The respiratory structures of insects are

Analyze the question: It asks which structures insects use for gas exchange (breathing).

Explain the concept: Different animals have different respiratory organs:

• Body surface (skin): earthworms, amphibians (partly)
• Gills: fish, tadpoles, crabs, prawns
• Lungs: mammals, birds, reptiles, adult amphibians
• Tracheae (tracheal system): insects

Show the solution:

1. Insects have a network of tiny air tubes called tracheae, which branch into even finer tubes called tracheoles.
2. Air enters through small openings on the sides of the thorax and abdomen called spiracles.
3. Oxygen travels directly through the tracheae and tracheoles to the body cells, and carbon dioxide leaves by the same route. The blood does not carry oxygen in insects.

Now check the options:

• A. Body surfaces: used by earthworms, not insects, because insects have a waterproof exoskeleton.
• B. Gills: used by aquatic animals such as fish (some aquatic insect larvae have gills, but this is not the general respiratory structure of insects).
• C. Kidneys: these are excretory organs, not respiratory ones. Insects use Malpighian tubules for excretion.
• D. Lung: not present in insects.
• E. Tracheae: correct.

Answer: E. tracheae.

Tip: Remember "Insects = Spiracles → Tracheae → Tracheoles." The word trachea means air tube, and insects breathe through a system of air tubes.