Understanding Evolution

Respiration: The tracheal triple whammy

All arthropods molt and have an exoskeleton — two factors that, as we've just seen, limit the body size of terrestrial animals. Insects, however, got triple-whammied in this department because of the way they breathe. While crustaceans breathe via gills and spiders use gill-like structures called book lungs, insects employ a different system. They get oxygen through tubes called tracheae.

The Crustacean/Spider Model

The Insect Model

Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout the body. Tracheae and tracheoles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells.


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