CHAPTER 11

Unicellular Eukaryotes:Protozoan

Groups

EMERGENCE OF EUKARYOTESCellular Symbiosis First evidence of life

Dates to 3.5 billion years agoFirst cells were bacteria-like

Origin of complex eukaryote cellsMost likely symbiosis among prokaryotic cells

Changed the prokaryote that was “eaten” into an organelle: Primary endosymbiosis

Aerobic bacteria “eaten” by bacteria May have become mitochondria found in most

modern eukaryotic cells “Eaten” photosynthetic bacteria evolved into

chloroplasts Descendants in green algae lineage gave rise to

multicellular plants

EMERGENCE OF EUKARYOTES Protozoa

Lack a cell wallHave at least one motile stage in life cycleMotile- moving

Most ingest (eat) their food Other groups originated by

Secondary endosymbiosis One eukaryotic cell “ate” another eukaryotic cell

Latter became transformed into an organelle

EMERGENCE OF EUKARYOTES Protozoans

Carry on all life activities within a single cell

Can survive only within narrow environmental ranges

Very important ecologicallyAt least 10,000 species of protozoa

are symbiotic in or on other plants or animalsRelationships may be mutualistic, commensalistic, or parasitic

HOW DO WE DEFINE PROTOZOAN GROUPS? Heterotrophic protozoa obtain organic

molecules synthesized by other organismsPhagotrophs (holozoic feeders)

Feed on visible particlesOsmotrophs (saprozoic feeder)

Feed on soluble food Mode of nutrition employed by

unicellular organismsOften variable and opportunistic

HOW DO WE DEFINE PROTOZOAN GROUPS? Mode of locomotion

Used in the past to distinguish three of the four classes of the phylum Protozoa

Society of Protozoologists (1980) published a new classification with seven separate phyla

Molecular analyses have given scientists new insight into protozoan relationships.

There may be 250,000 protozoan species

FORM AND FUNCTION

LocomotionCilia and flagella

Both called undulipodiaCilia : Propel water parallel

to the cell surface Flagella : Propel water parallel

to the flagellum axis

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FORM AND FUNCTION 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 FormWhole body moves rather than sending out arms

Filopodia Thin extensions containing only ectoplasm

FORM AND FUNCTION How Pseudopodia Work

EndoplasmContains nucleus and cytoplasmic organelles

EctoplasmMore transparent (hyaline)Contains bases of cilia or flagellaOften more rigid Appears granular

FORM AND FUNCTIONA lobopodium forms by extending

ectoplasm (hyaline cap)Endoplasm flows into hyaline cap

FORM AND FUNCTIONFunctional Components of Protozoan Cells Nucleus

Membrane bound organelleContains DNA in the form of

chromosomesChromatin often clumps leaving

clear areasNucleoli are often present

FORM AND FUNCTIONNutrition Holozoic nutrition implies phagocytosis

In folding of cell membrane surrounds food particle

Then pinches offFood particle contained in

intracellular vesicleFood vacuole (phagosome)

Lysosomes fuse (binds) with phagosome and release enzymes

FORM AND FUNCTION Digested products absorbed across vacuole

membrane Undigestible material released to outside by

exocytosis

FORM AND FUNCTIONExcretion and Osmoregulation Excretion of metabolic wastes is by

diffusion Primary end product of nitrogen

metabolism Ammonia

Contractile vacuoles fill and empty to maintain osmotic balanceWater enters by osmosis

FORM AND FUNCTIONReproduction 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 FUNCTIONMultiple fission (schizogony)

Cytokinesis (part of mitosis) preceded by several nuclear divisions

May individuals formed simultaneously If union of gametes precedes multiple fission Called sporogony

FORM AND FUNCTION All of above accompanied by some

form of mitosisMitosis in protozoa divisions varies

from other mitosis Nuclear membrane often persistsCentrioles not observed in ciliates

FORM AND FUNCTION Sexual Processes

All protozoa reproduce asexuallySome exclusively

Sexual reproduction also occurs widely among protozoaMay precede phases of asexual reproduction

Isogametes Gametes look alike

AnisogametesGametes are dissimilarCharacteristic of most species

FORM AND FUNCTIONMeiosis

May occur during or just before gamete formation

In other groups, meiosis occurs after fertilization (zygotic meiosis)

FORM AND FUNCTION Fertilization of one gamete by another

Syngamy Some sexual phenomena do not involve

syngamyAutogamy

Gamete nuclei form by meiosis Fuse to form a zygote inside the parent organism

ConjugationGamete nuclei exchanged between paired organisms

MAJOR PROTOZOAN TAXA Phyla Retortamonada and Diplomonads

Divided into 2 exclusive clades: Retortamonds and Diplomonads

Retortamonds Include commensal and parasitic unicellsLack mitochondria and Golgi bodies

Diplomonads Lack mitochondria

Mitochondrial genes occur in the cell nucleus

Absence of mitochondria may be a secondary change

Giardia inhabit the digestive tract of humans, birds, and amphibians

MAJOR PROTOZOAN TAXAPhylum Euglenozoa

Generally considered as monophyletic

Have a series of longitudinal microtubules Stiffen the cell membrane into a pellicle

Two subphylumsSubphylum Euglenida

Chloroplasts surrounded by a double membrane

Secondary endosymbiosis

MAJOR PROTOZOAN TAXASubphylum Kinetoplasta Have kinetoplastids: round DNA Zooflagellates

Lack chromoplastsHolozoic or saprozoic nutritionMost are symbioticTrypanosoma

Important genus of protozoan parasitesSome not pathogenic*Affects birds, fish, amphibians, mammals. Can be passed by insects to humans.

• African sleeping sickness

MAJOR PROTOZOAN TAXAPhylum Ciliophora

Ciliates are the most diverse and specialized protozoans

Larger than most other protozoaMost free-living, some commensal

and parasiticUsually solitaire and motileMost free-living in freshwater or

marine habitats

Phylum CilliophoraCilia

Arranged in rowsPropel food to the cytopharynxFused cilia (cirri) used in locomotion

Most are holozoic

MAJOR PROTOZOAN TAXA Suctorians

Ciliates that paralyze their prey and

Ingest contents through tube-like tentacles

Trichocysts and toxicysts in someExpel long thread-like structures when stimulated

Believed to be defensive mechanism

EndoparasitesHosts are in many animal phylaGametes may be flagellated

The life cycle usually includes both sexual and asexual stagesInvertebrate may be an intermediate

host During life cycle

Form a spore (oocyst) Infective in the next host Protected by a resistant coat

MAJOR PROTOZOAN TAXA Plasmodium: The Malarial Organism

Most important infectious disease of humans

Four species infect humansEach produces different clinical symptoms

Anopheles mosquitoes carry all forms

Female injects the Plasmodium present in her saliva