Which term denotes the membranes involved in respiration for aquatic organisms?

• A. Gas Exchange
• B. Echolocation
• C. Gill Membranes
• D. Exoskeleton

Answer: (C)

The concept being tested is that aquatic respiration relies on specialized gas exchange membranes—the gill membranes. These membranes are thin, moist, and highly vascularized, forming a large surface area on the gills where water passing over them allows dissolved oxygen to diffuse into the blood and carbon dioxide to diffuse out. The thin epithelium and dense network of capillaries maximize diffusion, making gill membranes the primary site of respiration in most aquatic organisms. Water flow over these membranes, often with efficient exchange (such as countercurrent flow), further enhances gas transfer. The other terms don’t refer to a specific respiratory surface: gas exchange is the general process, echolocation is a sensory function, and an exoskeleton is a structural feature.