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2.2 Adaptations for gas exchange
1. Living things need to obtain materials such as carbon dioxide and oxygen from the environment and
remove waste from their cells to the environment.
Organisms are differently adapted so gas exchange can take place whether it be in
water or on land. In particular…

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be thin so diffusion paths are short
moist to allow a medium for gasses dissolve in before diffusion
maintain a concentration gradient so diffusion will take place.

9. The large moist area for gaseous exchange is a region of potential water loss.



10. Earthworms are multicellular, terrestrial animals restricted to…

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Fish can be further classified into two groups according to the material that makes up their
skeleton.
Cartilaginous fish:
Skeletons are made entirely of cartilage.
Normally live in the sea e.g. shark
Characterised by five gill clefts that
open at five gill slits.
Gas exchange involves parallel flow.
Therefore blood…

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14. Compared with parallel flow, counter current flow increases efficiency because the
diffusion gradient between the adjacent flows is maintained over the whole surface.

Blood flows between the gill plates under pressure in the opposite direction the blood in the
capillaries. The blood always meets water with higher oxygen content…

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