Fitoplankton are tiny organisms that float in both freshwater and marine environments, including oceans, lakes, and rivers. They are classified as plants, specifically as phytoplankton, which comes from the Greek words "phyto" meaning plant and "plankton" meaning drifters or organisms that move with the water currents [4] [7]. They are a crucial part of the aquatic food chain, serving as primary producers that convert sunlight, water, and carbon dioxide into oxygen and organic matter through photosynthesis [1] [3].

Fitoplankton are typically characterized by their small size, usually ranging between 2 to 200 micrometers in length [4]. Under the microscope, they exhibit diverse shapes and forms, including coccoid (spherical), bacillary (rod-shaped), and filamentous (thread-like) structures [6]. Visually, they may appear as green or brown specks when viewed from the surface of the water [6].

These microscopic organisms play a significant role in global carbon cycling. Through photosynthesis, fitoplankton absorb carbon dioxide from the atmosphere and release oxygen, contributing to the Earth's oxygen budget and helping mitigate climate change [2]. However, a portion of the fixed carbon is also released back into the environment as metabolic waste, which can be consumed by other organisms, such as bacteria, in the aquatic food chain [2].

In summary, fitoplankton are essential microscopic organisms that contribute to the aquatic food chain, global oxygen production, and carbon cycling. They are characterized by their small size, diverse shapes, and plant-like nature, drifting with water currents and converting sunlight, water, and carbon dioxide into oxygen and organic matter through photosynthesis.