Lecture #3
Protists
Chapter 28: the Protists
• Even a low-power
microscope can reveal a
great variety of organisms
in a drop of pond water
• These amazing organisms
belong to the diverse
kingdoms of mostly singlecelled eukaryotes
informally known as
protists
• Advances in eukaryotic
systematics have caused
the classification of
protists to change
significantly
Kingdom Protista??
• now part of the superkingdom Eukaryota
– eukaryotes = true nucleus
– evolution of a nucleus for the genetic information
– evolution of membrane-bound organelles
• diverse group of single and colonial forms informally known as The
Protists
• but Kingdom Protista really doesn’t exist anymore – too polyphyletic
• probably arose from more than one prokaryotic group
• include the algae and slime molds
• first observed in pond water by Antoni van Leeuwenhoek 300 years
ago
• 7 to 45 species recognized depending on zoologist
• some as small as prokaryotes
• molecular analysis has discovered many commonalities that make
them Protists
Protists
– include groups that are photoautotrophs,
heterotrophs and mixotrophs
• mixotrophs = combine photosynthesis and
heterotrophic nutrition
– divide the protists into three categories:
– 1. Photosynthetic – plant-like or algae
– 2. Ingestive – animal-like or protozoans
• amoeba
– 3. Absorptive – fungus-like
Cellular Anatomy
• most are unicellular
– but the cellular composition is extremely complex
• unicellular protists carry out similar functions to multi-cellular
eukaryotes with their organ systems
– do so using subcellular organelles
• many of these organelles are seen in higher organisms
– endoplasmic reticulum
– Golgi apparatus
– lysosomes
• other organelles are not found in the typical multicellular eukaryote
– contractile vacuoles for osmoregulation
Protists and Eukaryotic Evolution
•
•
•
•
Many components of the eukaryotic animal and plant cell were derived from protists
diversity of protists has its origins in endosymbiosis
process where a unicellular organism engulfs another cell – become endosymbionts and
eventually a new organelle
–
e.g. acquisition of mitochondria – ingestion by alpha-proteobacteria by an ancestral cell
early evolution – ingestion of a photosynthetic cyanobacteria through primary
endosymbiosis by a heterotrophic eukaryote
– eventual development into the plastids of the photosynthetic red and green algae
– DNA of red and green algae is very similar to that of cyanobacteria
– plastid membrane is dual layered – similar to the inner and outer membranes of the
cyanobacteria
•
Red and green algae also underwent secondary endosymbiosis – they were ingested by a
heterotrophic eukaryotic cell to become endosymbionts and eventual plastids of the
protists listed below in the figure
Plastid
Dinoflagellates
Secondary
endosymbiosis
Cyanobacterium
Apicomplexans
Red algae
Primary
endosymbiosis
Stramenopiles
Heterotrophic
eukaryote
Secondary
endosymbiosis
Plastid
Euglenids
Green algae
Secondary
endosymbiosis
Chlorarachniophytes
The 5 Supergroups of Eukaryotes
• 1. Excavata
• 2. Chromalveolata
– common ancestors – the alveolates and
stramenophiles
• 3. Rhizaria
• 4. Archaeplastida
– contains green algae and land plants
• 5. Unikonta
– slime molds, entamoebas, fungi and animals
Ancestral eukaryote
Plants
Charophyceans
(Opisthokonta)
Chlorophytes
Plantae
Charophyta
Chlorophyta
Rhodophyta
Animalia
Fungi
Unikonta
Red algae
Metazoans
Choanoflagellates
Amoebozoa
Fungi
Radiolaria
Rhizaria
Cellular slime molds
Plasmodial slime molds
Entamoebas
Gymnamoebas
Radiolarians
Cercozoa
Chromalveolata
Foraminiferans
Chlorarachniophytes
Brown algae
Golden algae
Diatoms
Excavata
Ciliates
Apicomplexans
Stramenopila
Oomycetes
Euglenozoa
Parabasala
Alveolata
Dinoflagellates
Euglenids
Kinetoplastids
Parabasalids
Diplomonads Diplomonadida
Eukaryotic Phylogenetic Tree
Archaeplastida
(Viridiplantae)
Clade: Excavata
•
•
•
•
A. Diplomonads
B. Parabasilids
C. Euglenozoans
Diplomonads & Parabasilids
– protists in these two clades lack plastids (no photosynthesis)
– mitochondria do not have DNA or the enzymes for the citric acid cycle or proteins
for the electron transport chain
– cannot use O2 to help extract energy from carbohydrates
– therefore they are found in anaerobic environments
• A. Diplomonads
– two equal-sized nuclei and multiple flagella
– flagella is very different from prokaryotic flagella
• eukaryotic flagella is an extension of the cytoplasm and are made of microtubules
composed of tubulin in a distinct 9+2 array pattern
– have modified mitochondria = mitosomes
– many are parasites
• e.g. giardia intestinalis – intestinal protist in contaminated drinking water – severe
diarrhea
• B. Parabasalids
– also have reduced/modified mitochondria = hydrogenosomes
• generate some energy anaerobically – releasing H2 gas as a by-product
– include the protists called trichomonads – Trichomonas vaginalis
• disturbance in the normal pH of the vagina allows this protist to outcompete
beneficial microbes and infect the vaginal lining – sexually transmitted to males also
• probable acquisition of parasitic behavior through genetic recombination
(conjugation) with a parasitic bacteria also within the vagina
– mobility through an undulating membrane in addition to flagella
LE 28-5b
Flagella
Undulating membrane
5 µm
Trichomonas vaginalis, a parabasalid (colorized SEM)
• C. Euglenozoans
– belong to a diverse clade – includes heterotrophs, photosynthetic
autotrophs and parasites
– like algae – the photosynthetic protists have chlorophyll a and b in
chloroplasts
– distinguishing feature – a rod with either a spiral or crystalline structure
inside each of their flagella
• unknown function
– divided into the groups:
– 1. the Kinetoplastids
– 2. the Euglenoids
1. Kinetoplastids
– used to be called the zoomastigophores
– defined by a single, large mitochondrion that contains an organized mass
of DNA = kinetoplast
– free-living forms in freshwater, marine and soil – feed on the prokaryotes
in these ecosystems
– some are parasites of animals, plants and other protists
• Trypanosoma gambienese – sleeping sickness (neurological disease) &
Chagas’ disease (congestive heart failure) in humans
• Coated with millions of copies of a single protein
• Evade detection by the host using a “bait and switch” mechanism which
allows the trypanosome to change the composition of theis surface protein to
a different molecular structure
• about 1/3 of the trypanosomes genome is devoted to making these surface
proteins!
Kinetoplastids: Trypanosoma
– unicellular protist with two flagella that emerge from a
“pocket” structure
• at the pocket is a large contractile vacuole that connects to
the outside
• continuously collects water from the cell and returns it to the
outside – regulates osmotic pressure
• two flagella arise at this reservoir
• only one emerges from the canal and actively beats for
locomotion
2. Euglenoids
– most are autotrophic
• several chloroplasts with chlorophyll a and b and carotenoid
pigments
• some can also be mixotrophic – photosynthetic in sunlight,
engulfs prey in absence of sunlight
– inside the plasma membrane is a structure called the
pellicle
• articulated strips of protein lying side by side
• elastic enough to enable turning and flexing of the cell
• but rigid enough to prevent major changes in shape
– eyespot (stigma) - near the flagella
• functions as a pigment shield allowing only certain
wavelengths of light to strike the light detector
– light detector (photoreceptor) – detects the filtered light
and results in movement toward the light direction
• probably developed in order to maximize its photosynthetic
potential
used to be classified as the
Class Phytomastigophorea
Clade: Chromalveolata
• originated more than a billion years ago when their ancestor
ingested a photosynthetic red algae (via secondary
endosymbiosis)
– plastids within these protists have red algae origins (DNA analysis)
– divided into two major groups: Alveolates & Stremenophiles
– A. Alveolates:
• 1. Dinoflagellates
• 2. Apicomplexans
• 3. Ciliates
– B. Stramenophiles
•
•
•
•
1. Diatoms
2. Golden Algae
3. Brown Algae
4. Oomycetes
A. Alveolates
• characterized by membrane-bound sacs called alveoli
– just under the plasma membrane
– function unknown – may be involved in the stabilization of the cell
membrane or may regulate the entrance and exit of ions and water
(osmolarity)
• 1. Dinoflagellates – move through flagellar action
• 2. Apicomplexans - parasites
• 3. Ciliates – move through ciliary action
• Dinoflagellates – several thousand
species
1. Dinoflagellates
– “dinos” = whirling
– components of both marine and
freshwater phytoplankton
– some can be heterotrophic (phagocytic)
– most are autotrophic with well-formed
plastids for photosynthesis
• chlorophylls a and c + carotenoids and
xanthophylls – yellowish green color
Flag
3 µm
– possess mitochondria with tubular cristae
(similar to animals)
– characteristic shapes – reinforced by
internal plates of cellulose that become
encrusted with silica - act as “armor”
LE 28-10
– two flagellae – located in perpendicular grooves in these plates
• one groove is transverse = cingulum – propels the dinoflagellate
forward and causes it to spin
• other groove is longitudinal = sulcus – acts as the rudder
– capable of proliferating explosively – “blooms”
• “red tide” (carotenoid pigments found in the plastids) can result from
blooms of certain dinoflagellates – produce a toxin that kills off
invertebrates
– some can be bioluminescent – ATP driven reaction that creates a
glow at night
• may be a defense mechanism
• if the water is lit-up by predators that eat dinoflagellates – it may
attract fish to eat those predators
2. Apicomplexans
• nearly all are animal parasites
• spread through the formation of tiny infectious cells = sporozoites
• named because one end (apex) contains a complex of organelles
specialized for penetrating host tissues and cells
• have a non-photosynthetic plastid = apicoplast which has many
functions including the synthesis of fatty acids for its membranes
• life cycle – includes sexual and asexual stages
• best known is the Plasmodium – causes malaria
– rivals tuberculosis as the leading cause of human death by infectious disease
– can be reduced by insecticides that kill the Anopheles mosquito (DDT) and by
drugs that kill the Plasmodium (quinine based drugs)
– vaccines hard to develop – Plasmodium lives inside the RBC (hidden)
– carriers of sickle cell anemia gene – resistant to malaria
• plasmodium killed by the “leakiness” of the affected RBCs
• Sexual and asexual reproduction that
requires more than one host to complete
• 1. infected Anopheles mosquito bites a
person injecting its sporozoites (n)
• 2. sporozoites enter the liver and undergo
division to become merozoites (n)
Plasmodium
– merozoites enter RBCs by using their apical
complex
• 3. the merozoites asexually divide into
more merozoites
– every 48 to 72 hrs – merozoites will break
out of some RBCs – fever and chills
– some will go on to infect more RBCs and
multiply
• 4. other merozoites develop into
gametocytes
• 5. gametocytes picked up by a new
mosquito
• 6. gametes form and fertilization takes
place in the mosquito’s digestive tract
– the fertilized cell = zygote
• 7. an oocyst develops from the zygote and
adheres to the wall of the mosquito’s gut
– produces more sporozoites
LE 28-11
Inside mosquito
Inside human
Merozoite
Sporozoites
(n)
Liver
Liver
cell
Oocyst
MEIOSIS
Apex
Merozoite
(n)
Zygote
(2n)
Red blood
cell
0.5 µm
Red blood
cells
FERTILIZATION
Key
Gametes
Gametocytes
(n)
Haploid (n)
Diploid (2n)
3. Ciliates
• use of cilia to move and feed
• cilia may completely cover the protist or may cluster in
a few rows or tufts
• distinguished by the presence of two types of nuclei:
macronucleus (large) and micronucleus (small)
– may have one or more of each type
– macronucleus – contains dozens of copies of the genome
• not organized as chromosomes
• packed into smaller units each bearing duplicates of just a few genes
• control the everyday functions of the ciliate
– micronucleus – function in reproduction
• exchanged between two ciliates during conjugation
LE 28-12
Paramecium
• freshwater protist –
constantly takes on water
from its hypotonic
environment
• they contain contractile
vacuoles for the regulation
of osmotic pressure –
accumulate excess water
via radial canals and then
expel it through the plasma
membrane back into the
environment
FEEDING, WASTE REMOVAL, AND WATER BALANCE
Paramecium, like other
freshwater protists, constantly
takes in water
by osmosis from the hypotonic
environment. Bladderlike
contractile vacuoles
accumulate excess water from
radial canals and periodically
expel it through the plasma
membrane.
Thousands of cilia cover the
surface of Paramecium.
Contractile
vacuole
50 µm
Micronucleus
Macronucleus
Paramecium feeds mainly on
bacteria. Rows of cilia along a
funnel-shaped oral groove move
food into the cell mouth, where the
food is engulfed into food vacuoles
by phagocytosis.
Oral groove
Cell mouth
Food vacuoles combine with
lysosomes. As the food is digested, the
vacuoles follow a looping path through
the cell.
The undigested contents of
food vacuoles are released
when the vacuoles fuse with a
specialized region of the
plasma membrane that
functions as an anal pore.
• cilia participate in movement
– but also gather food and move it
toward the oral groove which
holds the cell mouth at the bottom
– food is then engulfed into a food
vacuole via phagocytosis
• food vacuoles combine with
lysosomes containing digestive
enzymes
– undigested food particles are
carried to the opposite end of the
cell as the cell mouth
– fuse with the plasma membrane in
a specific region – acts as an “anal
pore”
Paramecium
•
•
asexual reproduction – through binary fission
sexual reproduction involving conjugation
– 1. two compatible mating strains align side by
side and partially fuse
– 2. meiosis of their micronuclei produces a total
of 4 haploid micronuclei in each cell
– 3. three of these in each disintegrate & the
remaining micronuclei in each divides by
mitosis- resulting in 2 micronuclei in each
– 4. the cells swap one of their micronuclei –
genetic recombination
– 5. the cells separate
– 6. the two micronuclei in each cell fuse to
produce a diploid nuclei
– 7. three round of mitosis without fission results in
8 micronuclei in each paramecium
– 8. the original macronuclei disintegrates and 4
micronuclei become 4 macronuclei to replace it
– leaves 4 micronuclei
– 9. two rounds of binary fission now happen
results in 4 daughter cells
– 10. the micronuclei (4) and macronuclei (4) then
partition into the four daughter cells – each ends
up with 1 micronuclei and 1 macronuclei
CONJUGATION AND REPRODUCTION
Meiosis of
Three micronuclei in each cell
micronuclei produces
disintegrate. The remaining microfour haploid micronuclei nucleus in each cell divides by
in each cell.
mitosis.
Two cells of compatible
mating strains align side by
side and partially fuse.
Compatible
mates
The cells swap
one micronucleus.
Macronucleus
MEIOSIS
Haploid
micronucleus
Diploid
micronucleus
Diploid
micronucleus
MICRONUCLEAR
FUSION
The
cells
separate.
Two rounds of
cytokinesis
partition one
maccronucleus
and one
macronucleus into
each of four
daughter cells.
The original
macronucleus
disintegrates. Four
micronuclei
become
macronuclei, while
the other four
remain
micronuclei.
Micronuclei
Three rounds
fuse, forming a
of mitosis
diploid
without
micronucleus.
cytokinesis
produce eight
micronuclei.
Key
Conjugation
Reproduction
-partially fuse
-1 micronuclei becomes 4 haploid micronuclei (meiosis)
-3 disappear
-1 micronuclei becomes 2 (mitosis)
-“swap” 1 micronuclei and separate
-fuse 2 micronuclei into 1 (diploid)
-2 micronuclei become 8 (mitosis/no division)
-macronuclei disappears
-4 of the 8 micronuclei develop into 4 macronuclei
-4 of the micronuclei stay micronuclei
-2 rounds binary fission = 4 daughter paramecia
-each daughter cell gets a macronuclei and a micronuclei
B. Stramenophiles
• stramen = “straw”; pilos – “hair”
• comprised of several groups of heterotrophs and several groups of
phototrophs (algae)
• flagella are said to be “hairy” – have numerous hair-like projections
along the length
• this hairy flagellum is paired with a smooth flagellum
• 1. oomycetes – water molds
• 2. bacillariophytes - diatoms
• 3. chrysophytes – golden algae
• 4. charophyceans – brown algae
Smooth
flagellum
5 µm
Hairy
flagellum
Algae: Photosynthetic Protists
• study of algae = phycology
• no longer any formal classification schemes
– scattered across many phyla = polyphyletic
• algae = eukaryotic organisms with chlorophyll a pigments that carry out
oxygen-producing photosynthesis
• differ from the plants – lack a well-organized vascular system and they have a
simple reproductive system
• reproduce sexually and asexually
• occur most often in water
– fresh and marine – may be suspended as planktonic organisms or attached to the
bottom (benthic)
• plankton = free-floating microscopic aquatic organisms
– phytoplankton – made up of algae and small plants
– zooplankton – non-photosynthetic protists and animals
• some classical algae are now grouped together with the plants (green algae),
some are a separate lineage (red algae), some are grouped with the
stremenophiles (yellow and brown algae, diatoms), some are grouped with the
alveolates (diatoms) and some with the protozoans (euglenoids)
Algae: Photosynthetic Protists
• important properties that classify them:
– 1. cell wall composition – rigid cell wall
• some have an outer membrane outside the wall – similar to the bacterial capsule
– 2. form in which food is stored
– 3. chlorophyll molecules and accessory pigments (carotenoids)
• chloroplasts have membrane-bound sacs (thylakoids) for the light-reactions of photosynthesis
– 4. flagella number and location of their insertion into the cell
• flagella are used for locomotion
– 5 morphology of the cells and/or body
• comprised of a vegetative body = thallus
– 6. habitat: marine or freshwater
• unicellular, colonial, filamentous, membranous, blade-like or tubular
– 7. reproductive structures: reproduction is asexual or sexual
• asexual – seen in unicellular forms
• three forms: 1. fragmentation, 2. spores and 3. binary fission
• sexual – generation of eggs within modified vegetative cells (oogonia) or sperm by
antheridia
– 8. mitochondria cristae structure: tubular, disc or plate-like (lamellar)
– chlorophyta, charophyta, euglenophyta, chrysophyta, phaeophyta, rhodophyta,
pyrrophyta
1. Oomycetes: Water molds
•
•
•
•
•
•
•
•
•
oomycete = “egg fungus”
water molds, white rusts and downey mildews
used to be considered fungi – have multinucleate
filaments called hyphae that resemble those seen in
fungi
but the oomycetes have cell walls made of cellulose
(fungus – chitin) and the diploid condition
predominates (reduced in fungi)
molecular data also cannot confirm fungal origins
similarities are an example of convergent evolution
derived from a plastid containing ancestor - no longer
have plastids and do not carry out photosynthesis –
non-autotrophic
acquire nutrients as decomposers – grow as cottony
masses on dead animals and algae = heterotrophic
white rusts and downey mildews live as parasites on
land plants
– Phytophthora infestans – potato blight
– contributed to the Irish famine of the 19th century
– today still leads to crop losses of close to 15% (North
America) and as high as 70% (Russia)
– molecular engineers have transferred blight-resistant
genes into domestic potato crops to protect them
Water mold oogonium
water mold
•
life cycle: can alternate between asexual and
sexual forms
– asexual cell called a zoospore develops via mitosis
into a hyphae
– the zoospore is biflagellated with one smooth
flagella and the other “hairy”
– this hyphae develops sexual structures that
produce gametes or alternatively can form
zoospores asexually
– in the sexual life cycle - one region of the hyphae
undergoes meiosis to produce egg nuclei (n) within a
structure called an oogonium
– other branches can develop sperm nuclei (n) via
meiosis – contained within an antitheridial hyphae
– these antitheridial hyphae grow and “hook” around
the oogonium and deposit their nuclei through
fertilization tubes = fertilization
– the hyphae then becomes dormant – wall of the
oogonium breaks apart and releases the zygotes
– these zygotes germinate to regenerate hyphae which
then develops into a new sexual structure –
completes the sexual life cycle
– however some zygotes will form a zoosporangium
which produces zoospores asexually
– germination of these zoospores starts the asexual life
cycle
Oogonium
Germ tube
Egg nucleus (n)
Cyst
Antheridial hypha
with sperm nuclei (n)
MEIOSIS
ASEXUAL
REPRODUCTION
Zoospore
(2n)
FERTILIZATION
Zygote
germination
Zoosporangium
(2n)
SEXUAL
REPRODUCTION
Zygotes
(2n)
Key
Haploid (n)
Diploid (2n)
Water mold zoospores
2. Diatoms
•
•
100,000 species of unicellular algae
with a unique glass-like wall made of silica embedded in an organic matrix
–
–
–
–
•
reproduce asexually via mitosis
–
•
•
•
•
daughter receives half of the parental cell wall and generates a new half
sexual reproduction is not common
photosynthetic – chlorophylls a and c and carotenoids
some are heterotrophic – absorb carbon-containing molecules through holes in their
walls
major component of phytoplankton in fresh and marine environments in cooler waters
–
–
–
–
–
•
•
two parts that overlap like a shoe box and lid
upperlid = epitheca, lowerlid = hypotheca
effective protection against extreme crushing forces
wall is a lacework of holes and grooves
source of food for fish and other marine animals
upon death –sink to the bottom = diatomaceous earth
not broken down by decomposers – carbon remains on the sea floor and is not released as
CO2
may be able to decrease global warming – by taking CO2 out of the environment
active ingredient in detergents, fine abrasive polishes, paint removers, decoloring oils, filtering
agents, components of insulation and soundproofing products, reflective paint additive
store their food reserves in the form of a glucose polymer = laminarin
modern uses in nanotechnology – mechanism of assembly of their cell walls is being
used as a model for miniature models and lasers
3. Golden Algae: Chrysophyta
•
•
•
•
•
•
•
•
all species are photosynthetic but some can be
mixotrophic by absorbed dissolved organic
compounds or ingesting good particles by
phagocytosis
major photosynthetic pigments: chlorophylls a and c
+ carotenoids (fucoxanthin)
dominant pigment is fucoxanthin – golden-brown
color
major carbohydrate reserve = chrysolaminarin
some have cell walls
some have intricate external coverings = scales, walls
and plates
most are unicellular but some are colonial
most are biflagellated – both attached near one end
of the cell
Dinobryon
• brown algae – most complex algae
– all are multicellular and marine
– some have the most complex
multicellular anatomy of all algae
– some have specialized tissues like
animals and plant
– include the seaweeds
– giant seaweeds in intertidal zones –
kelps
– carotenoid pigments located in plastids
also found in the golden algae and
diatoms
– sugar storage form = laminarin
– composed of a thallus = algal body that
is plant-like
– thallus has a rootlike hold-fast which
anchors the seaweed and a stem-like
stipe that supports leaf-like blades
– BUT there are no true roots, stems and
leaves!
– blades – surface for photosynthesis
– blades can come equipped with floats
to keep them near the surface
4. Brown algae:
Phaeophyta
LE 28-18
Brown algae Thallus
Brown algae: Life cycle
•
brown algae exhibit alternation of
generations
– alternation between haploid and diploid
multicellular forms
– only applies to multicellular stages in the life
cycle
– if the two multicellular forms are structurally
different = heteromorphic
– 1. diploid multicellular individual = sporophyte
– adult algae with hold-fast, stipe and blades
– 2. on the blade – development of sporangia
from the sporophyte
– 3. sporangia develop haploid zoospores by
meiosis
– 4. 50% of zoospores develop into male
gametophytes and 50% into female
gametophytes – these are multicellualr
– 5. the gametophytes produce and release the
gametes that will fuse and form the zygote
•
•
eggs remain attached to the female gametophyte
eggs can release a chemical that will attract sperm
– 6. zygote develops into a new sporophyte
which grows via mitosis to form a new adult
algae
Key
Haploid (n)
Diploid (2n)
Sporangia
Sporophyte
(2n)
Zoospores
Female
Gametophytes
(n)
Male
e.g. Laminaria
Clade Rhizaria
• characterized by the presence of threadlike pseudopodia = extensions of the
cytoplasm that bulge anywhere along the cell’s surface
– “false –feet”
– used in locomotion and prey capture
– extend and contract by reversible assembly of actin subunits into microfilaments
• contraction requires interaction between actin and myosin
– first formed through the projection of a lamellipodium – actin assembles in the leading
edge until it forms a microfilament network
• cytoplasm flows in forming the pseudopodium
– locomotion: anchor a tip to the surface – stream cytoplasm into the pseudopodium
– prey capture: pseudopodia senses the prey through physical contact and surrounds it
– types of pseudopodia:
• 1. Lobopodia – blunt shaped
– possess forms of cytoplasm called ectoplasm and endoplasm
– locomotion and feeding
• 2. Filopodia – football shaped
– ectoplasm only, two-way streaming to move food like a conveyor belt
• 3. Reticulopodia – branching filopodia
– complex and bear individual pseudopodia that form an irregular net
– used for primarily ingestion, can be used for locomotion
• 4. Axiopodia – long and thin
– reinforced by microtubule arrays enveloped by cytoplasm
– responsible for phagocytosis NOT locomotion
Clade Rhizaria
• A. Radiolarians: delicate, intricately symmetrical internal skeletons made of silica
– pseudopodia which “radiate” out from a central body – reinforced by microtubultes
– pseudopodia are also capable of phagocytosing food – cytoplasmic streaming then
carries the food inro the central body
• B. Forams: formerly called foraminiferans
– named for their porous shells – holes are called foramen
– shell is called a test = single piece of organic material hardened with calcium
carbonate
– pseudopodia extend through the holes – function in swimming, in making the test and
feeding
– marine and freshwater – in sand or attached to rocks or algae
• C. Cercozoans – the amoebas
LE 28-23
Forams
Axopodia
Radilarins
200 µm
C. Cercozoans
• contain the organisms called amoebas
• amoeba species are also found in other clades
• most are heterotrophs – many are parasites of plants and animals; many are
predators
• predators species include the most important predators of bacteria in many
ecosystems
Clade Archaeplastida
• more than a billion years ago – heterotrophic protist acquired a
cynanobacterial endosymbiont
– gave rise to red algae and green algae
• 475 million years ago – green algae ancestors evolved into land
plants
• red algae, green algae and land plants are now placed into the
same clade based on molecular data – Archaeplastida
• divided into:
• A. Red algae
• B. Green algae
• C. Charophytes – includes Plants
Plastid
Dinoflagellates
Secondary
endosymbiosis
Cyanobacterium
Apicomplexans
Red algae
Primary
endosymbiosis
Stramenopiles
Heterotrophic
eukaryote
Secondary
endosymbiosis
Plastid
Euglenids
Green algae
Secondary
endosymbiosis
Chlorarachniophytes
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red algae – 6000 species
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A. Red Algae:
Rhodophyta
multicellular
most are autotrophic – photosynthesis
possess plastids that contain numerous pigments
red pigment = phycoerythritin and blue pigment = phycocyanin (phycobilins)
• masks the green of the chlorophyll in the plastids
– pigments allow for the absorption of green and blue light which have long
wavelengths and can penetrate the deeper waters where the red algae are found
• blue and red wavelengths are absorbed by the phycobilins and the light energy is then
transferred to the chlorophylls for photosynthesis
• shallow water algae may not have as much phycoerythritin and may be more green
– sugar storage form = floridean
– some can be parasitic on other red algae – lack pigmentation for photosynthesis
– cell wall includes a rigid inner part of microfibrils and a matrix of proteins and
sugars
– this matrix is also called agar = sulfated polymers of galactose
– largest red aldae are included in a group called seaweeds (e.g. nori)
– life cycle does not include a flagellated step – must rely on ocean currents to
deliver gametes for fertilization
B. Green algae: Chlorophyta
• green algae
– named for the green chloroplasts –pigments and structure are
very similar to plants
– divide into two groups:
– 1. Charophytes – most closely related to plants
– 2. Chlorophytes – 7000 species
• chloro = “green”
• unicellular forms
• unicellular forms live symbiotically with other eukaryotes –
contributing to photosynthetic output
• also live symbiotically with fungus – as lichens
• some are also multicellular - colonial, filamentous and sheetlike
forms
• mostly freshwater
• chlorophylls a and b + carotenoid pigments
• sugar storage form = starch
• cell walls made of cellulose
Chlorophytes
• e.g. Chlamydomonas – example of a
unicellular algae
– two flagella of equal length at the anterior
end
– one conspicuous pyrenoid
» organelle found in or beside the
chloroplasts of algae
» involved in carbohydrate synthesis from
CO2
– eyespot or stigma
» movement towards light
– two small contractile vacuoles at the base of
the flagella – function as osmoregulatory
organs
– sexual reproduction is also possible – cell
division produces gametes of each “sex”
Chlorophytes
•
size and complexity of green algae has evolved one of three ways:
– 1. formation of colonies of individual cells – e.g. Volvox
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colony or 500 to 60,000 cells – mostly smaller vegetative cells
individual cells resemble Chlamydomonas - biflagellated
cells are connected by thin strands of cytoplasm
flagella all beat in a coordinated fashion – rotates the colony in a clock-wise fashion
cells have eyespots – will orient toward the light
some cells reproduce asexually
other cells are reproductive - develop from the cells at the equator = called gonads
zygote undergo mitosis until they form a sphere – flagella are on the inside!! therefore it must
invert before leaving
• the daughter colony remains in the parental colony until it ruptures
– 2. repeated division of nuclei with no cytoplasmic division – multinucleate filaments
(pond scum)
– 3. formation of true multicellular forms by mitosis and cytokinesis
Volvox, a colonial freshwater chlorophyte. The colony is a hollow ball
whose wall is composed of hundreds or thousands of biflagellated
cells embedded in a gelatinous matrix. The cells are usually
connected by strands of cytoplasm; if isolated, these cells cannot
reproduce. The large colonies seen here will eventually release the
small “daughter” colonies within them.
– life cycle: sexual and asexual stages
• mature cells are haploid – single cell with a cup-like chloroplast and 2
flagellae
• asexual reproduction: the cell reabsorbs its 2 flagellae and divides by
mitosis to form four identical cells (zoospores) within a capsule
– cells are released as swimming zoospores
• sexual reproduction: upon shortage of nutrients
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haploid zoospore develops into gametes – male and female
gametes of opposite mating types fuse to form the zygote (diploid + 4 flagella)
zygote loses its flagellae and surrounds itself by a coat to protect itself
meiosis in the zygote results in 4 haploid cells – two from each mating type
these released haploid cells develop into biflagellated mature cells that can continue the
sexual life cycle or reproduce asexually
Flagella
1 µm
Cell wall
Green algae:
Reproduction
Nucleus
Zoospores
Regions
of single
chloroplast
Key
Haploid (n)
Diploid (2n)
ASEXUAL
REPRODUCTION
Mature cell
(n)
SEXUAL
REPRODUCTION
SYNGAMY
MEIOSIS
Zygote
(2n)
Clade Unikonta
• recently proposed clade
• supergroup of eukaryotes that includes
animals, fungi and some protists
• denotes “one flagella”
• two major clades:
• A. Amoebozoans: the amoebas & slime molds
• B. Opisthokonts: fungi and animals
A. Amoebozoans
• lobe or tube-shaped pseudopodia rather than threadlike
• 1. Gymnamoebas
– unicellular
– soil, freshwater and marine
– most are heterotrophic – consume bacteria and other protists plus detritus
(decomposers)
– some can possess shells = tests
– particle feeders – use their pseudopodia to capture food
• 2. Entamoebas
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parasitic amoebae
infect all classes of vertebrates and some invertebrates
humans are host to at least 6 species
Entamoeba histolytica – amoebic dysentery
• third leading cause of death in the world due to parasites – 100,000 deaths each year
• 3. Mycetezoans = Slime molds
– cellular
– plasmodial
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brightly pigmented – orange or yellow
named for the formation of a feeding stage = plasmodium in the life cycle
many similarities to fungus – including the formation of fruiting bodies & spores
plasmodium – very large but still is unicellular
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takes on a web-like form and undergoes sexual reproduction when conditions become harsh
these bodies develop into fruiting bodies or sporangium via meiosis which are released as haploid spores
(n)
germination of the spores takes place in the presence of adequate moisture
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cell undergoes mitosis but fails to divide through cytokinesis – “super-cell”
lives on organic matter
takes up food via phagocytosis
then undergoes cytoplasmic streaming – cytoplasm streams first one way then the next – distribution of nutrients
and O2
results in the production of either amoeboid cells (myxoamoebae) or flagellated cells (swarm cells) - haploid
fertilization (syngamy) requires the fusion of the same type of cell – i.e. swarm with swarm
production of the zygote (2n) and development of a new plasmodium forms – mitosis without cytokinesis
Zygote
(2n)
3. Mycetozoans:
Plasmodial slime molds
Feeding
plasmodium
Mature
plasmodium
(preparing to fruit)
Young
sporangium
SYNGAMY
1 mm
Amoeboid cells
(n)
Mature
sporangium
Key
Flagellated cells
(n)
Germinating
spore
Spores
(n)
MEIOSIS
Stalk
Haploid (n)
Diploid (2n)
SYNGAMY
3. Mycetozoans:
Cellular slime molds
Spores
(n)
Emerging
amoeba
Solitary amoebas
(feeding stage)
Zygote
(2n)
SEXUAL
REPRODUCTION
MEIOSIS
Amoebas
Fruiting
bodies
ASEXUAL
REPRODUCTION
Aggregated
amoebas
Key
Haploid (n)
Diploid (2n)
Migrating
aggregate
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feeding stage is a solitary amoeboid form = myxoameoba
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can undergo asexual or sexual reproduction
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determined by food supply
200 µm
sexual reproduction: takes place in presence of abundant food
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engulfs bacteria and yeasts by phagocytosis
two halpoid amoebae fuse and form the zygote
the zygote engulfs more haploid amoebae to form a giant cell (2n)
forms a cell wall and begins to divide into numerous haploid amoebae via meiosis then mitosis
the newly formed amoebae are release when the cell wall bursts
asexual reproduction: occurs upon food depletion
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aggregation of hundreds of amoebae and their migration = multicellular organism called a
pseudoplasmodium
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myxoameobae secrete cAMP upon the decrease in food supply
cAMP attracts other myxoameobae – secrete more cAMP etc…. (positive feedback)
the pseudoplasmodium is capable of migration
once it stops moving – some amoebae differentiate into a stalk others differentiate into an asexual
fruiting body and form spores (n) = sorus or the sorocap
formation of the stalk requires the death and dessication of many of amoebae in the aggregation
genetic information that directs formation of a stalk cell and a spore-forming cell???
spores are released – in the presence of food – haploid myxoamoebae emerge from spores
600 µm