Barnacles and whales have a commensal relationship in the marine biome. Barnacles attach themselves to the skin of whales and feed on plankton and other small organisms in the water that the whales swim through. The barnacles benefit from the free transportation and food source provided by the whale, while the whale is not significantly affected by the presence of the barnacles.

Rephrase this sentence like a biology 9th grader

In the marine biome, barnacles and whales have a commensal relationship where the barnacles attach to the whales and feed on small organisms in the water. The barnacles benefit from the ride and food, while the whale is not harmed by their presence.