Protistscontain

Protistscontain is an informal term used to describe the cellular contents and internal organization common to protists, a diverse collection of mainly unicellular eukaryotes that are not animals, plants, or fungi. Protists are characterized by a nucleus and a range of organelles bounded by membranes, reflecting the general eukaryotic cell plan. Most contain mitochondria or mitochondrion-derived organelles and an endomembrane system, including endoplasmic reticulum and Golgi apparatus.

Photosynthetic protists, such as many algae, also contain plastids bound by two or more membranes and containing chlorophylls; in some groups plastids result from secondary or tertiary endosymbiosis. Nonphotosynthetic protists may lack plastids entirely.

Carbohydrate storage varies, with starch common in many algae and other groups. Structural coverings range from cellulose-based cell walls to silica-based tests in diatoms, to flexible pellicles in ciliates and some flagellates.

Functional components include contractile vacuoles in freshwater species, food vacuoles formed by phagocytosis, and a dynamic cytoskeleton that supports movement via cilia, flagella, or amoeboid motion. At the molecular level, protist cells house a nucleus containing DNA, mitochondria (and often hydrogenosomes or mitosomes in some lineages), and various organelles with their own ribosomes (70S in organelles, 80S in the cytoplasm). Many protists possess plastid genomes in photosynthetic lineages.

Reproduction is diverse, ranging from asexual binary fission to sexual processes such as conjugation or meiosis in certain groups. Taxonomically, protists form a paraphyletic assemblage rather than a single clade, and modern classifications emphasize molecular relationships to reorganize groups commonly treated as protists.

Ecologically, protists play critical roles as primary producers, predators, decomposers, and parasites in aquatic ecosystems and soils.