Chapter 23: Protists

protists

* eukaryotes
* most microscopic and unicellular
* abundant in soil, freshwater, brackish, and marine environments
* some have macroscopic cells
* some multicellular
* some parasitic

Antonie van Leeuwenhoek

first to observe protists

characteristics of eukaryotes

* Cells with nuclei surrounded by a nuclear envelope with nuclear pores
* Mitochondria
* Cytoskeleton of microtubules and microfilaments
* Flagella and cilia
* Chromosomes organized by histones
* Mitosis
* Sexual reproduction
* Cell walls

protist cell structure

* most unicellular
* some colonial and multicellular
* some have enormous, multinucleate, single cells
* some have animal-like cell membranes or plant-like cell walls

unicellular organelles

* nucleus: contains cell's genetic info
* endoplasmic reticulum: produce proteins for cells
* golgi apparatus: factory where proteins received from ER are further processed and sorted for transport
* lysosomes: digestive system of cell
* contractile vacuoles: controls the intracellular water balance by accumulating and expelling excess water out of cell

pellicle

* interlocking protein strips
* prevents protist from being torn up or pierced w/o compromising its range of motion

photoautotrophs

characterized by presence of chloroplasts and perform photosynthesis

heterotrophic protists

consume organic materials (other organisms) to obtain nutrients

phagocytosis

1. cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac/vesicle called a food vacuole
2. vesicle containing the ingested particle, the phagosome, then fuses with a lysosome containing hydrolytic enzymes to produce a phagolysosome
3. food particle is broken down into small molecules that can diffuse into cytoplasm and be used in cellular metabolism
4. undigested remains ultimately are expelled from cell via exocytosis

saprobes

subtypes of heterotrophs absorb nutrients from dead organisms or their organic waste

mixotrophs

combine photosynthesis and heterotrophic nutrition

flagella

A long, whip-like filament that helps in cell motility. some protists are flagellated.

cilia

Hairlike projections that extend from the plasma membrane and are used for locomotion

pseudopodia

A cellular extension of amoeboid cells used in moving and feeding.

taxis

Movement toward or away from a stimulus.

phototaxis

movement toward or away from light

accomplished by coupling locomotion strategy with a light-sensing organ

asexual reproduction

* binary fission
* multiple fission
* budding

binary fission

* produces 2 daughter cells
* can be divided into transverse or longitudinal

longitudinal binary fission

plane of division passes along the longitudinal axis of the organism

* ex: Euglena

transverse binary fission

plane of division is through the transverse axis of the organism

* ex: Paramecium

multiple fission

some protists exhibit multiple fission and simultaneously divide into many daughter cells

* ex: true slime molds

budding

some protists produce tiny bids that go on to divide and grow to the size of the parental protist

sexual reproduction

* involves meiosis and fertilization
* associated with periods when nutrients are depleted or environmental changes occur
* recombine genes and produce new variations of progeny

protist life cycles

* can be simple or elaborate
* parasitic protists have complicated life cycles where they must infect different host species at different developmental stages to complete life cycle
* some protists are unicellular in haploid (n) form and multicellular in diploid (2n) form
* alternation of generations

alternation of generations

strategy where protists have multicellular stages in both haploid and diploid forms

cysts

* protective resting stage
* adaptive strategy against adverse environment conditions
* could be resistant to temperature extremes, desiccation, or low pH
* allows protist to "wait out" stressors until environment becomes favorable for survival or until its carried to a different environment
* exhibit no cellular metabolism

eukaryotic supergroups

* six of them
* monophyletic (the organisms within each supergroup believed to have evolved from single common ancestor)
* protists in all six

Archaeplastida

red algae

* phycoerythrin (photosynthetic pigment)
* primarily multicellular
* ex: Porphyra

green algae

* plant-type chloroplasts
* some unicellular (Chlamydomonas)
* some colonial (Volvox)


* some multinucleate (Caulerpa)
* some multicellular (Ulva)

Amoebozoa

slime molds

gymnamoeba

entamoeba

* amoebas with lobe/tube-shaped pseudopodia
* ex: Amoeba, Dictyostelium

Opisthokonta

choanoflagellates

* single posterior flagellum (flagella pushes)
* ex: Mesomycetozoa (parasite)

Excavata

diplomonads and parabasalids

* modified mitochondria
* mitosomes
* parabasal apparatus
* ex: Giardia, Trichomonas

euglenozoans

* contain eyespot
* crystalline rod inside flagella
* ex: Trypanosoma, Euglena

"SAR" Clade

Stramenopiles

* diatoms
* golden algae
* brown algae, oomycetes


* hairy and smooth flagella
* ex: Phytophthora, Laminaria

Alveolates

* dinoflagellates
* apicomplexans
* ciliates
* membrane-enclosed sacs (alveoli) beneath plasma membrane
* ex: Plasmodium (causes malaria), Paramecium

Rhizarians

* radiolarians
* forams
* cercozoans
* amoebas with threadlike pseudopodia
* contains tests


* ex: Ammonia tepida

Archaeplastida: Red Algae

mostly marine, multicellular seaweeds

chloroplasts include red phycoerythrin accessory pigment

* helps absorb light in deeper water (green/yellow light that have longer wavelengths)
* macroscopic
* have cellulose + unique cell wall polysaccharides
* ex: Porphyra, carrageenan thickener (ice cream), and agar (petri dish, food)

Archaeplastida: Chlorophytes

green algae

* chloroplasts same as plants
* mostly freshwater and marine
* many bi-flagellated

unicellular forms:

* phytoplankton
* ex: Chlamydomonas

colonial forms:

* ex: Volvox, Scenedesmus, Gonium

multinucleate, large body forms:

* ex: Caulerpa (intertidal chlorophyte, look like fern)

multicellular forms:

* freshwater algae
* ex: Cladophora (filamentous)
* seaweeds
* ex: Ulva (edible "sea lettuce") (thallose)

Amoebozoans: Slime Molds

live in moist terrestial habitats (rotting wood)

use pseudopodia to move & ingest bacteria

* plasmodial slime mold
* cellular slime mold

plasmodial slime mold

feed as a multinucleate plasmodium

* ex: "dog vomit" plasmodial slime mold

cellular slime molds

feed as single cells, then gather as an "aggregate" when food is gone to form spores

* aggregate moves like a slug

Amoebozoans: Gymnamoebas

found in soil, freshwater, and marine habitats

moves with fat pseudopodia, feed on bacteria and other protists

* ex: Amoeba proteus

Amoebozoans: Entamoebas

unicellular parasites of animals

kills and feeds on host cells

spreads by durable cyst form

* ex: Entamoeba histolytica (causes amebic dysentery)

Excavata: Diplomonads

unicellular, multiple flagella, no cell wall

anaerobic, reduced mitochondria (mitosomes)

most are parasitic

* ex: Giardia intestinalis (intestinal parasite)

Excavata: Parabasalids

unicellular, multiple flagella, no cell wall

anaerobic, reduced mitochondria, asexual

most are symbiotic

* ex: Trichomonas vaginalis (human vaginal parasite STD)
* ex: in termites, they containt symbiotic bacteria that help the termites digest wood

Excavata: Euglenozoans

unicellular, no cell wall, flagella with crystalline rod

ex: Euglenas (free-living, aquatic)

* can be autotrophs with green chloroplasts (secondary endosymbiosis) or heterotrophs or mixotrophs
* eyespot helps them sense sunlight
* contractile vacuole is for osmoregulation
* have pellicle

ex: Trypanosoma (blood parasite)

* present in Africa
* causes "sleeping sickness" (carried by tse-tse fly)
* symptoms: personality changes, seizure, etc because it infiltrates central nervous system

Stramenopiles: Diatoms

unicellular phytoplankton ("algae")

key primary producers (aquatic)

have yellow and brown accessory pigments

* carotenoids (one of the photosynthetic pigments in diatoms) —> carotenes + xanthophylls

made of silica (SiO2) walls (glass-like)

"diatomaceous earth" deposits: fossilized remains of diatoms, used in water filters

no flagellum except in gamete

photoautotrophs

all with chloroplasts containing chlorophyll a

accessory pigments vary

some chloroplasts from secondary endosymbiosis

Stramenopiles: Brown Algae

multicellular, mostly marine "seaweeds"

* major primary producers
* with brownish accessory pigments
* large thallose (plant-like) form

cell wall with cellulose & algin

* ex: kelp (Laminaria & other species)
* humans eat it
* algin used as commercial food thickener

has alternation of generations (haploid & diploid forms) (common in plants)

thallus

the body of a plant-like organism that is not divided into leaves, roots, or stems

* blade (top/leaves)
* stipe (stem)
* holdfast (roots)

sporophyte

Diploid (2n), or spore-producing, phase of an organism. Makes haploid spores by meiosis.

zoospores

flagellated spores, haploid (n), and unicellular

gametophytes

male and female haploid plants that produce gametes

MULTICELLULAR

zygote

a diploid (2n) cell resulting from the fusion of two haploid gametes

sporangia

located on the tip of the mature sporophyte, where meiosis occurs, producing haploid spores (multicellular)

Stramenopiles: Oomycetes

filamentous, multinucleate, absorptive heterotrophs (like fungi); some infest plants

* superficially resemble fungi

cell walls with cellulose, not chitin

filamentous growth (mycelia) is diploid

* ex: Phytophthora infestans "potato late blight" (plant parasite: caused Irish famine)

spores have flagella!

Alveolates: Dinoflagellates

unicellular aquatic heterotrophs or phytoplankton with reddish accessory pigments

pair of flagella in perpendicular grooves

* ex: Pfiesteria (chemoheterotroph)
* ex: Akashiwo (photoautotroph; chloroplasts likely from secondary endosymbiosis)

many are photosynthetic mutualists within corals

* give nutrition to coral and coral gives them a place to live

"blooms" of some species kill fish or create toxic "red tides"

* ex: Pfiesteria cause lesions and Karenia brevis (brevetoxins, neurotoxic) cause "red tide"

some are bioluminescent

Alveolates: Apicomplexans

unicellular parasites of animals; no cell wall

apical complex helps them enter host cells

complex life cycles

* requires more than one host
* multiple "forms"
* ex: Plasmodium (causes malaria, carried by mosquitos) KNOW THE LIFE CYCLE
* other ex: Toxoplasma, Cryptosporidium

Alveolates: Ciliates

unicellular ingestive heterotrophs with no cell wall; aquatic

cilia for feeding & locomotion

animal-like in function

* ex: Paramecium

most reproduction is asexual division

* both macronucleus & micronucleus divide

sexual reproduction in ciliates occurs via conjugation

macronucleus

polyploid; controls cell functions

micronucleus

used only for genetic recombination

Rhizaria: Radiolarians

\-unicellular marine plankton

\-feed with threadlike pseudopodia

\-symmetric silica "skeletons"

\-ingestive heterotrophs

\-reinforced by microtubules from cytoskeleton

Rhizaria: Foraminiferans

"forams"

\-unicellular, mostly marine plankton

\-feed with threadlike pseudopodia

\-porous shells (tests) of calcium carbonate

\-ingestive heterotrophs but some mutualists with algae

\-pseudopodia (reinforced by microtubules) extend through pores in test

Rhizaria: Cercozoans

morphologically and metabolically diverse

include both naked and shelled forms

Chlorarachniophytes (marine & unicellular) have acquired chloroplasts by secondary endosymbiosis

* are mixotrophic

Secondary Endosymbiosis Examples

* Dinoflagellates from red alga (ex: Akashiwa)
* Stramenopiles from red alga
* Euglenids from green alga
* Chlorarachniophytes from green alga (from Rhizaria: Cercozoa)