Which group of organisms commonly forms the base of many aquatic food webs and performs photosynthesis?

• A. Bacteria
• B. Algae
• C. Fungi
• D. Protozoa

Answer: (B)

Photosynthesis by photosynthetic organisms that are abundant in the water column provides the energy foundation for aquatic ecosystems. In sunlit waters, microscopic algae—collectively called phytoplankton—convert light and inorganic carbon into organic matter that becomes food for a wide range of consumers, from zooplankton to fish. This makes algae the most typical base of many aquatic food webs because they are the primary source of new organic energy input in these environments. Some bacteria can photosynthesize, but they do not universally serve as the main base in most habitats, and fungi do not photosynthesize, while protozoa are generally consumers rather than primary producers.