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
- 19 subtopics
- 57 things to know
- Papers 1 and 3
What Organisms Exchange Substances with Their Environment covers
Organisms Exchange Substances with Their Environment is examined on Paper 1 of AQA Biology, which covers topics 1 to 4, and on Paper 3, which can draw on any topic. 303 recall questions across 19 subtopics.
Where it is assessed
Papers 1 and 3
Topics 1 to 4, then the synoptic paper.
Check the AQA specification ↗The 19 subtopics
Each one has its own page.
- Surface area to volume ratio, metabolic rate and calculationsRecall questions on why surface area to volume ratio falls as size increases, why large organisms need exchange surfaces and transport systems, and calculating the ratio for cubes, spheres and cylinders.Open →
- Gas exchange in single-celled organisms, insects and fishRecall questions on diffusion across the surface of single-celled organisms, spiracles and tracheoles in insects, gill filaments, lamellae and the counter-current principle in fish, and dissecting fish gills.Open →
- Leaf gas exchange, insect water loss and xerophytesRecall questions on stomata and air spaces in the mesophyll of dicotyledonous leaves, how insects limit water loss through their spiracles, and the adaptations of xerophytic plants.Open →
- Trachea, bronchi, alveoli and lung dissectionRecall questions on the lungs, trachea, bronchi, bronchioles and alveoli, how the alveolar epithelium and blood supply suit gas exchange, ventilation, and what a lung dissection shows.Open →
- Inspiration, expiration and pulmonary ventilation rateRecall questions on the roles of the diaphragm and external and internal intercostal muscles in breathing in and out, forced expiration, and calculating pulmonary ventilation from tidal volume and breathing rate.Open →
- Lung disease, correlation, insect tracheae and Spearman's rankRecall questions on how lung disease reduces gas exchange, correlation, causation and risk-factor data, the insect tracheal system, and using scattergrams and Spearman's rank correlation coefficient.Open →
- Digestion of carbohydrates and lipidsRecall questions on digestion by hydrolysis, amylases and membrane-bound disaccharidases such as maltase, sucrase and lactase, and lipid digestion by lipase after emulsification by bile salts.Open →
- Endopeptidases, exopeptidases and dipeptidasesRecall questions on where endopeptidases, exopeptidases and membrane-bound dipeptidases hydrolyse peptide bonds, why they work faster together, and where and how the products of digestion are absorbed.Open →
- Co-transport of amino acids, micelles and chylomicronsRecall questions on co-transport of sodium ions with glucose and amino acids in the ileum, how micelles deliver fatty acids and monoglycerides to epithelial cells, and how chylomicrons enter the lacteals.Open →
- Haemoglobin, red blood cells and the dissociation curveRecall questions on the quaternary structure and haem groups of haemoglobin, how red blood cells suit oxygen transport, loading and unloading of oxygen, and the shape of the oxyhaemoglobin dissociation curve.Open →
- Cooperative binding, the Bohr effect and different haemoglobinsRecall questions on how binding of the first oxygen molecule makes further binding easier, the Bohr effect of carbon dioxide on the dissociation curve, and why organisms have different haemoglobins.Open →
- Double circulation and the major blood vesselsRecall questions on the pulmonary and systemic circulations of mammals, the advantage of a double circulation, the vessels entering and leaving the heart and kidneys, and the coronary arteries.Open →
- Heart chambers, the cardiac cycle and heart dissectionRecall questions on the chambers, septum and valves of the heart, pressure and volume changes in atrial systole, ventricular systole and diastole, cardiac output, and safely dissecting and drawing a heart.Open →
- Arteries, arterioles, veins and capillariesRecall questions on how the walls and lumen of arteries, arterioles and veins relate to their functions, the valves in veins, and how thin walls and narrow lumens suit capillaries.Open →
- Tissue fluid, cardiovascular risk factors and semilunar valvesRecall questions on how tissue fluid forms and returns to capillaries and the lymph, risk factors for cardiovascular disease and correlation versus causation, and the position and action of the semilunar valves.Open →
- Xylem structure and the cohesion-tension theoryRecall questions on the hollow, lignified vessels and pits of xylem, and how transpiration, cohesion and adhesion move water up the stem by cohesion-tension without using ATP.Open →
- Phloem structure, companion cells and translocationRecall questions on translocation, sieve tube elements with their sieve plates and reduced cytoplasm, companion cells and plasmodesmata, and loading sucrose at the source in the mass flow hypothesis.Open →
- Mass flow from source to sink, tracers and ringingRecall questions on how water entering at the source and leaving at the sink drives mass flow in phloem, why translocation needs energy, and what tracer and ringing experiments show.Open →
- Evaluating mass flow, potometers and transpiration rateRecall 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.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Why might conflicting evidence arise about risk factors for cardiovascular disease?
Key term
What happens to the surface area to volume ratio of an organism as its size increases?
Process
By what process do single-celled organisms exchange gases with their environment?
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What are spiracles in the insect tracheal system?
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What structural feature of the mesophyll allows gases to move between stomata and photosynthesising cells?
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Describe the diffusion pathway for gases in a dicotyledonous leaf.
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What is the trachea in the human respiratory system?
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What are bronchi?
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How does the movement of the ribs during inspiration affect the thoracic cavity?
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Explain how changes in thoracic volume cause air to enter the lungs during inspiration.
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How could increased diffusion distance impair gas exchange in lung disease?
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In what way can impaired ventilation reduce gas exchange?
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What is digestion?
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Where are membrane-bound disaccharidases located?
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At what position in a polypeptide chain do endopeptidases hydrolyse peptide bonds?
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Why is protein digestion faster when endopeptidases and exopeptidases work together rather than separately?
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What substances are carried simultaneously by co-transporter proteins in the ileum?
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What are micelles composed of?
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How many polypeptide subunits make up a haemoglobin molecule?
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How many haem groups does each polypeptide subunit of haemoglobin contain?
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When the first oxygen molecule binds to haemoglobin, does it bind with high or low affinity?
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What happens to haemoglobin's structure when the first oxygen molecule binds?
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What type of circulatory system do mammals have?
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What does the pulmonary circulation connect?
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What causes heart valves to open and close?
Process
Name the three stages of the cardiac cycle.
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Describe the wall structure of arteries in terms of thickness.
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How does the lumen of arteries compare to their wall thickness, and why?
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How is tissue fluid formed at the arterial end of a capillary?
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What is the function of xylem tissue in plants?
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What is the state of xylem vessel cells when they are functional?
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What type of substances does phloem tissue transport?
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Define translocation.
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How does water enter sieve tube elements at the source?
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What happens to sucrose at the sink, and how does this affect water potential?
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State two pieces of evidence that support the mass flow hypothesis.
Process
Describe the mechanism by which companion cells actively load sucrose into sieve tube elements.
Key term
Between two organisms of the same shape but different sizes, which has the larger surface area to volume ratio?
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How does oxygen reach the respiring cells of an insect from the tracheoles?
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What features of spongy mesophyll make it well-suited for gas exchange?
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What are bronchioles?
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What role does elastic recoil play in expiration?
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What is required to establish a causal relationship between two variables?
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What are the products when maltase hydrolyses maltose?
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In which part of the gut are the products of digestion absorbed?
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What is the key difference between where endopeptidases and exopeptidases cleave peptide bonds?
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What ion is found within each haem group, and what is its function?
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After the first oxygen binds to haemoglobin, what happens to the affinity of the remaining binding sites?
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What does the systemic circulation connect?
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What happens during atrial systole?
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What feature of arteriole walls allows them to control blood flow to tissues?
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How does hydrostatic pressure at the venous end of a capillary compare to the arterial end?
Evaluation
What substance strengthens the walls of xylem vessels?
Key term
Name the two cell types that make up phloem tissue.
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How does water leave sieve tube elements at the sink?
Key term
What does a potometer measure?
Take Organisms Exchange Substances with Their Environment further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Inspiration vs Expiration
Inspiration: air movement into lungs following increased thoracic volume and reduced pressure. Expiration: air movement from lungs following decreased thoracic volume and increased pressure.
Artery vs Vein
Artery: a vessel carrying blood away from the heart under relatively high pressure. Vein: a vessel carrying blood towards the heart under relatively low pressure.
Xylem vs Phloem
Xylem: dead lignified tissue transporting water and mineral ions upwards. Phloem: living tissue translocating assimilates between sources and sinks.
Questions from this topic
Each one with the model answer underneath.
- 1
What happens to the surface area to volume ratio of an organism as its size increases?
Model answer
The surface area to volume ratio decreases.
- 2
Explain why surface area to volume ratio decreases as an object gets larger.
Model answer
Surface area increases as the square of linear dimensions, while volume increases as the cube of linear dimensions, so volume increases faster than surface area.
- 3
Between two organisms of the same shape but different sizes, which has the larger surface area to volume ratio?
Model answer
The smaller organism has the larger surface area to volume ratio.
- 4
How is surface area to volume ratio calculated?
Model answer
By dividing total surface area by total volume.
- 5
Why do larger organisms need specialised exchange systems?
Model answer
Their surface area to volume ratio is too small for diffusion across the body surface alone to meet their metabolic demands.
- 6
Name one adaptation that increases surface area relative to volume in organisms.
Model answer
Flattened body shape.
What is inside Levo
Six ways to work the same material.
Organisms Exchange Substances with Their Environment revision questions
- What does Organisms Exchange Substances with Their Environment cover in AQA A-Level Biology?
- 19 subtopics: surface area to volume ratio, metabolic rate and calculations, gas exchange in single-celled organisms, insects and fish, leaf gas exchange, insect water loss and xerophytes, trachea, bronchi, alveoli and lung dissection, inspiration, expiration and pulmonary ventilation rate, lung disease, correlation, insect tracheae and spearman's rank, digestion of carbohydrates and lipids, endopeptidases, exopeptidases and dipeptidases, co-transport of amino acids, micelles and chylomicrons, haemoglobin, red blood cells and the dissociation curve, cooperative binding, the bohr effect and different haemoglobins, double circulation and the major blood vessels, heart chambers, the cardiac cycle and heart dissection, arteries, arterioles, veins and capillaries, tissue fluid, cardiovascular risk factors and semilunar valves, xylem structure and the cohesion-tension theory, phloem structure, companion cells and translocation, mass flow from source to sink, tracers and ringing and evaluating mass flow, potometers and transpiration rate. Each one has its own page with questions and model answers.
- How is Organisms Exchange Substances with Their Environment organised?
- By the AQA 7402 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Organisms Exchange Substances with Their Environment, on a schedule.
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