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					Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

Chapter 28: Protists

Overview: Living Small

The kingdom you learned as Protista is no longer recognized as an
official taxon. Work in Protista systematics has revealed that the
kingdom is paraphyletic and in need of extensive reworking. The
kingdom, formally known as Protista, has been divided into many
separate kingdoms. Biologists now use the term Protista in a general,
nontechnical way to refer to eukaryotes that are neither plants nor
animals, nor fungi. As we move through this chapter, we will concentrate
on the evolutionary events of significance and the specific protists that
are important.

•Even a low-power microscope can reveal a great variety of organisms in
a drop of pond water
•Protist is the informal name of the kingdom of mostly unicellular
eukaryotes
•Advances in eukaryotic systematics have caused the classification of
protists to change significantly
•Protists constitute a paraphyletic group, and Protista is no longer valid
as a kingdom

Concept 28.1 Most eukaryotes are single-celled organisms

1. Protists vary in structure and function more than any other group of
organisms. However, here are some common traits:

a. All have membrane-bounded organelles, and so are Eukaryotes.

b. Most are single-celled, or Unicellular.

c. They get their food in several ways. Some contain chloroplasts and do
photosynthesis, and so are considered Photoautotrophs. Others ingest
food particles and so are Heterotrophs.
•Protists, the most nutritionally diverse of all eukaryotes, include:
– Also, include mixotrophs, which combine photosynthesis and
heterotrophic nutrition
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte


2. Endosymbiosis is a key component of eukaryotic evolution. Many
protists are also the result of secondary endosymbiosis. Using Figure
28.2 from the text, label the figure below to show the key steps in
several secondary endosybiotic events.




3. Define secondary endosymbiosis.
A process in eukaryotic evolution in which a heterotrophic eukaryotic cell
engulfed a photosynthetic eukaryotic cell, which survived in a symbiotic
relationship inside the heterotrophic cell.
•The plastid-bearing lineage of protists evolved into red algae and green
algae
•On several occasions during eukaryotic evolution, red and green algae
under went secondary endosymbiosis, in which they were ingested by a
heterotrophic eukaryote

Concept 28.3 Chromalveolates may have originated by secondary
endosymbiosis
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte


4. Malaria is a leading cause of infectious disease. Over 300 million
people in the tropics are infected each year, and the death rate is 2
million people per year. The parasites that cause malaria are in the
genus Plasmodium. Plasmodium uses both mosquitoes and humans in its
complex life cycle, shown below.
Explain the eight steps in the Plasmodium life cycle.
Apicomplexans
•Apicomplexans are parasites of animals, and some cause serious human
diseases
•One end, the apex, contains a complex of organelles specialized for
penetrating a host
•They have a nonphotosynthetic plastid, the apicoplast
•Most have sexual and asexual stages that require two or more
different host species for completion
•The apicomplexan Plasmodium is the parasite that causes malaria
•Plasmodium requires both mosquitoes and humans to complete its life
cycle
•Approximately 2 million people die each year from malaria
•Efforts are ongoing to develop vaccines that target this pathogen
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte




  1. An      infected Anopheles mosquito bites a person, injecting
       Plasmodium sporocytes in its saliva.
  2.    The sporocytes enter a person’s liver cells. in its saliva. After
       several days, the sporocytes undergo multiple divisions and become
       merozoites, which use their apical complex to penetrate red blood
       cells (rbc’s). See TEM from Figure 28.10 in your text.
  3.    The merozoites divide asexually in the rbc’s. At the intervals of
       48 – 72 hours (depending on the species), large numbers of
       merozoites break out of the rbc’s causing periodic chills and fever.
       Some of the merozoites infect other rbc’s.
  4.    Some merozoites form gametocytes.
  5.   Another Anopheles mosquito bites the infected person and picks up
       Plasmodium gametocytes along with blood.
  6.   Gametes form from gametocytes, each male gametocyte produces
       several slender male gametes.
  7.    Fertilization occurs in the mosquito’s digestive tract, and a
       zygote forms .
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

   8. An oocyst develops from the zygote in the wall of the mosquito’s
      gut. The oocyst releases thousands of sporozoites, which migrate
      to the mosquito’s salivary gland.

5. Answer these questions about the ciliate Paramecium.
•Ciliates, a large varied group of protists, are named for their use of
cilia to move and feed
•They have large macronuclei and small micronuclei
•The micronuclei function during conjugation, a sexual process that
produces genetic variation
•Conjugation is separate from reproduction, which generally occurs by
binary fission

How does the Paramecium obtain food?
Oral groove and cell mouth




How do food vacuoles and lysosomes help with nutrition?
Food vacuoles fuse with lysosomes. As the food is digested, the vacuoles
follow a looping path through the cell. Wastes are released when the
vacuoles fuse with a specialized region of the plasma membrane that
functions as an anal pore.
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte


The Paramecium is hypertonic to its surroundings, so how does this
organism maintain water balance?
Paramecium, constantly, take in water by osmosis from its hypotonic
environment. Bladder-like contractile vacuoles accumulate excess water
from radial canals and periodically expel it through the plasma
membrane.
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

Concept 28.3 Protists play key roles in ecological relationships
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

6. Describe one mutualistic symbiotic relationship and one parasitic
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

relationship involving protists.
Mutualistic example: (sim'-be-ont) The smaller participant in a symbiotic
relationship, living in or on the host.
•Some protist symbionts benefit their hosts
–Dinoflagellates nourish coral polyps that build reefs
–Hypermastigotes digest cellulose in the gut of termites
Parasitic example:
•Some protists are parasitic
–Plasmodium causes malaria
–Pfesteria shumwayae is a dinoflagellate that causes fish kills
–Phytophthora ramorum causes sudden oak death

7. What is a key ecological role of protists in many aquatic food webs?
•Protists are found in diverse aquatic environments
•Protists often play the role of symbiont or producer

8. This is a large chapter with a great deal of information about many
different protists. To give you an idea of some of them, here is a short
list gleaned from your text.
You may recognize many of these protists:


a. Giardia intestinalis: Causes “hiker’s diarrhea”; always treat your
water!

b. Trichomonas vaginalis: Sexually transmitted infection.

c. Trypanosoma sp.: Sleeping sickness and Chagas’ disease.

d. Euglena: Remember seeing the tiny flagellated green cell with a red
eyespot in Bio. I?

e. Dinoflagellates: Blooms cause “red tides” and many are
bioluminescent.

f. Plasmodium: Causative agent of malaria.

g. Ciliates: Paramecium and Stentor are examples; micro- and
macronuclei.

h. Amoeba: Move by pseudopodia.
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

i. Diatoms: •Diatoms are unicellular algae with a unique two-part, glass-
like wall of hydrated silica •Diatoms usually reproduce asexually, and
occasionally sexually

•Diatoms are a major component of phytoplankton and are highly diverse

•Fossilized diatom walls compose much of the sediments known as
diatomaceous earth

j. Golden algae: •Golden algae are named for their color, which results
from their yellow and brown carotenoids •The cells of golden algae are
typically biflagellated, with both flagella near one end •All golden algae
are photosynthetic, and some are also heterotrophic

Most are unicellular, but some are colonial




Figure 28.14 Dinobryon, a colonial golden alga found in fresh water (LM)

k. Brown algae: Kelp. •Brown algae are the largest and most complex
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

algae •All are multicellular, and most are marine•Brown algae include
many species commonly called “seaweeds”•Brown algae have the most
complex multicellular anatomy of all algae •Giant seaweeds called kelps
live in deep parts of the ocean •The algal body is plantlike but lacks
true roots, stems, and leaves and is called a thallus •The rootlike
holdfast anchors the stemlike stipe, which in turn supports the leaflike
blades

Figure 28.16 Below is the life cycle of the brown alga Laminaria: an
example of alternation of generations
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte




Figure 28.15 Above seaweeds: adapted to life at the ocean’s margins

l. Oomycetes: Water molds and their relatives; includes causative agent
of potato blight.

Figure 28.17 Below is the life cycle of a water mold
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte




m. Red algae: (Multicellular; some found at great depths; sushi wraps.)

•Red algae are reddish in color due to an accessory pigment call
phycoerythrin, which masks the green of chlorophyll

•The color varies from greenish-red in shallow water to dark red or
almost black in deep water

•Red algae are usually multicellular; the largest are seaweeds

•Red algae are the most abundant large algae in coastal waters of the
tropics

Figure 28.19 Below are pictured Red algae
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte




n. Green algae: (Clamydomonas, Ulva, Volvox; this group is the closest
relative of land plants.)

•Green algae are named for their grass-green chloroplasts

•Plants are descended from the green algae

•The two main groups are chlorophytes and charophyceans

•Most chlorophytes live in fresh water, although many are marine

•Other chlorophytes live in damp soil, as symbionts in lichens, or in snow
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

Figure 28.20 Below is pictured Watermelon snow




•Chlorophytes include unicellular, colonial, and multicellular forms
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

Figure 28.21 Below are pictured Multicellular chlorophytes
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte




o. Slime molds:
•Slime molds, or mycetozoans, were once thought to be fungi
•Molecular systematics places slime molds in the clade Amoebozoa

•Many species of plasmodial slime molds are brightly pigmented, usually
yellow or orange

•Cellular slime molds form multicellular aggregates in which cells are
separated by their membranes
•Cells feed individually, but can aggregate to form a fruiting body
•Dictyostelium discoideum is an experimental model for studying the
evolution of multicellularity

Testing Your Knowledge: Self-Quiz Answers
Now you should be ready to test your knowledge. Place your answers
here:
Figure 28.22 Below is pictured the life cycle of Chlamydomonas, a
unicellular chlorophyte

1.________ 2.________ 3.________

				
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