Which of the following organisms is typically unable to move freely?

The correct option identifies organisms that are typically unable to move freely as sessile organisms. Sessile organisms are those that permanently attach themselves to a substrate and do not have the ability to relocate on their own. Common examples include barnacles, corals, and some types of algae. These organisms are often anchored to surfaces like rocks or the ocean floor and rely on currents or other external forces to bring food to them or help with reproduction.

In contrast, nekton refers to active swimmers in aquatic environments, such as fish and dolphins, which are capable of moving freely through the water. Plankton includes organisms that drift with currents; while they are not stationary in the same way as sessile organisms, they also can’t swim against currents to reach specific locations. Motile organisms, as the term suggests, are characterized by their ability to move independently and actively through their environment. This stark difference in mobility highlights why sessile organisms are considered the correct response in this case.