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Cards In This Set
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Why do multicellular organisms need specialised exchange surfaces?
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They have a small surface area to volume ration and so can't diffuse in everything they need as it can't get everywhere.
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Why can single celled organisms simply diffuse in all of their nutrients and oxygen?
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They have a small surface area to volume ratio and so the diffused substances reach everywhere.
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What features make for a good exchange surface?
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Large surface area - folding walls and membranesThin barrier to reduce diffusion distanceFresh supply of molecules on one sideRemoval of required molecules maintaining gradient
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What sized surface area is best for the lungs?
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Large surface area provides more space for molecules to pass through.
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What kind of barrier is best suited for the lungs?
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The plasma membrane surrounding the thin cytoplasm of the cells form the barrier to exchange.Barrier PERMEABLE to oxygen and carbon dioxide
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How thick is the alveolus wall?
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One cell thick
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How thick is the capillary wall?
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One cell thick
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What type of cells do both walls consist of?
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Squamous cells - meaning flattened or very thing
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Why are the capillaries so narrow?
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So erythrocytes are squeezed against the wall making them closer to the alveoli and reducing rate of blood flow.
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What is the total diffusion distance for the carbon dioxide to diffuse against?
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2 flattened cells thick - less than 1um
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How does the thin layer of moisture in the alveoli help diffusion?
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Gasses absorbed by moisture making it easier for substances to diffuse into capillaries.
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Why must the lungs produce a surfactant?
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Moisture of the lungs evaporates when we breathe out and without the surfactant to reduce cohesive forces between water molecules the alveoli would collapse.
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Outline the steps of inspiration
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Diaphragm contracts to become flatter, External intercostal muscles contract to raise ribs,Volume of chest cavity increasesPressure in chest cavity drops below atmospheric pressureAir moves into lungs
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Outline the steps of expiration
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Diaphragm relaxes and is pushed up,External intercostal muscles relax, ribs fall,Volume of chest cavity decreases,Pressure in lungs increases and rises above atmospheric pressure,Air moves out of lungs
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What can be found in the bronchioles?
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Larger may have some cartilage - not muchSmooth muscleBlood vesselsLoose tissue with elastic fibresCiliated epitheliumGoblet cell
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