Numbers
Edexcel A-Level Biology B 9BI0
Biological Molecules
Topic overviewMonosaccharides, disaccharides and polysaccharidesGlycosidic bonds and condensation reactionsStarch, glycogen and cellulose structureTriglycerides and phospholipidsSaturated and unsaturated fats and lipid propertiesAmino acid structure and the peptide bondPrimary, secondary, tertiary and quaternary structureFibrous and globular proteinsThe structure of DNADNA replication and gene mutationsThe structure of RNATranscription and translationEnzymes as globular proteinsFactors affecting enzyme activityMeasuring the rate of enzyme activityUnits, uncertainty and experimental errorEnzyme inhibitionInorganic ionsThe properties of water
Cells, Viruses and Reproduction of Living Things
Topic overviewCell theory and eukaryotic cell structureProkaryotic cells and Gram stainingMicroscopy, magnification and resolutionSignificant figures, estimates and mathematical symbolsVirus structure and classificationThe lytic cycle and latencyTreating viral disease and the ethics of untested drugsThe cell cycle and its regulationMitosis and the behaviour of chromosomesMitosis in growth, repair and root tip squashesMeiosis, genetic variation and chromosome mutationsGametogenesis in mammalsFertilisation and early embryo developmentPollen and embryo sac formationDouble fertilisation in flowering plantsInvestigating pollen tube growth
Classification and Biodiversity
Exchange and Transport
Topic overviewSurface area to volume ratioThe fluid mosaic modelDiffusion, osmosis and facilitated diffusionActive transport, endocytosis and exocytosisGas exchange in insects, fish and mammalsDissecting the insect gas exchange systemGas exchange in flowering plantsThe structure of the heart and blood vesselsThe double circulatory systemThe cardiac cycleMyogenic stimulation and ECG tracesThe composition of bloodThe functions of blood and clottingAtherosclerosis and its risk factorsHaemoglobin and the Bohr effectOxygen dissociation curvesFormation of tissue fluidThe lymphatic systemXylem and phloem structureApoplastic and symplastic pathwaysThe cohesion-tension theoryMeasuring transpiration with a potometerTranslocation and the mass flow hypothesis
Energy for Biological Processes
Topic overviewAn overview of aerobic respirationGlycolysisThe link reaction and the Krebs cycleThe electron transport chainChemiosmosis and ATP yieldAnaerobic respiration and ATP yieldMeasuring respiration with a respirometerAbsorption and action spectraPhotosynthetic pigments and chromatographyChloroplast structure and the light-dependent stageThe Calvin cycleLimiting factors in photosynthesis
Microbiology and Pathogens
Topic overviewCulturing microorganisms and aseptic techniqueMeasuring bacterial growthThe bacterial growth curveBacteria as pathogensThe action of antibioticsAntibiotic resistanceOther pathogenic agentsControlling endemic diseasePhagocytosis and the humoral responseThe cell-mediated immune responseMemory cells and the secondary responseNatural and artificial immunityVaccination and herd immunity
Modern Genetics
Origins of Genetic Variation
Topic overviewMutation, meiosis and random fertilisationGenotype, phenotype and monohybrid inheritanceDihybrid crosses and pedigree diagramsAutosomal linkage and sex linkageThe chi-squared test in geneticsSelection pressures and allele frequencyGenetic drift and the founder effectThe Hardy-Weinberg equation
Control Systems
Topic overviewHomeostasis and negative feedbackChemical control in mammalsPlant growth substancesAuxins, cytokinins and apical dominancePhytochrome and photomorphogenesisThe organisation of the nervous systemBrain regions and divisions of the peripheral nervous systemThe autonomic nervous systemResting potential and the action potentialPropagation and saltatory conductionSynaptic transmissionEffects of drugs on the nervous systemThe structure of the retina and rhodopsinRods, cones and visual acuityControl of heart rateKidney structure and ultrafiltrationSelective reabsorption and the loop of HenleADH and osmoregulationThermoregulation in endotherms
Ecosystems
Topic overviewEcosystems, habitats and nichesPyramids of numbers, biomass and energyEcological techniques for measuring distributionChoosing the right ecological techniquePresenting data in tables and graphsStatistical tests in ecologyProductivity and energy transfer efficiencyDecomposers and nutrient cyclingSuccessionBiotic and abiotic factors in population changeHuman influences on ecosystemsSustainability, resource management and peer review
Exchange and Transport
- 23 subtopics
- 71 things to know
- Papers 1, 2 and 3
What Exchange and Transport covers
Why size forces multicellular organisms to evolve exchange surfaces, how substances cross membranes, gas exchange in insects, fish, mammals and plants, the mammalian circulatory system and the blood, and how water and sugars move through a plant.
Where it is assessed
Papers 1, 2 and 3
Examined on every paper.
Check the Pearson Edexcel specification ↗The 23 subtopics
Each one has its own page.
- Surface area to volume ratioRecall questions on why surface area to volume ratio falls with size and what that means for exchange surfaces and mass transport, and on calculating the ratio for cubes, spheres, cylinders and rectangular prisms.Open →
- The fluid mosaic modelRecall questions on the fluid mosaic model, membrane thickness, intrinsic and extrinsic proteins, cholesterol, glycoproteins, glycolipids and receptors, and the beetroot investigation of how temperature affects membrane permeability.Open →
- Diffusion, osmosis and facilitated diffusionRecall questions on passive transport and simple diffusion, facilitated diffusion through carrier and channel proteins, osmosis and aquaporins, which molecules cross the bilayer directly, the water potential equation, and finding the water potential of plant tissue with sucrose solutions.Open →
- Active transport, endocytosis and exocytosisRecall questions on endocytosis, exocytosis, phagocytosis and pinocytosis, active transport by carrier proteins, the role of ATP, and how phosphorylation of ADP and hydrolysis of ATP make it the universal energy currency.Open →
- Gas exchange in insects, fish and mammalsRecall questions on tracheae and spiracles, the counter-current gill, and alveolar structure and ventilation.Open →
- Dissecting the insect gas exchange systemRecall questions on dissecting an insect to reveal its gas exchange system: the tools used, removing the exoskeleton, identifying spiracles and silvery-white tracheae, recording observations, and the ethical handling and disposal of the organisms.Open →
- Gas exchange in flowering plantsRecall questions on stomata and guard cells, gas exchange through the air spaces and moist cell walls of the spongy mesophyll, the balance with water loss, and lenticels in woody stems and roots.Open →
- The structure of the heart and blood vesselsRecall questions on the chambers, valves and vessels, and on how artery, vein and capillary structure fits function.Open →
- The double circulatory systemRecall questions on the advantages over a single circulation, and on the comparison with bony fish.Open →
- The cardiac cycleRecall questions on the atrioventricular and semilunar valves, atrial and ventricular systole and diastole, cardiac output, stroke volume and heart rate calculations, and reading valve movements and pressure changes from a pressure graph.Open →
- Myogenic stimulation and ECG tracesRecall questions on the SAN, AVN and bundle of His, and on interpreting the P, QRS and T features of an ECG.Open →
- The composition of bloodRecall questions on plasma, erythrocytes, and the leucocytes including neutrophils, eosinophils, monocytes and lymphocytes.Open →
- The functions of blood and clottingRecall questions on what blood transports and how it defends against pathogens, platelets, and the clotting cascade from thromboplastin and calcium ions through prothrombin and thrombin to a fibrin mesh.Open →
- Atherosclerosis and its risk factorsRecall questions on the stages of atherosclerosis from endothelial damage to atheroma, arteriosclerosis and thrombosis, its effects on the heart and brain, its risk factors, and reading scatter diagrams and correlation against causation for lifestyle data.Open →
- Haemoglobin and the Bohr effectRecall questions on the quaternary structure of haemoglobin and its haem groups, cooperative binding, the Bohr effect and its mechanism through carbonic acid and hydrogen ions, and the forms in which carbon dioxide is carried in the blood.Open →
- Oxygen dissociation curvesRecall questions on reading the sigmoid curve, comparing foetal and adult haemoglobin, and myoglobin.Open →
- Formation of tissue fluidRecall questions on hydrostatic and oncotic pressure at each end of a capillary bed, and what tissue fluid contains.Open →
- The lymphatic systemRecall questions on lymph, why about a tenth of tissue fluid is not reabsorbed into capillaries, its drainage through blind-ended lymphatic capillaries and vessels, its return to the blood, and how the system prevents oedema.Open →
- Xylem and phloem structureRecall questions on xylem vessels and lignification, and on sieve tube elements and companion cells.Open →
- Apoplastic and symplastic pathwaysRecall questions on the two routes across a root, the Casparian strip, and where each pathway is blocked.Open →
- The cohesion-tension theoryRecall questions on cohesion and adhesion, how transpiration pulls an unbroken column of water up the xylem, embolisms, and how temperature, light intensity, humidity and air movement affect the rate of transpiration.Open →
- Measuring transpiration with a potometerRecall questions on setting up a potometer underwater without air bubbles, calculating the rate of water uptake from bubble movement, the variables to change and control, why uptake is not exactly transpiration, and reducing percentage error in the distance measured.Open →
- Translocation and the mass flow hypothesisRecall questions on source and sink, active loading at the source, and the evidence for and against mass flow.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State three factors that would increase the rate of simple diffusion across a membrane.
Key term
Define active transport.
Key term
How is the water potential of plant tissue found from changes in mass or length, and why is percentage change used?
Evaluation
How does the countercurrent system in fish gills maximise oxygen uptake?
Key term
What would happen to oxygen extraction efficiency if blood and water flowed in the same direction across fish gills?
Key term
How does ventilation maintain efficient gas exchange in mammalian lungs, and what would happen if ventilation stopped?
Process
Why must the cell walls of mesophyll cells be moist for gas exchange?
Process
Explain why arteries have a thick tunica media containing elastic fibres and smooth muscle, and a narrow lumen.
Key term
Describe the wall thickness and lumen of capillaries, and why the thin wall is significant.
Key term
Define systemic circulation.
Key term
Why can a mammal drive blood round its body faster than a fish can?
Process
What does the term myogenic mean in relation to the heart?
Key term
When do the semilunar valves open and close during the cardiac cycle?
Process
Why does aortic pressure remain relatively high during diastole?
Key term
Where are semilunar valves located and what is their function?
Process
How is tissue fluid formed at the arterial end of capillaries, and what is its function?
Key term
What is the Bohr effect, and how does it shift the oxygen dissociation curve?
Key term
What polypeptide chains make up fetal haemoglobin, and how does this differ from adult haemoglobin?
Key term
Define hydrostatic pressure and oncotic pressure in the context of the circulatory system.
Process
At the venous end of a capillary, why has hydrostatic pressure fallen and what happens to tissue fluid?
Numbers
How do plasma proteins contribute to fluid movement across capillary walls?
Key term
What drives the mass flow of phloem sap from source to sink, and what pressure exists at each end?
Process
How does water move through the apoplastic pathway, and how does its speed compare with the symplastic pathway?
Process
At the source, how does sugar loading cause water to enter sieve tubes, and what pressure results?
Key term
How is the rate of water uptake calculated from a potometer, and what does the 'distance' term represent?
Key term
How is a potometer set up without air bubbles, and how is the rate of water uptake then found?
Numbers
State the formula for calculating surface area to volume ratio.
Numbers
State the approximate thickness of a cell surface membrane.
Key term
What conditions can result from atherosclerosis in the coronary arteries?
Process
Where is the sinoatrial node located and what is its function?
Key term
What reaction does thrombin catalyse?
Evaluation
State one lifestyle factor related to physical activity that increases atherosclerosis risk.
Key term
How many polypeptide subunits make up a haemoglobin molecule?
Key term
What is the partial pressure of oxygen like in fetal blood at the placenta?
Key term
Explain why high humidity decreases the rate of transpiration.
Process
State the mass-flow hypothesis for phloem transport.
Key term
What is facilitated diffusion?
Key term
How does a carrier protein move a molecule by facilitated diffusion?
Key term
Describe the structure of erythrocytes and their main function.
Key term
How does the biconcave shape of erythrocytes aid their function?
Key term
How is tissue fluid formed from blood?
Key term
What substance is produced when fluid is forced out of capillaries at the arterial end?
Key term
Describe the lumen of a xylem vessel.
Key term
What does the cohesion-tension model explain?
Key term
Why does the surface area to volume ratio decrease as an organism grows larger?
Key term
The cell surface membrane is described as a fluid mosaic. What does each of those two words describe?
Key term
Why does the rate of facilitated diffusion level off even when the external concentration keeps rising?
Key term
How does the size of a molecule affect the way it is transported across a membrane?
Key term
How does oxygen reach respiring tissues in insects?
Key term
What structures are found on gill filaments that increase surface area?
Process
What ethical guidelines must be followed when dissecting an insect?
Process
Why do tracheae appear silvery-white during dissection?
Key term
Name the two upper chambers of the heart.
Key term
Name the atrioventricular valve found on the right side of the heart.
Key term
Describe what occurs during diastole in the cardiac cycle.
Key term
What are neutrophils and what is their function?
Key term
What is the tunica adventitia of an artery?
Key term
What happens when platelets encounter a damaged blood vessel?
Key term
What prosthetic group is found in each subunit of haemoglobin?
Key term
How many alpha chains are present in adult haemoglobin?
Key term
List the main components found in tissue fluid.
Process
Why do tissue fluid and lymph have lower protein concentration than plasma?
Process
What approximate percentage of tissue fluid is not reabsorbed at the venous end of capillaries?
Process
Where is lymph returned to the blood circulation?
Key term
What material impregnates the walls of xylem vessels?
Key term
How does transpiration create the driving force for water movement in xylem?
Process
In the formula for rate of water uptake, what does the 'distance' term represent?
Process
What would happen to the reliability of potometer results if air bubbles were present in the capillary tube?
Process
Why is water uptake measured by a potometer not exactly equal to transpiration?
Key term
Name the two cell types that make up phloem tissue.
Take Exchange and Transport further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Diffusion vs Active transport
Diffusion: net particle movement down a concentration gradient. Active transport: energy-dependent movement against a concentration gradient.
Systole vs Diastole
Systole: phase of cardiac muscle contraction. Diastole: phase of cardiac muscle relaxation.
Xylem vs Phloem
Xylem: vascular tissue carrying water and mineral ions. Phloem: vascular tissue translocating organic assimilates.
Questions from this topic
Each one with the model answer underneath.
- 1
Why does the surface area to volume ratio decrease as an organism grows larger?
Model answer
Volume increases as the cube of linear dimensions while surface area only increases as the square, so volume grows faster than surface area.
- 2
How does a low surface area to volume ratio affect exchange in large organisms?
Model answer
It limits the rate at which substances can be exchanged across the surface relative to the metabolic demands of the larger volume.
- 3
What does the surface area to volume ratio tell you about an organism?
Model answer
It indicates the amount of surface available for exchange relative to the volume of tissue that requires substances, affecting how efficiently exchange can occur.
- 4
Why can small organisms rely on diffusion alone for gas exchange without specialised systems?
Model answer
They have a sufficiently high surface area to volume ratio that diffusion across their body surface can meet all their exchange needs.
- 5
Why do larger organisms require specialised gas exchange surfaces?
Model answer
As organisms increase in size, their surface area to volume ratio decreases, so they need specialised surfaces to increase the area available for diffusion to meet metabolic demands.
- 6
Why do large organisms require a mass transport system in addition to exchange surfaces?
Model answer
Diffusion distances between exchange surfaces and metabolically active tissues become too great for diffusion alone to supply substances quickly enough.
What is inside Levo
Six ways to work the same material.
Exchange and Transport revision questions
- What does Exchange and Transport cover in Edexcel A-Level Biology B?
- 23 subtopics: surface area to volume ratio, the fluid mosaic model, diffusion, osmosis and facilitated diffusion, active transport, endocytosis and exocytosis, gas exchange in insects, fish and mammals, dissecting the insect gas exchange system, gas exchange in flowering plants, the structure of the heart and blood vessels, the double circulatory system, the cardiac cycle, myogenic stimulation and ecg traces, the composition of blood, the functions of blood and clotting, atherosclerosis and its risk factors, haemoglobin and the bohr effect, oxygen dissociation curves, formation of tissue fluid, the lymphatic system, xylem and phloem structure, apoplastic and symplastic pathways, the cohesion-tension theory, measuring transpiration with a potometer and translocation and the mass flow hypothesis. Each one has its own page with questions and model answers.
- How is Exchange and Transport organised?
- By the Edexcel 9BI0 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Exchange and Transport, 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.
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