Which organisms are classified as microscopic, free-floating, autotrophic plants that act as producers in aquatic ecosystems?

Phytoplankton are microscopic, free-floating autotrophic organisms that are essential primary producers in aquatic ecosystems. These organisms, which include various types of algae and cyanobacteria, perform photosynthesis, converting sunlight, water, and carbon dioxide into organic matter and oxygen. This process contributes significantly to the overall productivity of marine and freshwater environments, providing the foundational energy source for a wide array of aquatic food webs.

Phytoplankton's role as primary producers is critical as they support higher trophic levels, such as zooplankton, fish, and other marine animals. Due to their small size, they can float and drift with water currents, allowing them to inhabit the upper layers of oceans and lakes where sunlight penetrates, which is necessary for photosynthesis.

The other options represent different categories of organisms; nekton refers to larger, swimming organisms that can move independently of water currents, while zooplankton are small, often microscopic animals that drift in water and primarily feed on phytoplankton. Plankton is a broad term encompassing both phytoplankton and zooplankton, rather than specifically identifying the autotrophic producers. Therefore, the identification of phytoplankton as the correct answer underscores their unique role as the