Key term
CCEA A-Level Biology 1010
Biological Molecules
Topic overviewWater as a solventInorganic ions and their rolesMonosaccharides and the glycosidic bondDisaccharides and polysaccharidesLipids, triglycerides and phospholipidsAmino acids and protein structureProtein shape, conjugated proteins and prionsNucleic acids: nucleotides, DNA and RNADNA replication and the Meselson–Stahl experimentBiochemical tests and paper chromatography
Enzymes
Topic overviewEnzymes as globular proteins and the active siteSpecificity, cofactors and coenzymesActivation energy and models of enzyme actionThe effect of temperature and pHThe effect of substrate and enzyme concentrationCompetitive and non-competitive inhibitionEnzymes as biomarkers of disease and inhibitors as drugsImmobilised enzymes and biosensors
Viruses and Cell Structure
Topic overviewBacteriophage and HIV structureViral replication in host cellsProkaryotic and eukaryotic cells comparedMembrane structure: the fluid mosaic modelFunctions of membrane componentsMitochondria and chloroplastsRibosomes, endoplasmic reticulum, Golgi apparatus and lysosomesThe nucleus, the cytoskeleton and plasmodesmataPlant, fungal and animal cellsMicroscopy, cell measurement and cell fractionation
Cell Physiology and Transport
Continuity of Cells
Topic overviewThe cell cycle: interphase and the gap phasesControl points in the cell cycle and cancerChromosome structure, haploidy and diploidyMitosis: the events of the four stagesCytokinesis and the significance of mitosisAnticancer drugs and the cell cycleMeiosis I and the first divisionMeiosis II and the significance of meiosisPreparing and examining slides of cell division
Tissues and Organs
Exchange Surfaces and Gas Exchange
Topic overviewSurface area, volume and the surface area to volume ratioFeatures of efficient exchange surfacesThe need for mass transport systemsFick's law and the rate of gas exchangeGas exchange in plants and the compensation pointGas exchange at the alveolusThe respiratory tree and the mechanism of ventilationThe effects of smoking on the breathing systemUsing a respirometer to measure gas exchange
Transport in Plants
Topic overviewEpidermis, endodermis and the tissues of the rootXylem vessels and their lignification patternsPhloem: sieve-tube elements and companion cellsWater and mineral ion uptake by root hairsThe apoplast and symplast pathwaysTranspiration and the factors affecting its rateCohesion-tension theory and the transpiration streamTranslocation of organic solutes in the phloemXerophytes and hydrophytes
The Circulatory System in Mammals
Topic overviewDouble circulation and the major blood vesselsThe structure and function of arteries, veins and capillariesAtherosclerosis, atheroma and the investigation of blood vesselsThe structure of the mammalian heartThe cardiac cycle and the operation of the valvesMyogenic stimulation and the electrocardiogramBlood cells and the stained blood filmPlasma, tissue fluid and blood clottingHaemoglobin and the oxygen dissociation curveThe Bohr effect, myoglobin and altitude
Adaptation and Biodiversity
Topic overviewAdaptation and the ways organisms meet environmental challengesEcological factors and the ecological nicheSampling procedures and sampling devicesEstimating abundance, density, frequency and percentage coverThe biochemical basis of life and the levels of biodiversityMeasuring species diversity with Simpson's indexHandling data: averages, spread and the t-testTaxonomy, nomenclature and the binomial systemThe concept of a speciesThe taxonomic hierarchy from genus to kingdomPhylogenetic taxonomy and molecular evidenceThe five kingdom system: prokaryotae, protoctista and fungiPlantae, animalia and alternative classification systems
Human Impact on Biodiversity
Topic overviewMonoculture, polyculture and intensive agricultureCrop rotation and hedgerow conservationPredator strips, pesticides and integrated pest managementOrganic pollution of waterways by slurry and silage effluentEutrophication and fertiliser run-offBiological oxygen demand and reducing aquatic pollutionConservation initiatives and habitat protectionGlobal warming, climate change and biodiversity
Homeostasis and Excretion
Topic overviewPrinciples of homeostasis and negative feedbackExcretion, osmoregulation and nitrogenous wasteGross structure of the kidney and the urinary systemStructure of the nephron and its blood supplyEpithelia of the nephron and their adaptationsThe glomerular filterUltrafiltration and the forces that drive itSelective reabsorption in the proximal convoluted tubuleThe loop of Henlé and the medullary salt gradientADH, osmoreceptors and the control of water balance
Immunity
Topic overviewNatural barriers to infectionAntigens, antibodies and the antigen–antibody reactionAntibody-mediated immunity and B-lymphocytesCell-mediated immunity and T-lymphocytesActive immunity, passive immunity and vaccinationTransplant rejection and immunosuppressionBlood group polymorphism and the rhesus factorTransfusion compatibility and its consequencesAntibiotic resistance and the search for new antimicrobialsELISA and the detection of disease biomarkers
Co-Ordination and Control
Topic overviewPhytochromes and the control of floweringPlant growth substances and stem elongationThe structure of a neuroneResting potential, threshold and the action potentialImpulse propagation and the speed of conductionSynapse structure and chemical transmissionExcitatory and inhibitory post-synaptic potentialsGross structure of the eye and accommodationThe retina, rods and conesSkeletal muscle and the sliding filament theory
Populations and Communities
Topic overviewPopulation growth curves, carrying capacity and environmental resistancer-selected and K-selected speciesInteractions between populationsBiological control of pest speciesPopulation dynamics and changes in population sizeEstimating population size in the field and the laboratoryCommunities and ecosystemsSuccession and climax communities
Ecological Energetics and Nutrient Cycling
Topic overviewFood chains, food webs and detritus food chainsTrophic levels, gross and net primary productionEcological pyramids and their usefulnessEnergy transfer efficiency between trophic levelsWhy energy is lost at each trophic levelImplications for agriculture and intensive farmingThe carbon cycleThe nitrogen cycle and the role of bacteria
Respiration
Topic overviewATP and the ATP/ADP cycleGlycolysisThe mitochondrion and the sites of aerobic respirationThe link reaction and the Krebs cycleThe electron transport chain and oxidative phosphorylationATP yield from one molecule of glucoseAnaerobic respiration in animals, plants and fungiAerobic and anaerobic respiration compared, and oxygen debtRespiratory quotient and measuring respiration
Photosynthesis
Topic overviewChloroplast structure and the sites of photosynthesisPhotosynthetic pigments and paper chromatographyAbsorption spectra and action spectraPhotosystems, photoactivation and the Z-schemePhotolysis of water, reduced NADP and redox indicatorsCarbon dioxide fixation and rubiscoReduction of glycerate phosphate and regeneration of ribulose bisphosphateLimiting factors, the compensation point and measuring photosynthesis
DNA as the Genetic Code
Topic overviewGenes and the nature of the genetic codeExons, introns and RNA splicingComparing DNA and RNATranscription and RNA polymeraseTransfer RNA, ribosomes and the sites of translationTranslation and polypeptide synthesisOne gene, one polypeptide and the control of the phenotypeEpigenetics, methylation and histone modification
Gene Technology
Topic overviewThe polymerase chain reactionDNA probes and genetic markersMicroarrays, pharmacogenetics and personalised medicineGenetic fingerprinting and gel electrophoresisThe stages of gene transferGenetically modified microorganismsTransgenic animals and plantsGene therapyGenome sequencing and the Human Genome ProjectGene inactivation and knockout organismsSocial, ethical and ecological issues of gene technology
Genes and Patterns of Inheritance
Topic overviewGenotype, phenotype and the environmentChromosomes, genes and allelesMonohybrid inheritance and Mendel's first lawCodominance, multiple alleles and lethal allelesTest crossesDihybrid inheritance and Mendel's second lawAutosomes, sex chromosomes and sex determinationGene interaction and epistasisPolygenic inheritance and continuous variationThe chi-squared test
Population Genetics and Evolution
Evolutionary Trends in Plants
Cell Physiology and Transport
Membrane permeability
- 3 things to know
- Unit AS 1
Overview
Why a fat-soluble substance crosses the bilayer easily, three substances that cross a membrane through the bilayer itself and why an ion cannot cross the bilayer directly.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Name three substances that cross a membrane through the bilayer itself.
Key term
Explain why water can cross the bilayer even though it is a polar molecule.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Why is a cell surface membrane described as partially permeable?
Model answer
It allows some substances to pass through freely while restricting or excluding others.
- 2
Which substances can pass directly through the phospholipid bilayer?
Model answer
Fat-soluble substances pass through directly, and so does water because its molecules are sufficiently small.
- 3
Explain why a fat-soluble substance crosses the bilayer easily.
Model answer
It dissolves in the hydrophobic fatty acid tails that form the interior of the bilayer, so it can pass straight through.
- 4
Name three substances that cross a membrane through the bilayer itself.
Model answer
Oxygen, carbon dioxide and steroid hormones all cross through the bilayer.
- 5
Explain why water can cross the bilayer even though it is a polar molecule.
Model answer
A water molecule is small enough to slip between the phospholipid molecules despite being polar.
- 6
Explain why an ion cannot cross the bilayer directly.
Model answer
The ion carries a charge and is repelled by the hydrophobic interior of the bilayer, so it cannot dissolve in it.
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