Gas Exchange in mammals

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Gases + nutrients need to enter organisms across exchange surfaces (usually cell membranes)

They also need to exchange waste products eg CO2

Smaller organisms have a higher SA:V ratio (think of mouse Vs hippo)

Amoeba have a v. high SA:V ratio - this is why they can exchange substances over a whole surface by diffusion

Larger, multicellular organsisms have a lower SA:V ratio - they require specialised exchange surfaces with large SA's

Animals release heat from respiration, so larger animals are more likely to overheat, and smaller animals spend a lot of energy keeping warm as they easily lose heat (high SA:V ratio).


In mammals, the specialised exchange surface is the lungs

Cartilage: add strength + flexibility, keep trachaea open

Cilia: line the trachaea, bronchi, bronchioles. Waft mucous + trapped particles up and out to protect the lungs

Goblet cells: produce mucous to trap dust + other inhaled particles

Smooth muscle: around bronchi + bronchioles. Involuntary muscle contractions can narrow airways


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