What Are Protists?
• A group of one-celled organisms with well
defined nuclei
• All protists live in moist surroundings
• Many protists possess both plant-like and
animal-like features
• Animal like protists are called
PROTOZOAN
We will take a close look at four protists that are
similar in some respects and are also very different in
others.
Similarities:
All have cytoplasm surrounded by a protective
covering
All have a well-defined nucleus
All reproduce asexually by cell division (binary fission)
All have vacuoles
All move about their environment
Amoeba
• The amoeba is a tiny, one-celled organism
• The name amoeba comes from the Greek word
amoibe, which means change
• They are legendary as the ultimate shape
shifters
• Amoeba are quite hard to find
Amoeba
• An amoeba consists of a single
blobby cell surrounded by a porous
cell membrane.
• The amoeba "breathes" using this
membrane
• Amoebas move by changing the
shape of their body, forming
pseudopods (temporary foot-like
structures).
• The word pseudopod means "false
foot."
• The pseudopodia movement that enables the
amoeba to capture prey.
• Usually the pseudopods form a kind of dome
that makes escaping impossible.
• They must have some sort of chemical detection
since they notice a prey without having to touch
it.
These two images
of Amoeba proteus
shows how a fast
moving ciliate is
surrounded by quick
developing
pseudopodia.
Paramecium
• The paramecium is larger than
the amoeba
• Shaped like a slipper, its name
comes from the Greek word
for “oval”
• It is common in ponds throughout the world
• Paramecium is a good example of cell
complexity.
• The paramecium has two nuclei, a big and small
one
• The big one operates as the director of the cell's
activities, rather like a little brain
• The smaller one is used for reproduction
• It is covered with tiny hairs called cilia that help it
move
• The paramecium is able to move in all directions
with these cilia
• The cilia also propels the food into a tiny mouth
called the oral groove
Euglena
• The euglena is unique because it is sort of like a
plant and also like an animal
• It is pear shaped
• It has a whippy tail called a flagellum that allows
it to move through the water
• The euglena is able to make its own food
like a plant when it is in the sunlight
• When it is in darkness, however, it can
find food like an animal
• It takes in tiny plants and animals much
like the amoeba and paramecium.
Interesting Fact
• When it is too hot or cold for a euglena, it forms
a protective casing called a cyst around its body
that protects it until conditions outside the cyst
become better.
Volvox
• Volvox is a green algae
• It exists as a grand spherical colony
• The bright green spheres within are "daughter
colonies"
The individual algae are
connected by thin strands of
cytoplasm.
• The volvox resembles a little planet
• In the northern region the eyespots are more developed
• This differentiation of cells make Volvox quite unique
Each little
alga within
the colony
bears two
flagella,
whip-like
hairs.
The individual alga also have small
red eye spots.
One of the 7 Wonders of the Micro World
Sometimes we can find inhabitants
within the colony. There is a small
rotifer, called Proales parasita that
lives inside Volvox and feeds on the
cells.