Protists
Protists
NOT your average plant, animals,
bacteria, or fungi!!
All protists are eukaryotes with nuclei and
other membrane-bound organelles. Most
are unicellular, but some are multicellular
organisms.
They can be divided into 3 groups based on
how they get their nutrition:
1. Protozoans: animal-like protists that are
heterotrophs
2. Algae: plant-like protists that are autotrophs
3. Slime Molds: fungus-like protists that are
decomposers
A. Protozoans
1. Amoebas
Resemble animals in two ways: they
eat other organisms for food
(heterotrophs), and they can move
around.
Are different from animals in that they
are unicellular, not multicellular
4 types: Amoeba, Flagellate, Ciliates,
and Sporozoan.
Move by extending lobes of
cytoplasm, called PSEUDOPODS
Take in food, such as bacteria and
smaller protists, by forming
pseudopods
Many have hard shells of calcium
carbonate or silica and live in the
ocean, providing food for many marine
animals
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2. Flagellates
Move by means of flagella
Examples:
Some are free living freshwater or marine
organisms,
Others live inside other organisms in symbiotic
relationships (Flagellates inside termites break
wood into useable carbohydrate for host and
self)
Still others are parasitic and cause disease
(African Sleeping Sickness in humans)
Paramecium (Ciliate)
3. Ciliates
Largest and most diverse group of
protozoans
Covered with short hair-like projections
called CILIA that propel them through
water
Live mostly in freshwater.
Example: Paramecium
Paramecium Structure
Cilia: paramecium moves by beating
cilia
Oral groove: Bacteria are swept into
the gullet by cilia lining of oral groove
Gullet: food becomes enclosed at end
of gullet in a vacuole filled with
enzymes to break it down into nutrients
Anal pore: where waste materials leave
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Contractile Vacuole: pumps out excess
water, since paramecium live in freshwater
and thus water constantly enters the cell
through osmosis
Micronucleus: involved in genetic exchange
during sexual reproduction (conjugation)
Macronucleus: controls the everyday
functions of the cell and asexual
reproduction
The contractile vacuole when full (top)
and after contraction (bottom)
4. Sporozoans
Asexual Reproduction:
Binary Fission
Sexual Reproduction:
Conjugation
Interesting Note: Parameciums shoot out
TRICHOCYSTS, tiny toxic darts that are used
to capture prey.
Form spores (reproductive cell that
forms without fertilization)
Parasitic: live as internal parasites in
areas of an animal host with a ready
food supply (blood stream or intestines)
Examples: Plasmodiums cause malaria
(see page 509 of text)
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Review Questions:
B. Algae
1. Describe how each of the four major
groups of protozoans are animal-like.
2. List and explain the differences that
exist between ciliates and flagellates.
3. What makes a sporozoan different
from other protozoan groups?
4. What role do contractile vacuoles play
in helping freshwater protozoans
maintain homeostasis?
Plant-like protists that perform
photosynthesis. They contain
chlorophyll and produce oxygen as a
by-product of photosynthesis.
Live wherever there is sufficient water.
Divided into two groups:
Unicellular Algae
Multicellular Algae
Unicellular Algae: Dinoflagellates
Two flagella that spin the cells
Covered by cellulose plates
Majority grow in salt water habitats
Can be free living or in a symbiotic
relationship with jellyfish and other
organisms that live near coral reefs
Gonyaulax: toxic species that causes red
tide (an overabundance of these – can be as
many as 40-60 million per litre of seawater)
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Unicellular Algae- Diatoms
Lack both cilia and flagella
Glasslike walls contain silica and fit
together like a lid on a Petri dish
Among the most abundant organism in
the oceans
Unicellular Algae - Euglenoids
Resemble both algae and protozoans
No rigid cell wall: instead they have a
flexible protein covering called a
PELLICLE
Also have chloroplasts but can move
around like an animal
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Multicellular Algae
Many algae have multi-celled bodies
called THALLUS. A thallus can have
many specialized structures including
string-like filaments, leaf-like sheets
(seaweed) or root-like holdfasts.
Muliticellular Algae Green Algae (Chlorophyta)
Multicellular
Grow as filaments with cells linked end
to end, or as flat, leaf-like sheets of
cells
Live in fresh water, moist soil, or on
shallow ocean floor
May have symbiotic relationships with
fungi (This is called LICHEN)
Volvox
Netrium digitus
Pediastrum: a colony of
green algae
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Multicellular Algae –
Red Algae (Rhodophyta)
Multicellular
Grow in warm saltwater habitats
Have pigments that enable them to use
the light that penetrates in to deep
water for photosynthesis (may be red,
blue, etc)
Multicellular Algae –
Brown Algae (Phaeophyta)
Multicellular
Grow in cool saltwater habitats
The THALLI of many brown algae
have root-like structures called
holdfasts that anchor the algae to rocks
Example: Giant Kelps
Giant Kelps
Have specialized air bladders that act
as balloons to keep the leaf-like
structure close to the surface and
absorb sunlight for photosynthesis
Life-cycle is ALTERNATION OF
GENERATION: a diploid sporeproducing phase alternates with a
haploid, gamete producing phase
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Review:Plant-like Protists
(ALGAE)
1. Use a table to list the reasons why
euglenoids should be classified as
protozoans and also as algae
2. In what ways do the sporophyte and
gametophyte generation of an alga
differ from each other?
3. Phycobilins, pigments that absord
green, biolet and blue light, are an
important part of red algae. Explain
why.
C. Fungus-like Protists
Most of these protists are small and
live in damp or watery places, helping
to break down dead organic matter.
Divided into three groups:
Plasmodial Slime Molds
Cellular Slime Molds
Water Molds
1. Plasmodial Slime Molds
Alternate between an emoeboid form and a
spore-producing fruiting body
When feeding, they form a mass of
cytoplasm called a PLASMODIUM
If the slime mold cannot find enough food, it
will stop feeding and fomr a fruiting body that
produces spores. These spores can spread
by wind or animals and they remain dormant
until conditions become favourable
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Slime molds reproduce by sending out spores, yet their bodies
are continually pulsating, allowing them to actually travel
through the forest in search of food. Slime molds are
continually circulating their cellular material, creating the
pulsations which control their movement. But the pulsations
are not constant--they may decrease or accelerate depending
on what the Slime mold encounters along its path. In the
course of his experiments, Dr. Laane made some interesting
discoveries about the Slime mold's tastes. Exposed to
cigarette smoke, the pulsations sped up.
Given its first stiff drink, the Slime Mold's
pulsations also increased, but not for long.
A slime mold (Physarum polycephalum),
showing a creeping mass of yellowish
protoplasm called a plasmodium.
2. Cellular Slime Molds
Move about as single,
unattached amoebas for
most of their lives, until
a chemical, produced by
one of them, signals that
the single life is over.
Eventually, not even the Slime mold could
avoid a hang-over and its pulsations slowed to a temporary
stand-still.
Then, one by one, up to 100,000
amoeba in an area will find each other
and fuse into a single, multicellular
body called a PSEUDOPLASMODIUM:
like a plasmodium, but each individual
cell remains a separate unit.
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The Pseudoplasmodium forms a fruiting
body in order to reproduce spores.
A composite photograph of the
Dictyostelium discoideum life cycle.
3. Water Molds
Decomposers or parasites
Typically grow in fresh water on
decaying plants and animals
Example: Plasmopara viticol is a water
mold that almost wiped out France’s
vineyards
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Review: Fungus-like Protists
(Slime Molds)
Plasmopara viticol
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