Protozoa, being a diverse group of single-celled eukaryotic organisms, exhibit a wide array of nutritional modes that allow them to thrive in various environments. These modes can broadly be categorized into autotrophic (self-feeding) and heterotrophic (feeding on others).

Some protozoa are holophytic, meaning they are plant-like and capable of synthesizing their own food through photosynthesis. Organisms like Euglena, when possessing chloroplasts, can utilize sunlight to convert carbon dioxide and water into organic compounds. This makes them photoautotrophic.

The most common heterotrophic mode is holozoic nutrition, where protozoa ingest solid food particles, much like animals. This often involves phagocytosis, where the cell membrane engulfs the food particle, forming a food vacuole. Inside this vacuole, digestive enzymes break down the food. Amoeba and Paramecium are classic examples, capturing bacteria, algae, or smaller protozoa using pseudopodia or cilia, respectively.

Another heterotrophic mode is saprozoic nutrition. Here, protozoa absorb dissolved organic matter directly from their environment through their cell surface. This is common in some free-living forms inhabiting decaying matter or in certain parasitic species that absorb nutrients from their host's body fluids.

Finally, many protozoa are parasitic. These organisms live within or on a host, obtaining nutrients directly from the host's tissues, cells, or bodily fluids, often causing disease. Examples include Plasmodium, which causes malaria, and Trypanosoma, responsible for sleeping sickness, both of which derive their sustenance from their vertebrate hosts.

This spectrum of nutritional strategies underscores the ecological versatility and evolutionary success of protozoa.