Which structure is used for gas exchange in aquatic animals?

Which structure is used for gas exchange in aquatic animals?

• A. Gills
• B. Fins
• C. Eyes
• D. Head

Answer: (A)

Gas exchange in aquatic animals relies on structures that maximize contact between water and a blood supply. Gills are specialized for this, with a large surface area formed by thin filaments and lamellae, plus a rich network of capillaries. Water flowing over the gills brings oxygen that diffuses into the blood, while carbon dioxide diffuses out into the water. The high efficiency is often aided by countercurrent flow, where water and blood move in opposite directions to maintain a favorable diffusion gradient. Fins are for swimming and steering, not for exchanging gases. Eyes are for vision, and the head houses the brain and sensory organs, not gas exchange.

Gas exchange in aquatic animals relies on structures that maximize contact between water and a blood supply. Gills are specialized for this, with a large surface area formed by thin filaments and lamellae, plus a rich network of capillaries. Water flowing over the gills brings oxygen that diffuses into the blood, while carbon dioxide diffuses out into the water. The high efficiency is often aided by countercurrent flow, where water and blood move in opposite directions to maintain a favorable diffusion gradient.

Fins are for swimming and steering, not for exchanging gases. Eyes are for vision, and the head houses the brain and sensory organs, not gas exchange.