Protists- The Simplest Eukaryotes

AP BiologySpring 2011

Describe the criteria for the Kingdom Protista

Describe the origin of the various protistans

Tell how protists differ from bacteria Be able to compare protists with other

eukaryotes Distinguish each of the major groups

within the Protista

An Evolutionary Road Map

Protists: are the most like the first Eukaryotic cells◦ Have a nucleus ◦ Most have mitochondria, ER, and Golgi bodies ◦ Ribosomes are larger than bacteria’s◦ Have more than one chromosome, consisting of

DNA with many proteins attached ◦ Have cytoskeleton (microtubules)◦ Many have chloroplasts◦ Divide by mitosis, meiosis, or both ◦ Eukaryotes

Protists A diverse

group

Most single celled There are colonial and multicelled species Some:

◦ Photoautotrophs◦ Preditors ◦ Parasites ◦ Decomposers

Many can form spores

A kingdom that represents an evolutionary crossroads between prokaryotes and “higher” forms of life

Recently the polyphyletic kingdom is being split into monophyletic groups ◦ Fig. 22.2

The 7 monophyletic groups:◦ Diplomonads and Parabasalids ◦ Kinetoplastids and Euglenoids ◦ Foraminiferans and Radiolarians ◦ Stramenopiles and Alveolates ◦ Amoebozoans ◦ Red Algae◦ Chlorophytes (green algae)

Basal Groups22.2: Parabasalids and Diplomonads22.3: Euglenoids and Kinetoplastids

22.4: Forams and Radiolarians

Most evolutionary distant groups Consist of heterotrophic flagellates Are sac like or elongated and live in many

oxygen poor or anaerobic habitats Have few mitochondria or none at all

Parabasalids:◦ Have equivalent of backbone

Bundled microtubules extending the length of the cell

◦ Have flagella

Diplomonads:◦ Have 3 flagella at their anterior and and one at

the trailing end ◦ Girardia lamblia:

No lysosomes, mitochondria, or golgi bodies, does not form bipolar spindle at mitosis

This lineage may have started more than a billion years ago

Common intestinal parasite in humans and cattle Anaerobic but can survive as cysts outside bodies

Cyst: resting stage with a covering of cell secretions

Flagellated Single celled Thickened flagellum reinforced along nearly

all lengths by a crystalline rod-shaped structure

Euglenoids:◦ Free living cells of fresh

water ◦ 1/3 of modern species are

heterotrophs, other 2/3 are photoautotrophs that acquired chloroplasts

◦ Have a long and short flagellum

◦ Long flagellum is thicker and stiffened by an adjoining rod

◦ Eyespot: guides them toward light◦ Pellicle: flexible, translucent cover, made of

protein rich material Responsible for movement

◦ Contractile Vacuole: Euglenoid has a higher internal solute concentration Counteracts water’s tendency to diffuse in

◦ Reproduce by binary fission

Kinetoplastids:◦ Heterotrophic, colourless flagellates◦ Nearly all are parasites that can survive anaerobic

and aerobic conditions ◦ Large mass of mitochondrial DNA, used for

adjusting mode of ATP formation under different conditions

◦ Parasites Trypsanosoma, Leishmania (tropics), T. brucei (African sleeping sickness, tsetse fly is vector), T. cruzi (Chagas disease)

Faraminiferans:◦ Start out in a one-chambered shell◦ As single celled heterotrophs increase in size,

most add more chambers and occupy them◦ Psudopods interconnect

Probe water and spaces between sand grains for bacteria and other prey

◦ Some harbor photosynthetic symbionts (dinoflagellates, golden alga, diatoms)

Radiolarian:◦ Cell body has distinct outer zone with vacuoles

that impart buoyancy and assist in prey capture and digestion

◦ Outer perforated shell made of short silica rods ◦ Most live in deep ocean water◦ Some part of marine plankton

The Alveolates22.5:Ciliated Alveolates

22.6: Flagellated Alveolates22.7: Malaria

Monophyletic group consisting of ciliates, dinoflagellates, apicomplexans

Have small membrane bound sacs beneath the plasma membrane (alveoli)

Ciliates:◦ Live in seas and fresh water◦ Most free-living heterotrophs◦ 1/3 parasites or endosymbionts of animals◦ Few are colonial

Cilia◦ Cover the surface of some species but are

confined to specific regions on others◦ Beat in synchronized patterns◦ Moves body, directs food toward oral cavity

Paramecium:◦ Cilia all over body surface ◦ Gullet: starts at an oral depression

Cilia sweep food-laden water inside ◦ Contractile vacuole: expel excess water from

body ◦ Pellicle: array of flattened sacs under plasma

membrane Store calcium ions which dictate ciliary beating

◦ Trichocysts: bottle shaped capsules hold a long shaft with a barb at the tip Defends against predetors

Ciliates:◦ Reproduce both sexually and asexually ◦ Micronucleus and macronucleus, both have to

divide (not that efficient or effective)◦ Conjugation occurs between ciliates

Dinoflagellates: ◦ Live in freshwater and marine habitats ◦ Half are heterotrophs, half are photoautotrophs ◦ All deposit cellulose in their alveoli

Often thick enough to form armor plates in pellicle Species that have thin deposits considered

unarmored◦ Most have 2 flagella ◦ Part of plankton ◦ Can undergo algal blooms when abundant

nutrients Red tide: tint water red

Apicomplexans:◦ Parasitic alveolates ◦ Microtubular device that attaches to and pierces a

host cell ◦ Adults have no flagella or cilia but their gametes

are flagellated ◦ Ex. Plasmodium

Malaria symptoms:◦ Start when liver cells rupture and release

meroziotes, cellular debris, and metabolic wastes into blood

◦ Shaking, chills, burning fever, sweats ◦ After one episode will relapse weeks to months

later◦ Later outcomes: jaundice, kidney failure,

convulsions, coma

Bite of female Anopheles mosquitos can transmit a motile infective stage to human hosts

Life cycle:◦ Sporozoite travels from mosquito to blood vessels to

liver cells◦ Reproduces asexually by fission◦ Some offspring (meroziotes) reproduce asexually in

RBC, which they rupture and kill◦ Other meroziotes develop into make and female

gametocytes ◦ Gametocytes do not mature into gametes until they

enter the gut of another mosquito

Plasmodium is the protist responsible As of 2007, every 30 seconds one African

child dies of malaria

The Stramenopiles22.8: The (Mostly) Photosynthetic

Stramenopliles22.9: The Colourless Stramenopiles

Have flagella that bristle with tinsel-like filaments

Single celled and multicelled Most photosynthetic

Chrysophytes:◦ Free living photosynthetic cell with chloroplasts◦ Includes golden algae, yellow-green algae,

coccolithophores, and diatoms

Golden algae:◦ Have covering of silica scales or other hard parts◦ Producers in many fresh water habitats ◦ Yellow-brown because produce carotenoid

fucoxanthin (masks chlorophylls)

Yellow-green algae:◦ Do not make fucoxanthin◦ Chlorophylls c gives yellowish-green colour ◦ Common in salt marshes and freshwater habitats◦ Most immotile, gametes bear flagellum

Coccolithophores:◦ Parts of calcium carbonate form under plasma

membrane of coccolithophores ◦ Each year these cells die and sink to seafloor

Form calcium carbonate deposits Deposits become part of limestone formations

Diatoms:◦ Have silica “shell” which has two perforated parts

that overlap ◦ Important primary producers, among fastest

reproducers ◦ Release free oxygen

Can convert bicarbonate back into carbon dioxide, makes them best at fixing carbon dioxide

Brown Algae:◦ Olive-green and brown

seaweeds◦ Live in cool or temperate

waters ◦ Range from microscopic

species to giant kelp ◦ Diverse life cycles: sexual

and asexual phases

Oomycotes: (egg-fungi)◦ Once classified as fungi

because have similar growth pattern and feed the same way

◦ Spores give rise to a mesh of thin filaments that absorb nutrients from host tissues or decaying organic matter

◦ Nuclei are diploid, not haploid as fungi

◦ Cell wall has cellulose not chitin (fungi)

Water molds:◦ Decomposers of aquatic habitats ◦ Some parasites

Some aquatic, others ruin plants on land

Water mold on dead larval mayfly

The Closest Relatives of Land Plants22.10: Red Algae

22.11 Green Algae

Red Algae:◦ Most live in warm marine currents and clear

tropical seas◦ Photoautotrophic algae: live in the deepest water ◦ Hold phycobilins and chlorphyll a

Phycobilins are red accessory pigments ◦ Endosymbiosis: chloroplasts of red algae may

have evolved from ancient cyanobacteria

Most red algae show branching or sheet like patterns of multicellular growth

True tissues do not form Life cycles diverse: asexual and sexual

phases Gametes are not flagellated

Green Algae:◦ Closest relative of land plants ◦ Most green algae now classified as

chlorophytes, other group called charophytes (more closely related to land plants, discussed in that section)

Green Algae (chlorophytes):◦ Chloroplasts contain chlorophylls a and b, store

sugars as starch ◦ Cellulose fibers strengthen the cell walls◦ Most aquatic ◦ Sheetlike, filamentous, cuplike, and colonial types

Fig. 22.19 p. 364

Amoeboid Cells at the Crossroads

Shape shifters◦ Werewolves? NOOOOOOOOOOO

Use cytoplasmic extensions to move Most solitary cells, some display communal

behavior and cell differentiation that relate to fungi and animals

Vast majority do not have cell walls, shell, or pellicle

Most form pseudopods

Soft-bodied, free living cells that move on pseudopods

Often prey on bacteria, other protists, or tiny multicelled animals

Some parasitic: E.histolytica causes amoeba dysentery

“Social amoebas” Common in leaf litter and forest soil Important in nutrient cycling Plasmodium: stage of life cycle

Multinucleated mass arises from single diploid cell that undergoes repeated rounds of mitosis without cytoplasmic division Fans out in what appears to be a network of veins; mass digests and absorbs microbes and decaying organic matter in its path

Plasmodium:◦ When stressed, gives rise to many spore-bearing

fruiting bodies ◦ Fruiting bodies consist of haploid spores on a

cellular stalk ◦ When conditions improve spores germinate ◦ Amoeba like cells form that may bear flagella◦ Fusion of 2 haploid cells results in diploid cell,

which may give rise to new plasmodium

Hallmark of multicellularity is the capacity of body to behave in a coordinated way, to respond to external stimuli as a unit

Requires cell-to-cell communication May have originated with common amoeba

like ancestor

http://www.youtube.com/watch?v=sv2q1t9YjsM

Remember the 7 monophyletic groups Characteristics of the different groups How is this kingdom unique? What does this kingdom seem to be leading

up to?