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Protists
Recap of Bacteria and Intro to Protists
• https://www.youtube.com/watch?v=vAR47g6tlA
• The protist kingdom is the most challenging
group of organisms to classify.
• There are 115 000 species of protists which
display great variation.
• Protists have characteristics that are similar to
organisms found in each of the other
kingdoms. Some are unicellular which is
similar to bacteria.
• However, one distinguishing characteristic
that separates bacteria from protists is the
presence of a nucleus.
• Remember, bacteria are
prokaryotic because their
DNA is free floating within
the cytoplasm.
• All protists are eukaryotic
which means they contain a
distinct nucleus which
surrounds their DNA.
• This evolutionary
development generated the
need for a distinct
classification for these
organisms.
• Classifying protists becomes challenging
because of their vast differences.
• Most protists are unicellular, but there are
some that are multicellular.
• Some are autotrophs while others feed on
organic matter and are heterotrophic.
• Scientists have organized protists into three
different groups: animal-like protists, plantlike protists, and fungi-like protists.
• In all, there are 11 phyla in the protist
kingdom.
Animal-like Protists (Protozoa)
• Protozoans are classified by their type of
locomotion, life cycle, reproduction, nutrition and
whether the protist is parasitic or free-living.
• All animal-like protists are heterotrophs. Similar
to organisms in the animal kingdom, these
protists have to be motile to search out food.
• Protozoans can either absorb pre-digested
materials through their cell membrane or they
can engulf their food.
• Sarcodina, Mastigophora, Ciliophora, and
Sporozoa are the four phyla of animal-like
protists. You will now learn about each phylum in
greater detail.
Sarcodina
• The amoeba is probably
the most famous protist in
this phylum. Perhaps you
even had the opportunity
to view an amoeba under a
microscope.
• One of the interesting
characteristics of protists in
this phylum is the way they
• The image above shows an
move.
amoeba moving toward a
• By extending and retracting
its cytoplasm, an amoeba is group of cells. The movement
of the cytoplasm forms the
able to create “false feet”
pseudopods as the amoeba
called pseudopods.
moves towards the food.
• Pseudopods also enable an amoeba to capture and
engulf its food by phagocytosis.
• Below is a sequence of pictures showing an amoeba
engulfing an algal cell.
• In the fourth sequence you will notice the appearance
of the pseudopods surrounding the algal cells.
Mastigophora
• In the phylum Mastigophora, the protists contain
one or more flagellum (pl.flagella) for
locomotion.
• A flagellum resembles a tail and is attached to the
cell body of the protozoan. A protist will generate
motion when the flagellum begins to rotate.
• Most of these protozoans are harmless.
• However, Giardia lamblia, a parasitic
protozoan causes upset stomach and diarrhea
in humans.
• This parasite lives in the digestive tract of
animals, like cows.
• Humans can contract the parasite when they
consume food or water that has come in
contact with the feces of infected animals.
Ciliophora
• Cilates contain cilia, tiny
hair-like structures,
throughout the outer
covering of their cell body.
• In the image on the right,
the cilia appear clear. The
dark spot in the centre of
the paramecium is the
macronucleus which
functions like a nucleus.
• A micronucleus, not shown,
is smaller and is involved in
reproduction.
• Most paramecium
reproduce by binary
fission; however, they can
also undergo conjugation.
Sporozoa
• Sporozoans rely on other
organisms for movement.
They lack cilia, pseudopods,
and flagella. Therefore,
these protists are
all parasitic.
• Malaria is caused by
Plasmodium. Symptoms
include fever, headache,
and vomiting: malaria can • Approximately 40% of the
quickly become lifeworld's population, mostly those
threatening if not treated.
living in the world's poorest
• Malaria can be spread from
countries, are at risk of malaria.
person to person and
• Every year, more than 500 million
through mosquito bites.
people become severely ill with
malaria. (WHO, May 2007)
Homework
• Giardia lamblia is a parasite that affects humans. Applying
your knowledge, how could you protect yourself from
getting this parasite?
• Plasmodium vivax is the parasite responsible for malaria.
Describe in detail how the parasite is spread via
mosquitoes.
• In 1962 Rachel Carson published a book titled “Silent
Spring” in which she condemned the use of DDT. DDT at the
time was a pesticide used to destroy mosquitoes that
transmitted malaria and it had been linked to cancer
development in animals and humans. In 1969, Canada
banned the use of DDT and subsequently so did the United
States and other countries. It is highly unlikely that you will
contract malaria while living in Ontario. However, 40% of
the world's population is at risk of becoming infected with
this parasite. What advantages do we have over these
other populations?