Process
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
Cells, Viruses and Reproduction of Living Things
Significant figures, estimates and mathematical symbols
- 3 things to know
- Papers 1, 2 and 3
Overview
Recall questions on giving biological calculations to an appropriate number of significant figures, standard form, estimating a result to check a calculation, spotting an implausible cell size, and the symbols <, <<, >> and ~.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Process
How can estimating a result help when carrying out a biological calculation?
Process
A student calculates the diameter of a human red blood cell from a micrograph as 750 µm. Why should the answer be recognised as wrong?
Questions from this subtopic
Each one with the model answer underneath.
- 1
To how many significant figures should the result of a biological calculation be given?
Model answer
To no more significant figures than the least precise (fewest significant figures) measurement used in the calculation.
- 2
Why should a calculated cell size not be given to more significant figures than the raw data?
Model answer
Extra figures would claim a precision that the measurements do not have, because a result can only be as precise as the least precise measurement used.
- 3
A mitochondrion is recorded as 0.00340 mm long. How many significant figures does the value have?
Model answer
Three; the leading zeros only fix the decimal point and are not significant, but the final zero after the 4 is significant.
- 4
A cell diameter is recorded as 0.020 mm. Write the value in standard form, keeping the correct number of significant figures.
Model answer
2.0 × 10⁻² mm; the final zero is significant, so the value has two significant figures and must not be written as 2 × 10⁻² mm.
- 5
An eyepiece graticule is calibrated at 2.4 µm per division, and a cell spans 37 divisions. Calculate the length of the cell to an appropriate number of significant figures.
Model answer
Length = 2.4 × 37 = 88.8 µm, which is 89 µm to two significant figures, matching the calibration value.
- 6
A drawing of a guard cell is 48 mm long, and the actual cell is 0.042 mm long. Calculate the magnification to an appropriate number of significant figures.
Model answer
Magnification = 48 ÷ 0.042 = 1142.9, which is ×1100 to two significant figures.
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