What is the definition of plankton?

The term plankton refers specifically to the diverse community of microscopic organisms, both plant (phytoplankton) and animal (zooplankton), that drift or float in water bodies. This definition encompasses the vast variety of tiny organisms that are essential components of aquatic ecosystems, serving as the foundational food source for many larger aquatic species. Being microscopic, plankton are not usually visible to the naked eye, but they play critical roles in nutrient cycling and energy transfer in aquatic environments.

The other choices do not accurately capture this definition. For example, while there are indeed larger aquatic organisms, defining plankton simply as a group of large organisms would misrepresent the unique characteristics that distinguish plankton from other aquatic life forms. Similarly, large algae are not representative of the entirety of plankton, which includes much smaller varieties. Lastly, referring to soil at the bottom of a water body does not align with the defining characteristics of plankton, which are specifically organisms suspended in the water column.