Key term
Edexcel GCSE Combined Science Biology 1SC0
Key Concepts in Biology
Topic overviewEukaryotic and prokaryotic cellsSpecialised cells and their adaptationsMicroscopes and magnification calculationsSize, scale and units in cell biologyEnzyme action and denaturationFactors affecting enzyme activityEnzymes in synthesis and digestion, and rate calculationsDiffusion, osmosis and active transportOsmosis in potatoes and percentage change in mass
Cells and Control
Genetics
Topic overviewMeiosis and the formation of gametesDNA structure, genes and the genomeExtracting DNA from fruitAlleles, genotype and phenotypeMonohybrid crosses and sex determinationProbability and ratios from genetic crossesCauses of variation: genes and environmentThe Human Genome ProjectGenetic variation and the effects of mutation
Natural Selection and Genetic Modification
Health, Disease and the Development of Medicines
Topic overviewHealth, disease and susceptibilityPathogens and common infectionsHow pathogens spread, and the virus life cycleSexually transmitted infectionsPhysical barriers and chemical defencesThe immune system, immunisation and herd immunityAntibiotics and developing new medicinesLifestyle factors and non-communicable diseaseTreatments for cardiovascular disease
Plant Structures and Their Functions
Animal Coordination, Control and Homeostasis
Exchange and Transport in Animals
Topic overviewWhy multicellular organisms need exchange surfacesAlveoli and gas exchangeThe blood and its componentsArteries, veins and capillariesThe heart and the circulatory systemCellular respiration as an exothermic reactionAerobic and anaerobic respiration comparedInvestigating the rate of respirationCardiac output, stroke volume and heart rate
Ecosystems and Material Cycles
Key Concepts in Biology
Size, scale and units in cell biology
- 3 things to know
- Papers 1 and 2
Overview
Typical sizes of bacterial and animal cells, orders of magnitude and when to estimate, the prefixes milli, micro, nano and pico and the number of micrometres in a millimetre, and the symbols for much less than, much greater than, approximately and proportional to.
What you need to know
Answer each one before you reveal it.
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Key term
State a typical width for an animal cell such as a cheek cell.
Numbers
Roughly how many times wider is a typical animal cell than a typical bacterium?
Questions from this subtopic
Each one with the model answer underneath.
- 1
State a typical diameter for a bacterial cell.
Model answer
A bacterial cell is typically about 1 µm across.
- 2
State a typical width for an animal cell such as a cheek cell.
Model answer
An animal cell is typically in the range 10–100 µm across.
- 3
Roughly how many times wider is a typical animal cell than a typical bacterium?
Model answer
About 10 to 20 times wider, since a typical animal cell is about 10–20 µm across and a typical bacterium about 1 µm.
- 4
What is meant by an order of magnitude difference in size?
Model answer
It means one thing is about ten times larger than the other, so each order of magnitude is another factor of ten.
- 5
Explain when it is sensible to give an estimate of a cell measurement rather than an exact value.
Model answer
An estimate is sensible when only the approximate size matters, such as comparing two structures, or when the measuring method is not precise enough.
- 6
A student estimates that a cell is 5 times the width of a neighbouring cell that measures 12 µm. What is the estimated width of the larger cell?
Model answer
It is about 60 µm, because 12 µm multiplied by 5 gives 60 µm.
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