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Module 2: Exchange and Transport
1.2.1 Exchange Surfaces and Breathing

(a) Explain, in terms of surface area: volume ratio, why multicellular organisms need specialised exchange
surfaces and singlecelled organisms do not

Multicellular Organisms Singlecelled Organisms
Small surface area: volume ratio their outer surface Large surface area: volume ratio diffusion alone…

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Module 2: Exchange and Transport
Elastic Fibres Prevents the alveoli from bursting , returns them to their original size and shape and expels
air by recoiling and decreasing volume
(f) Outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function
of the rib cage, intercostal…


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