Protists Chapter 29

2 Eukaryotic Origins Eukaryotic cells differ from prokaryotes –Presence of a cytoskeleton –Compartmentalization (nucleus and organelles) Appearance of eukaryotes in microfossils occurred about 1.5 BYA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 50 µm © Andrew H. Knoll/Harvard University

The nucleus and endoplasmic reticulum arose from infoldings of prokaryotic cell membrane 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Plasma membrane plasma membrane Endoplasmic reticulum (ER) Nuclear Nucleus Plasma membrane Eukaryotic cell envelope Infolding of the of eukaryotic cells Prokaryotic ancestor Prokaryotic cell

4 Many organelles evolved via endosymbiosis between an ancestral eukaryote and a bacterial cell –Mitochondria Aerobic bacteria engulfed by larger bacteria Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chloroplast Eukaryotic cell with chloroplast and mitochondrion Endosymbiosis Photosynthetic bacterium Mitochondrion Aerobic bacterium Eukaryotic cell with mitochondrion Endosymbiosis Internal membrane system eukaryotic cell Ancestral

5 Chloroplasts –Larger bacteria engulfed smaller photosynthetic bacteria –Chloroplasts come from single line of cyanobacteria –Hosts are not monophyletic Brown algae engulfed red algae that already had chloroplasts –Secondary endosymbiosis Organelle with four membranes Red algal nucleus lost Brown alga Nucleus Secondary Endosymbiosis Chloroplast with two membranes Eukaryotic cell Primary Endosymbiosis Eukaryotic cell Nucleus Cyanobacteria Red alga Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Endosymbiosis supported by –DNA inside mitochondria and chloroplasts DNA similar to bacteria DNA in size and character –Ribosomes inside mitochondria similar to bacterial ribosomes –Chloroplasts and mitochondria replicate by binary fission – not mitosis Mitosis evolved in eukaryotes 6

Defining Protists Most diverse of the four eukaryotic kingdoms United on the basis that they are not fungi, plants, or animals Vary considerably in every other aspect –Unicellular, colonial, and multicellular groups –Most are microscopic but some are huge –All symmetries –All types of nutrition 7

8 Working model for protists classification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliates Apicomplexans ArchaeaEubacteriaChromalveolataRhizariaArchaeplastidaExcavataAmoebozaOpisthokonta Parabasalid Dinoflagellates AlveolataStramenopila RhodophytaChlorophytesDiplomonadsEuglenozoa Choanoflagellates Animals Fungi Amoebozoa Land plants Charophytes Cercozoa Foraminifera Radiolara Brown algae Diatoms Oomycetes

Locomotion –Flagella One or more –Cilia Shorter and more numerous than flagella –Pseudopodia (“false feet”) Lobopods – large, blunt Filopods – thin, branching Axopods – thin, long 9

Asexual reproduction –Typical mode of reproduction –Some species have an unusual mitosis Mitosis – equal size daughter cells Budding – one daughter cell smaller Schizogony – cell division preceded by several nuclear divisions; produces several individuals Sexual reproduction –May be obligate, or only under stress –Meiosis is a major eukaryote innovation –Union of haploid gametes which are produced by meiosis –Advantage in allowing frequent genetic recombination 10

Multicellularity –From single cells to colonies to true multicellularity –Arisen multiple times –Fosters specialization –Few innovations have had as great an influence on the history of life 11

Euglena –Two anterior (and unequal) flagella Attached at reservoir –Contractile vacuoles – collect excess water –Stigma – movement towards light –Numerous small chloroplasts From ingestion of green algae –Concept of a single Euglena genus is now being debated 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 6.5 µm © Andrew Syred/Photo Researchers, Inc.

13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Second flagellum Stigma Contractile vacuole Paramylon granule Nucleus Chloroplast Flagellum Pellicle Mitochondrion Basal bodies Reservoir b.

Apicomplexans Spore-forming animal parasites Apical complex is a unique arrangement of organelles at one end of the cell –Enables the cell to invade its host Plasmodium causes malaria –Complex life cycle – sexual, asexual, different hosts –Eradication focused on eliminating mosquito vector, drug development, vaccines DDT-resistant mosquitoes 14

15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside MosquitoInside Mammal Sporozoite Merozoite Gametocyte Fertilization Host ’s liver cell Host ’s red blood cell 1. While feeding, mosquito injects Plasmodium sporozoites into human. 2. Sporozoites enter the liver, reproduce asexually and release merozoites into the bloodstream. 6. The game- tocytes develop into gametes and reproduce sexually, forming sporozoites within the mosquito. 5. Gametocytes are ingested by another, previously uninfected mosquito. 4. Certain merozoites develop into gametocytes. 3. Merozoites multiply Inside red blood cells and are released. The cycle repeats. Oocyst Sporozoite Gametes

Brown algae Conspicuous seaweeds of northern regions Life cycle involves alternation of generations –Sporophyte – multicellular and diploid –Gametophyte – multicellular and haploid Not plants 16

17 MEIOSIS n2n2n Sporophyte (2n) Zygote (2n) Sperm Egg Zoospores (n) Gametophytes (n) Developing sporophyte Germinating zoospores MITOSIS FERTILIZATION Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Green Algae Land plants arose from an ancestral green alga only once during evolution Green alga consist of 2 monophyletic groups –Chlorophyta –Charophytes 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5 µm © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited

19 Chlamydomonas life cycle. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – + – Gamete Asexual reproduction MITOSIS Strain FERTILIZATION Zygospore (diploid) +Gamete Pairing of positive and negative mating strains n 2n MEIOSOS

Cell specialization in colonial chlorophytes –Multicellularity arose many times in the eukaryotes –Colonial chlorophytes are examples of cellular specialization Volvox - hollow sphere made up of a single layer of 500 to 60,000 individual cells each with 2 flagella 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vegetative cells Reproductive cells © Wim van Egmond/Visuals Unlimited 20 nm

Haplodiplontic Life Cycle Multicellular diploid stage – sporophyte –Produces haploid spores by meiosis –Diploid spore mother cells (sporocytes) undergo meiosis in sporangia Produce 4 haploid spores First cells of gametophyte generation Multicellular haploid stage – gametophyte –Spores divide by mitosis –Produces gametes by mitosis –Gametes fuse to form diploid zygote First cell of next sporophyte generation 21