Which gas is required for most aquatic animal life?

Which gas is required for most aquatic animal life?

• A. Nitrogen
• B. Methane
• C. Carbon dioxide
• D. Dissolved oxygen

Answer: (D)

Respiration for most aquatic animals relies on oxygen dissolved in the water. These creatures extract O2 from the water through their gills or other respiratory surfaces, so the amount of dissolved oxygen available directly regulates their metabolism, activity, and survival. Oxygen dissolves in water more readily when the water is cooler, well-mixed, and not overly salty, and it can be depleted if respiration is rapid or water is stagnant. While nitrogen, carbon dioxide, and methane are present in aquatic environments, they do not serve as the primary respiratory gas for most aquatic animals—carbon dioxide is mainly a waste product of respiration (and can be used by photosynthetic organisms), nitrogen is largely inert in this context, and methane is produced under anaerobic conditions and not used for animal respiration. Therefore, dissolved oxygen is the gas essential for most aquatic life.

Respiration for most aquatic animals relies on oxygen dissolved in the water. These creatures extract O2 from the water through their gills or other respiratory surfaces, so the amount of dissolved oxygen available directly regulates their metabolism, activity, and survival. Oxygen dissolves in water more readily when the water is cooler, well-mixed, and not overly salty, and it can be depleted if respiration is rapid or water is stagnant. While nitrogen, carbon dioxide, and methane are present in aquatic environments, they do not serve as the primary respiratory gas for most aquatic animals—carbon dioxide is mainly a waste product of respiration (and can be used by photosynthetic organisms), nitrogen is largely inert in this context, and methane is produced under anaerobic conditions and not used for animal respiration. Therefore, dissolved oxygen is the gas essential for most aquatic life.