Explain the link between the size of an organism and the way in which its cells are supplied with oxygen.
(6)
mark scheme:
Note: Accept converse argument throughout
Small organisms have large surface/volume ratio;
as, for example, most protoctista/single-celled
organisms/platyhelminths/cnidaria; diffusion/exchange over body surface/skin;
(the need for) specialised respiratory/gas-exchange surfaces in larger
animals;
diffusion is a slow process;
cells of larger organisms are a long way from gas exchange surface;
must be supplied by transport system/circulatory system/blood;
max 6
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