Which statement about euryhaline organisms is correct?

Which statement about euryhaline organisms is correct?

• A. Live only in freshwater
• B. Require constant salinity to survive
• C. Tolerate a narrow range of salinities
• D. Tolerate a wide range of salinities

Answer: (D)

Euryhaline organisms can survive a wide range of external salinities because they actively regulate their internal water and salt balance as conditions change. This osmoregulatory flexibility is essential in habitats where salinity fluctuates, such as estuaries where freshwater mixes with seawater. By adjusting gill ion transport, kidney function, and hormonal controls, they maintain stable internal conditions despite outside changes. Because of this broad tolerance, the statement that they tolerate a wide range of salinities best describes euryhaline organisms. The other ideas imply a constant salinity, freshwater-only lifestyle, or a narrow tolerance, which don’t fit how euryhaline species cope with their environment. For example, some species migrate between freshwater and seawater and adjust their physiology accordingly.

Euryhaline organisms can survive a wide range of external salinities because they actively regulate their internal water and salt balance as conditions change. This osmoregulatory flexibility is essential in habitats where salinity fluctuates, such as estuaries where freshwater mixes with seawater. By adjusting gill ion transport, kidney function, and hormonal controls, they maintain stable internal conditions despite outside changes. Because of this broad tolerance, the statement that they tolerate a wide range of salinities best describes euryhaline organisms. The other ideas imply a constant salinity, freshwater-only lifestyle, or a narrow tolerance, which don’t fit how euryhaline species cope with their environment. For example, some species migrate between freshwater and seawater and adjust their physiology accordingly.