The respiratory system of an insect is relatively simple. Insects have
about twenty holes, called spiracles, in their exoskeletons, which
allow air to pass into tubes called trachea. The
trachea in turn branch out into smaller and smaller tubes
which reach out to each cell of the insect's body. Most insects have ten
spiricles on each side of their body for a total of
twenty spiracles. The tubes carry
oxygen directly to the cells and
carbon dioxide out of the cells. The passage of these materials into
and out of the cells takes place by diffusion. The only exceptions
are a few aquatic insects which have gill-like structures, and a few other insects which rely
only on diffusion to breath.
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