What experimental setup did Garza and Robles use to test their hypothesis about sea stars?

• A. They placed some sea stars in seawater tanks and others in tanks with a layer of fresh water on top.
• B. They placed all sea stars in seawater tanks and exposed them to light/dark cycles.
• C. They placed sea stars in freshwater and saltwater tanks at different temperatures.
• D. They placed sea stars in identical tanks with varying salinity.

Answer: (B)

The key idea is isolating the variable you want to test. To see how light affects sea stars, all animals should experience the same overall conditions except for light exposure. Placing every sea star in seawater tanks keeps salinity and osmotic conditions constant, so any differences in behavior or physiology can be attributed to the presence or absence of light (the light/dark cycles). This setup directly tests whether light cues influence the sea stars, without confounding factors like changes in salinity or temperature.

Other setups introduce additional variables that could cloud the results. A freshwater layer on top creates osmotic stress and a mixed environment, not just a light effect. Mixing freshwater and saltwater with different temperatures adds multiple changing factors. Varying salinity alone tests responses to salinity, not the impact of light cycles on the sea stars.