Which statement describes the insect's internal anatomy?

• A. Closed circulatory system, limbs without joints, and four-chambered digestive system
• B. Open circulatory system, tracheal breathing tubes, and a three-chambered digestive system
• C. Pseudocoelom with gills and single-chambered stomach
• D. Blood circulates in vessels only; no breathing tubes

Answer: (B)

The main idea being tested is how an insect’s body handles circulation, respiration, and digestion. Insects have an open circulatory system, meaning the heart pumps hemolymph into the body cavity rather than through closed vessels. They breathe through a tracheal system—air moves via spiracles into branching tracheae and tracheoles that deliver oxygen directly to tissues. Their digestive tract is organized into three main regions: foregut (which includes structures like the crop and proventriculus), midgut where most digestion and absorption occur, and hindgut. This combination—open circulatory system, tracheal breathing tubes, and a three-part digestive tract—matches the description in the statement. The other options conflict with these defining features: insects do not have a closed circulatory system, do have breathing tubes, and their digestion isn’t a single or four-chambered process nor is it tied to gills or pseudocoelom.