The respiratory organ of a cockroach

Analyze the question: The question asks which structure a cockroach uses for gaseous exchange (its respiratory organ).

Explain the concept: Insects like the cockroach don't use their blood to carry oxygen. Instead, they have a system of branching air tubes called tracheae.

• Air enters the body through small openings on the sides of the thorax and abdomen called spiracles.
• The spiracles lead into the tracheae, which branch into finer tubes called tracheoles.
• The tracheoles carry oxygen directly to the body cells, and carbon dioxide leaves by the same route.

Solution (eliminating the options):

• A. Air sac: Found in birds (and as small dilations in some insects), but it is not the main respiratory organ of the cockroach.
• B. Trachea: Correct. The tracheal system is the respiratory organ of insects.
• C. Lung book: Found in arachnids such as spiders and scorpions, not insects.
• D. Lung: Found in mammals, reptiles, birds and amphibians (adults), not insects.

Answer: The correct option is B. trachea.

Exam tip: Match the animal to its respiratory organ:

• Insects (cockroach, grasshopper) → tracheae through spiracles
• Fish → gills
• Mammals → lungs
• Spiders and scorpions → book lungs
• Earthworm and amphibian (young) → skin and gills

Remember: "Insects = Spiracles + Tracheae."