Chapter 28
Protista
The Origins of Eukaryotic Diversity
Overview
Protista; In the past, a single kingdom
Note; some closely related
to Plants
to Fungi
or to Animals
(So kingdom Protista has been abandoned !!! and
various lineages are recognized as kingdoms in their own right)
But; protist , eukaryotes that are not plants,
animals, or fungi
Protists Are Extremely Diverse
• With high structural and functional
diversity
• Most, unicellular, but colonial and
multicellular
• Complex cellular; a single cell carry out all
basic functions of specialized cells in a
multicellular organism
Nutrition most diverse of all eukaryotes
• Some are Photoautotrophs, containing chloroplasts.
or Heterotrophs, absorbing organic molecules
or Ingesting food particles
or Mixotrophs, combining photosynthesis
and heterotrophic nutrition
• Based on their roles in biological communities three
groups
a- Photosynthetic algal protists
b- Ingestive protozoans
c- absorptive protists
• Very diverse habitats
• Life cycles vary greatly
a- exclusively asexual
b- sexual life cycles, meiosis and syngamy (The fusion of
two gametes in fertilization)
Protistan Diversity
1. modified mitochondria
In Diplomonads and parabasalids (found in anaerobic
environments)
a- No plastids
b- No DNA in their mitochondria
c- electron transport chain (ETC), and the enzymes needed
for the citric acid cycle
d- Diplomonads have two equal-sized nuclei and multiple flagella
example; Giardia intestinalis; parasite that lives in the intestines
of mammals and causes diarrhea
dormant stage Giardia contaminated drinking water
from feces containing the parasite
Parabasalids include trichomonads
Example; Trichomonas vaginalis, inhabits the
vagina of human females
• T. vaginalis outcompete beneficial bacteria and
infect the vaginal lining when the normal acidity
of the vagina is disturbed
• The male urethra may also be infected but
without symptoms
• The infection is sexually transmitted.
• Genetic studies of T. vaginalis suggest that non
pathogenic species transformed by horizontal
gene transfer from other vaginal bacteria, the
gene allows T. vaginalis to feed on epithelial
cells
2. Internal structure
Euglenozoans have flagella with a unique
internal structure
• Euglenozoa (a clade) that includes
a- predatory heterotrophs
b- photosynthetic autotrophs
c- pathogenic parasites
Distinguished by
a- Presence of a spiral or crystalline rod inside
their flagella
b- disc-shaped mitochondrial cristae (infoldings)
• The best-studied groups of euglenozoans are
the kinetoplastids and euglenids
The kinetoplastids
* single large mitochondrion associated with a unique
organelle, the kinetoplast, carrying extranuclear DNA
* symbiotic and include pathogenic parasites
example,Trypanosoma causes
** African sleeping sickness, a disease spread by
the African tsetse fly
** Chagas’ disease (leads to congestive heart failure)
transmitted by bloodsucking bugs
• Trypanosomes evade immune detection by switching
surface proteins from generation to generation,
preventing the host from developing immunity
• One-third of Trypanosoma’s genome codes for these
surface proteins
Euglenids
Characterized by
a- an anterior pocket from which one or two flagella emerge
b- unique glucose polymer, paramylon (storage molecule)
c- Euglena are autotrophic but can become heterotrophic in the dark
d- Light detector: swelling near the base of the long flagellum; detects light
that is not blocked by the eyespot; as a result, Euglena moves toward light
of appropriate intensity, an important adaptation that enhances
photosynthesis
e- Long flagellum
f- Short flagellum
g- Nucleus
h- Plasma membrane
i- Paramylon granule
j- Chloroplast
k- Contractile vacuole
l- Eyespot: pigmented organelle that functions as a light shield, allowing light
from only a certain direction to strike the light detector
m- Pellicle: protein bands beneath the plasma membrane that provide
strength and flexibility)
Note; Euglena, no cell wall
Other euglenids can phagocytose prey
Long flagellum
Eyespot: pigmented
organelle that functions as a light
shield, allowing light from only a
certain
direction to strike the
light detector
Light detector: swelling near
the base of the long flagellum;
detects light that is not
blocked by the eyespot; as a
result, Euglena moves toward
light of appropriate intensity,
an important adaptation that
enhances photosynthesis
Short flagellum
Nucleus
Euglena (LM)
5 µm
Contractile vacuole
Plasma membrane
Chloroplast
Pellicle: protein bands beneath the
plasma membrane that provide strength
and flexibility (Euglena lacks a cell wall)
Paramylon granule
3. Sacs beneath the plasma membrane
Alveolates
Alveolata (a clade) have alveoli, small
membrane-bound cavities, under the plasma
membrane
• Alveoli function is not known, but they may
help stabilize the cell surface or regulate water
and ion content
• Alveolata includes
1) flagellated protists (dinoflagellates)
2) parasites (apicomplexans)
3) ciliates.
Apicomplexans
* parasites of animals
* some cause serious human diseases
* Sporozoites (tiny infectious cells)
* The parasites spread through their host as sporozoites
* The sporozoites have at their apex a complex of
organelles specialized for penetrating host cells and
tissues of the host
* Nonphotosynthetic plastid (apicoplast; vital functions
including the synthesis of fatty acids)
* Intricate life cycles
(sexual and asexual stages and often require two or more different
host species for completion. Example; Plasmodium, the parasite that
causes malaria, spends part of its life in mosquitoes and part in
humans)
The two-host life cycle of Plasmodium, the apicomplexan that
causes malaria
The Malaria, a human disease
Caused by Plasmodium, (spends part of its life in
mosquitoes (Anopheles) and part in humans)
• Managed In the 1960s through
a- insecticides against the Anopheles
mosquitoes
b- drugs that killed the parasites in humans
• But;
Resistant varieties of Anopheles, to insecticides
made;
Plasmodium come back ( 300 million people are
infected in the tropics, and up to 2 million die each year)
Plasmodium can escape from the immunity
system (is evasive)
* It can change its surface protein
* No successful vaccine developed
* thereby changing its “face” to the human immune
system
* It spends most of its time inside human liver and blood
cells
* The expression of most of the Plasmodium’s genes at
specific points in its life cycle identified (2003) potential
new targets for vaccines
• Chloroquine (an antimalarial drug)
** but malaria Plasmodium developed resistance
** Identification of the resistance gene
** block drug resistance in Plasmodium
Ciliates
a- diverse group of protists
b- use of cilia to move and feed
c- cilia
* cover the cell surface
* clustered into rows or tufts
* leg-like structures constructed from many cilia
* cilia are associated with a submembrane
* ciliary movements coordinated by
submembrane system of microtubules
Ciliates Nuclei
* Two types of nuclei;
1- Macronuclei, large macronucleus (general cell regulation)
2- Micronuclei, tiny micronucleus (reproduction)
* Macronucleus has dozens of copies of the ciliate’s
genome.
** The genes are not organized into chromosomes but are
packaged into small units with duplicates of a few genes
** Genes control the everyday functions of the cell such as
feeding, waste removal, and water balance
Ciliate reproduction
* generally, asexually by binary fission of the
macronucleus (no mitotic division)
Example:Paramecium caudatum
Paramecium conjugation
Genetic variation results from the sexual shuffling of genes which
occurs through conjugation, during which two individuals exchange
haploid micronuclei.
• In ciliates, reproduction and conjugation are separate processes.
• In a real sense, ciliates have “sex without reproduction.”
4. Stramenopiles have hairy and smooth flagella.
•
The clade Stramenopila includes both heterotrophic and photosynthetic protists (some group of
algae).
•
The name of this group is derived from the presence of numerous fine, hairlike projections on the
flagella.
•
The heterotrophic stramenopiles, the oomycetes, include water molds, white rusts, and downy
mildews.
Stramenopile flagella
•
Many oomycetes have multinucleate filaments that resemble fungal hyphae
.
Diatoms
* unicellular algae
* highly diverse group of protists, with an estimated 100,000 species
* They are abundant members of both freshwater and marine plankton
* store food reserves as the glucose polymer laminarin or, in a few diatoms, as
oil
* glasslike walls composed of hydrated silica embedded in an organic matrix
* Wall; divided into two parts that overlap (like a shoebox and lid)
* walls allow live diatoms to withstand immense pressure
* defense for them from the crushing jaws of predators
* Massive accumulations of fossilized diatoms are major constituents of
diatomaceous earth
Reproduction
• diatoms reproduce asexually by mitosis
• each daughter cell receiving half of the cell wall and regenerating a new
second half
• Some species form cysts as resistant stages
• Sexual stages are not common
• Sexual, involves the formation of eggs and amoeboid or flagellated sperm
Brown algae, or phaeophytes, (Seaweeds)
•
•
•
•
The largest and most complex protists known
Multicellular
most species are marine
Common along temperate coasts in areas of cool water and adequate
nutrients
• Their brown or olive color; presence of carotenoids in their plastids
• Seaweeds (largest marine algae),
•
Brown,
Red, &
green
Habitat
the intertidal and subtidal zones of coastal waters
• (This environment is characterized by extreme physical conditions, including wave
forces and exposure to sun and drying conditions at low tide)
Anatomy
• complex multicellular anatomy
• some differentiated tissues and organs that resemble those in plants
• thallus, or body, of the seaweed.
• a root-like holdfast
• a stem-like stipe,
• Leaf-like photosynthetic blades
• The term “seaweed” refers to brown algae as well as some species
of green and red algae.
• The giant seaweeds known as kelps live in deep water beyond the
intertidal zone (Kelp forest)
• The stipes of these algae may be as long as 60 m
Intertidal zone Seaweeds
• cope with rough water
• twice-daily low tides (expose the algae to hot sun and risk of desiccation)
Seaweeds as sources of food and commodities
• Many seaweeds are eaten by coastal people,
* Laminaria (“kombu” in Japan) in soup
* Porphyra (Japanese “nori”)
* sushi wraps
• Gel-forming substances, extracted in commercial operations
* Algin from brown algae
* Agar and carrageen from red algae are used as thickeners in
food, lubricants in oil drilling, or culture media in microbiology
5. Cercozoans have threadlike pseudopodia
• Cercozoa; a newly recognized clade
• Contains the amoebas (“amoeba” = protists that move
and feed by means of pseudopodia)
• Pseudopodia, cellular extensions that bulge from the
cell surface
• Amoeba movement,
* It extends a pseudopodium and anchors the tip
* Cytoplasm then streams into the pseudopodium
• Cercozoa; amoeba threadlike pseudopodia
• Cercozoans include;
* Foraminiferans and are closely related to Radiolarians,
which also have threadlike pseudopodia
Foraminiferans, or forams
* Named for their porous shells, or tests.
* Forams have
** multi-chambered, porous shells, consisting of
organic materials hardened with calcium carbonate
** Pseudopodia extend through the pores for swimming,
shell formation, and feeding
** symbioses with algae
** live in marine and fresh water
** Most live in sand or attach to rocks or algae
** abundant in the plankton
** forams fossils (90% of the described forams)
** calcareous skeletons of forams are important components
of marine sediments
Note: Fossil forams are often used as chronological markers
to correlate the ages of sedimentary rocks from different
parts of the world.
6. Amoebozoans have lobe-shaped pseudopodia
• Many species of amoebas that have lobe-shaped pseudopodia
belong to the clade Amoebozoans, a- gymnamoebas
b- entamoebas
c- slime molds
7. Red algae and green algae
* closest relatives of land plants
* Red algae have no flagellated stages in their life cycle
(other eukaryotic algae do)
* More than 6,000 known species of red algae,
* Reddish due to the accessory pigment phycoerythrin
* Coloration varies among species
* Coloration depends on the depth that they inhabit
* Some species lack pigmentation
* Not pigmented, parasites on other red algae.
• Red algae are the most common seaweeds in
the warm coastal waters of tropical oceans
• Inhabit deeper waters than other photosynthetic
eukaryotes
• Phycobilins; (photosynthetic pigment) allows
them to absorb blue and green wavelengths that
penetrate down to deep water, more than 260 m
(Bahamas cost)
• Some red algae live in fresh water or on land.
• Most red algae are multicellular, with some
reaching a size large enough to be called
“seaweeds.”
• The thalli of many red algal species are
filamentous
• The base of the thallus is usually
differentiated into a simple holdfast
• The life cycles of red algae are especially
diverse
• In the absence of flagella, fertilization
depends entirely on water currents to bring
gametes together
Green algae
* grass-green chloroplasts
* Similar in ultrastructure and pigment composition
to chloroplasts of plants
• Green algae and land plants are closely related evidence
from;
** Molecular systematics
** Cellular morphology provide considerable
• Divided into two main groups,
a- Chlorophytes; 7,000 species, most are identified
b- Charophyceans.
• Most live in fresh water, but many are marine
inhabitants.
• Some chlorophytes inhabit damp soil, while others are
specialized to live on glaciers and snowfields
Snow-dwelling chlorophytes carry out photosynthesis
despite;
* subfreezing temperatures
* intense visible and ultraviolet radiation
* protected by radiation-blocking compounds in
their cytoplasm and by the snow itself (shield)
• Some chlorophytes live symbiotically with fungi to
form lichens, a mutualistic collective.
• Large size and complexity in chlorophytes has evolved
by three different mechanisms:
– Formation of colonies of individual cells (e.g.,
Volvox).
– The repeated division of nuclei without cytoplasmic
division to form multinucleate filaments (e.g.,
Caulerpa).
– The formation of true multicellular forms by cell
division and cell differentiation (e.g., Ulva).
• Some multicellular marine chlorophytes
are seaweeds, large and complex
• Complex life cycles, with both sexual and
asexual reproductive stages
• Most sexual species have biflagellated
gametes with cup-shaped chloroplasts
• Alternation of generations evolved in the
life cycles of some green algae
• The other main group of green algae are
most closely related to land plants