A1.1.1 Water as the medium for life

A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

A1.1.3 Cohesion of water molecules due to hydrogen bonding and consequences for organisms

A1.1.4 Adhesion of water to materials that are polar or charged and impacts for organisms

A1.1.5 Solvent properties of water as a medium for metabolism and transport

A1.1.6 Physical properties of water and the consequences for animals in aquatic habitats

A1.1.7 Extraplanetary origin of water on Earth and reasons for its retention (HL only)

A1.1.8 Relationship between the search for extraterrestrial life and the presence of water (HL only)

A1.2.1 DNA as the genetic material of all living organisms

A1.2.2 Components of a nucleotide

A1.2.3 Sugar–phosphate bonding and the sugar–phosphate “backbone” of DNA and RNA

A1.2.4 Bases in each nucleic acid that form the basis of a code

A1.2.5 RNA as a polymer formed by condensation of nucleotide monomers

A1.2.6 DNA as a double helix linked by hydrogen bonding between complementary base pairs

A1.2.7 Differences between DNA and RNA

A1.2.8 Complementary base pairing in allowing genetic information to be replicated and expressed

A1.2.9 Diversity of possible DNA base sequences and its capacity for storing information

A1.2.10 Conservation of the genetic code as evidence of universal common ancestry

A1.2.11 Directionality of RNA and DNA (HL only)

A1.2.12 Purine-to-pyrimidine bonding as a component of DNA helix stability (HL only)

A1.2.13 Structure of a nucleosome (HL only)

A1.2.14 Evidence from the Hershey–Chase experiment for DNA as the genetic material (HL only)

A1.2.15 Chargaff’s data on pyrimidine and purine bases across diverse life forms (HL only)

A2.1.1 Conditions on early Earth and the pre-biotic formation of carbon compounds (HL only)

A2.1.2 Cells as the smallest units of self-sustaining life (HL only)

A2.1.3 Challenge of explaining the spontaneous origin of cells

A2.1.4 Evidence for the origin of carbon compounds

A2.1.5 Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers

A2.1.6 RNA as a presumed first genetic material

A2.1.7 Evidence for a last universal common ancestor

A2.1.8 Approaches used to estimate dates of the first living cells

A2.1.9 Evidence for the evolution of the last universal common ancestor

A2.2.1 Cells as the basic structural unit of all living organisms

A2.2.2 Microscopy skills

A2.2.3 Developments in microscopy

A2.2.4 Structures common to cells in all living organisms

A2.2.5 Prokaryote cell structure

A2.2.6 Eukaryote cell structure

A2.2.7 Processes of life in unicellular organisms

A2.2.8 Differences in eukaryotic cell structure between animals, fungi, and plants

A2.2.9 Atypical cell structure in eukaryotes

A2.2.10 Cell types and cell structures viewed in light and electron micrographs

A2.2.11 Drawing and annotation based on electron micrographs

A2.2.12 Origin of eukaryotic cells by endosymbiosis (HL)

A2.2.13 Cell differentiation (HL)

A2.2.14 Evolution of multicellularity (HL)

A2.3.1 Structural features common to viruses (HL)

A2.3.2 Diversity of structure in viruses (HL)

A2.3.3 Lytic cycle of a virus (HL)

A2.3.4 Lysogenic cycle of a virus (HL)

A2.3.5 Evidence for several origins of viruses from other organisms (HL)

A2.3.6 Rapid evolution in viruses (HL)

A3.1.1 Variation between organisms as a defining feature of life

A3.1.2 Species as groups of organisms with shared traits

A3.1.3 Binomial system for naming organisms

A3.1.4 Biological species concept

A3.1.5 Difficulties distinguishing between populations and species

A3.1.6 Diversity in chromosome numbers of plant and animal species

A3.1.7 Karyotyping and karyograms

A3.1.8 Unity and diversity of genomes within species

A3.1.9 Diversity of eukaryote genomes

A3.1.10 Comparison of genome sizes

A3.1.11 Current and potential future uses of whole genome sequencing

A3.1.12 Difficulties applying the biological species concept (HL)

A3.1.13 Chromosome number as a shared trait within a species (HL)

A3.1.14 Engagement with local plant or animal species to develop a dichotomous key (HL)

A3.1.15 Identification of species from environmental DNA in a habitat using barcodes (HL)

A3.2.1 Need for classification of organisms (HL)

A3.2.2 Difficulties classifying organisms into the traditional hierarchy of taxa (HL)

A3.2.3 Advantages of classification corresponding to evolutionary relationships (HL)

A3.2.4 Clades as groups of organisms with common ancestry and shared characteristics (HL)

A3.2.5 Gradual accumulation of sequence differences (HL)

A3.2.6 Base sequences of genes or amino acid sequences of proteins (HL)

A3.2.7 Analysing cladograms (HL)

A3.2.8 Using cladistics to investigate evolutionary relationships (HL)

A3.2.9 Classification of all organisms using evidence from rRNA base sequences (HL)

A4.1.1 Evolution as change in the heritable characteristics of a population

A4.1.2 Evidence for evolution from base sequences in DNA or RNA and amino acid sequences

A4.1.3 Evidence for evolution from selective breeding of domesticated animals and crop plants

A4.1.4 Evidence for evolution from homologous structures

A4.1.5 Convergent evolution as the origin of analogous structures

A4.1.6 Speciation by splitting of pre-existing species

A4.1.7 Roles of reproductive isolation and differential selection in speciation

A4.1.8 Differences and similarities between sympatric and allopatric speciation (HL)

A4.1.9 Adaptive radiation as a source of biodiversity (HL)

A4.1.10 Barriers to hybridization and sterility of interspecific hybrids (HL)

A4.1.11 Abrupt speciation in plants by hybridization and polyploidy (HL)

A4.2.1 Biodiversity as the variety of life in all its forms, levels and combinations

A4.2.2 Comparisons between current number of species on Earth and past levels of biodiversity

A4.2.3 Causes of anthropogenic species extinction

A4.2.4 Causes of ecosystem loss

A4.2.5 Evidence for a biodiversity crisis

A4.2.6 Causes of the current biodiversity crisis

A4.2.7 Need for several approaches to conservation of biodiversity

A4.2.8 Evolutionarily distinct and globally endangered species in conservation prioritization

B1.1.1 Chemical properties of a carbon atom

B1.1.2 Production of macromolecules by condensation reactions

B1.1.3 Digestion of polymers into monomers by hydrolysis reactions

B1.1.4 Form and function of monosaccharides

B1.1.5 Polysaccharides as energy storage compounds

B1.1.6 Structure of cellulose

B1.1.7 Role of glycoproteins in cell–cell recognition

B1.1.8 Hydrophobic properties of lipids

B1.1.9 Formation of triglycerides and phospholipids by condensation reactions

B1.1.10 Difference between saturated, monounsaturated and polyunsaturated fatty acids

B1.1.11 Triglycerides in adipose tissues for energy storage and thermal insulation

B1.1.12 Formation of phospholipid bilayers

B1.1.13 Ability of non-polar steroids to pass through the phospholipid bilayer

B1.2.1 Generalized structure of an amino acid

B1.2.2 Condensation reactions forming dipeptides and longer chains of amino acids

B1.2.3 Dietary requirements for amino acids

B1.2.4 Infinite variety of possible peptide chains

B1.2.5 Effect of pH and temperature on protein structure

B1.2.6 Chemical diversity in the R-groups of amino acids (HL)

B1.2.7 Impact of primary structure on the conformation of proteins (HL)

B1.2.8 Pleating and coiling of secondary structure of proteins (HL)

B1.2.9 Dependence of tertiary structure on functional groups (HL)

B1.2.10 Effect of polar and non-polar amino acids on tertiary structure of proteins (HL)

B1.2.11 Quaternary structure of non-conjugated and conjugated proteins (HL)

B1.2.12 Relationship of form and function in globular and fibrous proteins (HL)

B2.1.1 Lipid bilayers as the basis of cell membranes

B2.1.2 Lipid bilayers as barriers

B2.1.3 Simple diffusion across membranes

B2.1.4 Integral and peripheral proteins in membranes

B2.1.5 Movement of water molecules across membranes by osmosis and the role of aquaporins

B2.1.6 Channel proteins for facilitated diffusion

B2.1.7 Pump proteins for active transport

B2.1.8 Selectivity in membrane permeability

B2.1.9 Structure and function of glycoproteins and glycolipids

B2.1.10 Fluid mosaic model of membrane structure

B2.1.11 Relationships between fatty acid composition of lipid bilayers and their fluidity (HL)

B2.1.12 Cholesterol and membrane fluidity in animal cells (HL)

B2.1.13 Membrane fluidity and the fusion and formation of vesicles (HL)

B2.1.14 Gated ion channels in neurons (HL)

B2.1.15 Sodium–potassium pumps as an example of exchange transporters (HL)

B2.1.16 Sodium-dependent glucose cotransporters as an example of indirect active transport (HL)

B2.1.17 Adhesion of cells to form tissues (HL)

B2.2.1 Organelles as discrete subunits of cells that are adapted to perform specific functions

B2.2.2 Advantage of the separation of the nucleus and cytoplasm into separate compartments

B2.2.3 Advantages of compartmentalization in the cytoplasm of cells

B2.2.4 Adaptations of the mitochondrion for production of ATP by aerobic cell respiration (HL)

B2.2.5 Adaptations of the chloroplast for photosynthesis (HL)

B2.2.6 Functional benefits of the double membrane of the nucleus (HL)

B2.2.7 Structure and function of free ribosomes and of the rough endoplasmic reticulum (HL)

B2.2.8 Structure and function of the Golgi apparatus (HL)

B2.2.9 Structure and function of vesicles in cells (HL)

B2.3.1 Production of unspecialized cells following fertilization and their development

B2.3.2 Properties of stem cells

B2.3.3 Location and function of stem cell niches in adult humans

B2.3.4 Differences between totipotent, pluripotent and multipotent stem cells

B2.3.5 Cell size as an aspect of specialization

B2.3.6 Surface area-to-volume ratios and constraints on cell size

B2.3.7 Adaptations to increase surface area-to-volume ratios of cells (HL)

B2.3.8 Adaptations of type I and type II pneumocytes in alveoli (HL)

B2.3.9 Adaptations of cardiac muscle cells and striated muscle fibres (HL)

B2.3.10 Adaptations of sperm and egg cells (HL)

B3.1.1 Gas exchange as a vital function in all organisms

B3.1.2 Properties of gas-exchange surfaces

B3.1.3 Maintenance of concentration gradients at exchange surfaces in animals

B3.1.4 Adaptations of mammalian lungs for gas exchange

B3.1.5 Ventilation of the lungs

B3.1.6 Measurement of lung volumes

B3.1.7 Adaptations for gas exchange in leaves

B3.1.8 Distribution of tissues in a leaf

B3.1.9 Transpiration as a consequence of gas exchange in a leaf

B3.1.10 Stomatal density

B3.1.11 Adaptations of foetal and adult haemoglobin for the transport of oxygen (HL)

B3.1.12 Bohr shift (HL)

B3.1.13 Oxygen dissociation curves (HL)

B3.2.1 Adaptations of capillaries for exchange of materials

B3.2.2 Structure of arteries and veins

B3.2.3 Adaptations of arteries for the transport of blood away from the heart

B3.2.4 Measurement of pulse rates

B3.2.5 Adaptations of veins for the return of blood to the heart

B3.2.6 Causes and consequences of occlusion of the coronary arteries

B3.2.7 Transport of water from roots to leaves during transpiration

B3.2.8 Adaptations of xylem vessels for transport of water

B3.2.9 Distribution of tissues in a transverse section of the stem of a dicotyledonous plant

B3.2.10 Distribution of tissues in a transverse section of the root of a dicotyledonous plant

B3.2.11 Release and reuptake of tissue fluid in capillaries (HL)

B3.2.12 Exchange of substances between tissue fluid and cells in tissues (HL)

B3.2.13 Drainage of excess tissue fluid into lymph ducts (HL)

B3.2.14 Differences between circulation of bony fish and of mammals (HL)

B3.2.15 Adaptations of the mammalian heart for delivering pressurized blood to the arteries (HL)

B3.2.16 Stages in the cardiac cycle (HL)

B3.2.17 Generation of root pressure in xylem vessels by active transport of mineral ions (HL)

B3.2.18 Adaptations of phloem sieve tubes and companion cells for translocation of sap (HL)

B3.3.1 Adaptations for movement as a universal feature of living organisms

B3.3.2 Sliding filament model of muscle contraction

B3.3.3 Role of the protein titin and antagonistic muscles in muscle relaxation

B3.3.4 Structure and function of motor units in skeletal muscle

B3.3.5 Roles of skeletons as anchorage for muscles and as levers

B3.3.6 Movement at a synovial joint

B3.3.7 Range of motion of a joint

B3.3.8 Internal and external intercostal muscles

B3.3.9 Reasons for locomotion

B3.3.10 Adaptations for swimming in marine mammals

B4.1.1 Habitat as the place in which a community, species, population or organism lives

B4.1.2 Adaptations of organisms to the abiotic environment of their habitat

B4.1.3 Abiotic variables affecting species distribution

B4.1.4 Range of tolerance of a limiting factor

B4.1.5 Conditions required for coral reef formation

B4.1.6 Abiotic factors as the determinants of terrestrial biome distribution

B4.1.7 Biomes as groups of ecosystems with similar communities

B4.1.8 Adaptations to life in hot deserts and tropical rainforest

B4.2.1 Ecological niche as the role of a species in an ecosystem

B4.2.2 Organisms that are obligate anaerobes, facultative anaerobes and obligate aerobes

B4.2.3 Photosynthesis as the mode of nutrition

B4.2.4 Holozoic nutrition in animals

B4.2.5 Mixotrophic nutrition in some protists

B4.2.6 Saprotrophic nutrition in some fungi and bacteria

B4.2.7 Diversity of nutrition in archaea

B4.2.8 Dentition and the diet of omnivorous and herbivorous members of the family Hominidae

B4.2.9 Adaptations of herbivores for feeding on plants and of plants for resisting herbivory

B4.2.10 Adaptations of predators

B4.2.11 Adaptations of plant form for harvesting light

B4.2.12 Fundamental and realized niches

B4.2.13 Competitive exclusion and the uniqueness of ecological niches

C1.1.1 Enzymes as catalysts

C1.1.2 Role of enzymes in metabolism

C1.1.3 Anabolic and catabolic reactions

C1.1.4 Enzymes as globular proteins with an active site for catalysis

C1.1.5 Interactions between substrate and active site to allow induced-fit binding

C1.1.6 Role of molecular motion and substrate-active site collisions in enzyme catalysis

C1.1.7 The structure of the active site, enzyme–substrate specificity and denaturation

C1.1.8 Effects of temperature, pH and substrate concentration on the rate of enzyme activity

C1.1.9 Measurements in enzyme-catalysed reactions

C1.1.10 Effect of enzymes on activation energy

C1.1.11 Intracellular and extracellular enzyme-catalysed reactions (HL)

C1.1.12 Generation of heat energy by the reactions of metabolism (HL)

C1.1.13 Cyclical and linear pathways in metabolism (HL)

C1.1.14 Allosteric sites and non-competitive inhibition (HL)

C1.1.15 Competitive inhibition (HL)

C1.1.16 Regulation of metabolic pathways by feedback inhibition (HL)

C1.1.17 Mechanism-based inhibition (HL)

C1.2.1 ATP as the molecule that distributes energy within cells

C1.2.2 Life processes within cells that ATP supplies with energy

C1.2.3 Energy transfers during interconversions between ATP and ADP

C1.2.4 Cell respiration

C1.2.5 Differences between anaerobic and aerobic cell respiration in humans

C1.2.6 Variables affecting the rate of cell respiration

C1.2.7 Role of NAD as a carrier of hydrogen (HL)

C1.2.8 Conversion of glucose to pyruvate (HL)

C1.2.9 Conversion of pyruvate to lactate (HL)

C1.2.10 Anaerobic cell respiration in yeast and its use in brewing and baking (HL)

C1.2.11 Oxidation and decarboxylation of pyruvate (HL)

C1.2.12 Oxidation and decarboxylation of acetyl groups in the Krebs cycle (HL)

C1.2.13 Transfer of energy by reduced NAD (HL)

C1.2.14 Generation of a proton gradient (HL)

C1.2.15 Chemiosmosis and the synthesis of ATP in the mitochondrion (HL)

C1.2.16 Role of oxygen as terminal electron acceptor in aerobic cell respiration (HL)

C1.2.17 Differences between lipids and carbohydrates as respiratory substrates (HL)

C1.3.1 Transformation of light energy to chemical energy

C1.3.2 Conversion of carbon dioxide to glucose in photosynthesis

C1.3.3 Oxygen as a by-product of photosynthesis

C1.3.4 Separation and identification of photosynthetic pigments by chromatography

C1.3.5 Absorption of specific wavelengths of light by photosynthetic pigments

C1.3.6 Similarities and differences of absorption and action spectra

C1.3.7 The effects of limiting factors on the rate of photosynthesis

C1.3.8 Carbon dioxide enrichment experiments

C1.3.9 Photosystems (HL)

C1.3.10 Advantages of the structured array of different types of pigment molecules (HL)

C1.3.11 Generation of oxygen by the photolysis of water in photosystem II (HL)

C1.3.12 ATP production by chemiosmosis in thylakoids (HL)

C1.3.13 Reduction of NADP by photosystem I (HL)

C1.3.14 Thylakoids as systems for performing the light-dependent photosynthesis reactions (HL)

C1.3.15 Carbon fixation by Rubisco (HL)

C1.3.16 Synthesis of triose phosphate using reduced NADP and ATP (HL)

C1.3.17 Regeneration of RuBP in the Calvin cycle using ATP (HL)

C1.3.18 Synthesis of carbohydrates, amino acids and other carbon compounds (HL)

C1.3.19 Interdependence of the light-dependent and light-independent reactions (HL)

C2.1.1 Receptors

C2.1.2 Cell signalling by bacteria in quorum sensing

C2.1.3 Hormones, neurotransmitters, cytokines and calcium ions

C2.1.4 Chemical diversity of hormones and neurotransmitters

C2.1.5 Localized and distant effects of signalling molecules

C2.1.6 Transmembrane receptors VS Intracellular receptors

C2.1.7 Initiation of signal transduction pathways by receptors

C2.1.8 Transmembrane receptors for neurotransmitters and changes to membrane potential

C2.1.9 Transmembrane receptors that activate G proteins

C2.1.10 Mechanism of action of epinephrine (adrenaline) receptors

C2.1.11 Transmembrane receptors with tyrosine kinase activity

C2.1.12 Intracellular receptors that affect gene expression

C2.1.13 Effects of the hormones oestradiol and progesterone on target cells

C2.1.14 Regulation of cell signalling pathways by positive and negative feedback

C2.2.1 Neurons as cells within the nervous system that carry electrical impulses

C2.2.2 Generation of the resting potential by pumping

C2.2.3 Nerve impulses as action potentials that are propagated along nerve fibres

C2.2.4 Variation in the speed of nerve impulses

C2.2.5 Synapses as junctions between neurons and between neurons and effector cells

C2.2.6 Release of neurotransmitters from a presynaptic membrane

C2.2.7 Generation of an excitatory postsynaptic potential

C2.2.8 Depolarization and repolarization during action potentials (HL)

C2.2.9 Propagation of an action potential along a nerve fibre/axon (HL)

C2.2.10 Oscilloscope traces showing resting potentials and action potentials (HL)

C2.2.11 Saltatory conduction in myelinated fibres to achieve faster impulses (HL)

C2.2.12 Effects of exogenous chemicals on synaptic transmission (HL)

C2.2.13 Inhibitory neurotransmitters and generation of inhibitory postsynaptic potentials (HL)

C2.2.14 Summation of the effects of excitatory and inhibitory neurotransmitters (HL)

C2.2.15 Perception of pain by neurons with free nerve endings in the skin (HL)

C2.2.16 Consciousness (HL)

C3.1.1 System integration

C3.1.2 Cells, tissues, organs and body systems

C3.1.3 Integration of organs in animal bodies

C3.1.4 The brain as a central information integration organ

C3.1.5 The spinal cord as an integrating centre for unconscious processes

C3.1.6 Input to the spinal cord and cerebral hemispheres through sensory neurons

C3.1.7 Output from the cerebral hemispheres to muscles through motor neurons

C3.1.8 Nerves as bundles of nerve fibres of both sensory and motor neurons

C3.1.9 Pain reflex arcs

C3.1.10 Role of the cerebellum in coordinating skeletal muscle contraction and balance

C3.1.11 Modulation of sleep patterns by melatonin secretion as a part of circadian rhythms

C3.1.12 Epinephrine (adrenaline) secretion by the adrenal glands

C3.1.13 Control of the endocrine system

C3.1.14 Feedback control of heart rate

C3.1.15 Feedback control of ventilation rate

C3.1.16 Control of peristalsis in the digestive system

C3.1.17 Observations of tropic responses in seedlings (HL)

C3.1.18 Positive phototropism (HL)

C3.1.19 Phytohormones (HL)

C3.1.20 Auxin efflux carriers (HL)

C3.1.21 Promotion of cell growth by auxin (HL)

C3.1.22 Interactions between auxin and cytokinin (HL)

C3.1.23 Positive feedback in fruit ripening and ethylene production (HL)

C3.2.1 Pathogens as the cause of infectious diseases

C3.2.2 Skin and mucous membranes as a primary defence

C3.2.3 Sealing of cuts in skin by blood clotting

C3.2.4 Differences between the innate immune system and the adaptive immune system

C3.2.5 Infection control by phagocytes

C3.2.6 Lymphocytes as cells in the adaptive immune system that cooperate to produce antibodies

C3.2.7 Antigens as recognition molecules that trigger antibody production

C3.2.8 Activation of B-lymphocytes by helper T-lymphocytes

C3.2.9 Multiplication of activated B-lymphocytes

C3.2.10 Immunity as a consequence of retaining memory cells

C3.2.11 Transmission of HIV in body fluids

C3.2.12 Infection of lymphocytes by HIV with AIDS as a consequence

C3.2.13 Antibiotics

C3.2.14 Evolution of resistance to several antibiotics

C3.2.15 Zoonoses

C3.2.16 Vaccines and immunization

C3.2.17 Herd immunity and the prevention of epidemics

C3.2.18 Evaluation of data related to the COVID-19 pandemic

C4.1.1 Populations

C4.1.2 Estimation of population size by random sampling

C4.1.3 Random quadrat sampling to estimate population size for sessile organisms

C4.1.4 Capture–mark–release–recapture and the Lincoln index

C4.1.5 Carrying capacity and competition for limited resources

C4.1.6 Negative feedback control of population size by density-dependent factors

C4.1.7 Population growth curves

C4.1.8 Modelling of the sigmoid population growth curve

C4.1.9 Competition versus cooperation in intraspecific relationships

C4.1.10 A community as all of the interacting organisms in an ecosystem

C4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity

C4.1.12 Mutualism as an interspecific relationship that benefits both species

C4.1.13 Resource competition between endemic and invasive species

C4.1.14 Tests for interspecific competition

C4.1.15 Use of the chi-squared test for association between two species

C4.1.16 Predator–prey relationships

C4.1.17 Top-down and bottom-up control of populations in communities

C4.1.18 Allelopathy and secretion of antibiotics

C4.2.1 Ecosystems

C4.2.2 Sunlight

C4.2.3 Flow of chemical energy through food chains

C4.2.4 Construction of food chains and food webs

C4.2.5 Supply of energy to decomposers

C4.2.6 Autotrophs

C4.2.7 Use of light as the external energy source

C4.2.8 Heterotrophs

C4.2.9 Release of energy in both autotrophs and heterotrophs

C4.2.10 Classification of organisms into trophic levels

C4.2.11 Construction of energy pyramids

C4.2.12 Reductions in energy availability at each successive stage in food chains

C4.2.13 Heat loss to the environment in both autotrophs and heterotrophs

C4.2.14 Restrictions on the number of trophic levels in ecosystems

C4.2.15 Primary production as accumulation of carbon compounds in biomass by autotrophs

C4.2.16 Secondary production as accumulation of carbon compounds in biomass by heterotrophs

C4.2.17 Constructing carbon cycle diagrams

C4.2.18 Ecosystems as carbon sinks and carbon sources

C4.2.19 Release of carbon dioxide into the atmosphere during combustion

C4.2.20 Analysis of the Keeling Curve in terms of photosynthesis, respiration and combustion

C4.2.21 Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis

C4.2.22 Recycling of all chemical elements required by living organisms in ecosystems

D1.1.1 DNA replication

D1.1.2 Semi-conservative nature of DNA replication

D1.1.3 Role of helicase and DNA polymerase in DNA replication

D1.1.4 Polymerase chain reaction and gel electrophoresis

D1.1.5 Applications of polymerase chain reaction and gel electrophoresis

D1.1.6 Directionality of DNA polymerases (HL)

D1.1.7 Differences between replication on the leading strand and the lagging strand (HL)

D1.1.8 DNA primase, DNA polymerase I, DNA polymerase III and DNA ligase in replication (HL)

D1.1.9 DNA proofreading (HL)

D1.2.1 Transcription as the synthesis of RNA using a DNA template

D1.2.2 Role of hydrogen bonding and complementary base pairing in transcription

D1.2.3 Stability of DNA templates

D1.2.4 Transcription as a process required for the expression of genes

D1.2.5 Translation as the synthesis of polypeptides from mRNA

D1.2.6 Roles of mRNA, ribosomes and tRNA in translation

D1.2.7 Complementary base pairing between tRNA and mRNA

D1.2.8 Features of the genetic code

D1.2.9 Using the genetic code expressed as a table of mRNA codons

D1.2.10 Stepwise movement of the ribosome along mRNA

D1.2.11 Mutations that change protein structure

D1.2.12 Directionality of transcription and translation (HL)

D1.2.13 Initiation of transcription at the promoter (HL)

D1.2.14 Non-coding sequences in DNA do not code for polypeptides (HL)

D1.2.15 Post-transcriptional modification in eukaryotic cells (HL)

D1.2.16 Alternative splicing of exons to produce variants of a protein from a single gene (HL)

D1.2.17 Initiation of translation (HL)

D1.2.18 Modification of polypeptides into their functional state (HL)

D1.2.19 Recycling of amino acids by proteasomes (HL)

D1.3.1 Gene mutations as structural changes to genes at the molecular level

D1.3.2 Consequences of base substitutions

D1.3.3 Consequences of insertions and deletions

D1.3.4 Causes of gene mutation

D1.3.5 Randomness in mutation

D1.3.6 Consequences of mutation in germ cells and somatic cells

D1.3.7 Mutation as a source of genetic variation

D1.3.8 Gene knockout (HL)

D1.3.9 Use of the CRISPR sequences and the enzyme Cas9 in gene editing (HL)

D1.3.10 Hypotheses to account for conserved or highly conserved sequences in genes (HL)

D2.1.1 Generation of new cells in living organisms by cell division

D2.1.2 Cytokinesis as splitting of cytoplasm in a parent cell between daughter cells

D2.1.3 Equal and unequal cytokinesis

D2.1.4 Roles of mitosis and meiosis in eukaryotes

D2.1.5 DNA replication as a prerequisite for both mitosis and meiosis

D2.1.6 Condensation and movement of chromosomes as shared features of mitosis and meiosis

D2.1.7 Phases of mitosis

D2.1.8 Identification of phases of mitosis

D2.1.9 Meiosis as a reduction division

D2.1.10 Down syndrome and non-disjunction

D2.1.11 Meiosis as a source of variation

D2.1.12 Cell proliferation for growth, cell replacement and tissue repair (HL)

D2.1.13 Phases of the cell cycle (HL)

D2.1.14 Cell growth during interphase (HL)

D2.1.15 Control of the cell cycle using cyclins (HL)

D2.1.16 Consequences of mutations in genes that control the cell cycle (HL)

D2.1.17 Differences between tumours (HL)

D2.2.1 Gene expression

D2.2.2 Regulation of transcription by proteins

D2.2.3 Control of the degradation of mRNA

D2.2.4 Epigenesis

D2.2.5 Differences between the genome, transcriptome and proteome of individual cells

D2.2.6 Methylation of the promoter and histones in nucleosomes as examples of epigenetic tags

D2.2.7 Epigenetic inheritance through heritable changes to gene expression

D2.2.8 Examples of environmental effects on gene expression in cells and organisms

D2.2.9 Consequences of removal of most but not all epigenetic tags from the ovum and sperm

D2.2.10 Monozygotic twin studies

D2.2.11 External factors impacting the pattern of gene expression

D2.3.1 Solvation with water as the solvent

D2.3.2 Water movement from less concentrated to more concentrated solutions

D2.3.3 Water movement by osmosis into or out of cells

D2.3.4 Changes due to water movement in plant tissue

D2.3.5 Effects of water movement on cells that lack a cell wall

D2.3.6 Effects of water movement on cells with a cell wall

D2.3.7 Medical applications of isotonic solutions

D2.3.8 Water potential as the potential energy of water per unit volume (HL)

D2.3.9 Movement of water from higher to lower water potential (HL)

D2.3.10 Contributions of solute potential and pressure potential to the water potential (HL)

D2.3.11 Water potential and water movements in plant tissue (HL)

D3.1.1 Differences between sexual and asexual reproduction

D3.1.2 Role of meiosis and fusion of gametes in the sexual life cycle

D3.1.3 Differences between male and female sexes in sexual reproduction

D3.1.4 Anatomy of the human male and female reproductive systems

D3.1.5 Changes during the ovarian and uterine cycles and their hormonal regulation

D3.1.6 Fertilization in humans

D3.1.7 Use of hormones in in vitro fertilization (IVF) treatment

D3.1.8 Sexual reproduction in flowering plants

D3.1.9 Features of an insect-pollinated flower

D3.1.10 Methods of promoting cross-pollination

D3.1.11 Self-incompatibility mechanisms to increase genetic variation within a species

D3.1.12 Dispersal and germination of seeds

D3.1.13 Control of the developmental changes of puberty (HL)

D3.1.14 Spermatogenesis and oogenesis in humans (HL)

D3.1.15 Mechanisms to prevent polyspermy (HL)

D3.1.16 Development of a blastocyst and implantation in the endometrium (HL)

D3.1.17 Pregnancy testing by detection of human chorionic gonadotropin secretion (HL)

D3.1.18 Role of the placenta in foetal development inside the uterus (HL)

D3.1.19 Hormonal control of pregnancy and childbirth (HL)

D3.1.20 Hormone replacement therapy and the risk of coronary heart disease (HL)

D3.2.1 Production of haploid gametes in parents

D3.2.2 Methods for conducting genetic crosses in flowering plants

D3.2.3 Genotype as the combination of alleles inherited by an organism

D3.2.4 Phenotype

D3.2.5 Effects of dominant and recessive alleles on phenotype

D3.2.6 Phenotypic plasticity

D3.2.7 Phenylketonuria

D3.2.8 Single-nucleotide polymorphisms and multiple alleles in gene pools

D3.2.9 ABO blood groups as an example of multiple alleles

D3.2.10 Incomplete dominance and codominance

D3.2.11 Sex determination in humans and inheritance of genes on sex chromosomes

D3.2.12 Haemophilia as an example of a sex-linked genetic disorder

D3.2.13 Pedigree charts to deduce patterns of inheritance of genetic disorders

D3.2.14 Continuous variation due to polygenic inheritance and/or environmental factors

D3.2.15 Box-and-whisker plots to represent data for a continuous variable such as student height

D3.2.16 Segregation and independent assortment of unlinked genes in meiosis (HL)

D3.2.17 Punnett grids for predicting genotypic and phenotypic ratios in dihybrid crosses (HL)

D3.2.18 Loci of human genes and their polypeptide products (HL)

D3.2.19 Autosomal gene linkage (HL)

D3.2.20 Recombinants in crosses involving two linked or unlinked genes (HL)

D3.2.21 Use of a chi-squared test on data from dihybrid crosses (HL)

D3.3.1 Homeostasis

D3.3.2 Negative feedback loops in homeostasis

D3.3.3 Regulation of blood glucose as an example of the role of hormones in homeostasis

D3.3.4 Physiological changes that form the basis of type 1 and type 2 diabetes

D3.3.5 Thermoregulation as an example of negative feedback control

D3.3.6 Thermoregulation mechanisms in humans

D3.3.7 Role of the kidney in osmoregulation and excretion (HL)

D3.3.8 Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion (HL)

D3.3.9 Role of the loop of Henle (HL)

D3.3.10 Osmoregulation by water reabsorption in the collecting ducts (HL)

D3.3.11 Changes in blood supply to organs in response to changes in activity (HL)

D4.1.1 Natural selection as the mechanism driving evolutionary change

D4.1.2 Roles of mutation and sexual reproduction

D4.1.3 Overproduction of offspring and competition for resources

D4.1.4 Abiotic factors as selection pressures

D4.1.5 Differences between individuals in adaptation, survival and reproduction

D4.1.6 Requirement that traits are heritable for evolutionary change to occur

D4.1.7 Sexual selection as a selection pressure in animal species

D4.1.8 Modelling of sexual and natural selection

D4.1.9 Concept of the gene pool (HL)

D4.1.10 Allele frequencies of geographically isolated populations (HL)

D4.1.11 Changes in allele frequency in the gene pool (HL)

D4.1.12 Differences between directional, disruptive and stabilizing selection (HL)

D4.1.13 Hardy–Weinberg equation and calculations of allele or genotype frequencies (HL)

D4.1.14 Hardy–Weinberg conditions (HL)

D4.1.15 Artificial selection by deliberate choice of traits (HL)

D4.2.1 Stability as a property of natural ecosystems

D4.2.2 Requirements for stability in ecosystems

D4.2.3 Deforestation of Amazon rainforest

D4.2.4 Use of a model to investigate the effect of variables on ecosystem stability

D4.2.5 Role of keystone species in the stability of ecosystems

D4.2.6 Assessing sustainability of resource harvesting from natural ecosystems

D4.2.7 Factors affecting the sustainability of agriculture

D4.2.8 Eutrophication of aquatic and marine ecosystems due to leaching

D4.2.9 Biomagnification of pollutants in natural ecosystems

D4.2.10 Effects of microplastic and macroplastic pollution of the oceans

D4.2.11 Restoration of natural processes in ecosystems by rewilding

D4.2.12 Ecological succession and its causes (HL)

D4.2.13 Changes occurring during primary succession (HL)

D4.2.14 Cyclical succession in ecosystems (HL)

D4.2.15 Climax communities and arrested succession (HL)

D4.3.1 Anthropogenic causes of climate change

D4.3.2 Positive feedback cycles in global warming

D4.3.3 Change from net carbon accumulation to net loss in boreal forests

D4.3.4 Melting of landfast ice and sea ice as examples of polar habitat change

D4.3.5 Changes in ocean currents altering the timing and extent of nutrient upwelling

D4.3.6 Poleward and upslope range shifts of temperate species

D4.3.7 Threats to coral reefs as an example of potential ecosystem collapse

D4.3.8 Afforestation, forest regeneration and restoration of peat-forming wetlands

D4.3.9 Phenology as research into the timing of biological events (HL)

D4.3.10 Disruption to the synchrony of phenological events by climate change (HL)

D4.3.11 Increases to the number of insect life cycles within a year due to climate change (HL)

D4.3.12 Evolution as a consequence of climate change (HL)