Protozoans are tiny, single-celled organisms that belong to the kingdom Protista. They can be found in various environments, including soil, freshwater, and saltwater. Protozoans are diverse in shape and size, and they play important roles in ecosystems, such as breaking down organic material and serving as food for larger organisms. These microorganisms can move in different ways, using structures like cilia, flagella, or pseudopodia. Some protozoans are harmless, while others can cause diseases in humans and animals, such as malaria caused by the protozoan Plasmodium. Understanding protozoans helps scientists study health, ecology, and the balance of life on Earth.