Chapter 12 Characterizing and Classifying Eukaryotes
General Characteristics of Eukaryotic Organisms Five major groups Protozoa Fungi Algae Water molds Slime molds Include both human pathogens and organisms vital for human life © 2012 Pearson Education Inc.
General Characteristics of Eukaryotic Organisms Reproduction in Eukaryotes More complicated than reproduction in prokaryotes Eukaryotic DNA packaged as chromosomes in the nucleus Have variety of methods of asexual reproduction Many reproduce sexually by forming gametes and zygotes Algae, fungi, and some protozoa reproduce both sexually and asexually © 2012 Pearson Education Inc.
General Characteristics of Eukaryotic Organisms Reproduction in Eukaryotes Nuclear division Nucleus has one or two complete copies of genome Single copy (haploid) Most fungi, many algae, some protozoa Two copies (diploid) Remaining fungi, algae, and protozoa Two types Mitosis Meiosis © 2012 Pearson Education Inc.
General Characteristics of Eukaryotic Organisms Reproduction in Eukaryotes Nuclear division Mitosis Cell partitions replicated DNA equally between two nuclei Maintains ploidy of parent nucleus Four phases Prophase Metaphase Anaphase Telophase © 2012 Pearson Education Inc.
Mitosis Diploid nucleus(2n) Figure 12.1a Mitosis DNA replication Prophase I Chromosome(twochromatids) Centromere Metaphase Spindle Anaphase Telophase Nuclearenvelope Two diploid nuclei (2n)
General Characteristics of Eukaryotic Organisms Reproduction in Eukaryotes Nuclear division Meiosis Nuclear division that partitions chromatids into four nuclei Diploid nuclei produce haploid daughter nuclei Two stages – meiosis I and meiosis II Each stage has four phases Prophase Metaphase Anaphase Telophase © 2012 Pearson Education Inc.
Meiosis Diploid nucleus(2n) Figure 12.1b1 Meiosis I DNA replication Prophase I Tetrad(two homologouschromosomes,four chromatids) Late prophase I Crossing over MEIOSIS I Metaphase I Anaphase I Chromosome(two chromatids) Telophase I
Prophase II Figure 12.1b2 Meiosis II Metaphase II Anaphase II MEIOSIS II Telophase II Nuclear envelope Four haploid nuclei (1n)
General Characteristics of Eukaryotic Organisms Reproduction in Eukaryotes Cytokinesis (cytoplasmic division) Typically occurs simultaneously with telophase of mitosis In some algae and fungi, postponed or does not occur at all Results in multinucleated cells called coenocytes © 2012 Pearson Education Inc.
Figure 12.2 Different types of cytoplasmic division-overview
Figure 12.3 Schizogony Merozoites Nucleus Schizont Multiple mitoses Cytokinesis
Figure 12.4 The changing classification of eukaryotes over the centuries-overview
Protozoa Diverse group defined by three characteristics Eukaryotic Unicellular Lack a cell wall Motile by means of cilia, flagella, and/or pseudopodia Except subgroup, apicomplexans © 2012 Pearson Education Inc.
Protozoa Distribution of Protozoa Require moist environments Most live in ponds, streams, lakes, and oceans Critical members of plankton Others live in moist soil, beach sand, and decaying organic matter Very few are pathogens © 2012 Pearson Education Inc.
Protozoa Morphology of Protozoa Great morphologic diversity Some have two nuclei Macronucleus Contains many copies of the genome Micronucleus Variety in number and kinds of mitochondria Some have contractile vacuoles All produce trophozoites; some produce cysts © 2012 Pearson Education Inc.
Open vacuole Closed vacuole Figure 12.5 Contractile vacuole-overview
Protozoa Nutrition of Protozoa Most are chemoheterotrophic Obtain nutrients by phagocytizing bacteria, decaying organic matter, other protozoa, or the tissues of host Few absorb nutrients from surrounding water Dinoflagellates and euglenoids are photoautrophic © 2012 Pearson Education Inc.
Protozoa Reproduction in Protozoa Most reproduce asexually only Binary fission or schizogony Few also have sexual reproduction Some become gametocytes that fuse with one another to form diploid zygotes Some utilize a process called conjugation © 2012 Pearson Education Inc.
Diploid micronuclei Haploid micronuclei Meiosis of micronucleiproduces four haploidmicronuclei in each. Three micronuclei in eachdisintegrate; the remainingtwo replicate by mitosis. Compatiblemates Figure 12.6 Sexual reproduction via conjugation in ciliates Mates couple. Mates each swap one micronucleus. Haploidmicronucleus(1n) Diploidmicronucleus(2n) Micronucleus(50n) Partnersseparate. Original macronucleusdisintegrates. Fourmicronuclei becomemacronuclei by replicatingchromosomes numeroustimes; four micronucleiremain micronuclei. Three cytokinesespartition a macronucleusand a micronucleus intoeach of four daughter cells. Three mitoseswithoutcytokinesisproduce eightmicronuclei. The two differentmicronuclei fuseto form diploidmicronucleus.
Protozoa Classification of Protozoa Based on 18S rRNA and features visible by electron microscopy One scheme classifies into six taxa © 2012 Pearson Education Inc.
Figure 12.7 Trichonympha acuta, a parabasalid with prodigious flagella
Protozoa Classification of Protozoa Diplomonadida Lack mitochondria, Golgi bodies, peroxisomes Prominent example is Giardia © 2012 Pearson Education Inc.
Flagellum Figure 12.8a Euglena “Eyespot” Short second flagellum Contractile vacuole Paramylon granule Nucleus Chloroplasts Pellicle
Figure 12.8b Trypanosoma Kinetoplast Nucleus
Alveoli Figure 12.9 Alveoli membrane-bound structures found in some protozoa
Figure 12.10 A predatory ciliate, Didinium, devouring another ciliate, Paramecium
Cellulose plate Figure 12.11 Peridinium, a motile armored dinoflagellate Transverseflagellum Longitudinalflagellum
Figure 12.12 Rhizaria called foraminifera have multichambered, snail-like shells of calcium carbonate
Figure 12.13 Rhizaria called radiolarians have ornate shells of silica
Haploid Figure 12.14a A plasmodial (acellular) slime mold Compatiblemyxamoebae fuse. Myxamoebaegerminatefrom spores. Spore (n) Zygote (2n) Haploidsporesarereleased. Plasmodium Sporangium Coenocyticplasmodium(2n) Sporania grow fromplasmodial masses. Diploid
Figure 12.14b A cellular slime mold Spores arereleased. Haploid Nucleus Spore Myxamoebagerminatesfrom spore. Sporangium Fruiting body withsporangium Slug Slug forms stalk. Myxamoebae congregate to formpseudoplasmodium (slug), butthey retain their individuality.
Fungi Chemoheterotrophic Have cell walls typically composed of chitin Do not perform photosynthesis Lack chlorophyll Related to animals © 2012 Pearson Education Inc.
Fungi The Significance of Fungi Decompose dead organisms and recycle their nutrients Help plants absorb water and minerals Used for food and in manufacture of foods and beverages Produce antibiotics Serve as important research tools 30% cause diseases of plants, animals, and humans Can spoil fruit, pickles, jams, and jellies © 2012 Pearson Education Inc.
Fungi Nutrition of Fungi Acquire nutrients by absorption Most are saprobes Some trap and kill microscopic soil-dwelling nematodes Haustoria allow some to derive nutrients from living plants and animals May use ionizing radiation as energy source Most fungi are aerobic Many yeasts are facultative anaerobes © 2012 Pearson Education Inc.
Nematode Figure 12.17 Predation of a nematode by the fungus Arthrobotrys Hyphal loop
Fungi Reproduction in Fungi All have some means of asexual reproduction involving mitosis and cytokinesis Most also reproduce sexually © 2012 Pearson Education Inc.
Fungi Reproduction in Fungi Budding and asexual spore formation Yeasts bud in manner similar to prokaryotic budding Pseudohypha Series of buds that remain attached to one another and to parent cell Filamentous fungi produce lightweight spores that disperse over large distances © 2012 Pearson Education Inc.
Figure 12.18 Representative asexual spores of molds-overview
Tips fuse Figure 12.19 The process of sexual reproduction in fungi Dikaryoticstage(nn) Dikaryon 2 nucleiper cell Diploidstage(2n) Meiosis Nucleifuse Haploidstage(n)
Fungi Classification of Fungi Division Zygomycota Division Ascomycota Division Basidiomycota Deuteromycetes © 2012 Pearson Education Inc.
Figure 12.20 Life cycle of the zygomycete Rhizopus Asexual Reproduction Sexual Reproduction Zygosporangiummatures. Nuclear meioses occurs(not shown). Spore germinatesto produce aseptatemycelium (1n). Zygosporangiumproduces anasexual sporangium(1n). Vegetativemyceliumgrows. Zygosporangiumforms. (2n) Sporangiumbursts torelease spores. Mating hyphaejoin and fuse. Dikaryon(nn) Spores (1n)are releasedfromsporangium. Haploid nuclei (1n) Sporangiospores Sporangium(1n) Gameteforms attip ofhypha. Sporangio-phore Aerial hyphaproduces asporangium. Spore germinates.
Figure 12.21 Ascocarps (fruiting bodies) of the common morel, Morchella esculenta
Asexual Reproduction Sexual Reproduction (called Eupenicillium at this stage) Hyphal tip undergoescytoplasmic fusion withopposite mating type. Vegetative myceliumgrows. Figure 12.22 Life cycle of an ascomycete Conidiospore germinatesto producemycelium. Dikaryon (nn)forms. Nuclei fuse interminal cells toform 2n nuclei. Conidiosporesare releasedfrom conidiophore. Dikaryon Ascosporesgerminateto producemycelia. Ascus Ascospores Conidiospore Meiosisproducesfour haploid(1n) cells. Ascusopens toreleaseascospores. Conidiophore Hypha producesconidiophores andconidiospores. Ascus Ascospore Mitosis produces eighthaploid ascosporeson each tip.
Figure 12.23 Basidiocarps (fruiting bodies) of the bird's nest fungus, Crucibulum
Cross section of gillshowing hyphae.. Figure 12.24 Sexual life cycle of Amanita muscaria, a poisonous basidiomycete Pair of haploidnuclei fuse. 2n Meiosis producesfour haploidnuclei. Fourbasidiospores(1n) develop. Gills Basidium Basidiospore isreleased. Basidiospores germinateto produce mycelia. Dikaryotic myceliumgrowing in soil produces basidiocarp (mushroom). Dikaryon(nn) Hyphae of opposite matingtypes fuse belowgroundto produce dikaryoticmycelium.
Fungi Classification of Fungi Deuteromycetes Heterogeneous collection of fungi with unknown sexual stages rRNA analysis revealed that most deuteromycetes belong in the division Ascomycota © 2012 Pearson Education Inc.
Fungi Lichens Partnerships between fungi and photosynthetic microbes Abundant throughout the world, particularly in pristine habitats Grow in almost every habitat On soil, rocks, leaves, tree bark, other lichens, even tortoises Occur in three basic shapes Fruticose, crustose, foliose Create soil from weathered rocks Eaten by many animals © 2012 Pearson Education Inc.