Key term
AQA A-Level Biology 7402
Biological Molecules
Topic overviewMonomers, polymers, condensation and hydrolysisMonosaccharides, disaccharides and glycosidic bondsAlpha and beta glucose, amylose and amylopectinHow starch, glycogen and cellulose suit their functionsCellulose microfibrils and tests for sugars and starchTriglycerides, fatty acids and phospholipid structureProperties of lipids and the emulsion testThe general structure of amino acidsPeptide bonds, polypeptides and bonds in proteinsLevels of protein structure, the biuret test and chromatographyActivation energy, induced fit and enzyme specificityEnzyme and substrate concentration and inhibitionpH, temperature, initial rates and measurement uncertaintyDNA, RNA and the components of a nucleotideBase pairing in DNA and RNAPhosphodiester bonds and the DNA double helixDoubts about DNA, base ratios and RNA structureSemi-conservative replication, helicase and DNA polymeraseSteps of replication and the Meselson-Stahl experimentATP structure, hydrolysis and resynthesisWater as a metabolite, solvent and coolantHydrogen, iron, sodium and phosphate ions
Cells
Topic overviewCell-surface membrane, nucleus and mitochondriaChloroplasts, Golgi apparatus and lysosomesRibosomes, endoplasmic reticulum, cell walls and vacuolesCell specialisation, levels of organisation and organelle rolesProkaryotic cell structure and virus particlesOptical and transmission electron microscopesScanning electron microscopes, magnification and graticulesCell fractionation, homogenisation and ultracentrifugationOrder of sedimentation, artefacts and fractionation conditionsThe cell cycle, interphase and the stages of mitosisSpindle fibres, cytokinesis and uncontrolled cell divisionBinary fission, viral replication and root tip squashesMitotic index, mitosis stages and size calculationsThe fluid-mosaic model and cholesterolSimple diffusion, facilitated diffusion and membrane proteinsOsmosis, water potential and active transportCo-transport in the ileum and adaptations for rapid transportTransport rates, dilution series and membrane permeabilityAntigens, cell recognition and phagocytosisAntigen-presenting cells, T cells and clonal selectionAntibody structure, agglutination and antigen-antibody complexesMemory cells, vaccination and active and passive immunityHIV structure and replicationAIDS, monoclonal antibodies, ELISA and clinical trials
Organisms Exchange Substances with Their Environment
Topic overviewSurface area to volume ratio, metabolic rate and calculationsGas exchange in single-celled organisms, insects and fishLeaf gas exchange, insect water loss and xerophytesTrachea, bronchi, alveoli and lung dissectionInspiration, expiration and pulmonary ventilation rateLung disease, correlation, insect tracheae and Spearman's rankDigestion of carbohydrates and lipidsEndopeptidases, exopeptidases and dipeptidasesCo-transport of amino acids, micelles and chylomicronsHaemoglobin, red blood cells and the dissociation curveCooperative binding, the Bohr effect and different haemoglobinsDouble circulation and the major blood vesselsHeart chambers, the cardiac cycle and heart dissectionArteries, arterioles, veins and capillariesTissue fluid, cardiovascular risk factors and semilunar valvesXylem structure and the cohesion-tension theoryPhloem structure, companion cells and translocationMass flow from source to sink, tracers and ringingEvaluating mass flow, potometers and transpiration rate
Genetic Information, Variation and Relationships Between Organisms
Topic overviewProkaryotic and eukaryotic DNA, chromosomes and histonesDNA in mitochondria and chloroplasts, genes and lociFeatures of the genetic code, exons and intronsGenome, proteome, mRNA and tRNATranscription, RNA polymerase and splicingTranslation at the ribosome and the role of tRNAGene mutations, mutagens and chromosome non-disjunctionMeiosis, independent segregation and crossing overMeiosis compared with mitosis and random fertilisationGenetic diversity and the spread of advantageous allelesDirectional and stabilising selectionDefining adaptations and how antibiotic resistance spreadsSelection on birth weight, aseptic technique and antimicrobialsClassifying anatomical, physiological and behavioural adaptationsDefining a species, courtship and phylogenetic classificationThe taxonomic hierarchy, binomial names and molecular evidenceSpecies richness, the index of diversity and farmingComparing genetic diversity, standard deviation and the t-test
Energy Transfers in and Between Organisms
Topic overviewPhotoionisation and ATP from the light-dependent reactionChemiosmosis, photolysis and products for the Calvin cycleCarbon fixation, triose phosphate and limiting factorsGlasshouse conditions, pigment chromatography and DCPIPGlycolysis and its productsAnaerobic respiration and the oxidation of pyruvateAcetylcoenzyme A and the Krebs cycleOxidative phosphorylation, other substrates and respirometersBiomass and gross and net primary productionNet production of consumers and productivityFarming practices, transfer efficiency and the production equationsSaprobionts and the phosphorus cycleMycorrhizae, ammonification and nitrificationNitrogen fixation, denitrification and fertilisersLeaching, eutrophication and nutrient cycles reviewed
Organisms Respond to Changes in Their Internal and External Environments
Topic overviewIAA, gravitropism and phototropismTaxes, kineses, reflex arcs and choice chambersThe Pacinian corpuscle and generator potentialsRods, cones, colour vision and visual acuityThe SAN, AVN, bundle of His and Purkyne tissueChemoreceptors, baroreceptors and cardiac outputMotor neurone structure and the resting potentialDepolarisation, action potentials and saltatory conductionThe refractory period and speed of conductionSynapse structure and the neuromuscular junctionTransmission at a cholinergic synapseAcetylcholinesterase, summation and inhibitory synapsesNeuromuscular junctions compared, agonists and antagonistsDrug effects and potassium channels in hyperpolarisationAntagonistic muscle pairs and muscle fibre structureSarcomere bands, actin, myosin and tropomyosinThe sliding filament cycle, ATP and phosphocreatineSlow twitch and fast twitch muscle fibresControl systems and why temperature, pH and glucose matterNegative and positive feedbackGlycogenesis, glycogenolysis and gluconeogenesisHow insulin, glucagon and adrenaline actThe second messenger model, diabetes and the sugar debateGlucose calibration curves and hormones affecting blood glucoseOsmoregulation, osmoreceptors and ADHNephron structure and ultrafiltrationThe proximal convoluted tubule and the loop of HenleThe distal tubule, collecting duct and urine concentration
Genetics, Populations, Evolution and Ecosystems
Topic overviewGenotype, phenotype and types of alleleMonohybrid and dihybrid crosses, sex linkage and autosomal linkageEpistasis, genetic diagrams and the chi-squared testGene pools, allele frequency and Hardy–WeinbergSources of variation and selection pressuresTypes of selection and allopatric and sympatric speciationGenetic drift, founder effects and the route to speciationCommunities, ecosystems, niches and carrying capacityCompetition, predation, quadrats and mark-release-recaptureMark-release-recapture assumptions and successionSuccession, conservation and evaluating the evidence
The Control of Gene Expression
Topic overviewTypes of gene mutation and mutagenic agentsSilent, frameshift, missense and nonsense mutationsTotipotent, pluripotent and induced pluripotent stem cellsTranscription factors, oestrogen, epigenetics and twin studiesDNA methylation, histone acetylation and cancerRNA interference and epigenetic drug targetsBenign and malignant tumours, suppressor genes and oncogenesAbnormal methylation, oestrogen and evidence on causes of cancerGenome projects, the proteome and sequencing methodsTransgenic organisms and making DNA fragmentsThe polymerase chain reactionPromoters, restriction endonucleases, sticky ends and ligaseTransformation, marker genes and uses of recombinant DNAThe humanitarian debate, cDNA and in vivo cloningDNA probes, hybridisation and screening for allelesGenetic counselling, personalised medicine and screening ethicsVNTRs, PCR and gel electrophoresisUsing and interpreting genetic fingerprints
Organisms Exchange Substances with Their Environment
Evaluating mass flow, potometers and transpiration rate
- 3 things to know
- Papers 1 and 3
Overview
Recall questions on the evidence for and against the mass flow hypothesis, how light, temperature, humidity and air movement affect transpiration, and measuring water uptake with a potometer.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Process
Describe the mechanism by which companion cells actively load sucrose into sieve tube elements.
Key term
What does a potometer measure?
Questions from this subtopic
Each one with the model answer underneath.
- 1
State two pieces of evidence that support the mass flow hypothesis.
Model answer
Phloem sap moves from high to low pressure regions, and flow rates are consistent with pressure gradients.
- 2
Describe the mechanism by which companion cells actively load sucrose into sieve tube elements.
Model answer
Companion cells use ATP to actively load sucrose via co-transport with hydrogen ions.
- 3
What does a potometer measure?
Model answer
A potometer measures the rate of water uptake by a cut shoot, which approximates the rate of transpiration.
- 4
How does increasing light intensity affect transpiration rate?
Model answer
Increasing light intensity increases transpiration rate, as stomata open wider for photosynthesis.
- 5
How does increasing temperature affect transpiration rate?
Model answer
Increasing temperature increases transpiration rate, as water molecules have more kinetic energy and evaporate faster.
- 6
How does high humidity affect transpiration rate?
Model answer
High humidity decreases transpiration rate by reducing the water potential gradient between the leaf and the air.
Other ways to work this
The same content, four other ways.
What is inside Levo
Six ways to work the same material.
Every question in Organisms Exchange Substances with Their Environment, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
Or £46 a year, about £3.83 a month. Cancel anytime.