Gas exchange

Definition

The passive movement of respiratory gases—principally oxygen and carbon dioxide—across a biological or environmental surface by diffusion, driven by partial pressure gradients rather than metabolic energy. In arthropods, this occurs across diverse interfaces: the cuticular lining of tracheae and tracheoles in insects and some arachnids; book lungs and book gills in chelicerates; the general body surface in many small or aquatic species; and rectal gills in dragonfly nymphs. The process also describes abiotic diffusion at air-water interfaces relevant to aquatic insect ecology.

Etymology

Example

A diving beetle carries an air bubble as a physical gill: as oxygen diffuses into the bubble from the water and CO2 diffuses out, the bubble's gas composition equilibrates with the surrounding water, extending submergence time through this cutaneous gas exchange.

Synonyms

• respiratory exchange
• diffusive respiration

Related Terms

• Trachea
• Tracheole
• Spiracle
• book lung
• cutaneous respiration
• physical gill
• Plastron
• partial pressure
• countercurrent exchange

Usage Notes

Distinguished from active ventilation (the mechanical movement of respiratory medium) and from cellular respiration (the metabolic oxidation of substrates). Specialists often reserve 'gas exchange' for the diffusive step itself, not the entire respiratory chain. In aquatic entomology, the term encompasses both biological membranes and the air-water interface of bubbles or compressible gills.