Gills are part of which body system in fish?

Gills are part of which body system in fish?

• A. Digestive
• B. Circulatory
• C. Respiratory
• D. Nervous

Answer: (C)

Gills are the respiratory organs of fish, specialized for gas exchange with the surrounding water. Oxygen dissolved in water diffuses into the blood through the gill membranes, while carbon dioxide diffuses out into the water. The gills are structured with a large surface area—thin filaments and many lamellae—to maximize this exchange, and they often use countercurrent flow, where water and blood move in opposite directions, making oxygen uptake very efficient. This function is distinct from digestion, which involves breaking down food, and from the nervous system, which processes signals. While the circulatory system carries gases once they’re in the blood, the gills themselves are defined by their role in respiration.