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 Respond to Changes in Their Internal and External Environments
- 28 subtopics
- 83 things to know
- Papers 2 and 3
What Organisms Respond to Changes in Their Internal and External Environments covers
Organisms Respond to Changes in Their Internal and External Environments is examined on Paper 2 of AQA Biology, which covers topics 5 to 8, and on Paper 3, which can draw on any topic. 354 recall questions across 28 subtopics.
Where it is assessed
Papers 2 and 3
Topics 5 to 8, then the synoptic paper.
Check the AQA specification ↗The 28 subtopics
Each one has its own page.
- IAA, gravitropism and phototropismRecall questions on why organisms respond to their environment, plant growth factors, how IAA affects cell elongation in roots and shoots, and how its redistribution causes gravitropism and phototropism.Open →
- Taxes, kineses, reflex arcs and choice chambersRecall questions on taxes and kineses, the three-neurone reflex arc and why reflexes protect, and investigating woodlice or maggots with a choice chamber and the chi-squared test.Open →
- The Pacinian corpuscle and generator potentialsRecall questions on why receptors are specific to one stimulus, generator potentials, and how pressure deforms the lamellae of a Pacinian corpuscle to open stretch-mediated sodium ion channels.Open →
- Rods, cones, colour vision and visual acuityRecall questions on the sensitivity and pigments of rods and cones, the three types of cone and colour vision, retinal convergence, visual acuity and where rods and cones lie in the retina.Open →
- The SAN, AVN, bundle of His and Purkyne tissueRecall questions on myogenic heart muscle, how the sinoatrial node starts atrial systole, the delay at the atrioventricular node, and how the bundle of His and Purkyne tissue make the ventricles contract.Open →
- Chemoreceptors, baroreceptors and cardiac outputRecall questions on where chemoreceptors and baroreceptors are and what they detect, how the medulla changes heart rate through sympathetic and parasympathetic nerves, and cardiac output and stroke volume.Open →
- Motor neurone structure and the resting potentialRecall questions on the cell body, dendrites, axon, myelin sheath and nodes of Ranvier of a motor neurone, and how the sodium-potassium pump and membrane permeability set up the resting potential.Open →
- Depolarisation, action potentials and saltatory conductionRecall questions on voltage-gated sodium and potassium channels in depolarisation and repolarisation, threshold, hyperpolarisation, the all-or-nothing principle, and conduction along non-myelinated and myelinated axons.Open →
- The refractory period and speed of conductionRecall questions on the absolute and relative refractory periods and how they separate impulses, make them one-way and limit their frequency, and how myelination, axon diameter and temperature affect speed.Open →
- Synapse structure and the neuromuscular junctionRecall questions on the synaptic cleft, presynaptic and postsynaptic membranes, synaptic vesicles, mitochondria and receptor proteins, and the folded motor end plate of a neuromuscular junction.Open →
- Transmission at a cholinergic synapseRecall questions on how an action potential opens calcium ion channels, how acetylcholine is released by exocytosis and binds its receptors, and how sodium ion entry triggers a new action potential.Open →
- Acetylcholinesterase, summation and inhibitory synapsesRecall questions on the breakdown and recycling of acetylcholine, why transmission is unidirectional, temporal and spatial summation, and how chloride ion channels at inhibitory synapses cause hyperpolarisation.Open →
- Neuromuscular junctions compared, agonists and antagonistsRecall questions on how a neuromuscular junction differs from a cholinergic synapse between neurones, and how agonist, antagonist and enzyme-inhibiting drugs change synaptic transmission.Open →
- Drug effects and potassium channels in hyperpolarisationRecall questions on predicting the effects of drugs that block reuptake, block calcium channels or force neurotransmitter release, and how potassium ions leaving the postsynaptic cell cause hyperpolarisation.Open →
- Antagonistic muscle pairs and muscle fibre structureRecall questions on how antagonistic pairs of muscles work against a skeleton to move a joint, fascicles, the multinucleate structure of muscle fibres, myofibrils and the sarcomere.Open →
- Sarcomere bands, actin, myosin and tropomyosinRecall questions on the A-band, I-band and H-zone and how they change in contraction, the structure of myosin and actin filaments, tropomyosin, and the release of calcium ions.Open →
- The sliding filament cycle, ATP and phosphocreatineRecall questions on how calcium ions move tropomyosin, cross-bridge formation, the power stroke and detachment, the roles of ATP in contraction and relaxation, and how phosphocreatine regenerates ATP.Open →
- Slow twitch and fast twitch muscle fibresRecall questions on how slow and fast twitch fibres contract, why they differ in mitochondria, colour and energy stores, the activities each suits, and what happens to muscle when ATP runs out.Open →
- Control systems and why temperature, pH and glucose matterRecall questions on homeostasis, the receptors, coordination centres and effectors of a control system, and why core temperature, blood pH and blood glucose concentration must stay within limits.Open →
- Negative and positive feedbackRecall questions on the stages of a negative feedback loop, why separate antagonistic mechanisms give finer control, why levels oscillate around a set point, and how positive feedback differs.Open →
- Glycogenesis, glycogenolysis and gluconeogenesisRecall questions on how diet and exercise change blood glucose concentration, and when and from what the liver carries out glycogenesis, glycogenolysis and gluconeogenesis.Open →
- How insulin, glucagon and adrenaline actRecall questions on how insulin binds its receptors and increases glucose uptake and glycogenesis, how glucagon acts on liver cells, and how adrenaline affects glycogen in liver and muscle.Open →
- The second messenger model, diabetes and the sugar debateRecall questions on adenylate cyclase, cyclic AMP and protein kinase in the second messenger model, the causes and control of Type I and Type II diabetes, and the positions of health advisers and the food industry on sugar.Open →
- Glucose calibration curves and hormones affecting blood glucoseRecall questions on measuring glucose concentration with a colorimeter and a calibration curve, signal amplification by second messengers, and the effects of insulin, glucagon and adrenaline on blood glucose.Open →
- Osmoregulation, osmoreceptors and ADHRecall questions on osmoregulation, osmoreceptors in the hypothalamus, where ADH is produced, stored and released, and how it makes the distal convoluted tubule and collecting duct more permeable to water.Open →
- Nephron structure and ultrafiltrationRecall questions on the Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct, and how ultrafiltration in the glomerulus forms glomerular filtrate.Open →
- The proximal convoluted tubule and the loop of HenleRecall questions on reabsorption of glucose and water in the proximal convoluted tubule and how its cells are adapted, and how the permeability of the two limbs of the loop of Henle concentrates the medulla.Open →
- The distal tubule, collecting duct and urine concentrationRecall questions on water reabsorption from the distal convoluted tubule and collecting duct, how high and low ADH levels change urine, loop of Henle length, and osmoregulation as negative feedback.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Process
How does a receptor respond to a stimulus?
Evaluation
Why are rods good for low light and cones for colour?
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How does muscle relaxation occur after contraction?
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What is indoleacetic acid (IAA)?
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Does IAA have the same effect on cell elongation in roots and shoots?
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What is a taxis?
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Why do different receptors respond to different types of stimuli?
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How does the brain enable colour vision using cone cells?
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What does it mean to say the heart is myogenic?
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What is the role of the SAN in controlling heartbeat?
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What do chemoreceptors involved in heart rate control detect?
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What do baroreceptors (pressure receptors) detect?
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What structure in a myelinated motor neurone contains the nucleus?
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What is the function of dendrites in a motor neurone?
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What type of ion channels open during depolarisation?
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How does membrane permeability to sodium change during depolarisation?
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Define the absolute refractory period.
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What characterises the relative refractory period?
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What is the approximate width of the synaptic cleft?
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Name the membrane that forms the boundary of the neurone transmitting the signal at a synapse.
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What ion channels open in the postsynaptic membrane when acetylcholine binds to its receptors?
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Explain how the opening of sodium ion channels in the postsynaptic membrane can lead to a new action potential.
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How is choline returned to the presynaptic knob after acetylcholine breakdown?
Process
What molecules are used to resynthesise acetylcholine, and what is required for this process?
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At a neuromuscular junction, what is the neurotransmitter and what is the effect on the muscle?
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Can acetylcholine have an inhibitory effect at a cholinergic synapse between neurones?
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What effect would a drug that inhibits neurotransmitter reuptake have on synaptic transmission?
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What would happen if a drug stimulated continuous release of neurotransmitter from the presynaptic knob?
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In an antagonistic muscle pair, what happens to one muscle when the other contracts?
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When an antagonistic muscle pair produces movement in one direction, what must happen to produce movement in the opposite direction?
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What defines the boundaries of a sarcomere?
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What is the A-band in a sarcomere?
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What happens to tropomyosin when calcium ions bind to regulatory proteins?
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Describe the contraction characteristics of slow twitch muscle fibres.
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Describe the contraction characteristics of fast twitch muscle fibres.
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What is homeostasis?
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Why is maintaining a stable core body temperature important for enzyme function?
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Define negative feedback.
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What type of response does an effector produce during negative feedback?
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Name three factors that influence blood glucose concentration.
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What effect does physical activity have on blood glucose concentration?
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How does insulin initially interact with its target cells?
Process
What metabolic process does insulin promote by activating specific enzymes?
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Which two hormones involved in blood glucose regulation act via the second messenger model?
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What is the first step in the second messenger model of hormone action?
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What variables are plotted on a glucose calibration curve?
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Does insulin use the second messenger model to exert its effects?
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What is the definition of osmoregulation?
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Which receptors detect changes in blood water potential, and where are they located?
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Which part of the nephron is located immediately after the Bowman's capsule?
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What is the name of the hairpin-shaped structure of the nephron that extends into the medulla?
Process
By what transport mechanisms is glucose reabsorbed from the filtrate in the proximal convoluted tubule?
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How is a concentration gradient established in the proximal convoluted tubule to drive reabsorption?
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What determines how much water is reabsorbed in the distal convoluted tubule?
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What type of urine is produced when ADH levels are high?
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How do low and high concentrations of IAA affect cell elongation in roots?
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What is a kinesis?
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What is established in a receptor when it is stimulated?
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Why are rod cells unable to provide colour vision?
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After the SAN generates an electrical impulse, how does atrial systole occur?
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Which part of the brain contains the cardiovascular centre that controls heart rate?
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What is the role of the axon in a motor neurone?
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In which direction do sodium ions move during depolarisation?
Numbers
If the refractory period is 2 milliseconds, how would you calculate the maximum frequency of impulse transmission?
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What is the name of the membrane that receives the signal at a synapse?
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Explain why synaptic transmission is unidirectional.
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State two structural differences between a neuromuscular junction and a typical neurone-to-neurone synapse.
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In which direction do potassium ions move when potassium channels open in the postsynaptic membrane?
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How does an antagonistic muscle pair produce movement at a joint?
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Define the H-zone.
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What is exposed on actin when tropomyosin changes position?
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Why do fast twitch muscle fibres appear paler than slow twitch fibres?
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What happens to enzymes if core body temperature rises too high?
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What is the overall outcome of a complete negative feedback loop?
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Define glycogenesis.
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How does glucagon interact with liver cells?
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What enzyme is activated when a hormone binds to its receptor in the second messenger model?
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What would happen to blood glucose levels if the liver could not perform glycogenolysis?
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Where is ADH stored and from where is it released into the blood?
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Which tubular region of the nephron comes after the loop of Henle?
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Describe how glucose enters proximal convoluted tubule cells from the filtrate.
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What happens to water reabsorption in the collecting duct when ADH levels are low?
Take Organisms Respond to Changes in Their Internal and External Environments further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
A taxis vs A kinesis
A taxis: a directional response in which an organism moves towards or away from a stimulus. A kinesis: a non-directional response in which the rate of turning changes with the intensity of a stimulus.
The resting potential vs The action potential
The resting potential: the difference in charge across an axon membrane when it is not conducting an impulse, about −70 mV. The action potential: the brief reversal of the resting potential when the membrane depolarises to about +40 mV.
Depolarisation vs Repolarisation
Depolarisation: the influx of sodium ions that makes the inside of the axon less negative. Repolarisation: the efflux of potassium ions that restores the negative charge inside.
Questions from this topic
Each one with the model answer underneath.
- 1
Why do organisms respond to changes in their environment?
Model answer
To increase their chance of survival.
- 2
Where are plant growth factors produced, and what happens to them after production?
Model answer
They are produced in growing regions and move to other tissues where they regulate growth.
- 3
What role do plant growth factors play in relation to directional stimuli?
Model answer
They regulate growth in response to directional stimuli.
- 4
What is indoleacetic acid (IAA)?
Model answer
A plant growth factor that affects cell elongation.
- 5
Does IAA have the same effect on cell elongation in roots and shoots?
Model answer
No, IAA has different effects on cell elongation in roots compared to shoots.
- 6
How do low and high concentrations of IAA affect cell elongation in roots?
Model answer
Low concentrations promote cell elongation in roots, while high concentrations inhibit it.
What is inside Levo
Six ways to work the same material.
Organisms Respond to Changes in Their Internal and External Environments revision questions
- What does Organisms Respond to Changes in Their Internal and External Environments cover in AQA A-Level Biology?
- 28 subtopics: iaa, gravitropism and phototropism, taxes, kineses, reflex arcs and choice chambers, the pacinian corpuscle and generator potentials, rods, cones, colour vision and visual acuity, the san, avn, bundle of his and purkyne tissue, chemoreceptors, baroreceptors and cardiac output, motor neurone structure and the resting potential, depolarisation, action potentials and saltatory conduction, the refractory period and speed of conduction, synapse structure and the neuromuscular junction, transmission at a cholinergic synapse, acetylcholinesterase, summation and inhibitory synapses, neuromuscular junctions compared, agonists and antagonists, drug effects and potassium channels in hyperpolarisation, antagonistic muscle pairs and muscle fibre structure, sarcomere bands, actin, myosin and tropomyosin, the sliding filament cycle, atp and phosphocreatine, slow twitch and fast twitch muscle fibres, control systems and why temperature, ph and glucose matter, negative and positive feedback, glycogenesis, glycogenolysis and gluconeogenesis, how insulin, glucagon and adrenaline act, the second messenger model, diabetes and the sugar debate, glucose calibration curves and hormones affecting blood glucose, osmoregulation, osmoreceptors and adh, nephron structure and ultrafiltration, the proximal convoluted tubule and the loop of henle and the distal tubule, collecting duct and urine concentration. Each one has its own page with questions and model answers.
- How is Organisms Respond to Changes in Their Internal and External Environments organised?
- By the AQA 7402 specification, subtopic by subtopic, so it matches the order you are taught it in.
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