Protozoan Groups Unicellular...

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CHAPTER 11

Protozoan Groups Unicellular Eukaryotes

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Cellular Symbiosis 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

Emergence of Eukaryotes

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Protozoa Lack a cell wall Have at least one motile stage in life cycle Most ingest their food

Other groups apparently originated bySecondary endosymbiosis

One eukaryotic cell engulfed another eukaryotic cell

Latter became transformed into an organelle


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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 animalsRelationships may be mutualistic,

commensalistic, or parasitic


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Heterotrophic protozoaobtain organic molecules synthesized by other organisms Phagotrophs (holozoic

feeders)Feed on visible

particles Osmotrophs (saprozoic

feeder)Feed on soluble food

How do we define protozoan groups?

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Mode of locomotion Used in the past to distinguish

three of the four classes of the phylum Protozoa

Cilia and flagellaBoth called undulipodiaCilia

Propel water parallel to the cell surface

Flagella Propel water parallel to

the flagellum axis

How do we define protozoan groups?

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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

Form and Function

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Pseudopodia 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

Form and Function

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How Pseudopodia Work Endoplasm

Contains nucleus and cytoplasmic organelles

EctoplasmMore transparent (hyaline)Contains the base for each cilia or

flagellaOften more rigid Most appears granular (except hyline

cap)

Form and Function

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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 actin-

binding protein to form semisolid gel

Form and Function

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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

Form and Function

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Mitochondria 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

Form and Function

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Nutrition Holozoic nutrition implies phagocytosis

Infolding of cell membrane surrounds food particle

Invagination pinches off Food particle contained in intracellular

vesicleFood vacuole (phagosome)

Lysosomes fuse with phagosome and release enzymes

Undigestible material released to outside by exocytosis

Form and Function

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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

Form and Function

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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

Form and Function

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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

Form and Function

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Multiple fission (schizogony) Cytokinesis preceded by several nuclear

divisions Many individuals formed simultaneously If union of gametes precedes multiple fission

Called sporogony

Form and Function

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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

Form and Function

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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

Form and Function

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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)

ExcystmentEscape from cysts when environmental

conditions are favorable

Form and Function

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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

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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


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Zygote Secretes a hard, spiny, protective shell and

overwinters In spring, repeated divisions allow it to break

out Asexual reproduction occur in the summer


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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


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Phylum Ciliophora Ciliates are the most

diverse and specializedprotozoans

Larger than most other protozoa

Most free-living, some commensal and parasitic

Usually solitaire and motile

Most free-living in freshwater or marine habitats


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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


StentorVorticella

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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


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Amebas 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


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Protozoan Groups Unicellular...

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