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A1.1A Water: the medium for life, polarity and hydrogen bonding
11 minute read
A1.1B Consequences of hydrogen bonding: cohesion, adhesion, solvent and thermal properties
31 minute read
A1.1C Water beyond Earth and the search for life
10 minute read
A1.2A DNA and RNA: nucleotides, bases and the genetic code
17 minute read
A1.2B The double helix, base pairing and code conservation
16 minute read
A1.2C Directionality, helix stability and nucleosomes (HL)
9 minute read
A1.2D Classic DNA experiments: Hershey–Chase and Chargaff's data (HL)
8 minute read
A2.1A Origin of life: early Earth, prebiotic chemistry and Miller-Urey (HL)
28 minute read
A2.1B Protocells, the RNA world and the last universal common ancestor (HL)
A2.2A Cell theory and microscopy
27 minute read
A2.2B Cell structure: common features, prokaryotic and eukaryotic cells
38 minute read
A2.2C Animal, plant, fungal cells and reading micrographs
42 minute read
A2.2D Endosymbiosis, differentiation and multicellularity (HL)
A2.3A Viruses: structural features and diversity (HL)
14 minute read
A2.3B Viral replication: the lytic and lysogenic cycles (HL)
12 minute read
A2.3C Origins and rapid evolution of viruses (HL)
A3.1A Variation, species, naming and the biological species concept
20 minute read
A3.1B Chromosome numbers, karyotyping and karyograms
A3.1C Genomes: unity, diversity, size and whole-genome sequencing
18 minute read
A3.1D Applying the species concept; keys and environmental DNA (HL)
26 minute read
A3.2A Classification: why we classify, clades and evolutionary relationships (HL)
21 minute read
A3.2B Molecular clocks, cladograms and the three domains (HL)
34 minute read
A4.1A What evolution is; evidence from molecules and breeding
A4.1B Evidence from structures; speciation and reproductive isolation
22 minute read
A4.1C Sympatric/allopatric speciation, adaptive radiation and polyploidy (HL)
A4.2A Biodiversity, extinction and ecosystem loss
44 minute read
A4.2B The biodiversity crisis and approaches to conservation
41 minute read
B1.1A Carbon chemistry, condensation and hydrolysis
B1.1B Carbohydrates and glycoproteins
B1.1C Lipids: hydrophobic properties, triglycerides and fatty acids
35 minute read
B1.1D Triglyceride storage, phospholipid bilayers and steroids
36 minute read
B1.2A Amino acids, peptide bonds and what affects proteins
B1.2B Protein structure: R-groups, primary and secondary (HL)
23 minute read
B1.2C Protein structure: tertiary, quaternary; globular vs fibrous (HL)
B2.1A Membranes: lipid bilayers, diffusion and proteins
B2.1B Transport across membranes: osmosis, channels and pumps
B2.1C Membrane structure: glycoproteins, glycolipids and the fluid mosaic model
B2.1D Membrane fluidity: fatty acids, cholesterol and vesicles (HL)
B2.1E Ion channels, pumps, cotransport and cell adhesion (HL)
B2.2A Organelles and the advantages of compartmentalization
B2.2B Mitochondria, chloroplasts and the nuclear envelope (HL)
B2.2C Ribosomes, endoplasmic reticulum, Golgi and vesicles (HL)
B2.3A Stem cells: properties, niches and potency
25 minute read
B2.3B Cell size and surface-area-to-volume ratio
B2.3C Specialized cells: pneumocytes, muscle fibres and gametes (HL)
37 minute read
B3.1A Gas exchange and the properties of exchange surfaces
B3.1B The mammalian lung: alveoli, ventilation and lung volumes
B3.1C Gas exchange in leaves: structure, transpiration and stomata
B3.1D Hemoglobin, the Bohr shift and dissociation curves (HL)
B3.2A Blood vessels: capillaries, arteries and veins
B3.2B Pulse, venous return and coronary heart disease
B3.2C Plant transport: xylem, transpiration and tissue distribution
B3.2D Tissue fluid and the lymphatic system (HL)
B3.2E Circulation types, the mammalian heart and the cardiac cycle (HL)
B3.2F Root pressure and phloem translocation (HL)
B3.3A Muscle contraction: sliding filament model, titin and motor units (HL)
24 minute read
B3.3B Skeletons, joints and range of motion (HL)
B3.3C Antagonistic breathing, locomotion and swimming adaptations (HL)
B4.1A Habitats, adaptation and range of tolerance
B4.1B Coral reefs, biomes and biome adaptations
33 minute read
B4.2A Ecological niches and oxygen requirements
B4.2B Modes of nutrition: autotrophic, holozoic and mixotrophic
B4.2C Saprotrophs, archaea, herbivory and dentition
B4.2D Predator/plant adaptations; fundamental vs realized niches
C1.1A What enzymes are: catalysts, metabolism and the active site
C1.1B How the active site works: induced fit, molecular motion and specificity
C1.1C Factors affecting enzyme rate and activation energy
C1.1D Metabolic pathways and intracellular/extracellular enzymes (HL)
C1.1E Enzyme inhibition and metabolic regulation (HL)
C1.2A ATP: the cell's energy currency
C1.2B Aerobic vs anaerobic respiration; measuring respiration
C1.2C Glycolysis, NAD and anaerobic pathways (HL)
C1.2D The link reaction and the Krebs cycle (HL)
C1.2E The electron transport chain, chemiosmosis and oxygen (HL)
C1.3A Photosynthesis overview: light to chemical energy
C1.3B Photosynthetic pigments, chromatography and spectra
C1.3C Limiting factors and carbon dioxide enrichment experiments
19 minute read
C1.3D Photosystems, light absorption and photolysis (HL)
C1.3E Light-dependent reactions: ATP and NADPH in thylakoids (HL)
C1.3F The Calvin cycle, products and reaction interdependence (HL)
C2.1A Receptors and bacterial quorum sensing (HL)
C2.1B Signalling chemicals and receptor location (HL)
C2.1C Signal transduction: neurotransmitter, G-protein and adrenaline receptors (HL)
30 minute read
C2.1D Tyrosine kinase, intracellular receptors, steroid hormones and feedback (HL)
C2.2A Neurons, resting and action potentials, and impulse speed
C2.2B Synapses and neurotransmitter release
C2.2C Action potentials in depth: depolarization, propagation, saltatory conduction (HL)
C2.2D Synaptic modulation: exogenous chemicals, inhibition and summation (HL)
C2.2E Pain perception and consciousness (HL)
C3.1A System integration and the body's hierarchy
C3.1B The brain, spinal cord, nerves and neural pathways
C3.1C Reflex arcs and the cerebellum
C3.1D Endocrine control: melatonin, epinephrine and the hypothalamus–pituitary axis
C3.1E Feedback control of heart rate, ventilation and digestion
C3.1F Plant responses: tropisms, phototropism and phytohormones (HL)
C3.1G Auxin, cytokinin and ethylene in plant growth and ripening (HL)
C3.2A Pathogens, primary defences and innate immunity
C3.2B Adaptive immunity: lymphocytes, antibodies and memory
C3.2C HIV/AIDS, antibiotics and antibiotic resistance
C3.2D Zoonoses, vaccines, herd immunity and COVID-19
C4.1A Populations and estimating population size
C4.1B Carrying capacity and population growth curves
29 minute read
C4.1C Communities and interspecific interactions
C4.1D Invasive species and testing for competition
C4.1E Predator-prey cycles, population control and allelopathy
C4.2A Ecosystems, energy from sunlight and food chains/webs
C4.2B Decomposers, autotrophs, heterotrophs and energy release
C4.2C Trophic levels, energy pyramids and energy loss
C4.2D Primary/secondary production and the carbon cycle
13 minute read
C4.2E Combustion, the Keeling Curve and element recycling
D1.1A DNA replication: semi-conservative copying by helicase and polymerase
D1.1B PCR and gel electrophoresis: amplifying, separating and applying DNA
D1.1C DNA replication in detail: directionality, leading/lagging strands and proofreading (HL)
D1.2A Transcription: making RNA from a DNA template
D1.2B Translation: mRNA, ribosomes and tRNA
D1.2C The genetic code, building polypeptides and mutations
D1.2E Transcription initiation and directionality (HL)
D1.2F Non-coding DNA, post-transcriptional modification and alternative splicing (HL)
D1.2G Translation initiation, polypeptide modification and recycling (HL)
D1.3A Gene mutations: substitutions, insertions and deletions
D1.3B Causes, randomness and effects of mutation
D1.3C Gene knockout, CRISPR editing and conserved sequences (HL)
D2.1A Cell division, cytokinesis and the roles of mitosis and meiosis
D2.1B DNA replication, chromosome movement and the phases of mitosis
D2.1C Meiosis: reduction division, non-disjunction and variation
D2.1D The cell cycle and interphase (HL)
D2.1E Cell cycle control: cyclins, mutations and cancer (HL)
D2.2A Gene expression and transcriptional regulation (HL)
D2.2B Epigenetics: epigenesis, the -omes, methylation and inheritance (HL)
D2.2C Environmental effects on gene expression; twin studies (HL)
D2.3A Solvation, osmosis and its direction
D2.3B Osmosis in cells; isotonic solutions and medical uses
D2.3C Water potential: solute and pressure potential (HL)
D3.1A Sexual vs asexual reproduction and the life cycle
D31.B Human reproduction: anatomy, cycles, fertilization and IVF
32 minute read
D3.1C Reproduction in flowering plants
40 minute read
D3.1D Puberty, gametogenesis, fertilization and implantation (HL)
D3.1F Pregnancy, the placenta, birth and hormone replacement therapy (HL)
D3.2A Gametes, genotype and phenotype
D3.2B Dominant/recessive alleles, phenotypic plasticity and PKU
D3.2C Multiple alleles: SNPs, ABO blood groups and codominance
D3.2D Sex linkage, haemophilia and pedigree charts
D3.2E Continuous variation, polygenic inheritance and box-and-whisker plots
D3.2F Meiosis genetics: segregation, assortment and dihybrid crosses (HL)
D3.2G Gene linkage, recombinants and the chi-squared test (HL)
D3.3A Homeostasis, feedback and blood glucose regulation (incl. diabetes)
D3.3B Thermoregulation
D3.3C The kidney: osmoregulation, filtration and water reabsorption (HL)
45 minute read
D4.1A Natural selection: variation, competition and selection pressures
D4.1B Survival, heritability, sexual selection and modelling
D4.1C Gene pools and changing allele frequencies (HL)
D4.1D Types of selection, Hardy-Weinberg and artificial selection (HL)
15 minute read
D4.2A Ecosystem stability, tipping points and modelling
D4.2B Keystone species, sustainable harvesting, agriculture and eutrophication
D4.2C Biomagnification, plastic pollution and rewilding
D4.2D Ecological succession: causes, primary, cyclical and climax communities (HL)
D4.3A Causes of climate change, feedback and habitat change
D4.3B Ocean currents, range shifts, coral reefs and habitat restoration
39 minute read
D4.3C Phenology, disrupted synchrony and evolution under climate change (HL)
