Gas Exchange in Other Organisms

This lesson covers gas exchange in organisms other than mammals, as required by the Edexcel A-Level Biology specification (9BI0). You need to understand gas exchange in fish, insects, and plants (including the leaf and stomata). The specification also expects you to compare the efficiency of different exchange systems and understand how each is adapted to the organism's environment.

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Gas Exchange in Fish — The Gills

Fish are aquatic organisms that extract dissolved oxygen from water. Water contains far less dissolved oxygen than air (approximately 1% compared with 21%), so fish require a highly efficient gas exchange system.

Structure of Fish Gills

Fish have four pairs of gills, located in gill chambers on either side of the head, protected by a bony flap called the operculum (in bony fish).

Each gill consists of:

1. Gill arch — a bony support structure
2. Gill filaments (primary lamellae) — long, thin projections extending from each gill arch
3. Secondary lamellae (gill plates) — thin, plate-like structures on each gill filament; these are the actual sites of gas exchange

Adaptations for Efficient Gas Exchange