IB Group 4 · Sciences

Biology

2025 syllabus · Standard & higher level

Every note below maps to an exact IB understanding statement — nothing more than the syllabus asks, nothing you can be examined on left out.

A. Unity and diversity

Common ancestry and the rich biodiversity that evolution has produced.

A1.1 — Water

A1.1.1 · Water as the medium for life — State that life began in water and that most processes of life still occur in water.

A1.1.2 · Hydrogen bonds as a consequence of the polar covalent bonds within water molecules — Explain how unequal sharing of electrons makes water polar, and how that polarity produces hydrogen bonds between water molecules. Represent them with the correct notation.

A1.1.3 · Cohesion of water molecules due to hydrogen bonding and consequences for organisms — Explain how cohesion lets water be pulled up xylem under tension, and how surface tension makes the water surface a habitat.

A1.1.4 · Adhesion of water to materials that are polar or charged and impacts for organisms — Explain how adhesion causes capillary action, in soil and in plant cell walls.

A1.1.5 · Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals — Explain how water's solvent properties make it the medium for metabolism and for transport in plants and animals, including why some molecules must be insoluble.

A1.1.6 · Physical properties of water and the consequences for animals in aquatic habitats — Contrast, using examples, how the physical properties of water and air have consequences for animals living in each.

A1.1.7 · Extraplanetary origin of water on Earth and reasons for its retention — Explain how water reached Earth from asteroids, and why it has been retained since.

A1.1.8 · Relationship between the search for extraterrestrial life and the presence of water — Explain why the search for extraterrestrial life is a search for liquid water, including the Goldilocks zone.

A1.2 — Nucleic acids

A1.2.1 · DNA as the genetic material of all living organisms — State that DNA is the genetic material of all living organisms, and explain why RNA viruses are not an exception.

A1.2.2 · Components of a nucleotide — Name the three components of a nucleotide, and draw one using the standard symbols.

A1.2.3 · Sugar–phosphate bonding and the sugar–phosphate “backbone” of DNA and RNA — Explain how sugar–phosphate bonding creates a strong backbone that conserves the base sequence.

A1.2.4 · Bases in each nucleic acid that form the basis of a code — Name the bases in DNA and in RNA, and state that their sequence is how information is coded.

A1.2.5 · RNA as a polymer formed by condensation of nucleotide monomers — Explain how RNA is built from nucleotide monomers by condensation, and draw a nucleotide and an RNA polymer.

A1.2.6 · DNA as a double helix made of two antiparallel strands of nucleotides with two strands linked by hydrogen bonding between complementary base pairs — Describe DNA as a double helix of two antiparallel strands held together by complementary base pairing, and draw it.

A1.2.7 · Differences between DNA and RNA — Distinguish DNA from RNA by strand number, bases and sugar, and sketch ribose against deoxyribose.

A1.2.8 · Role of complementary base pairing in allowing genetic information to be replicated and expressed — Explain how complementary base pairing allows genetic information to be replicated and expressed.

A1.2.9 · Diversity of possible DNA base sequences and the limitless capacity of DNA for storing information — Explain why any sequence of any length is possible, and why that gives DNA an enormous storage capacity.

A1.2.10 · Conservation of the genetic code across all life forms as evidence of universal common ancestry — Explain how a genetic code shared by all organisms is evidence of universal common ancestry.

A1.2.11 · Directionality of RNA and DNA — Explain the 5' to 3' directionality of DNA and RNA, and why replication, transcription and translation all follow it.

A1.2.12 · Purine-to-pyrimidine bonding as a component of DNA helix stability — Explain how pairing a purine with a pyrimidine keeps the helix a constant width, and therefore stable.

A1.2.13 · Structure of a nucleosome — Describe the structure of a nucleosome, and use visualization software to examine one.

A1.2.14 · Evidence from the Hershey–Chase experiment for DNA as the genetic material — Explain how the results of the Hershey–Chase experiment show that DNA, not protein, is the genetic material.

A1.2.15 · Chargaff’s data on the relative amounts of pyrimidine and purine bases across diverse life forms — Explain how Chargaff's data falsified the tetranucleotide hypothesis.

A2.1 — Origins of cells

A2.1.1 · Conditions on early Earth and the pre-biotic formation of carbon compounds — Describe conditions on early Earth, and explain how they allowed carbon compounds to form spontaneously.

A2.1.2 · Cells as the smallest units of self-sustaining life — Discuss what separates living from non-living, why the cell is the smallest self-sustaining unit, and why viruses are not living.

A2.1.3 · Challenge of explaining the spontaneous origin of cells — Explain why the spontaneous origin of cells is hard to account for, and name the four developments it required.

A2.1.4 · Evidence for the origin of carbon compounds — Evaluate the Miller–Urey experiment as evidence for the origin of carbon compounds.

A2.1.5 · Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers — Explain how fatty acids spontaneously form spherical bilayers, and why an enclosed compartment matters.

A2.1.6 · RNA as a presumed first genetic material — Explain why RNA is presumed to have been the first genetic material.

A2.1.7 · Evidence for a last universal common ancestor — Give the evidence for a last universal common ancestor.

A2.1.8 · Approaches used to estimate dates of the first living cells and the last universal common ancestor — Outline how the dates of the first cells and of LUCA are estimated.

A2.1.9 · Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents — Give the evidence that LUCA evolved near hydrothermal vents.

A2.2 — Cell structure

A2.2.1 · Cells as the basic structural unit of all living organisms — State that cells are the basic structural unit of all living organisms.

A2.2.2 · Microscopy skills — Carry out core microscopy skills, including measuring with a graticule, calculating magnification and adding a scale bar.

A2.2.3 · Developments in microscopy — Outline the advantages of the main developments in microscopy.

A2.2.4 · Structures common to cells in all living organisms — Describe the structures common to all cells, and explain why each is needed.

A2.2.5 · Prokaryote cell structure — Describe the structure of a prokaryotic cell.

A2.2.6 · Eukaryote cell structure — Describe the structure of a eukaryotic cell.

A2.2.7 · Processes of life in unicellular organisms — List the processes of life carried out by a unicellular organism.

A2.2.8 · Differences in eukaryotic cell structure between animals, fungi and plants — Distinguish animal, fungal and plant cells.

A2.2.9 · Atypical cell structure in eukaryotes — Explain how atypical cells differ from the usual pattern, using their numbers of nuclei.

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

A2.2.11 · Drawing and annotation based on electron micrographs — Draw and annotate cell structures from electron micrographs, including their functions.

A2.2.12 · Origin of eukaryotic cells by endosymbiosis — Explain the endosymbiotic origin of mitochondria and chloroplasts, and the evidence for it.

A2.2.13 · Cell differentiation as the process for developing specialized tissues in multicellular organisms — Explain how differences in gene expression produce specialized tissues.

A2.2.14 · Evolution of multicellularity — Explain how multicellularity evolved repeatedly, and what advantages it brings.

A2.3 — Viruses

A2.3.1 · Structural features common to viruses — State the structural features shared by all viruses.

A2.3.2 · Diversity of structure in viruses — Describe how viruses vary in structure, with examples.

A2.3.3 · Lytic cycle of a virus — Describe the phases of the lytic cycle, using bacteriophage lambda.

A2.3.4 · Lysogenic cycle of a virus — Describe the lysogenic cycle, using bacteriophage lambda.

A2.3.5 · Evidence for several origins of viruses from other organisms — Explain why the diversity of viruses suggests several separate origins.

A2.3.6 · Rapid evolution in viruses — Explain why some viruses evolve very rapidly, and what that means for treating the diseases they cause.

A3.1 — Diversity of organisms

A3.1.1 · Variation between organisms as a defining feature of life — Explain why variation between individuals is a defining feature of life.

A3.1.2 · Species as groups of organisms with shared traits — Define a species as a group sharing traits, the original morphological concept.

A3.1.3 · Binomial system for naming organisms — Explain the binomial system for naming organisms, and its conventions.

A3.1.4 · Biological species concept — State the biological species concept, and discuss the difficulties with it.

A3.1.5 · Difficulties distinguishing between populations and species due to divergence of non- interbreeding populations during speciation — Explain why deciding whether two diverging populations are separate species can be arbitrary.

A3.1.6 · Diversity in chromosome numbers of plant and animal species — State that chromosome number varies between species, using humans and chimpanzees.

A3.1.7 · Karyotyping and karyograms — Classify chromosomes in a karyogram, and evaluate the evidence that human chromosome 2 arose by fusion.

A3.1.8 · Unity and diversity of genomes within species — Explain what a genome is, and how genomes vary within a species.

A3.1.9 · Diversity of eukaryote genomes — Explain how eukaryote genomes vary in size and in base sequence.

A3.1.10 · Comparison of genome sizes — Compare genome size with organism complexity using data from a database.

A3.1.11 · Current and potential future uses of whole genome sequencing — Outline the current and potential future uses of whole genome sequencing.

A3.1.12 · Difficulties applying the biological species concept to asexually reproducing species and to bacteria that have horizontal gene transfer — Explain why the biological species concept fails for asexual species and for bacteria.

A3.1.13 · Chromosome number as a shared trait within a species — Explain why species with different chromosome numbers rarely produce fertile hybrids.

A3.1.14 · Engagement with local plant or animal species to develop a dichotomous key — Develop a dichotomous key for local plant or animal species.

A3.1.15 · Identification of species from environmental DNA in a habitat using barcodes — Explain how environmental DNA and barcodes identify the species present in a habitat.

A3.2 — Classification and cladistics

A3.2.1 · Need for classification of organisms — Explain why organisms need to be classified.

A3.2.2 · Difficulties classifying organisms into the traditional hierarchy of taxa — Explain why the traditional hierarchy of taxa does not always match evolutionary divergence.

A3.2.3 · Advantages of classification corresponding to evolutionary relationships — Explain the advantage of a classification that follows evolutionary relationships.

A3.2.4 · Clades as groups of organisms with common ancestry and shared characteristics — Define a clade, and state what evidence places organisms in the same one.

A3.2.5 · Gradual accumulation of sequence differences as the basis for estimates of when clades diverged from a common ancestor — Explain the molecular clock, and why it gives only estimates of divergence times.

A3.2.6 · Base sequences of genes or amino acid sequences of proteins as the basis for constructing cladograms — Construct a cladogram from base or amino acid sequence data.

A3.2.7 · Analysing cladograms — Deduce evolutionary relationships, common ancestors and clades from a cladogram.

A3.2.8 · Using cladistics to investigate whether the classification of groups corresponds to evolutionary relationships — Explain how cladistics is used to test whether an existing classification matches evolution.

A3.2.9 · Classification of all organisms into three domains using evidence from rRNA base sequences — State the classification of all organisms into three domains, based on rRNA sequences.

A4.1 — Evolution and speciation

A4.1.1 · Evolution as change in the heritable characteristics of a population — Define evolution as change in the heritable characteristics of a population, and distinguish it from Lamarckism.

A4.1.2 · Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins — Explain how DNA, RNA and protein sequence data give evidence of common ancestry.

A4.1.3 · Evidence for evolution from selective breeding of domesticated animals and crop plants — Explain how selective breeding of domesticated species is evidence for evolution.

A4.1.4 · Evidence for evolution from homologous structures — Explain how homologous structures are evidence for evolution, using the pentadactyl limb.

A4.1.5 · Convergent evolution as the origin of analogous structures — Explain how convergent evolution produces analogous structures, with an example.

A4.1.6 · Speciation by splitting of pre-existing species — Explain that new species arise only by the splitting of existing species.

A4.1.7 · Roles of reproductive isolation and differential selection in speciation — Explain the roles of reproductive isolation and differential selection in speciation.

A4.1.8 · Differences and similarities between sympatric and allopatric speciation — Give the differences and the similarities between sympatric and allopatric speciation.

A4.1.9 · Adaptive radiation as a source of biodiversity — Explain how adaptive radiation increases biodiversity.

A4.1.10 · Barriers to hybridization and sterility of interspecific hybrids as mechanisms for of preventing the mixing of alleles between species — Explain how barriers to hybridization and hybrid sterility keep species separate.

A4.1.11 · Abrupt speciation in plants by hybridization and polyploidy — Explain how hybridization and polyploidy cause abrupt speciation in plants.

A4.2 — Conservation of biodiversity

A4.2.1 · Biodiversity as the variety of life in all its forms, levels and combinations — Define biodiversity, at its three levels.

A4.2.2 · Comparisons between current number of species on Earth and past levels of biodiversity — Compare the current number of species on Earth with past levels of biodiversity.

A4.2.3 · Causes of anthropogenic species extinction — Explain the causes of the current, human-driven extinction of species, using case studies.

A4.2.4 · Causes of ecosystem loss — Explain the human causes of ecosystem loss, using case studies.

A4.2.5 · Evidence for a biodiversity crisis — Evaluate the evidence for a biodiversity crisis.

A4.2.6 · Causes of the current biodiversity crisis — Explain the causes of the biodiversity crisis, from population growth down to the specific pressures.

A4.2.7 · Need for several approaches to conservation of biodiversity — Explain why conserving biodiversity needs several different approaches.

A4.2.8 · Selection of evolutionarily distinct and globally endangered species for conservation prioritization in the EDGE of Existence programme — Explain the rationale for prioritizing evolutionarily distinct and globally endangered species.

B. Form and function

How adaptations of form correspond to biological function at every scale.

B1.1 — Carbohydrates and lipids

B1.1.1 · Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based — Explain how carbon's four covalent bonds allow chains, branches and rings, and give examples of each.

B1.1.2 · Production of macromolecules by condensation reactions that link monomers to form a polymer — Explain condensation, and name examples of polysaccharides, polypeptides and nucleic acids.

B1.1.3 · Digestion of polymers into monomers by hydrolysis reactions — Explain hydrolysis, including how the split water supplies the -H and -OH the monomers take up.

B1.1.4 · Form and function of monosaccharides — Recognize pentoses and hexoses from ring diagrams, and link glucose's four properties to how it is used.

B1.1.5 · Polysaccharides as energy storage compounds — Explain why starch and glycogen suit energy storage: compact, insoluble, and easy to build up or mobilize.

B1.1.6 · Structure of cellulose related to its function as a structural polysaccharide in plants — Explain how alternating beta-glucose gives straight chains, bundled and cross-linked by hydrogen bonds.

B1.1.7 · Role of glycoproteins in cell–cell recognition — Explain how glycoproteins allow cell-cell recognition, using ABO antigens.

B1.1.8 · Hydrophobic properties of lipids — Define lipids by their solubility, and name the four classes.

B1.1.9 · Formation of triglycerides and phospholipids by condensation reactions — Explain how condensation builds a triglyceride and a phospholipid from glycerol.

B1.1.10 · Difference between saturated, monounsaturated and polyunsaturated fatty acids — Distinguish saturated, monounsaturated and polyunsaturated by C=C bonds, and link this to melting point.

B1.1.11 · Triglycerides in adipose tissues for energy storage and thermal insulation — Explain why triglycerides suit long-term storage, and relate their insulating role to habitat.

B1.1.12 · Formation of phospholipid bilayers as a consequence of the hydrophobic and hydrophilic regions — Explain why amphipathic phospholipids form bilayers on their own.

B1.1.13 · Ability of non-polar steroids to pass through the phospholipid bilayer — Identify a steroid from a diagram, and explain why non-polar steroids cross the bilayer.

B1.2 — Proteins

B1.2.1 · Generalized structure of an amino acid — Draw a generalized amino acid: alpha carbon with amine group, carboxyl group, R-group and hydrogen.

B1.2.2 · Condensation reactions forming dipeptides and longer chains of amino acids — Write the word equation for condensation and draw a generalized dipeptide.

B1.2.3 · Dietary requirements for amino acids — Distinguish essential from non-essential amino acids, and explain why vegan diets need planning.

B1.2.4 · Infinite variety of possible peptide chains — Explain why the variety of peptide chains is effectively infinite, and name examples of polypeptides.

B1.2.5 · Effect of pH and temperature on protein structure — Explain how pH and temperature denature proteins.

B1.2.6 · Chemical diversity in the R-groups of amino acids as a basis for the immense diversity in protein form and function — Explain how R-groups determine a protein's properties, and how they divide by hydrophobicity and charge.

B1.2.7 · Impact of primary structure on the conformation of proteins — Explain why the amino acid sequence determines a protein's precise, predictable three-dimensional shape.

B1.2.8 · Pleating and coiling of secondary structure of proteins — Explain how hydrogen bonding stabilizes alpha helices and beta-pleated sheets.

B1.2.9 · Dependence of tertiary structure on hydrogen bonds, ionic bonds, disulfide covalent bonds and hydrophobic interactions — Explain the four bonds holding tertiary structure, and how R-groups become charged.

B1.2.10 · Effect of polar and non-polar amino acids on tertiary structure of proteins — Explain why hydrophobic amino acids cluster in a globular core, and form the membrane-embedded belt.

B1.2.11 · Quaternary structure of non-conjugated and conjugated proteins — Explain quaternary structure using insulin and collagen (non-conjugated) and haemoglobin (conjugated).

B1.2.12 · Relationship of form and function in globular and fibrous proteins — Contrast globular and fibrous protein shape, and relate each to function using insulin and collagen.

B2.1 — Membranes and membrane transport

B2.1.1 · Lipid bilayers as the basis of cell membranes — Explain how amphipathic lipids form continuous sheet-like bilayers in water.

B2.1.2 · Lipid bilayers as barriers — Explain why the hydrophobic core blocks large molecules, ions and polar molecules.

B2.1.3 · Simple diffusion across membranes — Explain simple diffusion using oxygen and carbon dioxide moving between phospholipids.

B2.1.4 · Integral and peripheral proteins in membranes — Distinguish integral from peripheral proteins by where they sit in the membrane.

B2.1.5 · Movement of water molecules across membranes by osmosis and the role of aquaporins — Explain osmosis in terms of random motion, solute concentration and impermeability, plus aquaporins.

B2.1.6 · Channel proteins for facilitated diffusion — Explain how channel proteins make a membrane selectively permeable, and how gating changes it.

B2.1.7 · Pump proteins for active transport — Explain how pump proteins use ATP to move particles against the concentration gradient.

B2.1.8 · Selectivity in membrane permeability — Explain why facilitated diffusion and active transport are selective, but simple diffusion is not.

B2.1.9 · Structure and function of glycoproteins and glycolipids — Describe glycoproteins and glycolipids, and their roles in cell adhesion and cell recognition.

B2.1.10 · Fluid mosaic model of membrane structure — Draw the fluid mosaic model, labelling proteins, phospholipids, cholesterol and the hydrophobic region.

B2.1.11 · Relationships between fatty acid composition of lipid bilayers and their fluidity — Explain how saturated and unsaturated fatty acids change fluidity, with an example adapted to habitat.

B2.1.12 · Cholesterol and membrane fluidity in animal cells — Explain where cholesterol sits, and how it modulates fluidity at both high and low temperatures.

B2.1.13 · Membrane fluidity and the fusion and formation of vesicles — Explain endocytosis and exocytosis as consequences of membrane fluidity, with examples of each.

B2.1.14 · Gated ion channels in neurons — Explain neurotransmitter-gated and voltage-gated ion channels in neurons.

B2.1.15 · Sodium–potassium pumps as an example of exchange transporters — Explain the sodium-potassium pump as an exchange transporter, and how it generates membrane potentials.

B2.1.16 · Sodium-dependent glucose cotransporters as an example of indirect active transport — Explain sodium-dependent glucose cotransport in the small intestine and the nephron.

B2.1.17 · Adhesion of cells to form tissues — Explain how cell-adhesion molecules bind cells into tissues.

B2.2 — Organelles and compartmentalization

B2.2.1 · Organelles as discrete subunits of cells that are adapted to perform specific functions — State which structures are organelles and which are not, and why.

B2.2.2 · Advantage of the separation of the nucleus and cytoplasm into separate compartments — Explain how separating the nucleus allows mRNA to be modified before it meets ribosomes.

B2.2.3 · Advantages of compartmentalization in the cytoplasm of cells — Explain how compartmentalization concentrates enzymes and separates incompatible processes.

B2.2.4 · Adaptations of the mitochondrion for production of ATP by aerobic cell respiration — Explain three mitochondrial adaptations: double membrane, cristae, and the enzyme-filled matrix.

B2.2.5 · Adaptations of the chloroplast for photosynthesis — Explain three chloroplast adaptations: thylakoid area, small thylakoid volume, and the stroma.

B2.2.6 · Functional benefits of the double membrane of the nucleus — Explain why the nucleus needs a double membrane: large pores, and breaking into vesicles during division.

B2.2.7 · Structure and function of free ribosomes and of the rough endoplasmic reticulum — Contrast free ribosomes (proteins kept in the cell) with rough ER ribosomes (proteins for export).

B2.2.8 · Structure and function of the Golgi apparatus — Explain the Golgi apparatus in processing and secreting protein.

B2.2.9 · Structure and function of vesicles in cells — Explain vesicle structure and function, including the role of clathrin in forming them.

B2.3 — Cell specialization

B2.3.1 · Production of unspecialized cells following fertilization and their development into specialized cells by differentiation — Explain differentiation, and how gradients of signalling chemicals control gene expression in the embryo.

B2.3.2 · Properties of stem cells — State the two properties of stem cells: endless division, and differentiation along different pathways.

B2.3.3 · Location and function of stem cell niches in adult humans — Describe two stem cell niches in adults, and how a niche either maintains or activates the cells.

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

B2.3.5 · Cell size as an aspect of specialization — Explain how the size of a human cell is itself an adaptation to its function.

B2.3.6 · Surface area-to-volume ratios and constraints on cell size — Explain why exchange depends on surface area while the need for it depends on volume.

B2.3.7 · Adaptations to increase surface area-to-volume ratios of cells — Explain flattening, microvilli and invagination, using erythrocytes and proximal tubule cells.

B2.3.8 · Adaptations of type I and type II pneumocytes in alveoli — Contrast type I pneumocytes (thinness) with type II (surfactant), in one tissue with two cell types.

B2.3.9 · Adaptations of cardiac muscle cells and striated muscle fibres — Contrast cardiac and striated muscle by branching, length and nuclei; discuss whether a fibre is a cell.

B2.3.10 · Adaptations of sperm and egg cells — Explain the adaptations of human sperm and egg cells.

B3.1 — Gas exchange

B3.1.1 · Gas exchange as a vital function in all organisms — Explain why gas exchange gets harder with size, as SA:V falls and diffusion distance rises.

B3.1.2 · Properties of gas-exchange surfaces — State the four properties of a gas-exchange surface: permeable, large, moist and thin.

B3.1.3 · Maintenance of concentration gradients at exchange surfaces in animals — Explain how capillary networks, blood flow and ventilation maintain concentration gradients.

B3.1.4 · Adaptations of mammalian lungs for gas exchange — Explain four adaptations of mammalian lungs: surfactant, bronchioles, capillary beds, surface area.

B3.1.5 · Ventilation of the lungs — Explain ventilation using the diaphragm, intercostal muscles, abdominal muscles and ribs.

B3.1.6 · Measurement of lung volumes — Measure tidal volume, vital capacity, and the inspiratory and expiratory reserves.

B3.1.7 · Adaptations for gas exchange in leaves — Explain six leaf adaptations for gas exchange, from waxy cuticle to veins.

B3.1.8 · Distribution of tissues in a leaf — Draw and label a plan diagram of a transverse section of a dicotyledonous leaf.

B3.1.9 · Transpiration as a consequence of gas exchange in a leaf — Explain transpiration as a consequence of gas exchange, and the factors affecting its rate.

B3.1.10 · Stomatal density — Determine stomatal density from micrographs or leaf casts, using repeat counts.

B3.1.11 · Adaptations of foetal and adult haemoglobin for the transport of oxygen — Explain cooperative binding and allosteric CO2 binding, and why foetal haemoglobin binds more strongly.

B3.1.12 · Bohr shift — Explain how increased carbon dioxide increases oxygen dissociation, and why that helps active tissue.

B3.1.13 · Oxygen dissociation curves as a means of representing the affinity of haemoglobin for oxygen at different oxygen concentrations — Explain the S-shape of the oxygen dissociation curve, and how to read a shifted curve.

B3.2 — Transport

B3.2.1 · Adaptations of capillaries for exchange of materials between blood and the internal or external environment — Explain three capillary adaptations: large surface area, thin walls, and fenestrations.

B3.2.2 · Structure of arteries and veins — Distinguish arteries from veins in micrographs by wall structure and thickness relative to the lumen.

B3.2.3 · Adaptations of arteries for the transport of blood away from the heart — Explain how muscle and elastic tissue let arteries withstand and maintain high blood pressure.

B3.2.4 · Measurement of pulse rates — Determine heart rate from the carotid or radial pulse, and compare with a digital method.

B3.2.5 · Adaptations of veins for the return of blood to the heart — Explain two vein adaptations: valves preventing backflow, and a wall flexible enough to be compressed.

B3.2.6 · Causes and consequences of occlusion of the coronary arteries — Explain the causes and consequences of coronary occlusion, and evaluate the epidemiological evidence.

B3.2.7 · Transport of water from roots to leaves during transpiration — Explain how transpiration generates tension in xylem, and how cohesion keeps the column continuous.

B3.2.8 · Adaptations of xylem vessels for transport of water — Explain four xylem adaptations: no contents, open end walls, lignified walls and pits.

B3.2.9 · Distribution of tissues in a transverse section of the stem of a dicotyledonous plant — Draw a plan diagram of a dicot stem, annotated with the function of each tissue.

B3.2.10 · Distribution of tissues in a transverse section of the root of a dicotyledonous plant — Draw a plan diagram of a dicot root, identifying the vascular tissue, cortex and epidermis.

B3.2.11 · Release and reuptake of tissue fluid in capillaries — Explain how pressure filtration forms tissue fluid near arterioles and reabsorbs it near venules.

B3.2.12 · Exchange of substances between tissue fluid and cells in tissues — Compare plasma and tissue fluid, and explain how cells exchange substances with it.

B3.2.13 · Drainage of excess tissue fluid into lymph ducts — Describe how lymph ducts drain excess tissue fluid and return it to the blood.

B3.2.14 · Differences between the single circulation of bony fish and the double circulation of mammals — Contrast the single circulation of bony fish with the double circulation of mammals.

B3.2.15 · Adaptations of the mammalian heart for delivering pressurized blood to the arteries — Explain the form-function adaptations of the heart, and trace the flow from named veins to arteries.

B3.2.16 · Stages in the cardiac cycle — Explain the cardiac cycle following the sinoatrial node, and interpret blood pressure data.

B3.2.17 · Generation of root pressure in xylem vessels by active transport of mineral ions — Explain how active transport of mineral ions generates root pressure when transpiration is insufficient.

B3.2.18 · Adaptations of phloem sieve tubes and companion cells for translocation of sap — Explain phloem adaptations, and how pressure differences drive sap from sources to sinks.

B3.3 — Muscle and motility

B3.3.1 · Adaptations for movement as a universal feature of living organisms — Explain movement as universal, considering one motile and one sessile species.

B3.3.2 · Sliding filament model of muscle contraction — Explain how a sarcomere contracts by actin and myosin filaments sliding.

B3.3.3 · Role of the protein titin and antagonistic muscles in muscle relaxation — Explain titin's role in recoil, and why muscles need antagonistic partners to lengthen.

B3.3.4 · Structure and function of motor units in skeletal muscle — Describe the motor unit: the motor neuron, its muscle fibres, and the neuromuscular junctions.

B3.3.5 · Roles of skeletons as anchorage for muscles and as levers — Explain how skeletons anchor muscles and act as levers, contrasting exoskeletons and endoskeletons.

B3.3.6 · Movement at a synovial joint — Explain movement at the human hip joint, naming the femur and pelvis.

B3.3.7 · Range of motion of a joint — Measure and compare a joint's range of motion in several dimensions.

B3.3.8 · Internal and external intercostal muscles as an example of antagonistic muscle action to facilitate internal body movements — Explain how internal and external intercostal muscles act antagonistically to move the ribcage.

B3.3.9 · Reasons for locomotion — Give four reasons for locomotion, with at least one example of each.

B3.3.10 · Adaptations for swimming in marine mammals — Explain adaptations for swimming in marine mammals: streamlining, flippers, flukes and airways.

B4.1 — Adaptation to environment

B4.1.1 · Habitat as the place in which a community, species, population or organism lives — Define habitat, including geographical location, physical conditions and ecosystem type.

B4.1.2 · Adaptations of organisms to the abiotic environment of their habitat — Explain adaptations to the abiotic environment, using a dune grass and a mangrove tree.

B4.1.3 · Abiotic variables affecting species distribution — Give abiotic variables affecting plant and animal distribution, and explain range of tolerance.

B4.1.4 · Range of tolerance of a limiting factor — Use transect data you collect yourself to correlate species distribution with an abiotic variable.

B4.1.5 · Conditions required for coral reef formation — Explain the five conditions required for coral reef formation.

B4.1.6 · Abiotic factors as the determinants of terrestrial biome distribution — Explain how temperature and rainfall determine which biome develops.

B4.1.7 · Biomes as groups of ecosystems with similar communities due to similar abiotic conditions and convergent evolution — Explain biome similarity through convergent evolution, and state the climate of each of the six biomes.

B4.1.8 · Adaptations to life in hot deserts and tropical rainforest — Give named plant and animal adaptations to hot deserts and to tropical rainforest.

B4.2 — Ecological niches

B4.2.1 · Ecological niche as the role of a species in an ecosystem — Define ecological niche, including the biotic and abiotic interactions and how a species obtains food.

B4.2.2 · Differences between organisms that are obligate anaerobes, facultative anaerobes and obligate aerobes — Distinguish obligate anaerobes, facultative anaerobes and obligate aerobes by oxygen tolerance.

B4.2.3 · Photosynthesis as the mode of nutrition in plants, algae and several groups of photosynthetic prokaryotes — State the three groups that photosynthesize: plants, algae and some prokaryotes.

B4.2.4 · Holozoic nutrition in animals — Explain holozoic nutrition: food ingested, digested internally, absorbed and assimilated.

B4.2.5 · Mixotrophic nutrition in some protists — Explain mixotrophic nutrition using Euglena, distinguishing obligate from facultative mixotrophs.

B4.2.6 · Saprotrophic nutrition in some fungi and bacteria — Explain saprotrophic nutrition in fungi and bacteria, and why they are called decomposers.

B4.2.7 · Diversity of nutrition in archaea — Explain how archaea use light, inorganic chemicals or carbon compounds to produce ATP.

B4.2.8 · Relationship between dentition and the diet of omnivorous and herbivorous representative members of the family Hominidae — Infer diet from dentition in the Hominidae, using human, floresiensis and Paranthropus skulls.

B4.2.9 · Adaptations of herbivores for feeding on plants and of plants for resisting herbivory — Explain herbivore mouthparts, and how plants resist herbivory with structures and toxic compounds.

B4.2.10 · Adaptations of predators for finding, catching and killing prey and of prey animals for resisting predation — Explain chemical, physical and behavioural adaptations in both predators and prey.

B4.2.11 · Adaptations of plant form for harvesting light — Explain six strategies plants use to harvest light in forests.

B4.2.12 · Fundamental and realized niches — Distinguish fundamental niche (potential) from realized niche (actual, under competition).

B4.2.13 · Competitive exclusion and the uniqueness of ecological niches — Explain competitive exclusion, including both outcomes: elimination, or restriction of both species.

C. Interaction and interdependence

Systems whose interacting parts produce emergent properties.

C1.1 — Enzymes and metabolism

C1.1.1 · Enzymes as catalysts — Define catalyst and enzyme, and explain why cells need reactions speeded up.

C1.1.2 · Role of enzymes in metabolism — Explain metabolism as a network of pathways, and why enzyme specificity gives cells control.

C1.1.3 · Anabolic and catabolic reactions — Distinguish anabolism from catabolism, with examples of each.

C1.1.4 · Enzymes as globular proteins with an active site for catalysis — Explain the active site, and why the enzyme's whole 3D structure matters.

C1.1.5 · Interactions between substrate and active site to allow induced-fit binding — Explain induced-fit binding, and why it replaced the lock-and-key model.

C1.1.6 · Role of molecular motion and substrate-active site collisions in enzyme catalysis — Explain how molecular motion brings substrate and active site together, and which partner moves.

C1.1.7 · Relationships between the structure of the active site, enzyme–substrate specificity and denaturation — Explain how active site structure gives specificity, and why that makes enzymes easy to denature.

C1.1.8 · Effects of temperature, pH and substrate concentration on the rate of enzyme activity — Explain the effects of temperature, pH and substrate concentration, and interpret the graphs.

C1.1.9 · Measurements in enzyme-catalysed reactions — Determine reaction rates experimentally, controlling variables correctly.

C1.1.10 · Effect of enzymes on activation energy — Explain how enzymes lower activation energy, and interpret the energy graphs.

C1.1.11 · Intracellular and extracellular enzyme-catalysed reactions — Contrast intracellular and extracellular enzymes, with examples of each.

C1.1.12 · Generation of heat energy by the reactions of metabolism — Explain why metabolism inevitably generates heat, and which animals depend on it.

C1.1.13 · Cyclical and linear pathways in metabolism — Contrast linear and cyclical pathways, using glycolysis, the Krebs cycle and the Calvin cycle.

C1.1.14 · Allosteric sites and non-competitive inhibition — Explain allosteric sites and how non-competitive inhibitors work.

C1.1.15 · Competitive inhibition as a consequence of an inhibitor binding reversibly to an active site — Explain competitive inhibition using statins, and contrast it with non-competitive inhibition.

C1.1.16 · Regulation of metabolic pathways by feedback inhibition — Explain end-product feedback inhibition, using the isoleucine pathway.

C1.1.17 · Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor — Explain mechanism-based inhibition using penicillin, including how resistance arises.

C1.2 — Cell respiration

C1.2.1 · ATP as the molecule that distributes energy within cells — Explain why ATP's properties suit it to distributing energy within cells.

C1.2.2 · Life processes within cells that ATP supplies with energy — Give the three kinds of cell activity that ATP supplies with energy.

C1.2.3 · Energy transfers during interconversions between ATP and ADP — Explain the energy transfers between ATP and ADP, and where the energy to rebuild ATP comes from.

C1.2.4 · Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds — Explain cell respiration as ATP production from oxidizing carbon compounds, and its link to gas exchange.

C1.2.5 · Differences between anaerobic and aerobic cell respiration in humans — Contrast aerobic and anaerobic respiration in humans, and explain the oxygen debt.

C1.2.6 · Variables affecting the rate of cell respiration — Measure respiration rate with a respirometer, controlling temperature and pressure.

C1.2.7 · Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration — Explain oxidation and reduction, and NAD's role as a hydrogen carrier.

C1.2.8 · Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD — Explain the four stages of glycolysis and its net yield per glucose.

C1.2.9 · Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration — Explain how converting pyruvate to lactate regenerates NAD.

C1.2.10 · Anaerobic cell respiration in yeast and its use in brewing and baking — Explain ethanol fermentation in yeast and its use in brewing and baking.

C1.2.11 · Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration — Explain the link reaction, and why pyruvate must first enter the mitochondrion.

C1.2.12 · Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD — Explain the Krebs cycle and state the net effects of one turn.

C1.2.13 · Transfer of energy by reduced NAD to the electron transport chain in the mitochondrion — Explain how reduced NAD delivers energy to the electron transport chain.

C1.2.14 · Generation of a proton gradient by flow of electrons along the electron transport chain — Explain how electron flow pumps protons to generate a gradient.

C1.2.15 · Chemiosmosis and the synthesis of ATP in the mitochondrion — Explain chemiosmosis and how ATP synthase uses rotation to make ATP.

C1.2.16 · Role of oxygen as terminal electron acceptor in aerobic cell respiration — Explain oxygen as terminal electron acceptor, and why everything stops without it.

C1.2.17 · Differences between lipids and carbohydrates as respiratory substrates — Contrast lipids and carbohydrates as respiratory substrates.

C1.3 — Photosynthesis

C1.3.1 · Transformation of light energy to chemical energy when carbon compounds are produced in photosynthesis — Explain photosynthesis as the conversion of light energy into chemical energy.

C1.3.2 · Conversion of carbon dioxide to glucose in photosynthesis using hydrogen obtained by splitting water — Write the word equation, and explain how splitting water supplies hydrogen.

C1.3.3 · Oxygen as a by-product of photosynthesis in plants, algae and cyanobacteria — State that oxygen is a by-product of photolysis, and name the three groups that photosynthesize.

C1.3.4 · Separation and identification of photosynthetic pigments by chromatography — Separate photosynthetic pigments by chromatography and identify them by colour and Rf value.

C1.3.5 · Absorption of specific wavelengths of light by photosynthetic pigments — Explain why pigments absorb only certain wavelengths, and interpret absorption spectra.

C1.3.6 · Similarities and differences of absorption and action spectra — Compare absorption and action spectra, and plot an action spectrum from rate data.

C1.3.7 · Techniques for varying concentrations of carbon dioxide, light intensity or temperature experimentally to investigate the effects of limiting factors on the rate of photosynthesis — Vary carbon dioxide, light intensity or temperature to test limiting factors.

C1.3.8 · Carbon dioxide enrichment experiments as a means of predicting future rates of photosynthesis and plant growth — Explain greenhouse and FACE carbon dioxide enrichment experiments, and the lab-versus-field trade-off.

C1.3.9 · Photosystems as arrays of pigment molecules that can generate and emit excited electrons — Explain photosystems as pigment arrays that funnel energy to a reaction centre.

C1.3.10 · Advantages of the structured array of different types of pigment molecules in a photosystem — Explain the two advantages of a structured array over a single pigment molecule.

C1.3.11 · Generation of oxygen by the photolysis of water in photosystem II — Explain photolysis in photosystem II, and its consequences for Earth's atmosphere.

C1.3.12 · ATP production by chemiosmosis in thylakoids — Explain ATP production by chemiosmosis in thylakoids, from cyclic and non-cyclic sources.

C1.3.13 · Reduction of NADP by photosystem I — Explain how photosystem I reduces NADP, and how the two photosystems are linked.

C1.3.14 · Thylakoids as systems for performing the light-dependent reactions of photosynthesis — State where photolysis, ATP synthesis and NADP reduction happen in a thylakoid.

C1.3.15 · Carbon fixation by Rubisco — Explain carbon fixation by Rubisco, and why so much of the enzyme is needed.

C1.3.16 · Synthesis of triose phosphate using reduced NADP and ATP — Explain how ATP and reduced NADP convert glycerate 3-phosphate to triose phosphate.

C1.3.17 · Regeneration of RuBP in the Calvin cycle using ATP — Explain why five-sixths of triose phosphate must regenerate RuBP.

C1.3.18 · Synthesis of carbohydrates, amino acids and other carbon compounds using the products of the — Explain how Calvin cycle products plus mineral nutrients build all other carbon compounds.

C1.3.19 · Interdependence of the light-dependent and light-independent reactions — Explain why the two halves of photosynthesis depend on each other, and which limits the rate.

C2.1 — Chemical signalling

C2.1.1 · Receptors as proteins with binding sites for specific signalling chemicals — Explain receptors as proteins with ligand-binding sites, and how they differ from enzymes.

C2.1.2 · Cell signalling by bacteria in quorum sensing — Explain quorum sensing, and why the activities it triggers need a crowd.

C2.1.3 · Hormones, neurotransmitters, cytokines and calcium ions as examples of functional categories of signalling chemicals in animals — Describe hormones, neurotransmitters, cytokines and calcium ions as functional categories.

C2.1.4 · Chemical diversity of hormones and neurotransmitters — State the two requirements of a signalling chemical, and the chemical categories of each type.

C2.1.5 · Localized and distant effects of signalling molecules — Contrast localized and distant effects of signalling molecules.

C2.1.6 · Differences between transmembrane receptors in a plasma membrane and intracellular receptors in the cytoplasm or nucleus — Explain why some receptors are transmembrane and others intracellular.

C2.1.7 · Initiation of signal transduction pathways by receptors — Contrast signal transduction via transmembrane and via intracellular receptors.

C2.1.8 · Transmembrane receptors for neurotransmitters and changes to membrane potential — Explain how neurotransmitter receptors change membrane potential.

C2.1.9 · Transmembrane receptors that activate G proteins — Explain how a ligand binding a GPCR activates G protein.

C2.1.10 · Mechanism of action of epinephrine (adrenaline) receptors — Explain the epinephrine pathway, and how a secondary messenger amplifies the signal.

C2.1.11 · Transmembrane receptors with tyrosine kinase activity — Explain tyrosine kinase receptors using insulin and glucose transporters.

C2.1.12 · Intracellular receptors that affect gene expression — Explain how steroid hormones use intracellular receptors to change gene expression.

C2.1.13 · Effects of the hormones oestradiol and progesterone on target cells — Explain the effects of oestradiol and progesterone on their target cells.

C2.1.14 · Regulation of cell signalling pathways by positive and negative feedback — Contrast positive and negative feedback in cell signalling, with an example of each.

C2.2 — Neural signalling

C2.2.1 · Neurons as cells within the nervous system that carry electrical impulses — Describe neurons and the structures that carry impulses.

C2.2.2 · Generation of the resting potential by pumping to establish and maintain concentration gradients of sodium and potassium ions — Explain the three factors that generate and maintain the resting potential.

C2.2.3 · Nerve impulses as action potentials that are propagated along nerve fibres — Explain depolarization and repolarization, and how impulses are propagated one way.

C2.2.4 · Variation in the speed of nerve impulses — Explain how diameter and myelination change impulse speed, and apply correlation coefficients.

C2.2.5 · Synapses as junctions between neurons and between neurons and effector cells — Describe the three types of synapse, and explain why signals pass one way only.

C2.2.6 · Release of neurotransmitters from a presynaptic membrane — Explain how calcium influx triggers neurotransmitter release.

C2.2.7 · Generation of an excitatory postsynaptic potential — Explain how an excitatory postsynaptic potential is generated and then ended.

C2.2.8 · Depolarization and repolarization during action potentials — Explain voltage-gating and the sequence of an action potential.

C2.2.9 · Propagation of an action potential along a nerve fibre/axon as a result of local currents — Explain how local currents propagate the action potential along an axon.

C2.2.10 · Oscilloscope traces showing resting potentials and action potentials — Read resting and action potentials from an oscilloscope trace.

C2.2.11 · Saltatory conduction in myelinated fibres to achieve faster impulses — Explain saltatory conduction and why myelination speeds impulses up.

C2.2.12 · Effects of exogenous chemicals on synaptic transmission — Explain how neonicotinoids block transmission and how cocaine blocks reuptake.

C2.2.13 · Inhibitory neurotransmitters and generation of inhibitory postsynaptic potentials — Explain inhibitory postsynaptic potentials, contrasting GABA with acetylcholine.

C2.2.14 · Summation of the effects of excitatory and inhibitory neurotransmitters in a postsynaptic neuron — Explain summation of excitatory and inhibitory inputs, and why it underlies decision-making.

C2.2.15 · Perception of pain by neurons with free nerve endings in the skin — Explain how pain receptors generate impulses, and where pain is actually perceived.

C2.2.16 · Consciousness as a property that emerges from the interaction of individual neurons in the brain — Explain consciousness as an emergent property, and what can and cannot be claimed about it.

C3.1 — Integration of body systems

C3.1.1 · System integration — Explain system integration and its dependence on communication between components.

C3.1.2 · Cells, tissues, organs and body systems as a hierarchy of subsystems that are integrated in a multicellular living organism — Explain the hierarchy from organelles to organism, and why emergent properties arise.

C3.1.3 · Integration of organs in animal bodies by hormonal and nervous signalling and by transport of materials and energy — Contrast hormonal and nervous signalling, and explain transport by the circulatory system.

C3.1.4 · The brain as a central information integration organ — Explain the brain's four roles as the central integrating organ.

C3.1.5 · The spinal cord as an integrating centre for unconscious processes — Contrast unconscious and conscious processes, and where each is coordinated.

C3.1.6 · Input to the spinal cord and cerebral hemispheres through sensory neurons — Explain how sensory input reaches the spinal cord and cerebral hemispheres.

C3.1.7 · Output from the cerebral hemispheres to muscles through motor neurons — Explain how motor output reaches muscles from the cerebral hemispheres.

C3.1.8 · Nerves as bundles of nerve fibres of both sensory and motor neurons — Describe nerves as bundles of sensory and motor fibres.

C3.1.9 · Pain reflex arcs as an example of involuntary responses with skeletal muscle as the effector — Explain the pain reflex arc and its five components.

C3.1.10 · Role of the cerebellum in coordinating skeletal muscle contraction and balance — Explain what the cerebellum does, and what it does not do.

C3.1.11 · Modulation of sleep patterns by melatonin secretion as a part of circadian rhythms — Explain how melatonin modulates sleep, and how the rhythm stays synchronized with day and night.

C3.1.12 · Epinephrine (adrenaline) secretion by the adrenal glands to prepare the body for vigorous activity — Explain how epinephrine redistributes blood to prepare for vigorous activity.

C3.1.13 · Control of the endocrine system by the hypothalamus and pituitary gland — Explain how the hypothalamus and pituitary control the endocrine system.

C3.1.14 · Feedback control of heart rate following sensory input from baroreceptors and chemoreceptors — Explain feedback control of heart rate from baroreceptors and chemoreceptors.

C3.1.15 · Feedback control of ventilation rate following sensory input from chemoreceptors — Explain feedback control of ventilation rate, and why pH is what is monitored.

C3.1.16 · Control of peristalsis in the digestive system by the central nervous system and enteric nervous system — Explain peristalsis, and how the enteric and central nervous systems divide control.

C3.1.17 · Observations of tropic responses in seedlings — Observe tropic responses in seedlings, distinguishing qualitative from quantitative measures.

C3.1.18 · Positive phototropism as a directional growth response to lateral light in plant shoots — Explain positive phototropism as differential growth, and its benefit.

C3.1.19 · Phytohormones as signalling chemicals controlling growth, development and response to stimuli in plants — Explain what phytohormones control, with examples.

C3.1.20 · Auxin efflux carriers as an example of maintaining concentration gradients of phytohormones — Explain how auxin efflux carriers and the acid trap build a concentration gradient.

C3.1.21 · Promotion of cell growth by auxin — Explain how auxin acidifies the cell wall to allow it to extend.

C3.1.22 · Interactions between auxin and cytokinin as a means of regulating root and shoot growth — Explain apical dominance as the interaction of auxin and cytokinin.

C3.1.23 · Positive feedback in fruit ripening and ethylene production — Explain the positive feedback loop between ethylene and fruit ripening.

C3.2 — Defence against disease

C3.2.1 · Pathogens as the cause of infectious diseases — Define pathogen, name examples from each group, and place viruses and parasites correctly.

C3.2.2 · Skin and mucous membranes as a primary defence — Explain how skin and mucous membranes prevent pathogens entering.

C3.2.3 · Sealing of cuts in skin by blood clotting — Explain the clotting cascade and why clots matter for infection as well as blood loss.

C3.2.4 · Differences between the innate immune system and the adaptive immune system — Contrast the innate and adaptive immune systems.

C3.2.5 · Infection control by phagocytes — Explain how phagocytes engulf and digest pathogens.

C3.2.6 · Lymphocytes as cells in the adaptive immune system that cooperate to produce antibodies — Explain antibodies' two functional parts, and why one lymphocyte makes only one type.

C3.2.7 · Antigens as recognition molecules that trigger antibody production — Define antigen, state where antigens are found, and explain antibody-antigen binding.

C3.2.8 · Activation of B-lymphocytes by helper T-lymphocytes — Explain how macrophages and helper T-lymphocytes activate the correct B-lymphocytes.

C3.2.9 · Multiplication of activated B-lymphocytes to form clones of antibody-secreting plasma cells — Explain why activated B-lymphocytes clone before secreting antibody.

C3.2.10 · Immunity as a consequence of retaining memory cells — Explain why long-term immunity depends on memory cells rather than antibodies.

C3.2.11 · Transmission of HIV in body fluids — State the body fluids and routes by which HIV is transmitted.

C3.2.12 · Infection of lymphocytes by HIV with AIDS as a consequence — Explain how HIV destroys helper T-cells, and how AIDS follows.

C3.2.13 · Antibiotics as chemicals that block processes occurring in bacteria but not in eukaryotic cells — Explain how antibiotics target prokaryotes, and why they do not work against viruses.

C3.2.14 · Evolution of resistance to several antibiotics in strains of pathogenic bacteria — Explain how multiple antibiotic resistance spreads, and the four measures needed.

C3.2.15 · Zoonoses as infectious diseases that can transfer from other species to humans — Define zoonosis, give examples, and explain why they are a growing concern.

C3.2.16 · Vaccines and immunization — Explain how vaccines produce immunity, and contrast primary with secondary responses.

C3.2.17 · Herd immunity and the prevention of epidemics — Explain herd immunity and who it protects.

C3.2.18 · Evaluation of data related to the COVID-19 pandemic — Evaluate pandemic data using rates rather than totals, and calculate percentage change.

C4.1 — Populations and communities

C4.1.1 · Populations as interacting groups of organisms of the same species living in an area — Define population, and explain the interactions between its members.

C4.1.2 · Estimation of population size by random sampling — Explain random sampling and sampling error, and interpret standard deviation.

C4.1.3 · Random quadrat sampling to estimate population size for sessile organisms — Estimate population size for sessile organisms using randomly placed quadrats.

C4.1.4 · Capture–mark–release–recapture and the Lincoln index to estimate population size for motile organisms — Estimate population size for motile organisms using the Lincoln index, and state its assumptions.

C4.1.5 · Carrying capacity and competition for limited resources — Explain carrying capacity, and name the resources that limit it in plants and animals.

C4.1.6 · Negative feedback control of population size by density-dependent factors — Contrast density-dependent and density-independent factors, and give the three dependent groups.

C4.1.7 · Population growth curves — Explain the three phases of the sigmoid growth curve, and why exponential growth stops.

C4.1.8 · Modelling of the sigmoid population growth curve — Model sigmoid growth experimentally, and evaluate the strengths and limits of the model.

C4.1.9 · Competition versus cooperation in intraspecific relationships — Contrast competition and cooperation within a species, with examples of each.

C4.1.10 · A community as all of the interacting organisms in an ecosystem — Define community, and explain why no population lives in isolation.

C4.1.11 · Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationship within communities — Define the six categories of interspecific relationship, with examples.

C4.1.12 · Mutualism as an interspecific relationship that benefits both species — Explain mutualism using root nodules, mycorrhizae and zooxanthellae.

C4.1.13 · Resource competition between endemic and invasive species — Explain how alien species become invasive and displace endemic species.

C4.1.14 · Tests for interspecific competition — Test for association between species, and explain why association is not proof of competition.

C4.1.15 · Use of the chi-squared test for association between two species — Carry out a chi-squared test of association, and state its validity conditions.

C4.1.16 · Predator–prey relationships as an example of density-dependent control of animal populations — Explain the four-step predator-prey cycle and the time lag that makes it oscillate.

C4.1.17 · Top-down and bottom-up control of populations in communities — Contrast top-down and bottom-up control, using the Shropshire meres.

C4.1.18 · Allelopathy and secretion of antibiotics — Explain antibiotics and allelopathic agents as secondary metabolites.

C4.2 — Transfers of energy and matter

C4.2.1 · Ecosystems as open systems in which both energy and matter can enter and exit — Define ecosystem, and explain why ecosystems are open systems.

C4.2.2 · Sunlight as the principal source of energy that sustains most ecosystems — Explain sunlight as the principal energy source, and the chemosynthetic exception.

C4.2.3 · Flow of chemical energy through food chains — Explain the one-way flow of chemical energy along a food chain.

C4.2.4 · Construction of food chains and food webs to represent feeding relationships in a community — Construct food chains and food webs for a community.

C4.2.5 · Supply of energy to decomposers as carbon compounds in organic matter coming from dead organisms — Explain how dead organic matter supplies energy to saprotrophs and detritus feeders.

C4.2.6 · Autotrophs as organisms that use external energy sources to synthesize carbon compounds from simple inorganic substances — Define autotroph, and state what it needs to build carbon compounds.

C4.2.7 · Use of light as the external energy source in photoautotrophs and oxidation reactions as the energy source in chemoautotrophs — Contrast photoautotrophs and chemoautotrophs, and explain why an external energy source is needed.

C4.2.8 · Heterotrophs as organisms that use carbon compounds obtained from other organisms to synthesize the carbon compounds that they require — Define heterotroph, and distinguish saprotrophs from multicellular and unicellular consumers.

C4.2.9 · Release of energy in both autotrophs and heterotrophs by oxidation of carbon compounds in cell respiration — Explain that all organisms release energy by oxidation in cell respiration.

C4.2.10 · Classification of organisms into trophic levels — Classify organisms into trophic levels, and explain non-whole-number values.

C4.2.11 · Construction of energy pyramids — Construct a pyramid of energy with correct units and labelling.

C4.2.12 · Reductions in energy availability at each successive stage in food chains due to large energy losses between trophic levels — Explain the three reasons energy availability falls between trophic levels.

C4.2.13 · Heat loss to the environment in both autotrophs and heterotrophs due to conversion of chemical energy to heat in cell respiration — Explain why heat loss is inevitable, and why energy flows while matter cycles.

C4.2.14 · Restrictions on the number of trophic levels in ecosystems due to energy losses — Explain why energy losses restrict the number of trophic levels.

C4.2.15 · Primary production as accumulation of carbon compounds in biomass by autotrophs — Distinguish gross from net primary production, and state the units.

C4.2.16 · Secondary production as accumulation of carbon compounds in biomass by heterotrophs — Explain secondary production, and why it declines with each trophic level.

C4.2.17 · Constructing carbon cycle diagrams — Construct a carbon cycle diagram using pools and fluxes.

C4.2.18 · Ecosystems as carbon sinks and carbon sources — Explain when an ecosystem is a carbon sink and when a source, and how sequestration occurs.

C4.2.19 · Release of carbon dioxide into the atmosphere during combustion of biomass, peat, coal, oil and natural gas — Explain how the carbon sinks formed, and what releases their carbon on combustion.

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

C4.2.21 · Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis, and of photosynthesis on atmospheric carbon dioxide produced by respiration — Explain why respiration depends on photosynthesis for oxygen, and photosynthesis on respiration for CO2.

C4.2.22 · Recycling of all chemical elements required by living organisms in ecosystems — Explain how chemical elements are recycled, and the key role of decomposers.

D. Continuity and change

Mechanisms for maintaining equilibrium and driving transformation.

D1.1 — DNA replication

D1.1.1 · DNA replication as production of exact copies of DNA with identical base sequences — Define DNA replication, and state the two processes that require it.

D1.1.2 · Semi-conservative nature of DNA replication and role of complementary base pairing — Explain semi-conservative replication and the role of complementary base pairing.

D1.1.3 · Role of helicase and DNA polymerase in DNA replication — Explain the roles of helicase and DNA polymerase in replication.

D1.1.4 · Polymerase chain reaction and gel electrophoresis as tools for amplifying and separating DNA — Explain PCR and gel electrophoresis as tools for amplifying and separating DNA.

D1.1.5 · Applications of polymerase chain reaction and gel electrophoresis — Explain PCR in coronavirus testing and gel electrophoresis in DNA profiling.

D1.1.6 · Directionality of DNA polymerases — Explain what 5' and 3' mean, and why DNA polymerase works in only one direction.

D1.1.7 · Differences between replication on the leading strand and the lagging strand — Explain why one strand is replicated continuously and the other in Okazaki fragments.

D1.1.8 · Functions of DNA primase, DNA polymerase I, DNA polymerase III and DNA ligase in replication — State the functions of DNA primase, DNA polymerase I and III, and DNA ligase.

D1.1.9 · DNA proofreading — Explain how DNA polymerase III proofreads and corrects a mismatched base.

D1.2 — Protein synthesis

D1.2.1 · Transcription as the synthesis of RNA using a DNA template — Explain transcription and the roles of RNA polymerase.

D1.2.2 · Role of hydrogen bonding and complementary base pairing in transcription — Explain complementary base pairing in transcription, distinguishing sense from template strand.

D1.2.3 · Stability of DNA templates — Explain why DNA templates must remain stable through repeated transcription.

D1.2.4 · Transcription as a process required for the expression of genes — Explain gene expression, and why transcription is the key stage for switching genes on or off.

D1.2.5 · Translation as the synthesis of polypeptides from mRNA — Explain translation, and why it is named as it is.

D1.2.6 · Roles of mRNA, ribosomes and tRNA in translation — State the roles of mRNA, tRNA and ribosomes in translation.

D1.2.7 · Complementary base pairing between tRNA and mRNA — Explain how anticodon-codon pairing puts the right amino acid in the right place.

D1.2.8 · Features of the genetic code — Explain why the code is a triplet code, and what degeneracy and universality mean.

D1.2.9 · Using the genetic code expressed as a table of mRNA codons — Read the codon table to deduce amino acid sequences and the DNA that coded for them.

D1.2.10 · Stepwise movement of the ribosome along mRNA and linkage of amino acids by peptide bonding to the growing polypeptide chain — Explain the translation cycle through the A, P and E sites.

D1.2.11 · Mutations that change protein structure — Explain how a base substitution changes protein structure, using sickle cell disease.

D1.2.12 · Directionality of transcription and translation — Explain why both transcription and translation run 5' to 3'.

D1.2.13 · Initiation of transcription at the promoter — Explain how promoters, activators and repressors initiate or block transcription.

D1.2.14 · Non-coding sequences in DNA do not code for polypeptides — Give five examples of non-coding sequences and their functions.

D1.2.15 · Post-transcriptional modification in eukaryotic cells — Explain 5' capping, poly-A tails and the splicing of introns from exons.

D1.2.16 · Alternative splicing of exons to produce variants of a protein from a single gene — Explain alternative splicing, and why it increases the diversity of the proteome.

D1.2.17 · Initiation of translation — Explain the special steps that initiate translation.

D1.2.18 · Modification of polypeptides into their functional state — Explain the modifications that turn a polypeptide into a functional protein.

D1.2.19 · Recycling of amino acids by proteasomes — Explain how proteasomes destroy tagged proteins and recycle amino acids.

D1.3 — Mutations and gene editing

D1.3.1 · Gene mutations as structural changes to genes at the molecular level — Define gene mutation, and distinguish substitution, insertion and deletion.

D1.3.2 · Consequences of base substitutions — Explain same-sense, nonsense and mis-sense substitutions, and what SNPs are.

D1.3.3 · Consequences of insertions and deletions — Explain why insertions and deletions cause frameshifts, and why that is so damaging.

D1.3.4 · Causes of gene mutation — Explain how radiation and chemical mutagens increase mutation rate.

D1.3.5 · Randomness in mutation — Explain what randomness in mutation does and does not mean.

D1.3.6 · Consequences of mutation in germ cells and somatic cells — Contrast the consequences of mutation in germ cells and in somatic cells.

D1.3.7 · Mutation as a source of genetic variation — Explain why mutation is the original source of all genetic variation, and why it is needed.

D1.3.8 · Gene knockout as a technique for investigating the function of a gene by changing it to make it inoperative — Explain gene knockout as a way of discovering a gene's function.

D1.3.9 · Use of the CRISPR sequences and the enzyme Cas9 in gene editing — Explain what CRISPR sequences are and how Cas9 uses guide RNA to cut target DNA.

D1.3.10 · Hypotheses to account for conserved or highly conserved sequences in genes — Give two hypotheses that account for conserved and highly conserved sequences.

D2.1 — Cell and nuclear division

D2.1.1 · Generation of new cells in living organisms by cell division — Explain that new cells only ever arise by division of a pre-existing cell.

D2.1.2 · Cytokinesis as splitting of cytoplasm in a parent cell between daughter cells — Contrast cytokinesis in animal and plant cells, and explain why they differ.

D2.1.3 · Equal and unequal cytokinesis — Contrast equal and unequal cytokinesis, using budding in yeast and oogenesis.

D2.1.4 · Roles of mitosis and meiosis in eukaryotes — Contrast the roles of mitosis and meiosis, and explain why nuclear division comes first.

D2.1.5 · DNA replication as a prerequisite for both mitosis and meiosis — Explain why DNA replication precedes division, and define chromatid and cohesin.

D2.1.6 · Condensation and movement of chromosomes as shared features of mitosis and meiosis — Explain why chromosomes must condense, and how microtubules move them.

D2.1.7 · Phases of mitosis — Describe the four phases of mitosis and what happens in each.

D2.1.8 · Identification of phases of mitosis — Prepare a root tip squash and identify the phases of mitosis.

D2.1.9 · Meiosis as a reduction division — Explain meiosis as a reduction division, and why gametes must be haploid.

D2.1.10 · Down syndrome and non-disjunction — Explain non-disjunction and how it causes Down syndrome.

D2.1.11 · Meiosis as a source of variation — Explain how crossing over and random orientation of bivalents generate variation.

D2.1.12 · Cell proliferation for growth, cell replacement and tissue repair — Explain cell proliferation in growth, cell replacement and tissue repair.

D2.1.13 · Phases of the cell cycle — Describe the phases of the cell cycle, including G0.

D2.1.14 · Cell growth during interphase — Explain what a cell must double during interphase, and how each organelle is increased.

D2.1.15 · Control of the cell cycle using cyclins — Explain how cyclins and checkpoints control the sequence of the cell cycle.

D2.1.16 · Consequences of mutations in genes that control the cell cycle — Explain how mutations to proto-oncogenes and tumour-suppressor genes cause tumours.

D2.1.17 · Differences between tumours in rates of cell division and growth and in the capacity for metastasis and invasion of neighbouring tissue — Explain how tumours differ in growth rate and capacity for metastasis, and calculate a mitotic index.

D2.2 — Gene expression

D2.2.1 · Gene expression as the mechanism by which information in genes has effects on the phenotype — Explain the three stages by which a genotype produces a phenotype.

D2.2.2 · Regulation of transcription by proteins that bind to specific base sequences in DNA — Explain how transcription factors bind enhancers and silencers to regulate transcription.

D2.2.3 · Control of the degradation of mRNA as a means of regulating translation — Explain how the poly-A tail controls mRNA degradation and therefore translation.

D2.2.4 · Epigenesis as the development of patterns of differentiation in the cells of a multicellular organism — Explain epigenesis, and why epigenetic tags change phenotype but not genotype.

D2.2.5 · Differences between the genome, transcriptome and proteome of individual cells — Distinguish the genome, transcriptome and proteome of a cell.

D2.2.6 · Methylation of the promoter and histones in nucleosomes as examples of epigenetic tags — Explain methylation of promoters and of histone tails as epigenetic tags.

D2.2.7 · Epigenetic inheritance through heritable changes to gene expression — Explain how epigenetic tags are inherited, and the limits of transgenerational inheritance.

D2.2.8 · Examples of environmental effects on gene expression in cells and organisms — Give examples of environmental effects on gene expression, including phenotypic plasticity.

D2.2.9 · Consequences of removal of most but not all epigenetic tags from the ovum and sperm — Explain genomic imprinting as a consequence of incomplete removal of epigenetic tags.

D2.2.10 · Monozygotic twin studies — Explain how twin studies separate genetic from environmental influence.

D2.2.11 · External factors impacting the pattern of gene expression — Explain how nutrients, hormones and development alter the pattern of gene expression.

D2.3 — Water potential

D2.3.1 · Solvation with water as the solvent — Explain solvation, and why water's polarity makes it a good solvent.

D2.3.2 · Water movement from less concentrated to more concentrated solutions — Explain net water movement, and define hypotonic, hypertonic and isotonic.

D2.3.3 · Water movement by osmosis into or out of cells — Explain osmosis across a membrane, and how cells can change its rate and direction.

D2.3.4 · Changes due to water movement in plant tissue bathed in hypotonic and those bathed in hypertonic solutions — Investigate water movement in plant tissue bathed in solutions of different concentration.

D2.3.5 · Effects of water movement on cells that lack a cell wall — Explain what happens to cells without a cell wall in hypotonic and hypertonic solutions.

D2.3.6 · Effects of water movement on cells with a cell wall — Explain turgor, flaccidity and plasmolysis in cells with a cell wall.

D2.3.7 · Medical applications of isotonic solutions — Explain why isotonic solutions are used in medical procedures.

D2.3.8 · Water potential as the potential energy of water per unit volume — Define water potential, and state the two contributors that vary in living systems.

D2.3.9 · Movement of water from higher to lower water potential — Explain why water moves from higher to lower water potential, and read negative values correctly.

D2.3.10 · Contributions of solute potential and pressure potential to the water potential of cells with walls — Explain solute potential and pressure potential, and their possible signs.

D2.3.11 · Water potential and water movements in plant tissue — Explain water movement in plant tissue bathed in hypotonic and hypertonic solutions.

D3.1 — Reproduction

D3.1.1 · Differences between sexual and asexual reproduction — Contrast sexual and asexual reproduction across six points.

D3.1.2 · Role of meiosis and fusion of gametes in the sexual life cycle — Explain why meiosis and gamete fusion must balance in a sexual life cycle.

D3.1.3 · Differences between male and female sexes in sexual reproduction — Contrast male and female gametes, and distinguish isogamy from anisogamy.

D3.1.4 · Anatomy of the human male and female reproductive systems — Annotate the human male and female reproductive systems with the function of each structure.

D3.1.5 · Changes during the ovarian and uterine cycles and their hormonal regulation — Explain the ovarian and uterine cycles and the roles of the four hormones.

D3.1.6 · Fertilization in humans — Explain the steps of fertilization in humans.

D3.1.7 · Use of hormones in in vitro fertilization (IVF) treatment — Explain the use of down-regulation, FSH and hCG in IVF treatment.

D3.1.8 · Sexual reproduction in flowering plants — Explain pollination, fertilization and embryo development in flowering plants.

D3.1.9 · Features of an insect-pollinated flower — Draw a half-view of an insect-pollinated flower and explain its features.

D3.1.10 · Methods of promoting cross-pollination — Explain the three methods of promoting cross-pollination, and why inbreeding is costly.

D3.1.11 · Self-incompatibility mechanisms to increase genetic variation within a species — Explain self-incompatibility and its genetic basis.

D3.1.12 · Dispersal and germination of seeds — Explain seed dispersal and its methods, and distinguish it from pollination.

D3.1.13 · Control of the developmental changes of puberty by gonadotropin-releasing hormone and steroid sex hormones — Explain how GnRH and the steroid sex hormones control the changes of puberty.

D3.1.14 · Spermatogenesis and oogenesis in humans — Contrast spermatogenesis and oogenesis across the four stages.

D3.1.15 · Mechanisms to prevent polyspermy — Explain the acrosome and cortical reactions as mechanisms preventing polyspermy.

D3.1.16 · Development of a blastocyst and implantation in the endometrium — Explain blastocyst development and implantation in the endometrium.

D3.1.17 · Pregnancy testing by detection of human chorionic gonadotropin secretion — Explain hCG's role in pregnancy and how a pregnancy test detects it.

D3.1.18 · Role of the placenta in foetal development inside the uterus — Explain the structure of the placenta and what crosses it in each direction.

D3.1.19 · Hormonal control of pregnancy and childbirth — Explain the hormonal control of pregnancy, and the positive feedback loop of childbirth.

D3.1.20 · Hormone replacement therapy and the risk of coronary heart disease — Explain why the apparent link between HRT and reduced coronary heart disease was not causal.

D3.2 — Inheritance

D3.2.1 · Production of haploid gametes in parents and their fusion to form a diploid zygote as the means of inheritance — Explain how haploid gametes and their fusion form the basis of inheritance.

D3.2.2 · Methods for conducting genetic crosses in flowering plants — Carry out a genetic cross in flowering plants, and name the P, F1 and F2 generations.

D3.2.3 · Genotype as the combination of alleles inherited by an organism — Define genotype, allele, homozygous and heterozygous.

D3.2.4 · Phenotype as the observable traits of an organism resulting from genotype and environmental factors — Define phenotype, and classify traits by whether genotype, environment or both determine them.

D3.2.5 · Effects of dominant and recessive alleles on phenotype — Explain dominance and recessiveness, and the molecular reason behind them.

D3.2.6 · Phenotypic plasticity as the capacity to develop traits suited to the environment experienced by an organism, by varying patterns of gene expression — Explain phenotypic plasticity, and why it is not heritable.

D3.2.7 · Phenylketonuria as an example of a human disease due to a recessive allele — Explain PKU as a recessive disorder, and how screening and diet prevent its effects.

D3.2.8 · Single-nucleotide polymorphisms and multiple alleles in gene pools — Explain SNPs and multiple alleles in a gene pool.

D3.2.9 · ABO blood groups as an example of multiple alleles — Explain the ABO blood groups, and why two alleles are codominant and one recessive.

D3.2.10 · Incomplete dominance and codominance — Contrast incomplete dominance with codominance, with an example of each.

D3.2.11 · Sex determination in humans and inheritance of genes on sex chromosomes — Explain sex determination, and how genes on sex chromosomes are inherited.

D3.2.12 · Haemophilia as an example of a sex-linked genetic disorder — Explain haemophilia, and why males are affected far more often than females.

D3.2.13 · Pedigree charts to deduce patterns of inheritance of genetic disorders — Deduce patterns of inheritance from pedigree charts.

D3.2.14 · Continuous variation due to polygenic inheritance and/or environmental factors — Contrast discrete and continuous variation, using skin colour as a polygenic example.

D3.2.15 · Box-and-whisker plots to represent data for a continuous variable such as student height — Construct and read box-and-whisker plots, and choose the right measure of central tendency.

D3.2.16 · Segregation and independent assortment of unlinked genes in meiosis — Explain segregation and independent assortment as consequences of meiosis.

D3.2.17 · Punnett grids for predicting genotypic and phenotypic ratios in dihybrid crosses involving pairs of unlinked autosomal genes — Use a Punnett grid to predict genotypic and phenotypic ratios in a dihybrid cross.

D3.2.18 · Loci of human genes and their polypeptide products — Explain what a gene locus is, and how to find a gene's locus and product.

D3.2.19 · Autosomal gene linkage — Explain autosomal gene linkage, and how to represent it in a diagram.

D3.2.20 · Recombinants in crosses involving two linked or unlinked genes — Explain recombinants, and use their frequency to tell linked from unlinked genes.

D3.2.21 · Use of a chi-squared test on data from dihybrid crosses — Use a chi-squared test to assess whether dihybrid cross data fit a predicted ratio.

D3.3 — Homeostasis

D3.3.1 · Homeostasis as maintenance of the internal environment of an organism — Explain homeostasis, and give examples of variables kept constant.

D3.3.2 · Negative feedback loops in homeostasis — Contrast positive and negative feedback, and state the parts of a negative feedback loop.

D3.3.3 · Regulation of blood glucose as an example of the role of hormones in homeostasis — Explain how insulin and glucagon regulate blood glucose.

D3.3.4 · Physiological changes that form the basis of type 1 and type 2 diabetes — Contrast type 1 and type 2 diabetes, and explain how each is managed.

D3.3.5 · Thermoregulation as an example of negative feedback control — Explain thermoregulation as negative feedback, and the role of thermoreceptors.

D3.3.6 · Thermoregulation mechanisms in humans — Explain vasoconstriction, vasodilation, shivering and sweating in humans.

D3.3.7 · Role of the kidney in osmoregulation and excretion — Explain the kidney's twin roles of osmoregulation and excretion, and name the parts of a nephron.

D3.3.8 · Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion — Explain ultrafiltration and selective reabsorption in the proximal convoluted tubule.

D3.3.9 · Role of the loop of Henle — Explain how the loop of Henle establishes the osmotic gradient in the medulla.

D3.3.10 · Osmoregulation by water reabsorption in the collecting ducts — Explain how ADH and aquaporins vary water reabsorption in the collecting duct.

D3.3.11 · Changes in blood supply to organs in response to changes in activity — Explain how blood is redistributed between organs as activity changes.

D4.1 — Natural selection

D4.1.1 · Natural selection as the mechanism driving evolutionary change — Explain the four statements that make up the theory of evolution by natural selection.

D4.1.2 · Roles of mutation and sexual reproduction in generating the variation on which natural selection acts — Explain how mutation and sexual reproduction generate the variation selection acts on.

D4.1.3 · Overproduction of offspring and competition for resources as factors that promote natural selection — Explain how overproduction of offspring and competition promote natural selection.

D4.1.4 · Abiotic factors as selection pressures — Explain how abiotic factors act as selection pressures.

D4.1.5 · Differences between individuals in adaptation, survival and reproduction as the basis for natural selection — Explain how differences in adaptation affect survival and reproduction.

D4.1.6 · Requirement that traits are heritable for evolutionary change to occur — Explain why acquired traits cannot be inherited, and so cannot drive evolution.

D4.1.7 · Sexual selection as a selection pressure in animal species — Explain sexual selection, and why costly traits can persist.

D4.1.8 · Modelling of sexual and natural selection based on experimental control of selection pressures — Model selection experimentally by controlling the selection pressure.

D4.1.9 · Concept of the gene pool — Define gene pool and allele frequency.

D4.1.10 · Allele frequencies of geographically isolated populations — Explain why geographically isolated populations differ in allele frequency.

D4.1.11 · Changes in allele frequency in the gene pool as a consequence of natural selection between individuals according to differences in their heritable traits — Explain why only a change in allele frequency counts as evolution.

D4.1.12 · Differences between directional, disruptive and stabilizing selection — Contrast stabilizing, disruptive and directional selection, with an example of each.

D4.1.13 · Hardy–Weinberg equation and calculations of allele or genotype frequencies — Use the Hardy-Weinberg equation to calculate allele and genotype frequencies.

D4.1.14 · Hardy–Weinberg conditions that must be maintained for a population to be in genetic equilibrium — State the five conditions for genetic equilibrium, and how departures detect evolution.

D4.1.15 · Artificial selection by deliberate choice of traits — Explain artificial selection, and why improvement slows over generations.

D4.2 — Stability and change

D4.2.1 · Stability as a property of natural ecosystems — Define stability, resistance and resilience, with examples of long-persisting ecosystems.

D4.2.2 · Requirements for stability in ecosystems — State the three requirements for ecosystem stability, and what disrupts them.

D4.2.3 · Deforestation of Amazon rainforest as an example of a possible tipping point in ecosystem stability — Explain the Amazon as a possible tipping point, and calculate percentage change in forest area.

D4.2.4 · Use of a model to investigate the effect of variables on ecosystem stability — Use mesocosms to model ecosystems, and evaluate their limitations.

D4.2.5 · Role of keystone species in the stability of ecosystems — Explain keystone species using Paine's sea star experiment.

D4.2.6 · Assessing sustainability of resource harvesting from natural ecosystems — Use the sigmoid growth curve to judge whether harvesting is sustainable.

D4.2.7 · Factors affecting the sustainability of agriculture — Explain feed conversion ratios and greenhouse gas emissions in food production.

D4.2.8 · Eutrophication of aquatic and marine ecosystems due to leaching — Explain how leaching causes eutrophication and raises biochemical oxygen demand.

D4.2.9 · Biomagnification of pollutants in natural ecosystems — Explain biomagnification, and why it differs between aquatic and terrestrial food webs.

D4.2.10 · Effects of microplastic and macroplastic pollution of the oceans — Explain the effects of macroplastic and microplastic pollution of the oceans.

D4.2.11 · Restoration of natural processes in ecosystems by rewilding — Explain rewilding as restoration of natural processes.

D4.2.12 · Ecological succession and its causes — Explain ecological succession and its cause in reciprocal interactions.

D4.2.13 · Changes occurring during primary succession — Describe primary succession at Glacier Bay and the soil changes that accompany it.

D4.2.14 · Cyclical succession in ecosystems — Explain cyclical succession as a repeating sequence of stages.

D4.2.15 · Climax communities and arrested succession — Explain climax communities and how succession can be arrested.

D4.3 — Climate change

D4.3.1 · Anthropogenic causes of climate change — Explain greenhouse gases as the principal driver of anthropogenic climate change.

D4.3.2 · Positive feedback cycles in global warming — Explain positive feedback cycles in global warming, using methane release.

D4.3.3 · Change from net carbon accumulation to net loss in boreal forests as an example of a tipping point — Explain the shift of boreal forests from carbon sink to carbon source as a tipping point.

D4.3.4 · Melting of landfast ice and sea ice as examples of polar habitat change — Explain how melting landfast ice and sea ice change polar habitats.

D4.3.5 · Changes in ocean currents altering the timing and extent of nutrient upwelling — Explain how changing ocean currents alter the timing and extent of nutrient upwelling.

D4.3.6 · Poleward and upslope range shifts of temperate species — Explain poleward and upslope range shifts, and why upslope shifts run out of room.

D4.3.7 · Threats to coral reefs as an example of potential ecosystem collapse — Explain ocean acidification and coral bleaching as threats of ecosystem collapse.

D4.3.8 · Afforestation, forest regeneration and restoration of peat-forming wetlands as approaches to carbon sequestration — Explain afforestation, forest regeneration and peatland restoration as carbon sequestration.

D4.3.9 · Phenology as research into the timing of biological events — Explain phenology, and why photoperiod is unaffected by climate change.

D4.3.10 · Disruption to the synchrony of phenological events by climate change — Explain how climate change desynchronizes phenological events, using great tits and caribou.

D4.3.11 · Increases to the number of insect life cycles within a year due to climate change — Explain how warming lets insect pests complete more life cycles per year.

D4.3.12 · Evolution as a consequence of climate change — Explain evolution driven by climate change, using tawny owls and two-spot ladybirds.

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