Which structures are part of the insect respiratory system?

• A. Spiracles and tracheal tubes
• B. Gills
• C. Book lungs
• D. Skin diffusion

Answer: (A)

Insects breathe through a dedicated internal network of air tubes called the tracheal system, beginning with external openings called spiracles. Air enters through these spiracles, travels down progressively finer tubes (tracheae) and reaches cells through the tiny endings (tracheoles), delivering oxygen directly where it’s needed and releasing carbon dioxide. This setup is why spiracles and tracheal tubes are the structures of the insect respiratory system. Gills are used by many aquatic organisms and aren’t part of the typical insect system, book lungs belong to arachnids, and skin diffusion is not the main mechanism for most insects.