Chapter 26 Protists an informal group of primarily aquatic eukaryotic organisms with diverse body forms types of reproduction modes of nutrition and lifestyles Protists which include algae water molds slime molds and protozoa are unicellular colonial or simple multicellular organisms that have a eukaryotic cell organization the word protists reflects the idea that protists were the first eukaryotes to evolve members of the domain Eukarya most protists are unicellular some are multicellular some form colonies loosely connected groups of cells some are coenocytic consisting of a multinucleate mass of cytoplasm have different forms of locomotion cilla short hairlike organelles flagella long whiplike organelles pseudopodia pushing out cytoplasmic extensions along the leading edge and retract ing the cytoplasm that trails behind eukaryotic cells descended from prokaryotic cells about 2 billion years ago the endosymbiotic theory first proposed by Lynn Margulis and others suggests that double membrane bound organelles such as mitochondria and chloroplasts evolved from a symbiotic relationship between a bacterium the endosymbiont and a host cell evidence includes the DNA present in both mitochondria and chloroplasts as well as their own ribosomes protists may be autotrophic or heterotrophic protists have evolved diverse cell structures ecological roles and life histories Supergroups Excavates Euglenoids unicellular protists with atypical greatly modified mitochondria bikonts Key Characters an unusual flagellum change shape continually as they move be cause their pellicle or outer covering is flexible Cell Structure unicellular Photosynthesis about 1 3 are photosynthetic Habitat commonly found in freshwater Reproduction asexual binary fission Example colorless and autotrophic Chromalveolates Dinoflagellates microorganisms for food diverse protists that may have originated as a result of secondary endosymbiosis in which an ancestral cell engulfed a red alga bikonts Cell Structure unicellular although a few are colonial Photosynthesis many are photosynthetic others are heterotrophic and ingest other Habitat some are endosimbiots that live in the bodies of marine invertebrates Reproduction asexual Example zooxanthellae Diatoms metry Key Characters two groups those with radial symmetry and those with bilateral sym Cell Structure unicellular few exist as colonies Photosynthesis producers in the food chair Habitat some are part of floating plankton others live on rocks and sediments where they move by gliding common in freshwater abundant in cool ocean water Reproduction asexually by mitosis some get progressively smaller with each suc ceeding generation when a diatom reaches a fraction of its original size sexual reproduction occurs which restores the diatom to its original size Golden Algae Key Characters compose a significant portion of the ocean s nanoplankton that are major producers because of their abundance Cell Structure biflagellate unicellular some are colonial Photosynthesis important producers a few ingest bacteria and other particles of food Habitat both freshwater and marine environments Reproduction primarily asexual and involves the production of bilflagellate motile spores called zoospores Brown Algae seaweed Key Characters largest and most complex of all algae seaweed important because their cell walls contain algin which is harvested and used in prod ucts ice cream shaving cream toothpaste hairspray lotion etc Cell Structure multicellular range from a few cm to 75 meters usually biflagellate Photosynthesis important producers Habitat commonly in cooler marine waters provide habitat for many marine inverte Reproduction both asexual zoospores and sexual gametes lifecycle that exhibits alter brates fish and mammals nation of generations Example kelps Archaeplastids Red Algae plastids bounded by outer and inner membranes include land plants biknots Key Characters some contain thick polysaccharides in their cell walls that can be harvested for commercial use like brown algae Cell Structure multicellular few unicellular species multicellular commonly consists of complex interwoven filaments that are delicate and feathery Photosynthesis can carry out photosynthesis in relatively deep waters because their red color allows them to absorb blue light which has shorter wavelengths and penetrates deeper Habitat attatch to rocks or other substrates by a basal holdfast primarily live in warm tropical ocean waters although a few occur in freshwater and in soil Reproduction complex with an alternation of sexual and asexual stages no flagellate cells develop during the life cycle Example coralline algae incorporate calcium carbonate in their cell walls from the ocean water Green Algae motile tant as producers Key Characters cell walls that are chemically identical to those of land plants biolo gists accept that land plants evolved from green algae Cell Structure unicellular colonial forms multinucleate multicellular most have or produce flagellate cells during their life cycle but some are totally non Photosynthesis photosynthetic with chloroplasts of a wide variety of shapes impor Habitat both aquatic and terrestrial environments aquatic primarily inhibit fresh water Reproduction both asexual by mitosis in single cells by fragmentation in multicellu lar and sexual involves gamete formation