O₂ used in respiration

End of tracheoles has low O₂ so gradient created

Diffuse along tracheae to tracheoles to cells

CO₂ produced in respiration

Opposing direction gradient

Diffuse from cells to tracheoles to tracheae to atmosphere

Quicker diffusion in air

Movement of muscles

Creates mass air movement in and out of tracheae

Speeds up gas exchange

Gas enters amd leaves the tracheae via these tiny pores

Opened and closed by valves

Open = water evaporates and gas exchange occurs

Closed = (most of the time) prevents water loss

Relies of diffusion

Need short pathway so insects must be small

Waterproof covering:

Rigid outer skeleton with waterproof cuticle

Over body surfaces

Small S.A:Vol ratio:

Minimise waterloss area

Strengthening rings to stop collapsing

Divide into smaller tubes - tracheoles

Extend throughout all tissues

Atmospheric air brought straight to respiring tissues