Which organisms primarily comprise the mass of passively floating organisms in a body of water?

Plankton are the primary organisms that make up the mass of passively floating organisms in aquatic environments. These organisms are typically microscopic and include both phytoplankton, which are plant-like and perform photosynthesis, and zooplankton, which are small animals that feed on phytoplankton or other zooplankton. Because plankton drift with the currents and are unable to swim against them, they play a vital role in the aquatic food web as foundational producers and consumers.

In contrast, duckweed, while also found in water, is a type of aquatic plant that does not primarily float in the same way as plankton do, as they have a more stable structure. Jidda and scorns do not directly relate to the context of passively floating organisms in water, further clarifying why plankton is the most accurate answer for this question.