Biology — A2 Level Biology

ATP as the universal energy currency, the four aerobic stages and their locations, anaerobic pathways in mammals and yeast, and the rice adaptation to flooded roots.

Chloroplast structure, chloroplast pigments and their absorption spectra, the light-dependent stage (cyclic and non-cyclic photophosphorylation, photolysis, chemiosmosis), the Calvin cycle (carbon fixation by rubisco, GP → TP, RuBP regeneration), uses of Calvin cycle intermediates, and the limiting factors and redox-indicator investigations that the practical papers re-examine.

Negative feedback, urea and the ornithine cycle, kidney gross anatomy, the nephron and the three filtration barriers, ultrafiltration at the glomerulus, selective reabsorption in the PCT, the counter-current multiplier of the loop of Henle, ADH and aquaporins in osmoregulation, blood-glucose regulation by insulin and glucagon, the cAMP second-messenger cascade, glucose test strips and biosensors, guard-cell structure and stomatal opening, the daily rhythm of stomatal aperture, and the ABA–Ca²⁺ signalling pathway that closes the stomata in water stress.

The endocrine system (ADH, glucagon, insulin) versus the nervous system; structure of sensory and motor neurones; sensory receptor cells; the action potential in a chemoreceptor cell; the resting potential and how it is maintained; depolarisation, repolarisation, hyperpolarisation and the refractory period; saltatory conduction in myelinated axons; cholinergic synapses and the role of Ca²⁺; neuromuscular junctions, T-tubules and the sarcoplasmic reticulum; striated-muscle ultrastructure and the sarcomere; the sliding-filament model (troponin, tropomyosin, Ca²⁺, ATP); the Venus fly-trap; auxin in elongation growth; and gibberellin in barley germination and the DELLA-repressor mechanism.

Haploid and diploid cells, meiosis and the eight named stages, crossing over and independent assortment, random fusion at fertilisation, every genetics term, monohybrid / codominant / multi-allele / sex-linked / dihybrid / dihybrid-test-cross / autosomal-linkage / epistasis crosses, the chi-squared test, the four named gene→protein→phenotype examples (TYR/albinism, HBB/sickle cell, F8/haemophilia, HTT/Huntington's), structural vs regulatory genes, repressible vs inducible enzymes, the lac operon, transcription factors in eukaryotes, and the gibberellin/DELLA-repressor mechanism.

Genetic and environmental causes of variation, discontinuous vs continuous variation, the t-test, the five-step process of natural selection, stabilising / directional / disruptive selection, genetic drift with founder and bottleneck effects, antibiotic resistance and horizontal gene transfer, the Hardy-Weinberg principle and its conditions, selective breeding of wheat / rice / maize / cattle, evolution as a change in allele frequency, DNA sequence data and phylogenetic trees, and allopatric vs sympatric speciation.

The biological, morphological and ecological species concepts; the three domains (Archaea, Bacteria, Eukarya) and the differences between Archaea and Bacteria; the taxonomic hierarchy from kingdom to species; characteristic features of the kingdoms Protoctista, Fungi, Plantae and Animalia; classification of viruses by nucleic acid; ecosystem and niche; the three levels of biodiversity; random sampling with frame quadrats, line and belt transects, and mark-release-recapture with the Lincoln index; Spearman's rank and Pearson's linear correlation; Simpson's index of diversity; the four named causes of extinction; reasons to maintain biodiversity; conservation in practice — zoos, botanic gardens, conserved areas, frozen zoos, seed banks, and assisted reproduction (IVF, embryo transfer and surrogacy); the negative effects of invasive alien species; and the conservation roles of the IUCN and CITES.

The seven-step pipeline of recombinant DNA technology; sources of the gene for transfer (gene banks, cDNA via reverse transcriptase, chemical synthesis); restriction enzymes, DNA ligase, plasmids, DNA polymerase and reverse transcriptase; promoters and marker genes including insertional inactivation; gene editing with CRISPR/Cas9 and chemical synthesis; the polymerase chain reaction (PCR) and the role of Taq polymerase; gel electrophoresis; DNA microarrays and sequence databases (BLAST and bioinformatics); recombinant proteins — insulin, factor VIII and ADA; genetic screening for BRCA1, BRCA2, Huntington's and cystic fibrosis; gene therapy for SCID and inherited eye diseases (LCA2, LCA10); the ethics of genetic screening and gene therapy; GM crops and animals — herbicide-resistant soybean, insect-resistant cotton and AquAdvantage salmon; and the implications of GMOs in food production.