Phytoplankton are microscopic plants that live in aquatic environments and are crucial to the Earth's ecosystems. They perform photosynthesis, converting sunlight, carbon dioxide, and nutrients into oxygen and organic matter, forming the base of the aquatic food web. Additionally, phytoplankton play a significant role in regulating the global climate by absorbing carbon dioxide from the atmosphere. Their health and abundance are vital indicators of oceanic and freshwater ecosystem health.