Final answer:
Katie's experiment most likely represents the interactions between the Atmosphere and Biosphere.
Step-by-step explanation:
Katie's experiment with a paint roller pan, sand, and water most likely represents the interactions between the Atmosphere and Biosphere. The paint roller pan can represent the atmosphere, while the sand and water can represent the biosphere. This experiment could simulate how the atmosphere interacts with living organisms, such as how air affects the movement of sand or water.