| Molecular Biology | Core | Nucleotide | Monomer of DNA/RNA; consists of phosphate, pentose sugar and nitrogenous base. | |
| Molecular Biology | Core | Complementary base pairing | A–T (DNA) / A–U (RNA) and C–G; held by hydrogen bonds. | |
| Molecular Biology | Core | Semi-conservative replication | Each new DNA molecule contains one original and one new strand. | |
| Molecular Biology | Advanced | PCR (Polymerase Chain Reaction) | Technique to amplify specific DNA sequences using cycles of heating and cooling. | |
| Molecular Biology | Advanced | Gel electrophoresis | Separates DNA fragments by size using electric current through agarose gel. | |
| Genetics | Essential | Gene | Heritable unit of information encoded in DNA; segment of DNA at a specific locus. | |
| Genetics | Essential | Allele | One of two or more alternative forms of a gene at the same locus. | |
| Genetics | Essential | Locus | Specific position of a gene on a chromosome. | |
| Genetics | Core | Dominant allele | Allele expressed in the phenotype when present in heterozygous or homozygous form. | |
| Genetics | Core | Recessive allele | Allele expressed in the phenotype only when homozygous. | |
| Genetics | Core | Codominance | Both alleles of a gene are expressed equally in the heterozygote. | |
| Genetics | Core | Genotype | Genetic constitution of an organism. | |
| Genetics | Core | Phenotype | Observable characteristics of an organism resulting from genotype and environment. | |
| Genetics | Core | Homozygous | Having two identical alleles at a locus. | |
| Genetics | Core | Heterozygous | Having two different alleles at a locus. | |
| Genetics | Core | Meiosis | Cell division producing four genetically unique haploid cells (gametes). | |
| Genetics | Core | Crossing over | Exchange of genetic material between homologous chromosomes during meiosis I. | |
| Genetics | Core | Independent assortment | Random distribution of homologous chromosome pairs during meiosis I. | |
| Genetics | Advanced | Polygenic inheritance | Trait controlled by two or more genes at different loci; produces continuous variation. | |
| Genetics | Advanced | Epistasis | Interaction where one gene affects the expression of another gene. | |
| Ecology | Essential | Population | Group of individuals of the same species occupying the same area at the same time. | |
| Ecology | Essential | Community | All populations of different species living in a defined area. | |
| Ecology | Essential | Ecosystem | Community of organisms plus their abiotic (non-living) environment. | |
| Ecology | Essential | Habitat | Physical environment in which an organism lives. | |
| Ecology | Core | Niche | Functional role of a species in its ecosystem, including its interactions and resource use. | |
| Ecology | Core | Producer | Autotrophic organism that synthesises organic molecules using energy from sunlight or chemicals. | |
| Ecology | Core | Consumer | Heterotrophic organism that obtains energy by ingesting other organisms. | |
| Ecology | Core | Decomposer | Organism that breaks down dead organic matter, recycling nutrients. | |
| Ecology | Core | Food chain | Linear sequence showing feeding relationships and energy flow between organisms. | |
| Ecology | Core | Food web | Network of interconnected food chains. | |
| Ecology | Core | Trophic level | Position of an organism in a food chain. | |
| Ecology | Core | Biomass | Total mass of organic matter in organisms at a trophic level; usually expressed as dry mass per unit area. | |
| Ecology | Core | Primary productivity | Rate of production of organic matter by producers per unit area per unit time. | |
| Ecology | Advanced | Carrying capacity (K) | Maximum population size an environment can support indefinitely. | |
| Ecology | Advanced | Keystone species | Species with a disproportionately large effect on ecosystem structure relative to its abundance. |
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Biology (HL/SL) — Keywords & Key Terms FAQ
- What is on this AQA International 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 IB Diploma Programme Biology (HL/SL) (HL/SL). 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 International A Level Biology (HL/SL) 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 HL/SL specification?
- Topic groupings and wording follow IB Diploma Programme Biology (HL/SL) for AQA International 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 International A Level, separate from longer notes or topic trackers.