11-1. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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1 11-1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 CHAPTER 11 Protozoan Groups Unicellular Eukaryotes 11-2

3 Cellular Symbiosis Emergence of Eukaryotes Origin of complex eukaryote cells Most likely symbiosis among prokaryotic cells Modification of engulfed prokaryote into an organelle: Primary endosymbiosis Aerobic bacteria engulfed by bacteria May have become mitochondria found in most modern eukaryotic cells Engulfed photosynthetic bacteria evolved into chloroplasts Descendants in green algae lineage gave rise to multicellular plants 11-3

4 Emergence of Eukaryotes Protozoa Lack a cell wall Have at least one motile stage in life cycle Most ingest their food Other groups apparently originated by Secondary endosymbiosis One eukaryotic cell engulfed another eukaryotic cell Latter became transformed into an organelle 11-4

5 Emergence of Eukaryotes Protozoans Carry on all life activities within a single cell Can survive only within narrow environmental ranges Very important ecologically At least 10,000 species of protozoa are symbiotic in or on other plants or animals Relationships may be mutualistic, commensalistic, or parasitic 11-5

6 How do we define protozoan groups? Heterotrophic protozoa obtain organic molecules synthesized by other organisms Phagotrophs (holozoic feeders) Feed on visible particles Osmotrophs (saprozoic feeder) Feed on soluble food 11-6

7 How do we define protozoan groups? Mode of locomotion Used in the past to distinguish three of the four classes of the phylum Protozoa Cilia and flagella Both called undulipodia Cilia Propel water parallel to the cell surface Flagella Propel water parallel to the flagellum axis 11-7

8 Form and Function Morphologically the same Contain 9 pairs of microtubules arranged around a central pair Arrangement called an axoneme Covered by plasma membrane Found in all motile flagella and cilia in animal kingdom 11-8

9 Pseudopodia 11-9 Form and Function Primary means of locomotion in Sarcodina, many flagellates and ameboid cells of many invertebrates and vertebrates Lobopodia Large blunt extensions of the cell body Contains both endoplasm and ectoplasm Limax Form Whole body moves rather than sending out arms Filopodia Thin extensions containing only ectoplasm Reticulopodia Repeatedly rejoin to form a netlike mesh

10 Form and Function How Pseudopodia Work Endoplasm Contains nucleus and cytoplasmic organelles Ectoplasm More transparent (hyaline) Contains the base for each cilia or flagella Often more rigid Most appears granular (except hyline cap) 11-10

11 Form and Function A lobopodium forms by extending ectoplasm (hyaline cap) Endoplasm flows into hyaline cap Flowing endoplasm contains actin subunits with proteins that prevent actin from polymerizing Lipids release the actin to polymerize Actin filaments cross-link by another actinbinding protein to form semisolid gel 11-11

12 11-12 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13 Form and Function Functional Components of Protozoan Cells Nucleus Membrane bound organelle Contains DNA in the form of chromosomes Chromatin often clumps irregularly leaving clear areas Imparts a vesicular appearance Nucleoli are often present Macronuclei of ciliates Compact or condensed with no clear areas 11-13

14 Mitochondria Form and Function Involved in energy production Golgi apparatus Part of the secretory system of the endoplasmic reticulum Plastids Organelles containing a variety of photosynthetic pigments Perhaps added when a cyanobacterium was engulfed but not digested Chloroplasts contain different types of chlorophylls Extrusomes General term applied to membrane-bound organelles used to extrude material from cell 11-14

15 Form and Function Nutrition Holozoic nutrition implies phagocytosis Infolding of cell membrane surrounds food particle Invagination pinches off Food particle contained in intracellular vesicle Food vacuole (phagosome) Lysosomes fuse with phagosome and release enzymes Undigestible material released to outside by exocytosis 11-15

16 Form and Function In ciliates, site of phagocytosis called a cytostome Many have a point for expulsion of wastes Cytopyge or cytoproct Saprozoic feeding may be by Pinocytosis Transport of solutes across cell membrane 11-16

17 Form and Function Excretion and Osmoregulation Excretion of metabolic wastes is by diffusion Primary end product of nitrogen metabolism Ammonia Contractile vacuoles fill and empty to maintain osmotic balance Water enters by osmosis 11-17

18 Form and Function Reproduction Asexual Processes Fission Produces more individuals than other forms of reproduction Binary fission is most common Two identical individuals produced Budding Occurs when a small progeny cell (bud) pinches off from parent cell Bud grows to adult size

19 Form and Function Multiple fission (schizogony) Cytokinesis preceded by several nuclear divisions Many individuals formed simultaneously If union of gametes precedes multiple fission Called sporogony 11-19

20 Form and Function Sexual Processes All protozoa reproduce asexually Some exclusively Sexual reproduction also occurs widely among protozoa May precede phases of asexual reproduction Isogametes Gametes look alike Anisogametes Gametes are dissimilar Characteristic of most species 11-20

21 Form and Function Fertilization Fertilization of one gamete by another Syngamy Some sexual phenomena do not involve syngamy Autogamy Gamete nuclei form by meiosis Fuse to form a zygote inside the parent organism Conjugation Gamete nuclei exchanged between paired organisms 11-21

22 Form and Function Encystment and Excystment Unicellular forms amazingly successful in extremely harsh conditions Related to the ability to form cysts Dormant forms that shut down metabolism and have a resistant external covering (secreted by Golgi apparatus) Excystment Escape from cysts when environmental conditions are favorable 11-22

23 Phylum Chlorophyta Flagellated, autotrophic, single-celled algae such as Chlamydomonas, as well as colonial forms like Gonium and Volvox Hollow ball of cells Each organism contains thousands of cells Cells resembles a euglenid: Nucleus, pair of flagella, large chloroplast, and stigma Most cells are somatic concerned with nutrition and locomotion Major Protozoan Taxa

24 Major Protozoan Taxa Reproduction Asexual Reproduction Repeated mitotic division form daughter colonies inside parent colony Rupture through wall to escape Sexual Reproduction Cells differentiate into macrogametes and microgametes Macrogametes (a.k.a egg) Larger, fewer, and store food for nourishment of young organisms Microgametes (a.k.a. sperm) Smaller and form bundles of flagellated sperm that swim freely until they find an ovum 11-24

25 Zygote Major Protozoan Taxa Secretes a hard, spiny, protective shell and overwinters In spring, repeated divisions allow it to break out Asexual reproduction occur in the summer 11-25

26 Major Protozoan Taxa Phylum Euglenozoa Cell membrane is stiffened into a pellicle Freshwater with abundant vegetation Flagellum extends anterior end Oval chloroplasts Stigma functions in orientation to light Normally autotrophic, but can make use of saprozoic nutrition 11-26

27 Major Protozoan Taxa Phylum Ciliophora Ciliates are the most diverse and specialized protozoans Larger than most other protozoa Most free-living, some commensal and parasitic Usually solitaire and motile Most free-living in freshwater or marine habitats 11-27

28 Major Protozoan Taxa Slipper shaped - Multinucleate At least one macronucleus and a micronucleus Macronuclei Metabolic and developmental functions Micronuclei Involved in sexual reproduction and give rise to macronuclei afterwards Pellicle varies from a simple membrane to thickened armor Cilia Arranged in rows Propel food to the cytopharynx Fused cilia (cirri) used in locomotion Most are holozoic Stentor Vorticella

29 Major Protozoan Taxa Paramecium may be studied as a typical free-living ciliate Trichocysts present Cytostome leads to a tubular cytopharynx Fecal material discharged from the cytoproct 2 contractile vacuoles Body is elastic Binary fission Conjugation 11-29

30 Amebas Major Protozoan Taxa Found in fresh and salt water, and moist soils Some planktonic, some require a substratum Most reproduce by binary fission Sporulation and budding are also seen Nutrition is holozoic May form lobopodia, filopodia, or rhizopodia Slow streams and ponds of clear water Require a substratum 11-30