Plant Biology Test 3 Objectives Lecture 20 Protista Green Algae Zygotic meiosis Meiosis by a zygote to form four haploid cells which divide by mitosis to produce either more haploid cells or a multicellular individual that eventually gives rise to gametes Occurs in fungi and some algae Zygote the diploid cell resulting from the fusion of male and female gametes Gamete a haploid reproductive cell gametes fuse in pairs forming diploid zygotes Gametic meiosis Meiosis resulting in the formation of haploid gametes from a diploid individual the gametes fuse to form a diploid zygote that divides to form another diploid individual Life cycle most familiar to us Animals some protists and algae Sporic meiosis Meiosis resulting in the formation of haploid spores by a diploid individual or sporophyte the spores give rise to haploid individuals or gametophytes which eventually produce gametes that fuse to form diploid zygotes the zygotes in turn develop into sporophytes the kind of life cycle is known as an alternation of generations Independent sporophytes and gametophytes Gametophyte the haploid gamete producing generation Spore A reproductive cell usually unicellular capable of developing into an adult without fusion with another cell Sporophyte The diploid spore producing generation Life cycle of Sea Lettuce Ulva Gametangium structure in which gametes are Plants many algae formed Sporangium structure in which spores are formed 2 Major Groups of Protists Protista primitive eukaryotes all eukaryotes excluding animals plants and fungi Autotrophic Algae photosynthesis some are the ancestor of plants Hetereotrophic slime mold nonphotosynthetic similar but not directly related to fungi Acritarch the earliest eukaryote extinct The first appearance of eukaryotes was estimated to be 1 8 byr evidenced by the fossil record of acritarch found in China Features that distinguish it from prokaryotes are the size and the complexity of its cell wall From the earliest eukaryotes are derived the animals fungi and plants There are still a large number of eukaryotes that are not animals fungi and plants and they still retain primitive features Although not related these lower organisms have been named as protists Algae From unicells to giant organisms mostly aquatic many are planktonic phytoplankton Plankton tiny photosynthetic cells and animals suspended in water 50 of the photosynthetic activity on earth base of the food chain in open seas Phytoplankton produce about 30 of atmospheric O2 Phytoplankton absorbs Ca half anthropogenic CO2 by producing CaCO3 Classification of Algae Criteria Chlorophyll and pigments cell wall composition morphological features flagella DNA sequence Major Groups Green algae Phylum Chorophyta uni to multi Euglenoids Phlym Euglenophyta mostly uni Cryptomonads Phylum Bacillariophyta mostly uni Dinoflagellates Phylum Dinophyta mostly uni Diatoms Phylum Bacillariophyta mostly uni Brown Algae Phylum Phaeophyta multi Red Algae Phylum Rhodophyta multi Primary and Secondary Endosymbiosis The bulk of evidence indicates that all chloroplasts resulted from a single primary At least three separate secondary endosymbiotic events led to plastids in different endosymbiotic event groups of algae Green Algae Closest relatives to plants Green algae land plants green plants Cell wall cellulose Chlorophyll a b and carotenoids Very diverse unicellular to multicellular land plants filaments blades giant cells colonies Mobile to immotile flagellum Reproduction asexual to sexual Mainly aquatic mostly freshwater other habitats too Some grow on surface of snow on tree trunks in soil Some in symbiotic association with other organisms e g lichens Land plants evolved from green algae Three major groups of green algae Chlorophyceae Ulvophyceae Charophyceae Clamydomonus simplest a single cell mobile two flagellates reproduction asexual and sexual a model system to study photosynthesis Asexual reproduction Phase of Clamydomonus 1 Algae absorbs its flagellum 2 Haploid algal cell then divides mitotically from 2 to 3 times 3 From 4 8 haploid flagellated cells called zoospores develop in this parent cell 4 Zoospores break out of the parent cell eventually grow to full size Sexual Reproduction phase of Clamydomonus triggered by starvation for nitrate and phosphate 1 Haploid cells dividing mitotically to produce either plus or minus gametes 2 A plus gamete and a minus gamete come into contact with one another shed their cell walls and fuse to form a diploid zygote 3 This resting stage of a zygote is called a zygospore and withstand bad environmental conditions Clamydomonus is isogamous 4 When conditions are better the thick wall opens and the living zoospore emerges Isogamy both gametes are the same size small Oogamy Egg large and nonmotile sperm small and motile parent can invest more resource Development from unicellular to multicellular Chlamydomonas Gonium Pandorina Eudorina Pleodorina Volvox All members belong to the family Volvocaceae except for clamydomonus Sexual reproduction of volvox is oogamous Some Chlotophyceae species are immotile Unicellular Chlorococcum Filament oedogonium Colonial Hydrodictyon Ulvophyceae mainly marine organisms Charaphyceae The charales The close relative of land plants Morphology like bryophyte Cell division Oogamous Sperm structure Oogonium structure in which one or more eggs are formed Antheridium structure in which sperm are formed Order Charales 250 spp represents the closest relatives to land plants Oogamous egg surrounded by a jacket of cells and not released even after Embryophytes fertilization Sexual reproduction in Spirogyra by conjugation Lecture 21 Protista Other Algae Major Groups A Green Algae Phylum Chlorophyta B Euglenoids Phylum Euglenophyta C Cryptomonads Phylum Bacillariophyta D Dinoflagellates Phylum Dinophyta E Diatoms Phylum Bacillariophyta F Brown Algae Phylum Phaeophyta G Red Algae Phylum Rhodophyta Green Algae Closest to land plants unicellular to multicellular life cycle simple to complex primary endosymbiosis Euglenoids Cryptomonads Dinoflagellates Diatoms mostly unicellular simple life cycle secondary endosymbiosis Brown Algae and Red Algae Multicellular life cycle simple secondary endosymbiosis A Euglenoids Phylum Euglenophyta Single cellular No Cell wall can take up particles Mobile a flagellum Stigma eyespots Chl a b and carotenoids Reproduce by division B Cryptomonads Phylum Bacillariophyta Tiny unicellular thus aptly named Mobile two flagellates Chl
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