Key term
Edexcel A-Level Biology A 9BN0
Lifestyle, Health and Risk
Topic overviewWater and the carbohydratesCondensation, hydrolysis and glycosidic bondsLipids, food tests and unitsThe cardiac cycle and the structure of the heartArteries, veins and capillariesCore practical: caffeine and the heart rate of DaphniaThe blood clotting cascadeThrombus, embolus and their consequencesAtherosclerosis and the risk factors for CVDTreatments for CVD, and cholesterol transportBMI, waist-to-hip ratio and energy balanceCore practical 2: the vitamin C content of food and drinkCorrelation, causation and the design of health studiesRisk perception, and handling quantitative data
Genes and Health
Topic overviewGas exchange surfaces and Fick's LawThe fluid mosaic model of the cell membraneOsmosis, diffusion and active transportSurface area and volume calculationsThe structure of DNA and RNATranscriptionTranslation and the genetic codeAmino acids and the levels of protein structureGlobular and fibrous proteins: haemoglobin and collagenAlternative splicing and tissue-specific proteinsEnzyme specificity, the active site and activation energyRates of reaction, Vmax and Core Practical 4Semi-conservative replication and Meselson-StahlTypes of mutation and the CFTR geneAlleles, genotype and monohybrid inheritancePedigree diagrams and the inheritance of cystic fibrosisThe effects of cystic fibrosis, and the chi-squared testPrenatal genetic testing: PGD, amniocentesis and CVSThe ethics of genetic screening
Voice of the Genome
Topic overviewProkaryotic cellsEukaryotic organelles and their functionsIdentifying organelles in an electron micrographProtein secretion, and levels of organisationMicroscopy: the graticule, magnification and standard formThe cell cycle and the stages of mitosisCore practical: the root tip squashMeiosis, linkage and sex linkageThe structure of sperm and egg cellsFertilisation: the acrosome and cortical reactionsTotipotency, pluripotency and sources of stem cellsThe ethics and risks of stem cell therapyDifferential gene expression and specialisationThe lac operonEpigenetics: DNA methylation and histone modificationPolygenic inheritance, continuous variation and statistics
Biodiversity and Natural Resources
Topic overviewBiodiversity, species richness and the index of diversityNiches and the three kinds of adaptationNatural selection and evolutionThe Hardy-Weinberg equation and its assumptionsReproductive isolation and speciationClassificationThe plant cell wall, chloroplast and amyloplastThe vacuole, plasmodesmata, pits and middle lamellaPlant cells in the electron microscopeStarch and celluloseLignin, xylem vessels and sclerenchyma fibresIdentifying plant tissues under the microscopeThe structure of xylem, phloem and sclerenchymaWater and the mineral nutrition of plantsCore practical: investigating mineral deficiencyCore practical: the tensile strength of plant fibresDrug development from Withering to modern trialsGrowing bacteria and aseptic techniqueCore practical: the antimicrobial properties of plantsSustainability and Conservation
On the Wild Side
Topic overviewPhotosynthesis: the light-dependent reactionsPhotosynthesis: the Calvin cycleChloroplast structure and the products of photosynthesisProductivity: GPP, NPP and energy transferCore practicals on temperature and growthTemperature, enzymes and Q10Sampling: quadrats and transectsSuccessionBiotic and abiotic factors, niches and competitionEcosystem terms, evolution, speciation and validating evidenceEvidence for climate changeClimate models and their limitationsCorrelation, causation and scientific objectivityThe effects of climate change on organismsHuman activities that raise greenhouse gas levelsThe greenhouse effectEvolution and natural selectionSpeciationHow new scientific evidence is validatedThe carbon cycleReforestation, biofuels and sustainability
Immunity, Infection and Forensics
Topic overviewDecomposition, succession and forensic entomologyBody cooling and rigor mortisDNA profiling and the polymerase chain reactionGel electrophoresisThe structure of bacteria and virusesDecomposition, and how pathogens enter the bodyThe body's barriers, and modelling bacterial growthTuberculosis and HIVThe non-specific immune responseAntigens, antibodies and B cellsT cells and cell-mediated immunityActive and passive immunity, natural and artificialThe evolutionary race and pathogen evasionAntibiotics and testing their effectivenessHospital acquired infections and their control
Run for Your Life
Topic overviewMuscles and MovementThe myofibril and the sarcomereThe sliding filament theory, calcium and ATPSlow-twitch and fast-twitch muscle fibresGlycolysis and the link reactionThe Krebs cycle, oxidative phosphorylation and oxygen debtThe conduction system: SAN, AVN and Purkyne fibresThe sequence of cardiac excitationThe electrocardiogram, cardiac output and stroke volumeThe cardiovascular and ventilation control centresSpirometry and ventilation during exerciseHomeostasis, feedback and gene control by hormonesThermoregulation and the hypothalamusThe effects of too much and too little exerciseMedical technology and performance-enhancing substances
Grey Matter
Topic overviewThe structure of neurones and myelinationThe action potential and saltatory conductionThe structure of a synapse and calcium entryNeurotransmitter release and acetylcholineRod cells and the detection of lightEffectors, the neuromuscular junction and the pupil reflexPhytochrome and the response to lightIAA, phototropism and gravitropismNervous against hormonal coordinationThe regions of the brain and their functionsBrain imaging: MRI, fMRI, PET and CTCritical periods and the Hubel and Wiesel experimentsNature, nurture, habituation and research ethicsDopamine, serotonin and their imbalanceL-Dopa and MDMAGenome sequencing, personalised medicine and its ethicsGenetically modified organisms: benefits and risks
Run for Your Life
The sequence of cardiac excitation
- 3 things to know
- Papers 2 and 3
Overview
Recall questions on the order in which the impulse spreads, why the delay at the AVN matters, and why the ventricles contract from the apex upward.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
After the SAN generates an impulse, how does it reach both atria?
Key term
What happens to the electrical impulse at the atrioventricular node?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Where does the electrical impulse that initiates each heartbeat originate?
Model answer
The sinoatrial node (SAN) in the right atrium.
- 2
Why is the SAN referred to as the pacemaker of the heart?
Model answer
Because it spontaneously generates the electrical impulses that set the rhythm of the heartbeat.
- 3
After the SAN generates an impulse, how does it reach both atria?
Model answer
The impulse spreads across the atrial muscle tissue, causing both atria to contract.
- 4
What is the functional significance of the impulse spreading across the atria before reaching the ventricles?
Model answer
It ensures both atria contract together, pushing blood into the ventricles before ventricular contraction begins.
- 5
What happens to the electrical impulse at the atrioventricular node?
Model answer
The AVN delays the impulse briefly before passing it to the ventricles.
- 6
Explain why the delay at the AVN is essential for efficient cardiac function.
Model answer
The delay allows time for the atria to complete their contraction and fully empty blood into the ventricles before ventricular contraction begins.
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