IB Diploma Programme Biology Higher Level
IB Diploma Programme Biology Higher Level (HL) is a rigorous 240-hour course structured around four unifying themes — Unity and Diversity, Form and Function, Interaction and Interdependence, and Continuity and Change — each explored at the molecular, cellular, organism, and ecosystem levels of organisation. HL students master 150 hours of shared SL content plus 90 hours of Additional Higher Level (AHL) material covering gene expression, chemical signalling, muscle physiology, origins of cells, classification and cladistics, and viruses, assessed through two written papers and an internal investigation (IA). The course is assessed on a 1–7 IB grade scale and is designed to prepare students for university studies in biological and health sciences.
255
Minutes
124
Questions
4/7
Passing Score
$124
Exam Cost
Who Should Take This
Pre-university students (ages 16–19) enrolled in the IB Diploma Programme who intend to pursue higher education in biology, medicine, biomedical science, veterinary science, or related disciplines, and require a challenging, concept-driven science credential recognised by universities worldwide.
Course Outline
1Theme A: Unity and Diversity 4 topics
A1 — Molecules
- A1.1 Water
- Recall the unique physical and chemical properties of water — cohesion, adhesion, specific heat capacity, latent heat of vaporisation, and universal solvent behaviour — that emerge from its polar covalent bonds and hydrogen bonding.
- Explain how water's polarity and hydrogen-bonding capacity make it an effective solvent for ionic and polar biomolecules, enabling metabolite transport and biochemical reactions in aqueous cytoplasm.
- A1.2 Nucleic Acids
- Recall the structure of nucleotides — pentose sugar, nitrogenous base, and phosphate group — and distinguish between deoxyribose and ribose, and between purine and pyrimidine bases in DNA versus RNA.
- Explain the antiparallel double-helix structure of DNA, including complementary base pairing via hydrogen bonds, the phosphodiester backbone, and how this structure supports both information storage and accurate replication.
A2 — Cells
- A2.2 Cell Structure
- Distinguish between prokaryotic and eukaryotic cell organisation, comparing size, compartmentalisation, membrane-bound organelles, and genetic material arrangement with reference to specific named cell types.
- A2.1 Origins of Cells (AHL)
- Evaluate the endosymbiotic theory for the origin of mitochondria and chloroplasts, citing structural and genomic evidence including circular DNA, 70S ribosomes, double membranes, and binary fission as shared features with ancestral prokaryotes.
- A2.3 Viruses (AHL)
- Recall the structural components of viruses — protein capsid, nucleic acid genome (DNA or RNA), and optional lipid envelope — and explain why viruses are classified as non-living obligate intracellular parasites lacking metabolic machinery.
- Compare lytic and lysogenic replication cycles of bacteriophages, explaining how integration of viral DNA into the host chromosome as a prophage allows latency and subsequent reactivation under environmental stress.
A3 — Organisms
- A3.1 Diversity of Organisms
- Recall the three-domain classification system (Bacteria, Archaea, Eukarya) and the kingdoms within Eukarya, identifying distinguishing structural and metabolic features at each hierarchical taxonomic level.
- A3.2 Classification and Cladistics (AHL)
- Construct and interpret cladograms using shared derived characters (synapomorphies), distinguishing monophyletic, paraphyletic, and polyphyletic groupings, and evaluate the relative merit of morphological versus molecular phylogenetic evidence.
A4 — Ecosystems
- A4.1 Evolution and Speciation
- Explain how reproductive isolation mechanisms — prezygotic (geographic, temporal, behavioural, mechanical, gametic) and postzygotic (hybrid inviability, hybrid sterility) — drive allopatric and sympatric speciation over evolutionary timescales.
- A4.2 Conservation of Biodiversity
- Analyse causes of species extinction — habitat loss, overexploitation, invasive species, pollution, and climate change — and evaluate in-situ versus ex-situ conservation strategies using quantitative population viability data.
2Theme B: Form and Function 4 topics
B1 — Molecules
- B1.1 Carbohydrates and Lipids
- Recall the structural differences between monosaccharides, disaccharides, and polysaccharides, and between saturated and unsaturated fatty acids, explaining how condensation polymerisation links monomers into functional storage and structural macromolecules.
- B1.2 Proteins
- Explain how primary amino acid sequence determines secondary structure — alpha-helices and beta-pleated sheets via hydrogen bonding — and how tertiary folding via R-group interactions (hydrophobic, ionic, disulfide, hydrogen bonds) creates the 3D conformation required for protein function.
- Apply knowledge of protein denaturation — disruption of non-covalent interactions by heat, extreme pH, or chemical denaturants — to predict loss of enzymatic activity and explain why denaturation is often irreversible when disulfide bonds are broken.
B2 — Cells
- B2.1 Membranes and Membrane Transport
- Explain the fluid-mosaic model of membrane structure — phospholipid bilayer with embedded and peripheral proteins, glycoproteins, glycolipids, and cholesterol — and how membrane fluidity varies with temperature and degree of fatty acid unsaturation.
- Apply membrane transport mechanisms — simple diffusion, facilitated diffusion via channel and carrier proteins, osmosis, active transport by Na/K-ATPase, endocytosis, and exocytosis — to predict net movement of specific molecules across a given electrochemical gradient.
- B2.2 Organelles and Compartmentalisation
- Explain how compartmentalisation into membrane-bound organelles — nucleus, ER, Golgi apparatus, mitochondria, chloroplasts, lysosomes — increases metabolic efficiency by concentrating enzymes, substrates, and optimal ionic/pH micro-environments.
- B2.3 Cell Specialisation
- Explain how differential gene expression produces specialised cell types with distinct ultrastructures — neurones, erythrocytes, guard cells, sperm — despite identical genomes, linking each structural modification to a specific functional advantage.
B3 — Organisms
- B3.1 Gas Exchange
- Explain structural adaptations of alveoli, fish gills, and insect tracheal systems — large surface area, thin diffusion distance, moist surface, ventilation maintaining steep concentration gradients — for efficient gas exchange at the organism level.
- B3.2 Transport
- Apply haemoglobin's cooperative oxygen-binding kinetics — sigmoidal dissociation curve, Bohr effect, influence of pCO2 and pH on oxygen affinity — to predict oxygen loading at the lungs and unloading at actively respiring peripheral tissues.
- Explain water transport in plants via apoplast, symplast, and transmembrane pathways, cohesion-tension theory for xylem ascent driven by transpiration, and source-to-sink phloem mass flow driven by osmotically generated pressure differentials.
- B3.3 Muscle and Motility (AHL)
- Explain the sliding filament mechanism of skeletal muscle contraction — myosin cross-bridge attachment to actin, ATP-driven power stroke, troponin-tropomyosin Ca2+ gated regulation, and sarcomere shortening without change in myofilament length.
B4 — Ecosystems
- B4.1 Adaptation to Environment
- Analyse specific morphological, physiological, and behavioural adaptations of organisms to abiotic factors — temperature, light intensity, water availability, salinity — explaining the selective advantage conferred in a named biome.
- B4.2 Ecological Niches
- Apply the concepts of fundamental versus realised niche, competitive exclusion, and resource partitioning to predict outcomes of interspecific competition and explain coexistence of ecologically similar species using experimental field data.
3Theme C: Interaction and Interdependence 4 topics
C1 — Molecules
- C1.1 Enzymes and Metabolism
- Explain enzyme catalysis via the induced-fit model — active site conformational change upon substrate binding lowers activation energy — and distinguish competitive, non-competitive, and uncompetitive inhibition by their contrasting effects on Km and Vmax.
- Analyse the effects of temperature, pH, and substrate concentration on reaction rate, interpreting Michaelis-Menten curves to extract Km and Vmax values and predict enzyme behaviour under physiological versus experimental extreme conditions.
- C1.2 Cell Respiration
- Explain aerobic cellular respiration as four linked stages — glycolysis in the cytoplasm, the link reaction, the Krebs cycle in the mitochondrial matrix, and oxidative phosphorylation on the inner mitochondrial membrane — identifying net ATP, NADH, and FADH2 yield per stage.
- Explain the chemiosmotic mechanism of ATP synthesis — electron transport chain pumps H+ across the inner mitochondrial membrane, generating a proton-motive force that drives ATP synthase rotation to phosphorylate ADP+Pi — contrasting with substrate-level phosphorylation.
- C1.3 Photosynthesis
- Explain the light-dependent reactions of photosynthesis — photosystem II and I, photolysis of water releasing O2, non-cyclic photophosphorylation generating ATP and NADPH via the thylakoid electron transport chain — and the role of plastocyanin and ferredoxin as electron carriers.
- Apply the Calvin cycle — CO2 fixation by RuBisCO onto RuBP, reduction of glycerate-3-phosphate to G3P using ATP and NADPH, and RuBP regeneration — to predict effects of changing CO2 concentration or light intensity on cycle intermediate accumulation.
C2 — Cells
- C2.1 Chemical Signalling (AHL)
- Compare signalling by lipid-soluble hormones — direct nuclear receptor binding activating transcription factors — versus hydrophilic hormones — membrane receptor binding triggering second-messenger cascades via cAMP or IP3/Ca2+ — explaining differences in response speed and duration.
- C2.2 Neural Signalling
- Explain action potential generation — voltage-gated Na+ channel opening causing depolarisation, K+ channel opening causing repolarisation, absolute and relative refractory periods — and propagation along myelinated axons via saltatory conduction at nodes of Ranvier.
- Explain synaptic transmission — Ca2+-triggered vesicle exocytosis releasing neurotransmitters, binding to postsynaptic receptors, generation or inhibition of postsynaptic potentials — and how spatial and temporal summation determines whether action potential threshold is reached.
C3 — Organisms
- C3.1 Integration of Body Systems
- Apply knowledge of nervous and endocrine integration to analyse coordinated physiological responses — blood glucose regulation by insulin and glucagon via negative feedback, heart rate control by sympathetic and parasympathetic branches — using real experimental data.
- C3.2 Defence Against Disease
- Explain innate immunity — skin and mucosal barriers, phagocytosis by neutrophils and macrophages, inflammatory response mediated by histamines and cytokines, complement cascade activation — as a non-specific first line of defence based on self/non-self discrimination.
- Apply the mechanism of adaptive immunity — B-lymphocyte clonal selection and antibody production, T-helper and cytotoxic T-cell roles, immunological memory cell formation — to explain how vaccination exploits these processes to confer long-term protection.
C4 — Ecosystems
- C4.1 Populations and Communities
- Analyse population growth models — exponential J-curve versus logistic S-curve — and apply the logistic equation to calculate carrying capacity, identifying density-dependent and density-independent limiting factors from field or experimental population data.
- Explain predator-prey population dynamics using Lotka-Volterra oscillations with time-lag effects, and analyse community succession from pioneer species through seral stages to a climax community with reference to changing abiotic and biotic conditions.
- C4.2 Transfers of Energy and Matter
- Calculate gross primary productivity, net primary productivity, and secondary productivity for given ecosystems, explaining energy losses at trophic levels via respiration and decomposition using quantitative trophic transfer efficiency data.
- Analyse the biogeochemical cycling of carbon and nitrogen — carbon through photosynthesis, respiration, decomposition, and combustion; nitrogen through fixation by Rhizobium, nitrification, denitrification, and ammonification — and evaluate human disruption of each cycle.
4Theme D: Continuity and Change 4 topics
D1 — Molecules
- D1.1 DNA Replication
- Explain semi-conservative DNA replication — helicase unwinding, primase synthesising RNA primers, DNA polymerase III extending 5' to 3', Okazaki fragments on the lagging strand, ligase sealing nicks — and how 3' to 5' exonuclease proofreading activity maintains replication fidelity.
- D1.2 Protein Synthesis
- Explain transcription — RNA polymerase binding to the promoter, template strand reading 3' to 5', pre-mRNA synthesis, 5' cap and 3' poly-A tail addition, and spliceosome removal of introns — as the first stage of gene expression in eukaryotes.
- Explain translation — ribosome assembly at the AUG start codon, tRNA anticodon-codon recognition, peptide bond formation at the peptidyl transferase centre, and termination at a stop codon — and explain how the genetic code's degeneracy buffers the functional impact of base substitution mutations.
- D1.3 Mutations and Gene Editing
- Analyse molecular consequences of point mutations — substitution (silent, missense, nonsense), insertion, and deletion causing frameshift — on protein primary structure and function, using the genetic code table to predict amino acid changes from given nucleotide sequences.
- Evaluate the mechanism and applications of CRISPR-Cas9 gene editing — guide RNA targeting complementary genomic DNA, Cas9 double-strand cleavage, and repair via NHEJ or HDR — discussing ethical distinctions between germline and somatic cell editing.
D2 — Cells
- D2.1 Cell and Nuclear Division
- Explain mitosis — prophase, metaphase, anaphase, telophase stages; spindle fibre attachment at kinetochores; sister chromatid separation; cytokinesis — and distinguish its biological purpose (growth, repair, asexual reproduction) from that of meiosis.
- Explain how meiosis generates genetic diversity through independent assortment of homologous chromosomes at metaphase I and crossing over (chiasma formation) at prophase I, and calculate the maximum number of genetically distinct gamete types possible for a given chromosome number.
- D2.2 Gene Expression (AHL)
- Explain transcriptional regulation in eukaryotes — transcription factor binding to enhancers and silencers, mediator complex assembly at the promoter, histone acetylation opening chromatin, and DNA methylation silencing genes — as the primary mechanism of cell-type-specific gene expression.
- Evaluate post-transcriptional and post-translational regulatory mechanisms — alternative splicing generating protein isoforms, miRNA-mediated mRNA silencing, protein phosphorylation and ubiquitination controlling activity and degradation — as layers of gene expression control beyond transcription.
- D2.3 Water Potential
- Apply water potential (psi = solute potential + pressure potential) to predict direction of osmosis between cells or compartments, using quantitative calculations to explain plasmolysis, turgor maintenance, and wilting in plant cells under varying external solute concentrations.
D3 — Organisms
- D3.1 Reproduction
- Explain gametogenesis — spermatogenesis yielding four functional sperm versus oogenesis yielding one oocyte and three polar bodies per meiotic division — and describe fertilisation, zona pellucida modifications blocking polyspermy, and implantation in human reproduction.
- Apply the hormonal regulation of the human menstrual cycle — FSH, LH, oestrogen, and progesterone negative and positive feedback loops governing follicular development, ovulation, corpus luteum maintenance, and menstruation — to predict effects of exogenous hormones.
- D3.2 Inheritance
- Apply Mendelian genetics — monohybrid and dihybrid crosses, incomplete dominance, codominance, multiple alleles including ABO blood groups, sex-linkage, and epistasis — to calculate expected offspring genotype and phenotype ratios and test predictions with chi-squared analysis.
- Analyse pedigree charts to determine pattern of inheritance — autosomal dominant or recessive, X-linked dominant or recessive — calculate carrier probabilities for individuals, and link identified inheritance patterns to underlying chromosomal mechanisms from meiosis.
- D3.3 Homeostasis
- Explain negative feedback as the universal homeostatic mechanism — receptor detects deviation from set point, control centre integrates signal, effector corrects deviation — and contrast with positive feedback, using thermoregulation and blood glucose regulation as named examples.
- Apply the hormonal and neural mechanisms of mammalian thermoregulation — peripheral thermoreceptors, hypothalamic set point, vasodilation, vasoconstriction, sweating, shivering, and piloerection — to analyse and predict thermoregulatory responses from quantitative data.
D4 — Ecosystems
- D4.1 Natural Selection
- Apply the four Darwinian conditions — heritable variation, overproduction of offspring, competition for limited resources, and differential reproductive success — to explain directional, stabilising, and disruptive natural selection using real population frequency data.
- Synthesise how antibiotic resistance in bacterial populations arises through natural selection of spontaneous mutations — random mutation, antibiotic selection pressure, survival and reproduction of resistant individuals — and evaluate evidence-based interventions to slow resistance spread.
- D4.2 Stability and Change
- Analyse how keystone species and trophic cascades maintain ecosystem structure — removal of a keystone predator releasing mesopredators that suppress primary consumers, reducing producer biomass — using empirical case studies such as sea otters, wolves in Yellowstone, or shark removal.
- D4.3 Climate Change
- Synthesise the biological consequences of rising atmospheric CO2 and temperature on biodiversity — coral bleaching from thermal expulsion of Symbiodinium, phenological mismatches from asynchronous seasonal timing, poleward range shifts, and increased extinction rates — evaluated against current IPCC climate scenarios.
What's Included in AccelaStudy® AI
Adaptive Knowledge Graph
Practice Questions
Lesson Modules
Console Simulator Labs
Exam Tips & Strategy
54 Activity Formats
Scope
Included Topics
- Theme A: Unity and Diversity — water, nucleic acids, cell structure, origins of cells (AHL), viruses (AHL), diversity of organisms, classification and cladistics (AHL), evolution and speciation, conservation of biodiversity
- Theme B: Form and Function — carbohydrates, lipids and proteins, membranes and transport, organelles and compartmentalisation, cell specialisation, gas exchange, transport systems, muscle and motility (AHL), ecological niches and adaptation
- Theme C: Interaction and Interdependence — enzymes and metabolism, cell respiration, photosynthesis, chemical signalling (AHL), neural signalling, integration of body systems, defence against disease, populations and communities, energy and matter transfers
- Theme D: Continuity and Change — DNA replication, protein synthesis, mutations and gene editing, cell and nuclear division, gene expression (AHL), water potential, reproduction, inheritance, homeostasis, natural selection, ecosystem stability, climate change
- Internal Assessment (IA) — individual scientific investigation worth 20% of final grade
- Assessment Objectives AO1–AO4 — knowledge recall, application of concepts, analysis of data, and synthesis/evaluation across all themes
Not Covered
- Standard Level (SL) exclusive teaching hours and assessment differentiation
- IB Diploma Programme Theory of Knowledge (TOK) linkages and extended essay requirements
- Pre-2025 legacy syllabus optional topics (neurobiology and behaviour, biotechnology and bioinformatics, ecology and conservation, human physiology options)
- Laboratory practical manual and specific prescribed practicals not assessed in written papers
- Group 4 collaborative project assessment criteria and process
Official Exam Page
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