CHAP. 3.1 – PROTISTS
I. WHAT IS A PROTIST?
A Protist is a eukaryotic organism that lives in a
moist environment.
The Protist kingdom is the most diverse of all the
kingdoms. As a result, they are grouped into
three categories:
1. animal-like protists;
2. fungus-like protists;
3. plant-like protists.
II. ANIMAL-LIKE PROTISTS
Animal-like protists are called protozoans.
Characteristics of animal-like protists are:
a. They are Heterotrophs;
b. They are able to move place to place to obtain
their food;
c. They are unicellular.
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d. They have a contractile vacuole.
- The problems protozoans face is that water
passes very easily through the cell
membrane and into the cytoplasm. It does
not leave as readily.
- As a result, this could cause the protozoan
to burst from too much water inside of it.
But, they have a contractile vacuole which
collect the extra water and expel it from the
cell.
Below is an example of a protozoan called
Trypanosome (Sleeping Sickness).
f. There are four types of animal-like protozoans:
1. those with pseudopods;
2. those with cilia;
3. those with flagella; and
4. those called sporozoans.
A. PROTOZOANS WITH PSEUDOPODS
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This first type of animal-like protozoan has a
pseudopod. Pseudopod means having a ‘false
foot’ and is called sarcodines.
A pseudopod is a temporary bulge of the cell
membrane when it fills with cytoplasm. This is
the way sarcodines move, such as away from
bright light or trapping food.
For movement, a pseudopod:
1. Pushed the cell membrane outward in one
location, creating a bulge.
2. The cytoplasm flows into the bulge.
3. The rest of the organism follows the path
of the bulge.
For trapping food, a pseudopod:
1. Extends two pseudopods around the food
particle.
2. Then, the two pseudopods join together to
seal it inside the food particle.
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Above is a picture of an ameba – a type
sacrodine.
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B. PROTOZOANS WITH CILIA
This second-type of animal-like protozoan has
cilia. Cilia are hair-like projections from cells
that move in a wavelike pattern.
Protozoans with cilia are called ciliates.
Cilia are used to obtain food, move, and sense the
environment.
A common type of ciliate is a paramecium. What
is unique about a paramecium is that it has two
nucleuses: one nucleus controls the everyday
function of the cell and the other nucleus handles
reproduction.
C. PROTOZOANS WITH FLAGELLA
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This third type of animal-like protozoan has
flagella. Flagellum is a long whip-like tail used
for movement.
Protozoans with flagella are called zoo flagellates.
Zoo flagellates survive inside another organism.
This relationship between two organisms is called
symbiosis. If both are receiving a benefit from
being together, this is called mutualism.
D. OTHER ANIMAL-LIKE PROTOZOANS
The last type of animal-like protozoans is called
sporozoans. Sporozoans are parasites that
negatively feed on the cells and body fluids of
their hosts.
III. FUNGUS-LIKE PROTISTS
Characteristics of fungus-like protists:
1. They are heterotrophs.
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2. Their cells have cell walls.
3. They reproduce via spores.
4. Able to move at some point during their life.
Three common types of fungus-like protists are
water molds, downy mildews, and slime molds.
A. WATER MOLDS
Water molds are always found in wet and moist.
It grows as tiny threads and looks like a fuzzy
covering and feed on decaying matter. SEE
FIGURE 5 ON PG. 85.
One type of water mold (Phytophthora infestans)
caused the Great Potato Famine that killed
nearly a million people in Ireland in 1846–1847.
The water mold virtually wiped out the country’s
potato crops, which were an essential staple in the
Irish diet (sometimes the only food on the table.)
B. DOWNY MILDEWS
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Downy mildew is very similar to water molds in
that they are always found in wet and moist
climates, grows as tiny fuzzy threads, and feed on
decaying matter.
It differs from water mold in that it attacks
plants such a grapes.
C. SLIME MOLDS
Slime molds live in moist soil and feed off of
decaying plants, trees & bacteria.
Slime molds differ from water molds and downy
mildews in that it can move by a pseudopod.
When food sources become hard to find, slime
molds come together and form a colony. This
colony can release spores for reproduction.
IV. PLANT-LIKE PROTISTS
The most common plant-like protists are algae
(like seaweed). Algae are an important food
source for organisms in the water.
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Characteristics of plant-like protists:
1. They are autotrophs.
2. They make most of the oxygen found present
on the Earth.
3. They can be unicellular or multicellular.
4. They come in a wide variety of colors due to
their differing pigments. Pigments are a
chemical that produces color.
The six types of plant-like protists we are going to
study are euglenoids, dinoflagellates, diatoms,
green algae, red algae, and brown algae.
A. EUGLENOIDS
Euglenoids are a green, unicellular algae found
mostly in fresh water.
Normally, if sun is present, euglenoids can make
their own food. If the sun is NOT present,
euglenoids become like animals and hunt out
food.
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The most common type of a euglenoids is a
Euglena.
The most important part on the Euglena is its
eyespot. The eyespot contains pigments that help
it sense out light.
B. DINOFLAGELLATES
Dinoflagellates are unicellular algae which are
covered by stiff plates made of cellulose.
They have two flagella which cause them to spin
like a top.
Dinoflagellates often glow in the water (called
bioluminescence) or cause the water to become
red (called red tide).
Below is a picture of bioluminescence in ocean
water.
Below is a picture of a red tide.
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C. DIATOMS
Diatoms are unicellular plant-like protists that
have glass-like cell walls to protect them.
They move by oozing chemical slime out of their
cell walls. The chemical slime helps diatoms glide
on top of it.
When diatoms die, they collect on the bottom of
oceans and lakes. This forms a crust on the earth
called diatomaceous earth. Diatomaceous earth
is collected and used in toothpastes, scouring
cleaners (such as Comet), swimming pool filters,
and insecticides.
D. GREEN, RED & BROWN ALGAE
Green, red and brown algae vary according to
their colors. All are used as a food source for
humans.
The seaweed you see on beaches is considered
brown algae.
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