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 biotechnology
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 reproductionContraceptionPlant hormones and their uses
Infection and Response
Inheritance, Variation and Evolution
Topic overviewSexual and asexual reproductionMeiosisAdvantages and disadvantages of sexual and asexual reproductionDNA and the genomeDNA as a polymer of four nucleotidesGenetic 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
Cell Biology
Calculating bacterial growth, and testing antiseptics and antibiotics
- 3 things to know
- Paper 1
Overview
Colony and clear-zone areas from πr², bacterial numbers after a run of divisions, and the agar plate method for testing antibiotics and antiseptics, zones of inhibition and the control disc.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
A clear area around a disc has a diameter of 10 mm. Calculate its area to one decimal place.
Key term
How is the number of divisions worked out from a growth time and a mean division time?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How is the cross-sectional area of a circular bacterial colony calculated?
Model answer
Using πr², where r is the radius of the colony.
- 2
A colony has a radius of 6 mm. Calculate its cross-sectional area to the nearest whole number.
Model answer
113 mm².
- 3
A clear area around a disc has a diameter of 10 mm. Calculate its area to one decimal place.
Model answer
78.5 mm², because the radius is 5 mm.
- 4
How is the number of divisions worked out from a growth time and a mean division time?
Model answer
Divide the total time by the mean division time.
- 5
One bacterium divides every 20 minutes. How many bacteria are there after 2 hours?
Model answer
64, because there are 6 divisions and 2⁶ is 64.
- 6
A culture starts with 20 bacteria and the mean division time is 25 minutes. How many bacteria are present after 100 minutes?
Model answer
320, because 4 divisions give 20 × 16.
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