Which describes the internal anatomy of insects?

• A. Closed circulatory system, lungs, and four-chambered heart
• B. Open circulatory system, multitude of breathing tubes and three-chambered digestive system
• C. Dorsal nerve cord and notochord
• D. Single-celled bacteria inside

Answer: (B)

Insects have an open circulatory system, where hemolymph is not confined to vessels but bathes the tissues directly. They breathe through a tracheal system—many breathing tubes that deliver air through openings called spiracles—providing gas exchange without lungs. Their digestive tract is organized into three main parts: foregut, midgut, and hindgut. This combination—the open circulatory system, a network of breathing tubes, and a three-part digestive system—best describes insect internal anatomy. The other descriptions align with mammals (closed circulatory system, lungs, four-chamber heart), chordates (dorsal nerve cord and notochord), or bacteria, which don’t fit insects.