Biology STAAR Test 2025 – 400 Free Practice Questions to Pass the Exam

Arthropods breathe primarily through a tracheal system, which consists of a network of tubes that transport air directly to their tissues and cells. This system is highly efficient for gas exchange because it allows oxygen to diffuse directly into the body without needing to pass through the circulatory system.

The tracheal system opens to the outside environment through small openings called spiracles, located on the sides of the body. These spiracles can be opened or closed to regulate airflow, helping to conserve water, which is particularly crucial for terrestrial arthropods. The air travels along the tracheae and reaches tiny tracheoles that deliver oxygen to individual cells throughout the organism.

While some arthropods, such as certain aquatic species, may have adaptations that include gills, the predominant mode of respiration for the majority of terrestrial arthropods involves this specialized tracheal system. Other options, like lungs and swim bladders, are associated with different groups of organisms—lungs are typical in mammals and some other vertebrates, while swim bladders are adaptations found in many fish to help with buoyancy rather than respiration. Thus, the presence of the tracheal system is a defining feature of arthropod respiration.