Chapter 21
Protists
Table of Contents
Section 1 Characteristics of Protists
Section 2 Protist Diversity
Section 3 Protists and Health
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Chapter 21
Section 1 Characteristics of Protists
Objectives
• List the characteristics of protists.
• List three environments where protists can be found.
• Identify the unifying features of protists.
• Distinguish asexual and sexual reproduction of
Protists.
• Differentiate two ways multicellular protists
reproduce sexually.
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Chapter 21
Section 1 Characteristics of Protists
Diversity
Characteristics
• The kingdom Protista consists of an unusually
diverse assortment of eukaryotes that exhibit a
broad array of characteristics.
• Some protists are photosynthetic (like plants),
some ingest food (like animals), and some absorb
their food (like fungi).
• Protists are found almost everywhere there is
water. Many live in lakes and oceans, floating as
plankton or anchored to rocks.
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Chapter 21
Section 1 Characteristics of Protists
Characteristics of Protists
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Chapter 21
Section 1 Characteristics of Protists
Diversity, continued
The First Eukaryotes
• Protists—the first eukaryotes—are thought to have
evolved about 1.5 billion years ago through the
process of endosymbiosis.
• The kingdom Protista contains life-forms similar to
those that gave rise to the three kingdoms of
multicellular organisms—fungi, plants, and animals.
• Two important eukaryotic features that evolved
among the protists are sexual reproduction and
multicellularity.
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Chapter 21
Section 1 Characteristics of Protists
Origin of Eukaryotic Cells
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Chapter 21
Section 1 Characteristics of Protists
Endosymbiosis
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Chapter 21
Section 1 Characteristics of Protists
Comparing Organisms That Are Unicellular
and Multicellular
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Chapter 21
Section 1 Characteristics of Protists
Sexual Reproduction
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Chapter 21
Section 1 Characteristics of Protists
Diversity, continued
What Unites Protists?
• The kingdom Protista contains all eukaryotes that
cannot be classified as animals, plants, or fungi.
• The major phyla of protists are very different from
one another and, with a few exceptions, are only
distantly related.
• Historically, scientists have referred to heterotrophic
protists as protozoa and to photosynthetic protists as
algae.
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Chapter 21
Section 1 Characteristics of Protists
Diversity, continued
What Unites Protists?
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Chapter 21
Section 1 Characteristics of Protists
Reproduction
• Reproduction in the unicellular green alga
Chlamydomonas is typical of unicellular protists.
• As a mature organism, the single-celled protist is
haploid.
• When it reproduces asexually, Chlamydomonas first
absorbs its tail and divides by mitosis, producing two
to eight haploid cells called zoospores, which remain
within the wall of the parent cell.
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Chapter 21
Section 1 Characteristics of Protists
Reproduction, continued
Sexual Reproduction in Unicellular Protists
• During environmental stress, such as a shortage of nutrients,
Chlamydomonas species reproduce sexually.
• The haploid cell divides by mitosis to produce gametes. After
they are released, a pair of gametes from different individuals
fuse to form a pair.
• This pair of gametes then shed their cell walls and fuse into a
diploid zygote with a thick protective wall called a zygospore.
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Chapter 21
Section 1 Characteristics of Protists
Reproduction of Chlamydomonas
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Chapter 21
Section 1 Characteristics of Protists
Sexual Reproduction in Unicellular Protists
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Chapter 21
Section 1 Characteristics of Protists
Reproduction, continued
Sexual Reproduction in Multicellular Protists
• The reproductive cycle of Ulva, called alternation of
generations, is characterized by two distinct
multicellular phases.
• The diploid, spore-producing phase is called the
sporophyte generation.
• The haploid, gamete-producing phase is called the
gametophyte generation. The adult sporophyte alga
has reproductive cells called sporangia, which
produce haploid spores by meiosis.
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Chapter 21
Section 1 Characteristics of Protists
Reproduction of Ulva
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Chapter 21
Section 1 Characteristics of Protists
Reproduction in Ulva
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Chapter 21
Section 1 Characteristics of Protists
Reproduction, continued
Sexual Reproduction in Multicellular Protists
• Conjugation is the temporary union of two protists to
exchange nuclear material.
• The process begins when two filaments align side by
side.
• The nucleus of one cell then passes through the tube
into the adjacent cell. The two nuclei eventually form
a resting spore, which produces a new haploid
filament.
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Chapter 21
Section 1 Characteristics of Protists
Protist Reproduction
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Chapter 21
Section 1 Characteristics of Protists
Conjugation
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Chapter 21
Section 2 Protist Diversity
Objectives
• Identify how amoebas and forams move.
• Describe the structure of diatoms.
• Contrast three kinds of algae.
• Differentiate three different kinds of flagellates.
• Summarize the general characteristics of a
Paramecium.
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Chapter 21
Section 2 Protist Diversity
Types of Animal-like Protists
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Chapter 21
Section 2 Protist Diversity
Ameboid Movement
Amoebas
• Amoebas, members of the phylum Rhizopoda,
are protists that move by using flexible,
cytoplasmic extensions.
• These extensions are called pseudopodia from
the Greek words pseudo, meaning ―false,‖ and
podium, meaning ―foot.‖
• During ameboid movement, a pseudopodium
bulges from the cell surface, stretches outward,
and anchors itself to a nearby surface.
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Chapter 21
Section 2 Protist Diversity
Parts of an Amoeba
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Chapter 21
Section 2 Protist Diversity
Movement of an Amoeba
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Chapter 21
Section 2 Protist Diversity
Feeding Habits of an Amoeba
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Chapter 21
Section 2 Protist Diversity
Ameboid Movement, continued
Foraminifera
• Members of the phylum Foraminifera, or forams, are
marine protists that typically live in sand or attach
themselves to other organisms or rocks.
• Forams are characterized by their porous shells,
called tests. Long, thin projections of cytoplasm
extend through the pores in the tests to aid in
swimming and in catching prey.
• Some forams also obtain nourishment from algae
that live symbiotically under their tests.
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Chapter 21
Section 2 Protist Diversity
Algae
Green Algae
• Most green algae (phylum Chlorophyta) are
freshwater unicellular organisms, but some are large,
multicellular marine organisms.
• They also exist as a major part of microscopic marine
plankton, inhabit damp soil, or even thrive within the
cells of other organisms as symbionts.
• Green algae contain the same pigments found in the
chloroplasts of plants.
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Chapter 21
Section 2 Protist Diversity
Algae, continued
Red Algae
• Red algae (phylum Rhodophyta) are multicellular
organisms found in warm ocean waters.
• Their red pigments are efficient at absorbing the light
that penetrates deep waters.
• Red algae have a complex life cycle, usually
involving alternation of generations.
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Chapter 21
Section 2 Protist Diversity
Algae, continued
Brown Algae
• Brown algae (phylum Phaeophyta) are
multicellular and are found mostly in marine
environments.
• The larger brown algae known as kelp grow along
coasts and provide food and shelter for many
different kinds of organisms.
• They are among the largest organisms on Earth.
Brown algae reproduce by alternation of
generations.
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Chapter 21
Section 2 Protist Diversity
Diatoms
• Diatoms, members of the phylum Bacillariophyta, are
photosynthetic, unicellular protists with unique double
shells.
• Diatoms can have one of two types of symmetry:
radial (like a wheel) or bilateral (two-sided).
• Diatoms secrete chemicals through holes in their
shells, enabling them to move by gliding.
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Chapter 21
Section 2 Protist Diversity
Flagellates
Dinoflagellates
• Dinoflagellates, members of the phylum
Dinoflagellata, are unicellular phototrophs, most of
which have two flagella.
• Most dinoflagellates have a protective coat made of
cellulose that is often encrusted with silica, giving
them unusual shapes.
• Their flagella beat in two grooves—one encircling the
body like a belt, the other perpendicular to it.
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Chapter 21
Section 2 Protist Diversity
Parts of a Flagellate
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Chapter 21
Section 2 Protist Diversity
Movement of a Flagellate
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Chapter 21
Section 2 Protist Diversity
Feeding Habits of a Flagellate
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Chapter 21
Section 2 Protist Diversity
Flagellates, continued
Euglenoids
• Euglenoids members of the phylum Euglenophyta,
are freshwater protists with two flagella.
• A member of Euglena has a protein scaffold called a
pellicle inside the cell membrane.
• A light-sensitive organ called the eyespot helps orient
the movements of these organisms toward light.
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Chapter 21
Section 2 Protist Diversity
Structure of Euglena
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Chapter 21
Section 2 Protist Diversity
Eyespot
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Chapter 21
Section 2 Protist Diversity
Flagellates, continued
Kinetoplastids
• Kinetoplastids, members of the phylum
Kinetoplastida, are unicellular heterotrophs that have
at least one flagellum, and some species have
thousands.
• Kinetoplastids are clearly related to euglenoids, and
many taxonomists merge the two phyla together.
• While most reproduce only asexually, some are
known to produce gametes and reproduce sexually.
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Chapter 21
Section 2 Protist Diversity
Flagellates, continued
Ciliates
• Ciliates are the most complex and unusual of the
protists. All members of the phylum Ciliophora have
large numbers of cilia, tightly packed rows of short
flagella used for movement.
• The body wall of ciliates is a tough but flexible outer
pellicle that enables the organism to squeeze
through or move around many obstacles.
• Reproduction in ciliates is usually by mitosis, with
the body splitting in half.
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Chapter 21
Section 2 Protist Diversity
Structure of Cilia and Flagella
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Chapter 21
Section 2 Protist Diversity
Movements of a Ciliate
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Chapter 21
Section 2 Protist Diversity
Feeding Habits of a Ciliate
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Chapter 21
Section 2 Protist Diversity
Paramecium
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Chapter 21
Section 2 Protist Diversity
Parts of a Paramecium
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Chapter 21
Section 2 Protist Diversity
Sexual Reproduction in Paramecium
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Chapter 21
Section 2 Protist Diversity
Protistan Molds
Cellular Slime Molds
• Cellular slime molds, members of the phylum
Acrasiomycota, resemble amoebas but have distinct
features.
• The individual organisms behave as separate
amoebas, moving through the soil and ingesting
bacteria.
• During environmental stress, the individual amoebas
gather together and move toward a fixed center.
There they form multicellular colonies called slugs.
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Chapter 21
Section 2 Protist Diversity
Protistan Molds, continued
Plasmodial Slime Molds
• Plasmodial slime molds, members of the phylum
Myxomycota, are a group of organisms that
stream along as a plasmodium, a mass of
cytoplasm that looks like an oozing slime.
• A plasmodial slime mold contains many nuclei, but
they are not separated by cell walls.
• If the plasmodium becomes stressed, it divides
into many small mounds that produce stalks tipped
with a capsule in which haploid spores develop.
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Chapter 21
Section 2 Protist Diversity
Protistan Molds, continued
Other Molds
• Oomycetes, members of the phylum Oomycota, are
the water molds, white rusts, and downy mildews that
often grow on dead algae and dead animals in fresh
water.
• Oomycetes are unusual in that their spores have two
flagella: one pointed forward, the other pointed
backward.
• Many oomycetes are plant pathogens.
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Chapter 21
Section 2 Protist Diversity
Sporozoans
• Parasitic protists that form spores during their
reproduction cycle are called sporozoans.
• All sporozoans are parasitic and cause many serious
diseases. Malaria, a sporozoan disease, kills more
people than any other infectious disease.
• Sporozoans have complex life cycles that involve
both asexual and sexual reproduction.
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Chapter 21
Section 3 Protists and Health
Objectives
• Identify two ways that protists affect human health.
• Name three human diseases, other than malaria,
caused by protists.
• Summarize how malaria is transmitted.
• Evaluate the methods used to control malaria.
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Chapter 21
Section 3 Protists and Health
Protists and Humans
• One of the greatest effects protists have on humans
is that they cause disease.
• Protists also affect humans through the diseases they
cause in livestock.
• The added cost of treating diseased livestock is
passed on to consumers in the form of higher meat
prices.
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Chapter 21
Section 3 Protists and Health
Diseases Caused by Protists
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Chapter 21
Section 3 Protists and Health
Protists and Humans, continued
Beneficial Protists
• Cattle could not digest the cellulose in the hay and
grass they eat without the aid of commensal protists
in their digestive tract.
• Protists are also the single largest group of
photosynthesizers on the planet.
• Many protists are also detritivores, so they help
recycle important chemicals, such as nitrogen,
carbon, and phosphorus, in the environment.
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Chapter 21
Section 3 Protists and Health
Malaria
• Malaria is one of the most deadly diseases in
humans.
• The symptoms include severe chills, fever, sweating,
confusion, and great thirst.
• Victims die of anemia, kidney failure, or brain
damage unless the disease is treated.
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Chapter 21
Section 3 Protists and Health
Malaria
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Chapter 21
Section 3 Protists and Health
Malaria, continued
Malaria Life Cycle
• Malaria is caused by several species of Plasmodium
and is spread by the bite of certain mosquitoes.
• If the mosquito is infected with Plasmodium, it will
also inject about 1,000 protists with its saliva. This
infective stage of Plasmodium is called the
sporozoite.
• Sporozoites infect the liver, where they rapidly divide
and produce millions of cells of the second stage of
the life cycle, called the merozoite.
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Chapter 21
Section 3 Protists and Health
Life Cycle of
Plasmodium
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Chapter 21
Section 3 Protists and Health
Malaria Life Cycle
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Chapter 21
Section 3 Protists and Health
Malaria, continued
Treating and Preventing Malaria
• In the middle of the seventeenth century, quinine, a
chemical derived from the bark of the cinchona tree
was discovered to be a remedy for malaria.
• Derivatives of quinine, such as chloroquine and
primaquine, are now used to treat malaria.
• Malaria can also be controlled by reducing mosquito
populations.
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Chapter 21
Standardized Test Prep
Multiple Choice
The chart below shows the daily temperature of a
patient who has malaria. Use the chart to answer
questions 1–3.
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Chapter 21
Standardized Test Prep
Multiple Choice, continued
1. This pattern of temperature variation occurs when
Plasmodium merozoites infect and destroy
A.
B.
C.
D.
liver cells.
red blood cells.
the digestive tract.
the salivary glands.
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Chapter 21
Standardized Test Prep
Multiple Choice, continued
1. This pattern of temperature variation occurs when
Plasmodium merozoites infect and destroy
A.
B.
C.
D.
liver cells.
red blood cells.
the digestive tract.
the salivary glands.
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Chapter 21
Standardized Test Prep
Multiple Choice, continued
2. If the pattern continues, what will be the approximate
temperature of the patient on Monday?
F.
G.
H.
J.
37
39
41
45
C
C
C
C
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Chapter 21
Standardized Test Prep
Multiple Choice, continued
2. If the pattern continues, what will be the approximate
temperature of the patient on Monday?
F.
G.
H.
J.
37
39
41
45
C
C
C
C
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Chapter 21
Standardized Test Prep
Multiple Choice, continued
3. In this patient, the cycle of fever and chills repeats
every
A.
B.
C.
D.
12 hours.
24 hours.
48 hours.
72 hours.
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Chapter 21
Standardized Test Prep
Multiple Choice, continued
3. In this patient, the cycle of fever and chills repeats
every
A.
B.
C.
D.
12 hours.
24 hours.
48 hours.
72 hours.
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