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
Exchange and Transport in Animals
Alveoli and gas exchange
- 3 things to know
- Paper 2
Overview
Alveoli as the site of gas exchange, how their number, one-cell-thick walls, capillary network, moist lining and ventilation keep the diffusion of oxygen and carbon dioxide fast, and the two cell layers oxygen crosses into the blood.
What you need to know
Answer each one before you reveal it.
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Key term
Explain how having millions of alveoli helps gas exchange.
Key term
Explain how the thickness of an alveolus wall helps gas exchange.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Name the tiny air sacs in the lungs where gas exchange takes place.
Model answer
Gas exchange takes place in the alveoli.
- 2
Explain how having millions of alveoli helps gas exchange.
Model answer
Together they provide a very large surface area, so far more oxygen and carbon dioxide can diffuse at the same time.
- 3
Explain how the thickness of an alveolus wall helps gas exchange.
Model answer
The wall is only one cell thick, giving a very short diffusion distance so gases cross quickly.
- 4
Describe the direction each gas moves in at an alveolus.
Model answer
Oxygen diffuses from the air in the alveolus into the blood, and carbon dioxide diffuses from the blood into the alveolus.
- 5
Explain how the capillary network wrapped around each alveolus keeps gas exchange fast.
Model answer
Flowing blood constantly carries oxygen away and brings carbon dioxide, which keeps the concentration gradients steep.
- 6
Explain why the inner lining of an alveolus is moist.
Model answer
Gases must dissolve in the film of moisture before they can diffuse across the alveolus wall.
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