Insects are invertebrates with relatively high oxygen demands.
Insect bodies have a branching system of tubes running through them (Tracheae and tracheoles). Tracheae are lined with spirals of chitin which keeps the structure but is also impermeable to gases.
Smaller tracheoles have no chitin so are freely permeable to gases.Tracheae open to the outside by pores called spiracles which are found along the thorax and abdomen.
The tracheal system:
Oxygen diffuses into the tracheae through the spiracles and then into tracheoles to eventually end up in cells of organs. CO2 leaves in the opposite way.
In large, very active insects the abdomen can be pumped in and out to draw in more air. This is called mechanical ventilation.
The insect gas exchange system therefore provides a large SA, with its network of tiny tracheoles, which have very thin surfaces.
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