What are the two major groups of phytoplankton?

Phytoplankton are microscopic organisms that live in the ocean, and they can be categorized into two major groups: diatoms and dinoflagellates. Diatoms are characterized by their unique silica-based cell walls and are often found in nutrient-rich waters, contributing significantly to primary production in marine ecosystems. Dinoflagellates, on the other hand, have a more complex structure and can exhibit a wide range of behaviors, including bioluminescence and the ability to form harmful algal blooms.

Understanding these two groups is crucial, as they play pivotal roles in the aquatic food web, serve as a primary source of energy for marine life, and are fundamental to the global carbon cycle. Their diversity and abundance make them key indicators of ocean health and productivity. The other choices, including corals, zooplankton, and mollusks, do not belong to the phytoplankton category; instead, they represent different organisms within marine ecosystems. Corals are colonial animals, zooplankton are small drifting animals, and mollusks are a diverse group of invertebrates. This distinction highlights the specificity of phytoplankton as primary producers in aquatic environments.