Key term
AQA GCSE Biology 8461
Bioenergetics
Cell Biology
Topic overviewEukaryotes and prokaryotesAnimal and plant cellsCell specialisation and differentiationMicroscopyGrowing bacteria and aseptic techniqueCalculating bacterial growth, and testing antiseptics and antibioticsChromosomes, mitosis and the cell cycleStem cells in embryos, adults and meristemsTherapeutic cloning, its risks, and cloning plantsDiffusion and the factors affecting its rateSurface area to volume ratio and exchange surfacesOsmosisActive transport
Ecology
Topic overviewLevels of organisation in an ecosystem, and what organisms needCompetition, interdependence and stable communitiesAbiotic factorsBiotic factorsAdaptationsProducers, food chains and sampling with quadrats and transectsPredators, prey and measuring population sizeHow materials are cycledDecompositionWaste management and biodiversityLand use, deforestation and global warmingMaintaining biodiversityTrophic levels and pyramids of biomassTransfer of biomassFactors affecting food securityFarming techniques and sustainable fisheriesRole of biotechnologyImpact of environmental change
Homeostasis and Response
Topic overviewHomeostasisThe nervous system and the reflex arcThe structure of the eye and accommodationMyopia, hyperopia and how they are correctedThe brain and the control of body temperatureHuman endocrine systemInsulin, glucagon and diabetesWater and ion loss, and the production of ureaThe kidneys, ADH and treating kidney failureHormones in human reproductionContraceptionThe use of hormones to treat infertilityNegative feedbackPlant hormones and their uses
Infection and Response
Topic overviewCommunicable (infectious) diseasesViral diseasesBacterial diseasesFungal and protist diseasesHuman defence systemsVaccinationAntibiotics and painkillersDiscovery and development of drugsProducing monoclonal antibodiesUses of monoclonal antibodiesDetection and identification of plant diseasesPlant defence responses
Inheritance, Variation and Evolution
Topic overviewSexual and asexual reproductionMeiosisAdvantages and disadvantages of sexual and asexual reproductionDNA and the genomeDNA as a polymer of four nucleotidesProtein synthesis and complementary base pairingMutations, protein shape and non-coding DNAGenetic terms, dominant and recessive allelesPunnett squares, probability and genetic crossesInherited disorders and sex determinationVariationEvolutionSelective breedingWhat genetic engineering is, and what it is used forGM crops, their risks, and the steps of the processCloningDarwin, Lamarck and the acceptance of evolutionSpeciationThe understanding of geneticsEvidence for evolution, and extinctionFossilsResistant bacteriaClassification of living organisms
Organisation
Topic overviewLevels of organisation, and how enzymes workAmylase, proteases and lipasesBile, food tests and the effect of pH on amylaseThe heart, the lungs and double circulationThe pacemaker, the blood vessels and the bloodCoronary heart disease: a non-communicable diseaseHealth issuesRisk factors and causal mechanisms in diseaseSampling, correlation and interpreting risk dataCancerPlant tissues, and transpiration and its rateRoot hair cells, xylem, phloem and stomata
Inheritance, Variation and Evolution
Punnett squares, probability and genetic crosses
- 2 things to know
- Paper 2
Overview
Characteristics controlled by several genes, why a cross predicts only probabilities, ratios and percentages from 3:1 and 1:1 crosses, and worked crosses in mice, cats, peas and a recessive disorder.
What you need to know
Answer each one before you reveal it.
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Key term
Why can a genetic cross only predict the likely proportions of the offspring?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Are most characteristics controlled by one gene or by many?
Model answer
Most are the result of several genes interacting rather than a single gene.
- 2
A characteristic shows a wide range of values across a population rather than two clear types. Suggest why.
Model answer
It is controlled by several genes interacting, not by a single gene.
- 3
In a single gene cross the chance of an offspring showing a phenotype is 1 in 4. If 100 offspring are produced, will exactly 25 show it?
Model answer
Not necessarily, because the chance applies separately to each offspring, so the actual number varies around 25.
- 4
Why can a genetic cross only predict the likely proportions of the offspring?
Model answer
Which allele each gamete carries is a matter of chance, so the result is a probability rather than a certainty.
- 5
A cross produces offspring in the ratio 3 round seeds to 1 wrinkled seed. What percentage of the offspring have wrinkled seeds?
Model answer
25%.
- 6
A cross gives 3 tall plants for every 1 short plant. Out of 60 offspring, how many are expected to be tall?
Model answer
45 plants.
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