Unicellular EukaryotesChapter 11

Emergence of Eukaryotes First evidence of life dates to 3.5 billion years

ago.First cells were bacteria-like.

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.

Emergence of Eukaryotes Other groups apparently originated by

secondary endosymbiosis.One eukaryotic cell engulfed another eukaryotic cell

and the latter became transformed into an organelle.

ProtozoansProtozoans are an extremely diverse

assortment of unicellular eukaryotes.

ProtozoansProtozoa

Lack a cell wallHave at least one motile stage in life cycleMost ingest their foodCarry 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.

ProtozoansProtozoans are more diverse than all other

eukaryotes.No longer classified in a single kingdom.Recently shown that there are at least seven or more

clades.May be more than 60 monophyletic eukaryotic

clades.

“Protozoa” is now used informally without implying phyletic relationship.

Cladogram of the Major Divisions of Organisms

Nutrition in ProtozoansAutotrophs - contain

chloroplasts.

Heterotrophs - absorb organic molecules or ingest larger food particles.Phagocytosis

Mixotrophs - combine photosynthesis and heterotrophic nutrition.

Protozoans Occur in Diverse Habitats

Freshwater and marine species.Require moisture

Free-living and symbiotic species.Mutualistic – benefits both.Commensalistic – one benefits,

the other is neutral.Parasitic – one benefits at a

cost to the other.

Locomotion in ProtozoansProtists have three

main methods of locomotion.

Some protists, like this Euglena, have one or two long flagella that they can whip around an propel themselves through the water.

http://www.youtube.com/watch?v=jl0TzaWUQWk

Locomotion in ProtozoansSome, like this

Tetrahymena, are covered with numerous, but shorter, cilia that facilitate movement and/or feeding.

http://www.youtube.com/watch?v=ApjDSGZWHsw

Locomotion in ProtozoansOthers use

ameboid movement to get around. A pseudopod is

extended forward, followed by the rest of the organism.

http://www.youtube.com/watch?v=7pR7TNzJ_pA

Form & Function - LocomotionCilia and flagella share

an internal structure of the axoneme (extending beyond the cell) consisting of 9 pairs of microtubules surrounding a central pair.

Inside the cell, the kinetosome consists of 9 triplets of microtubules just like centrioles.

Form & Function - LocomotionPseudopodia are extensions of the cell

cytoplasm used for locomotion.

Form & Function - LocomotionLobopodia – large

blunt extensions of the cell body.

Filopodia – are thin extensions, usually branching.

Reticulopodia – repeatedly rejoin to form a netlike mesh.

Form & Function - LocomotionAxopodia – long

thin pseudopodia supported by axial rods of microtubules.

Functional Components – Specialized Organelles

Nucleus – contains DNA.

Mitochondria – organelle used in energy production.

Golgi – part of the secretory system of the ER.

Plastids – organelles containing photosynthetic pigments.

Extrusomes – organelles that extrude something from the cell.

NutritionHolozoic feeders,

or phagotrophs, ingest particles of food.Food vacuole –

the membrane-bound vesicle containing the food.

Food vacuoles fuse with lysosomes containing digestive enzymes.

NutritionOften, the site of phagocytosis is a definite

mouth structure, the cytostome.

NutritionSaprozoic feeding

(ingestion of soluble food) may be by pinocytosis or by transport of solutes across the cell membrane.

Excretion and OsmoregulationContractile

vacuoles fill with fluid and then expel the fluid outside the cell.Function in

osmoregulation.More common in

freshwater species.

ReproductionFission is the cell

multiplication process in protozoa.Binary fission – one

individual splits into two equal sized individuals.

Budding – progeny cell much smaller than parent.

Multiple fission – multiple nuclear divisions followed by multiple cytoplasmic divisions producing several offspring.

ReproductionAll of above accompanied by some form of

mitosis.Mitosis in protozoa divisions varies from metazoan

mitosis.Nuclear membrane often persists.Spindle may form within the nuclear membrane.Centrioles not observed in ciliates.Macronucleus of ciliates elongates, constricts, and

divides without mitosis (amitosis).

ReproductionMany types of protists reproduce sexually as

well as asexually.Isogametes – all look alike.Anisogametes – two different types.

Syngamy – gametes from two individuals fuse to form the zygote.

Autogamy – gametes from one individual fuse.

Conjugation – gametic nuclei are exchanged.

CystsMany protists are

able to survive harsh conditions through the formation of cysts, dormant forms with resistant outer coverings and a shutdown of metabolism.

Major Protozoan TaxaAfter the eukaryotic cell evolved, diversification

followed, resulting in many clades.Opisthokonta is a very large clade characterized by a

combination of flattened mitochondrial cristae and one posterior flagellum on flagellated cells.Includes animals, fungi, chaonoflagellates and

microsporidians.

StramenopilaThe clade Stramenopila includes several

groups of heterotrophs as well as certain groups of algae.Most stramenopiles have a “hairy” flagellum

paired with a “smooth” flagellum.

StramenopilaWater molds, diatoms, golden algae, brown

algae.

ViridiplantaeThe clade

Viridiplantae contains unicellular and multicellular green algae, bryophytes and vascular plants.Phylum

Chlorophyta – single celled algae colonial forms.

ViridiplantaeVolvox is a colonial organism that shows a

division of labor where most cells are somatic cells concerned with nutrition & locomotion, but a few germ cells are responsible for reproduction. http://www.youtube.com/watch?v=9pjW1cMfTz8

EuglenozoaPhylum Euglenozoa is a

diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites. Kinetoplastids & Euglenids.Persistence of nucleoli

during mitosis.Cell membrane contains

microtubules to stiffen it into a pellicle.

EuglenidsSubphylum Euglenida have one or two flagella that

emerge from a pocket at one end of the cell.Contain chloroplasts surrounded by a double membrane

– may have arisen by secondary endosymbiosis.

KinetoplastidsSubphylum

Kinetoplasta have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast.Include free-living

consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems.

Others are parasitic.Trypanosoma

RetortamonadsPhylum Retortamonada includes commensal

and parasitic unicells.Lack mitochondria & Golgi

DiplomonadsPhylum Retortamonada: Diplomonads:

Are adapted to anaerobic environments.Lack plastids.Lack mitochondria but may have mitochondrial genes in

the nucleus.

Diplomonads have two nuclei and multiple flagella.Giardia

ParabasalidsParabasalids move by means of flagella and

an undulating part of the plasma membrane.This clade may have diverged from the main

eukaryotic clade very early.Trichomonas

AlveolataMembers of the

clade (superphylum) Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane.Dinoflagellates,

apicomplexans, ciliates.

Alveolata - CiliatesMembers of the

phylum Ciliophora use cilia to move and feed.

Ciliates have large macronuclei and small micronuclei.

Alveolata - CiliatesCiliates are a large, varied group of protists.

http://www.youtube.com/watch?v=yO0tRvYEXGc&feature=player_embedded

Alveolata - CiliatesCiliates are structurally complex.All ciliates have a kinety system made up of

the cilia, kinetosomes and other fibrils.Many have structures that can be expelled

such as trichocysts and toxicysts.Defensive function

Alveolata – Types of CiliatesSuctorians – ciliates that lose cilia as adults, grow a

stalk and become sessile.Use tubelike tentacles for feeding.

Symbiotic ciliates – some commensal, others parasitic.

Free-living ciliates – may be swimmers, or sessile.Stentor, Vorticella, Paramecium

Alveolata – Reproduction in Paramecium

Paramecium, as well as many other protists, reproduce asexually by binary fission.

Alveolata – Reproduction in Paramecium

Conjugation is a sexual process that produces genetic variation.

Conjugation is separate from reproduction which generally occurs by binary fission.

http://www.youtube.com/watch?v=rgkgD4XcqTk&feature=related

Alveolata – DinoflagellatesPhylum Dinoflagellata is a diverse group of

aquatic photoautotrophs and heterotrophs.Abundant in both marine and freshwater

phytoplankton.

Alveolata – DinoflagellatesEach has a

characteristic shape that in many species is reinforced by internal plates of cellulose.

Two flagella make them spin as they move through the water.

Alveolata – DinoflagellatesRapid growth of

some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans.

California Noctiluca Bloom

http://www.whoi.edu/redtide/index.html

Alveolata – DinoflagellatesSome dinoflagellates are bioluminescent.

Others live symbiotically with corals (zooxanthellae).

Alveolata – ApicomplexansApicomplexans are

parasites of animals and some cause serious human diseases.Named because one

end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues.

Have a non-photosynthetic plastid, the apicoplast.

Alveolata – ApicomplexansMost

apicomplexans have intricate life cycles with both sexual and asexual stages that often require two or more different host species for completion.

AmoebozoaAmebas are found

in fresh and salt water as well as moist soil.

An ameba feeds by wrapping a pseudopod around its food – phagocytosis.

EntamoebasEntamoebas are parasites of vertebrates and

some invertebrates.Entamoeba histolytica causes amebic dysentery in

humans.

Foraminifera

This Phylum has slender pseudopodia that extend through openings in the test, then branch and run together forming a net (reticulopodia).

Foraminiferans, or forams are named for their porous, generally multichambered shells, called tests.

ForaminiferaPseudopodia extend through the pores in the test.

Foram tests in marine sediments form an extensive fossil record.

RadiolariaRadiolaria refers to marine testate ameba with

intricate skeletons.They have very diverse and beautiful forms.Useful for determining the age of rock strata.

RadiolariaThe pseudopodia of radiolarians, known as

axopodia radiate from the central body.

Phylogeny and Adaptive Diversification

Phylum Retortamonada

Phylum Diplomonadea

Phylum Parabasala Order Trichomonadida

Phylum Euglenozoa Subphylum Euglenida

Class Euglenoidea Subphylum Kinetoplasta

Class Trypanosomatidea

Phylum Stramenopiles

Phylum Ciliophora

Phylum Dinoflagellata

Phylum Apicomplexa

Class Gregarinea

Class Coccidea

Phylum Foraminifera

Phylum Radiololaria

Phylum Viridiplantae

Phylum Amoebozoa

Phylum Opisthokonta