Plasmodial slime molds form a single-celled, multinucleate mass, whereas cellular slime molds form an aggregated mass of separate amoebas that are able to migrate as a unified whole.Slime molds are categorized on the basis of their life cycles into plasmodial or cellular types, both of which end their life cycle in the form of dispersed spores.Protists accomplish phototaxis, movement toward light, by coupling their locomotion strategy with a light-sensing organ. Some protists can move toward or away from a stimulus a movement referred to as taxis. Other protists, such at amoebae, form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a surface, and pull themselves forward. Paramecia are covered in rows of tiny cilia that they beat to swim through liquids. Protists such as euglena have one or more flagella, which they rotate or whip to generate movement. The majority of protists are motile, but different types of protists have evolved varied modes of movement. Some protists function as mixotrophs, obtaining nutrition by photoautotrophic or heterotrophic routes, depending on whether sunlight or organic nutrients are available. Subtypes of heterotrophs, called saprobes, absorb nutrients from dead organisms or their organic wastes. Protist metabolism: The stages of phagocytosis include the engulfment of a food particle, the digestion of the particle using enzymes contained within a lysosome, and the expulsion of undigested materials from the cell. Undigested remains ultimately exit the cell via exocytosis. The vesicle containing the ingested particle, the phagosome, then fuses with a lysosome containing hydrolytic enzymes to produce a phagolysosome, which breaks down the food particle into small molecules that diffuse into the cytoplasm for use in cellular metabolism. Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole. Other protists are heterotrophic and consume organic materials (such as other organisms) to obtain nutrition. Protists that store energy by photosynthesis belong to a group of photoautotrophs and are characterized by the presence of chloroplasts. Protists exhibit many forms of nutrition and may be aerobic or anaerobic. The pellicle functions like a flexible coat of armor, preventing the protist from external damage without compromising its range of motion. In other protists, glassy silica-based shells or pellicles of interlocking protein strips encase the cells. Animal-like cell membranes or plant-like cell walls envelope protist cells. Single protist cells range in size from less than a micrometer to thousands of square meters (giant kelp). Many protist cells are multinucleated in some species, the nuclei are different sizes and have distinct roles in protist cell function. Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, similar to ferns. A few protists live as colonies that behave in some ways as a group of free-living cells and in other ways as a multicellular organism. Most protists are microscopic and unicellular, but some true multicellular forms exist. The cells of protists are among the most elaborate and diverse of all cells. phagosome: a membrane-bound vacuole within a cell containing foreign material captured by phagocytosis.phagocytosis: the process where a cell incorporates a particle by extending pseudopodia and drawing the particle into a vacuole of its cytoplasm.taxis: the movement of an organism in response to a stimulus similar to kinesis, but more direct.pellicle: cuticle, the hard protective outer layer of certain life forms.multinucleate: having more than one nucleus.amorphous: lacking a definite form or clear shape.Most protists are motile and generate movement with cilia, flagella, or pseudopodia.Some protists are heterotrophs and ingest food by phagocytosis, while other types of protists are photoautotrophs and store energy via photosynthesis.Protists may have animal-like cell membranes, plant-like cell walls, or may be covered by a pellicle.Protist cells may contain a single nucleus or many nuclei they range in size from microscopic to thousands of meters in area.
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