Which describes the observed behavior of sea stars in the tank that contained only seawater?

• A. They remained at the bottom.
• B. They climbed to the top of the tank.
• C. They died.
• D. They moved randomly at mid-depth.

Answer: (B)

Sea stars respond to conditions in their environment, moving toward areas that meet their needs. In a tank filled with seawater, the dissolved oxygen is typically higher near the surface because of gas exchange with the air. To get more oxygen for their metabolism, sea stars use their tube feet to move upward, which is why they’re observed climbing to the top of the tank. This behavior reflects a natural tendency to seek out areas with better oxygen availability, allowing for more efficient respiration.