Which of the following structures enables the exchange of gases in insects?

Analyze the question: The question asks which structure insects use for gaseous exchange (taking in oxygen and removing carbon dioxide).

Explain the concept: Insects have an open circulatory system, so their blood (haemolymph) does not carry oxygen to the tissues. Instead, they use a network of air tubes called tracheae:

• Air enters through small openings on the body surface called spiracles.
• The spiracles lead into the tracheae, which branch into finer tubes called tracheoles.
• The tracheoles reach right down to the cells, so oxygen diffuses directly to the tissues and carbon dioxide diffuses out.

Check each option:

• A. Skin: This is the gaseous exchange organ in earthworms and amphibians, not in insects. Insects have a hard, waterproof exoskeleton.
• B. Tracheae: This is the correct answer. It is the respiratory system of insects.
• C. Malpighian tubules: These are the excretory organs of insects. They remove nitrogenous waste (uric acid) from the haemolymph.
• D. Flame cell: These are excretory and osmoregulatory structures in flatworms such as planaria.

Answer: B. tracheae

Exam tip: Match each organism to its organ.

• Insects → tracheae (spiracles)
• Fish → gills
• Earthworm and amphibians → moist skin
• Mammals → lungs
• Insect excretion → Malpighian tubules
• Flatworm excretion → flame cells

Remember: "Trachea = air tubes for insects."