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 Domain 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
• 7 to 45 species recognized depending on zoologist
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
• other organelles are not found in the typical
multicellular eukaryote
– contractile vacuoles for osmoregulation
Protist Evolution
• 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 alphaproteobacteria by an ancestral cell
Endosymbiosis
• early cellular evolution – ingestion of a photosynthetic cyanobacteria through
primary endosymbiosis by a primitive eukaryote
– eventual development into the plastids of the photosynthetic red and green algae
• Red and green algae then underwent secondary endosymbiosis
•
they themselves were ingested by another primitive eukaryotic cell to eventually
become the 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
• Phylogenetic classification of eukaryotes produces five
Clades:
• 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
Cellular slime molds
Radiolaria
Cercozoa
Rhizaria
Plasmodial slime molds
Entamoebas
Gymnamoebas
Radiolarians
Foraminiferans
Chromalveolata
Chlorarachniophytes
Brown algae
Golden algae
Diatoms
Ciliates
Clade: Excavata
Apicomplexans
Stramenopila
Oomycetes
Euglenozoa
Parabasala
Alveolata
Dinoflagellates
Euglenids
Kinetoplastids
Parabasalids
Diplomonads Diplomonadida
Eukaryotic Phylogenetic Tree
Archaeplastida
(Viridiplantae)
Clade: Excavata
• A. Diplomonads
• B. Parabasalids
• C. Euglenozoans
Clade: Excavata
• Diplomonads & Parabasilids
– protists in these two groups lack plastids (no photosynthesis)
– mitochondria do not have DNA or the enzymes for the citric acid cycle or
proteins for the electron transport chain
• anaerobic environments
Clade: Excavata
• A. Diplomonads
–
–
–
–
two equal-sized nuclei and multiple flagella
flagella is very different from prokaryotic flagella
have modified mitochondria = mitosomes
many are parasites
giardia intestinalis
• B. Parabasalids
– also have reduced/modified mitochondria
– include the protists called trichomonads – Trichomonas
vaginalis
– 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
– considered a photosynthetic protist similar to algae
– 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
– divided into the groups:
– 1. the Kinetoplastids
– 2. the Euglenoids
Crystalline rod
Cross-section of a Euglenozoan
Flagella (9+2 arrangement)
1. Kinetoplastids - Trypanosomes
– 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
Kinetoplastids: Trypanosoma
Life cycle
-cycles between the tse tse fly and
the human
-different forms of the
trypanosome depending on what
host (fly vs. human) and where it is
in the host
1.
2.
3.
4.
fly injects the trypanosome
multiplication in the human
host – e.g. in the blood
bit by fly and transfer back to
fly
multiplication in the fly’s gut
and then in the salivary gland
2. Euglenoids – The Euglena
– unicellular protist
– most are autotrophic
• several chloroplasts with chlorophyll a and b and
carotenoid pigments
– main characteristic - 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
• the long one emerges from the canal and actively
beats for locomotion
used to be classified as the
Class Phytomastigophorea
– inside the plasma membrane is a structure called
the pellicle
• articulated strips of protein lying side by side that
enable turning and flexing of the protist
– eyespot (stigma) - near the flagella
• allows 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
2. Euglenoids
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:
• 1. Alveolates
• 2. Stramenophiles
Clade: Chromalveolata
– A. Alveolates:
• 1. Dinoflagellates
• 2. Apicomplexans
• 3. Ciliates
– B. Stramenophiles
•
•
•
•
1. Diatoms
2. Golden Algae
3. Brown Algae
4. Oomycetes
Chromalveolata - A. Alveolates
• characterized by membrane-bound sacs called alveoli
– just under the plasma membrane
– function unknown
• 1. Dinoflagellates – move through flagellar action
• 2. Apicomplexans - parasites
• 3. Ciliates – move through ciliary action
Alveolates: 1. Dinoflagellates
LE 28-10
Flag
3 µm
• several thousand species
– “dinos” = whirling
– surrounded by a cell wall encrusted with silica act as “armor”
– most are autotrophic with well-formed plastids
for photosynthesis
– possess mitochondria with tubular cristae (similar
to animals)
– two flagellae – located in grooves
• one groove is transverse (around the protist)
= cingulum – its flagella propels the
dinoflagellate forward and causes it to spin
• other groove is perpendicular to that = sulcus
– the flagella acts as the rudder
– capable of proliferating explosively – “blooms”
• “red tide” (carotenoid pigments found in the plastids)
• dinoflagellates produce a toxin that kills off invertebrates
– some can be bioluminescent – ATP driven reaction that creates a
glow at night
Alveolates: 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
– requires more than one host to complete
Alveolates: 2. Apicomplexans
• 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
trophozoites
gametocyte
• 1. infected Anopheles mosquito bites a
person injecting its sporozoites (n)
• 2. sporozoites enter the liver and undergo
division to become merozoites (n)
• 3. the merozoites infect RBCs via their
apical complex
• 4. merozoites develop into gametocytes
which break out of the RBCs
Plasmodium Life
Cycle
LE 28-11
Inside mosquito
Inside human
Merozoite
Sporozoites
(n)
Liver
– fevers and chills
• 5. gametocytes picked up by a new
mosquito
• 6. gametes form and fertilization takes
place in the mosquito’s digestive tract 
zygote
• 7. an oocyst develops and produces more
sporozoites which are delivered to the
human when bitten again
Liver
cell
Oocyst
MEIOSIS
Zygote
(2n)
Apex
Merozoite
(n)
Red blood0.5 µm
cell
Red blood
cells
FERTILIZATION
Key
Gametes
Gametocytes
(n)
Haploid (n)
Diploid (2n)
Alveolates: 3. Ciliates - Paramecium
• 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
• control the everyday functions of the ciliate
– micronucleus – function in reproduction
• exchanged between two ciliates during conjugation
LE 28-12
Paramecium
FEEDING, WASTE REMOVAL, AND WATER BALANCE
• freshwater protist – constantly
takes on water from its
hypotonic environment
• they contain contractile
vacuoles for the regulation of
osmotic pressure – accumulate
excess water and then expel it
through the plasma membrane
back into the environment
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.
Paramecium
• 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
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.
Contractile
vacuole
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
Thousands of cilia cover the
surface of Paramecium.
50 µm
Food vacuoles combine with lysosomes. As the
food is digested, the vacuoles follow a looping
path through the cell.
Micronucleus
Macronucleus
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.
Paramecium
• asexual reproduction – through binary
fission
• sexual reproduction involves
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 micronuclei in each
disintegrate & the remaining
micronuclei in each divides by mitosisresulting in 2 micronuclei in each
paramecium
– 4. the cells swap one of their
micronuclei – genetic recombination
– 5. the cells separate
CONJUGATION AND REPRODUCTION
Two cells of
compatible mating
strains align side by side
and partially fuse.
Compatible
mates
Meiosis of
micronuclei
produces four
haploid micronuclei
in each cell.
Three micronuclei in each
cell disintegrate. The remaining
micro-nucleus in each cell
divides by mitosis.
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
fuse, forming a
rounds of
mitosis without diploid
micronucleus.
cytokinesis
produce eight
micronuclei.
Key
Conjugation
Reproduction
Paramecium
– 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
paramecium 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
Got all that??
-partially fuse
-1 micronucleus becomes 4 via meiosis
(haploid)
-3 disappear
-1 micronuclei becomes 2 via mitosis
-paramecia “swap” 1 micronuclei and
separate
-fuse 2 micronuclei into 1 (diploid)
-micronucleus becomes 8 (mitosis/no
cytokinesis)
-macronucleus disappears
-so 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
CONJUGATION AND REPRODUCTION
Two cells of
compatible mating
strains align side by side
and partially fuse.
Compatible
mates
Meiosis of
micronuclei
produces four
haploid micronuclei
in each cell.
Three micronuclei in each
cell disintegrate. The
remaining micro-nucleus in
each cell divides by mitosis.
The cells
swap one
micronucleus.
Macronucleus
MEIOSIS
Diploid
micronucleus
Haploid
micronucleus
Diploid
micronucleus
MICRONUCLEAR
FUSION
The
cells
separate.
Two rounds
of cytokinesis
partition one
macronucleus
and one
macronucleus
into each of
four daughter
cells.
The original
macronucleus
disintegrates.
Four
micronuclei
become
macronuclei,
while the other
four remain
micronuclei.
Three
rounds of
mitosis
without
cytokinesis
produce eight
micronuclei.
Micronuclei
fuse, forming
a diploid
micronucleus.
Key
Conjugation
Reproduction
Chromalveolata - B. Stramenophiles
•
•
•
•
•
•
•
•
stramen = “straw”; pilos – “hair”
contains several groups of phototrophs (considered to be algae)
flagella are said to be “hairy”
this hairy flagellum is paired with a smooth flagellum
1. oomycetes – water molds
2. bacillariophytes - diatoms
3. chrysophytes – golden algae
4. phyophyceans – brown algae
Smooth
flagellum
5 µm
Hairy
flagellum
First of All - What is Algae??
• photosynthetic protists
• algae = eukaryotic organism with chlorophyll a pigments
that carry out oxygen-producing photosynthesis
• study of algae = phycology
• no longer any formal classification schemes
– algae are scattered across many phyla = polyphyletic
• BUT they differ from plants – lack a well-organized
vascular system and they have a simple reproductive
system
• occur most often in water
– fresh and marine – may be suspended as planktonic organisms or
attached to the bottom (benthic)
Algae: Photosynthetic Protists
• algae frequently confused with plankton
• plankton = free-floating microscopic aquatic organisms
– phytoplankton – made up of algae and small plants
– zooplankton – non-photosynthetic protists and animals
• classical algae are now grouped together with the
plants - Phylum Chlorophyta
• some are a separate lineage - known as red algae
– Phylum Rhodophyta
• some are grouped with the stramenophiles - yellow
and brown algae
– Phyla Chrysophyta and Phaeophyta
Algae: Photosynthetic Protists
• important properties that classify them:
–
–
–
–
–
1. cell wall composition – rigid cell wall of cellulose
2. the form in which food is stored
3. chlorophyll molecules and accessory pigments (carotenoids)
4. flagella number and location of their insertion into the cell
5 morphology of the cells and/or body
• comprised of a vegetative body = thallus
– 6. habitat: marine or freshwater
– 7. reproductive structures: reproduction is asexual or sexual
– 8. mitochondria cristae structure: tubular, disc or plate-like
(lamellar)
Stramenophiles: 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
molecular data also cannot confirm fungal origins
do not carry out photosynthesis – non-autotrophic
acquire nutrients as decomposers – grow as cottony
masses on dead animals and algae = heterotrophic
water mold
Stramenophiles: 2. Diatoms
• 100,000 species of unicellular algae
• surrounded by unique glass-like wall made of silica
embedded in an organic matrix
– two parts that overlap like a shoe box and lid
– upperlid = epitheca, lowerlid = hypotheca
– effective protection against extreme crushing forces
• reproduce asexually via mitosis
– daughter receives half of the parental cell wall and
generates a new half
• most are photosynthetic – chlorophylls a and c and
carotenoids
Stramenophiles: 2. Diatoms
• major component of phytoplankton in fresh
and marine environments in cooler waters
– source of food for fish and other marine animals
– upon death –sink to the bottom = diatomaceous
earth
– active ingredient in detergents, fine abrasive
polishes, paint removers, decoloring oils, filtering
agents, components of insulation and
soundproofing products, reflective paint additive
Stramenophiles: 3. Golden Algae -Phylum Chrysophyta
•
•
•
•
•
all species are photosynthetic
photosynthetic pigments: chlorophylls a and c +
carotenoids found in plastids (like plants)
dominant pigment is a carotenoid called fucoxanthin
 golden-brown color
most are unicellular but some are colonial
most are biflagellated – both attached near one end
of the cell
Dinobryon
Stramenophiles: 4. Brown algae - Phylum
Phaeophyta
• brown algae – most complex
algae
– all are multicellular and all are
marine
– have the most complex
multicellular anatomy of all algae
– some have specialized tissues like
animals and plants
– include the seaweeds
– giant seaweeds in intertidal zones –
kelps
• brown algae
– composed of a thallus = algal
body that is plant-like
– thallus has a rootlike holdfast 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
e.g. Laminaria
• brown algae exhibit alternation
of generations
– alternate between haploid and
diploid multicellular forms
– only applies to multicellular
stages in the life cycle
– two forms seen that are
structurally different:
• A. diploid sporophyte – for the
production of haploid spores via
meiosis
• B. haploid gametophytes – for
the production of haploid
gametes via mitosis
Key
Haploid (n)
Diploid (2n)
Sporangia
Sporophyte
(2n)
Zoospores
Female
Gametophytes
(n)
Male
An overview of Alternation of
Generations
1. the spores develop into
gametophytes (n)
2. the gametophytes make gametes (n)
3. the gametes fuse and regenerate the
diploid sporophyte (2n)
Brown algae: Life cycle
– life cycle starts with the diploid
sporophyte (adult algae thallus)
– 1. on the blade of the sporophyte –
development of a sporangium
– 2. the diploid sporangium develops
haploid zoospores by meiosis
– 3. 50% of zoospores develop into male
gametophytes and 50% into female
gametophytes (small but multicellular)
– 4. the haploid gametophytes produce
haploid gametes via mitosis
– 5. gametes are released and fuse to form
the diploid zygote
– 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 pseudopodium by assembly and disassembly of actin subunits
into microfilaments
– locomotion: anchor a tip to the surface – stream cytoplasm into the pseudopodium
– prey capture: pseudopodia senses the prey through physical contact and surrounds it
– members of this clade:
• A. Radiolarins
• B. Forams
• C. Cercozoans
Clade Rhizaria
• A. Radiolarians: delicate, intricately symmetrical internal skeletons made of silica
– axiopodia which “radiate” out from a central body – reinforced by microtubultes
– pseudopodia are also capable of phagocytosing food – cytoplasmic streaming then
carries the food into the central body
LE 28-23
Radiolarins
Pseudopodia
200 µm
Clade Rhizaria
• B. Forams: formerly called foraminiferans
– named for their porous shells
– holes in the shells are called foramina
– 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
Forams
C. Cercozoans: The Amoeba
•
•
•
•
contain the organisms called amoebae
amoeba species are also found in other clades
most are heterotrophs – many are parasites of plants and animals
some can be predators!
– predators of bacteria
A word about amoebas
• no longer one specific clade
• too polyphyletic
• find amoebas in several clades – 2 major
ones:
– Cercozoa
– Amoebozoa
• amoeba = protist that does not have a
definitive shape
– eat via phagocytosis
– have an outer ectoplasm and an inner
endoplasm
– move by pseudopodia that form through
cytoplasmic streaming of their ectoplasm
and endoplasm
Clade Archaeplastida
• more than a billion years ago – heterotrophic protist acquired a
cynanobacterial endosymbiont
– gave rise to red algae and green algae
• these cyanobacteria evolved into plastids
– numerous functions: photosynthesis and storage
• 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
Plastid
Red algae
Cyanobacterium
Primary
endosymbiosis
Heterotrophic
eukaryote
Plastid
Green algae
Clade Archaeplastida
•
•
•
•
Archaeplastida can be divided into:
A. Red algae – Phylum Rhodophyta
B. Green algae – Phylum Chlorophyta
C. Charophytes – includes Plants; Phylum Charophyta
Archaeplastida - A. Red Algae: Phylum Rhodophyta
• red algae – 6000 species
– multicellular algae
– most are autotrophic – plastids for photosynthesis
– red pigment = phycoerythritin and blue pigment = phycocyanin
(phycobilins)
– 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
Archaeplastida - A. Red Algae: Phylum Rhodophyta
• red algae – 6000 species
– sugar storage form = floridean
– cell wall includes a matrix of proteins and sugars
• this matrix is also called agar = polymers of galactose
– largest red algae 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
Archaeplastida - B. Green algae: Phylum Chlorophyta
• green algae
– named for the green chloroplasts
– contain chlorophyll pigments that are very similar to
plants
– chloroplasts also have a similar structure to plants
• thylakoid membranes
– divide into two groups:
– 1. Charophytes – most closely related to plants
– 2. Chlorophytes – 7000 species of green algae
Archaeplastida - B. Green algae: Phylum Chlorophyta
• green algae
– 2. Chlorophytes – 7000 species
•
•
•
•
•
•
•
•
chloro = “green”
mostly freshwater
chlorophylls a and b + carotenoid pigments
sugar storage form = starch
cell walls made of cellulose
most are unicellular
some are colonial
some are also multicellular - filamentous (pond
scum) and sheet-like forms
• can also live symbiotically with fungus – as lichens
Unicellular Green Algae
• 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
– eyespot or stigma
» movement towards light
– two small contractile vacuoles at the base of
the flagella – function as osmoregulatory
organs
– asexual reproduction
– sexual reproduction is also possible – cell
division produces gametes of each “sex”
Green algae: Life Cycle
– life cycle: sexual and asexual stages
• mature green algae cells are haploid and have 2 flagellae
• asexual reproduction: the algae reabsorbs its flagellae and divides by mitosis
to form four identical haploid cells (zoospores) - held within a capsule
– zoospores are released  new mature green algae
Flagella
1 µm
Cell wall
Nucleus
Zoospores
Mature cell
(n)
Regions
of single
chloroplast
Key
Haploid (n)
Diploid (2n)
ASEXUAL
REPRODUCTION
SYNGAMY
SEXUAL
REPRODUCTION
MEIOSIS
Zygote
(2n)
Green algae: Life Cycle
• sexual reproduction: happens upon shortage of nutrients
–
–
–
–
–
haploid algae develops into male and female gametes
fusion  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 become new mature algal cells
Flagella
1 µm
Cell wall
Nucleus
Zoospores
Regions
of single
chloroplast
Key
Haploid (n)
Diploid (2n)
ASEXUAL
REPRODUCTION
Mature cell
(n)
SYNGAMY
SEXUAL
REPRODUCTION
MEIOSIS
Zygote
(2n)
Colonial Green Algae
• not really multicellular
• colony of unicellular algae
– e.g. Volvox
• colony or 500 to 60,000 cells – mostly small vegetative cells
– individual cells resemble Chlamydomonas – bi-flagellated
• cells have eyespots – will orient toward the light
• some cells are reproductive - develop from the cells at the equator = called
gonads  gametes for fertilization
• zygote undergoes mitosis to form a small daughter colony
• the daughter colony remains in the parental colony until it bursts free
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.
Clade Unikonta
• recently proposed clade
• supergroup of eukaryotes that includes animals, fungi and
some protists
• means “one flagella”
• two major clades:
• A. Amoebozoans: the amoebas & slime molds
• B. Opisthokonts: fungi and animals
Unikonta: A. Amoebozoans
• three types of Amoebozoans:
• 1. Gymnamoebas
– unicellular, one flagella
– soil, freshwater and marine
– most are heterotrophic – consume bacteria and other protists plus detritus
(decomposers)
Unikonta: A. Amoebozoans
• 2. Entamoebas
–
–
–
–
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 slime molds
– plasmodial slime molds
Plasmodial slime molds
•
•
•
•
brightly pigmented – orange or yellow
named for the formation of a feeding stage = plasmodium in the life cycle
capable of moving over a substrate
plasmodium – very large but still is unicellular
– single cell undergoes mitosis but fails to divide through cytokinesis – “supercell”
– feeding plasmodium lives on organic matter – takes in nutrients through
phagocytosis
Zygote
(2n)
Feeding
plasmodium
SYNGAMY
Mature
plasmodium
(preparing to fruit)
Young
sporangium
1 mm
Amoeboid cells
(n)
Mature
sporangium
Key
Flagellated cells
(n)
Germinating
spore
Spores
(n)
MEIOSIS
Stalk
Haploid (n)
Diploid (2n)
Plasmodial slime molds
• mature plasmodium undergoes sexual reproduction when conditions become
harsh
• plasmodium develops sporangia via meiosis which release haploid spores (n)
• germination of the spores takes place in the presence of adequate moisture
– results in the production of either amoeboid cells or flagellated cells – both are
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
Zygote
(2n)
SYNGAMY
Feeding
plasmodium
Mature
plasmodium
(preparing to fruit)
Young
sporangium
1 mm
Amoeboid cells
(n)
Mature
sporangium
Key
Flagellated cells
(n)
Germinating
spore
Spores
(n)
MEIOSIS
Stalk
Haploid (n)
Diploid (2n)
Cellular slime molds
SYNGAMY
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
200 µm
• feeding stage is a solitary amoeboid form – feeding stage
– engulfs bacteria and yeasts by phagocytosis
• can undergo asexual or sexual reproduction
– determined by food supply
• sexual reproduction: takes place in presence of abundant food
– two haploid amoebas fuse and form the zygote (2n)
– the zygote engulfs more haploid amoebae to grow larger – forms an aggregate
– aggregate develops fruiting sporangia - releases haploid spores  new amoeba
cells
600 µm