What type of plankton is composed of photosynthetic organisms, including algae, and is a crucial source of oxygen?

Phytoplankton refers to the diverse group of microscopic photosynthetic organisms found in aquatic environments, including oceans, rivers, and lakes. These organisms primarily include various types of algae and cyanobacteria. Phytoplankton play a vital role in the ecosystem as they are responsible for a significant portion of the primary production in marine and freshwater systems, contributing to oxygen production through photosynthesis.

In fact, it is estimated that phytoplankton generate about 50% of the Earth's oxygen, making them crucial for maintaining atmospheric oxygen levels and supporting life on the planet. Their presence serves as the foundation for aquatic food webs, as they provide energy and nutrients for a wide range of marine organisms, from small zooplankton to larger fish and marine mammals.

The other types of plankton mentioned do not fit the description. Zooplankton consists of small non-photosynthetic organisms that primarily consume phytoplankton and other organic materials. Meroplankton includes the larval stages of organisms that spend only part of their life cycle as plankton, and microplankton is a category based on size, often including both phytoplankton and zooplankton but not limited to photosynthetic organisms.