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Protists 1 Protista Classifying Protists General Biology of Protists The Kingdom Protista is divided into four major groups, not technical divisions but instead grouped by lifestyle: A- The protozoans. B- The slime molds. C- The unicellular algae. D- The multicellular algae. 2 2 Protista Protists are the most diverse of the four kingdoms in the domain Eukarya. Fossil history 2.5 billion years old artificial group of convenience single-celled eukaryotic organisms Not plant not animal not fungi little consensus about classification 3 3 They are first eukaryotes, having a well organized nucleus and complex membranous organelles. They are unicellular or colonial forms without distinct division of labor. 4 4 They are autotrophic or heterotrophic showing varieties of metabolic systems Locomotion is by pseudopodia, flagella or cilia. They show mitosis, meiosis and simplest type of sexual reproduction for the first time. Common examples are Ameba, Paramecium, Euglena, diatoms and dinoflagellates. 5 5 Ameba A single-celled (protozoan) organism that constantly changes shape. The word "ameba" is from the Greek "amoibe" meaning "change." 6 6 Structure of an amoeba: unicellular animal with pseudopods that lives in fresh or saltwater. Pseudopodium: part of the amoeba used for locomotion. Ectoplasm: vitreous superficial layer of an amoeba. Endoplasm: central part of an amoeba. Cell membrane: membrane covering an amoeba. Contractile vacuole: cavity of the amoeba that is able to contract. Food vacuole: cavity of the amoeba responsible for digestion. Nucleus: central organelle for an amoeba. Digestive vacuole: cavity of the amoeba responsible for digestion. 7 7 Classification Protozoans include all protists that ingest their food, they live primarily in aquatic habitats, such as ponds, drops of water in soil, or the digestive tracts of animals. A small group of protozoans function as parasites. The second group, the slime molds, are unique in having both unicellular and multicellular stages. 8 8 Theory of Endosymbiosis 9 9 Evidence for the endosymbiont theory is that mitochondria and chloroplasts: - Are appropriate size to be descendants of eubacteria. - Have inner membranes similar to those on prokaryotic plasma membranes. - Replicate by splitting, as in prokaryotes. - DNA is circular and different from the DNA of the cell's nucleus. - Contain their own components for DNA transcription and translation into proteins . - Have ribosomes similar to prokaryotic ribosomes. - Molecular systematics lend evidence to support this theory. - Many extant organisms are involved in endosymbiotic relationships. 10 10 Protist Classification 11 11 General Biology of the Protists Cell surface possess varied array of cell surfaces Plasma membrane only, extracellular material – cells walls (diatoms –silica) Locomotor organelles chiefly flagellar rotation or pseudopodial movement Pseudopodia – false foot – extension of body Cyst formation dormant form of a cell with resistant outer covering in which metabolism is essentially shut down (harsh environments – gastric secretions) 12 12 General Biology of the Protists Nutrition employ all forms but chemoautotrophic phototrophs heterotrophs phagotrophs - visible food particles osmotrophs - food in soluble form 13 13 General Reproduction Biology of the Protists typically reproduce asexually binary fission - equal halves budding - progeny cell smaller schizogony - multiple fission - multiple individuals simultaneously sexual reproduction in times of stress gametic meiosis - before gametes Diploid - haploid zygotic meiosis - after fertilization Individuals are Haploid until diploid zygote is produces intermediary meiosis – alternating (alternation of generation) haploid and diploid undergo mitosis 14 14 15 15 16 16 Protists Six identified lineages: Euglenozoa Alveolata Stramenopila Rhodophyta Chlorophyta Choanoflagellida 17 17 Euglenozoa Euglenoids most are freshwater about one-third are autotrophic, rest heterotrophic pellicle (interlocking proteinaceous strips in helical pattern (flexibility) lies within plasma membrane stigma - light sensitive organ that aids in orienting toward light Euglena two flagella attached to reservoir contain numerous chloroplasts 18 18 Euglenoids 19 19 Euglenozoand Kinetoplastids - 2 group within Euglenozoa unique, single mitochondrion in each trypanosome (2 types of DNA) mini-circles and maxi-circles Trypanosomes are kinetoplastids that cause many serious human diseases. Usually tropical African sleeping sickness Chagas 20 20 Alveolata Most are photosynthetic Dinoflagellates Fresh and Saltwater Encased in cellulose/silica plates distinctive flagella -single spins as it moves, protective coats (cellulose/silica plates), and biochemistry –chlorophyll a and c and carotenoids reproduce primarily by asexual cell division responsible for “red tides” – poisonous toxins inhibit diaphragm and cause respiratory failure in many vertebrates 21 21 Alveolata Apicomplexes spore-forming animal parasites unique arrangement of fibrils, microtubules, vacuoles, and other cell organelles Most famous - malarial parasite - Plasmodium malaria eradication eliminating mosquito vectors poison parasites inside human body - Quiinine develop vaccines 22 22 Plasmodium Life Cycle 23 23 Alveolata Ciliates most feature large numbers of cilia usually arranged in longitudinal rows or spirals around the body form vacuoles to ingest food and regulate water balance waste emptied through cytoproct Paramecium 24 24 Paramecium 25 25 Stramenopila and Rhodophyta Stramenopila includes brown algae, diatoms, and oomycetes brown algae - conspicuous seaweeds alternation of generations diatoms (phylum Chrysophyta) - photosynthetic, unicellular organisms with double shells of opaline silica 26 26 Brown Algae 27 27 Stramenopila and Rhodophyta Stramenopila oomycetes (water molds) - parasites or saprobes. comprise water molds, white rusts, and downy mildews motile zoospores bear two unequal flagella life cycles characterized by gametic meiosis and a diploid phase 28 28 Stramenopila and Rhodophyta Rhodophyta Red algae range in size from microscopic to very large. origin a source of controversy tentatively treated as a sister clade of green algae (Chlorophyta) 29 29 Chlorophyta Green algae are the ancestors of the plant kingdom. extensive fossil record dating back 900 million years mostly aquatic Chlamydomonas well-known genus probably represents primitive state Chlorophyta did not give rise to land plants. 30 30 Chlamydomonas Life Cycle 31 31 Choanoflagellida Choanoflagellates are most like the common ancestor of the sponges and all animals. contain a single emergent flagellum surrounded by a funnel-shaped, contractile collar 32 32 Amoebas contain pseudopods that can form at any point on the cell body and can move in any direction Phylum Actinopoda (radiolarians) secrete glassy exoskeletons of silica. 33 33 Foraminifera heterotrophic marine protists with porestudded shells complex life cycle with alternation between haploid and diploid generations 34 34 Slime Molds Slime molds originated at least three distinct times. plasmodial slime molds stream along as a non-walled, multinucleate mass of cytoplasm, plasmodium produces sporangium during times of resource shortage forms spores that quickly undergo meiosis 35 35 Slime Molds Cellular slime molds individual organisms behave as separate amoebas, moving through soil or other substrate and ingesting bacteria individual organisms aggregate and form moving mass “slug” when food becomes scarce 36 36 Cellular Slime Mold Development 37 37 Summary Endosymbiosis Classifying Protists General Biology of Protists Six Lineages Euglenozoa Alveolata Stramenopila Rhodophyta Chlorophyta Choanoflagellida 38 38 39 39