Chapter 26: Protozoa

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Chapter 26 Protozoa
26-1 Overview of Protozoa
26-2 Protozoan Diversity
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26-1 Overview of Protozoa
I. Protists

• A diversity of protozoa, algae, slime molds, and
  water molds that lack tissue differentiation and
  are eukaryotes. (A-L, P-L, F-L)

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II. Characteristics of Protozoa

• Approximately 65,000 microscopic species have
  been identified (half extinct), can have
  inhabited the marine, freshwater, and terrestrial
  habitats.

(1) Protozoa

• Unicellular and heterotrophic (most species),
  can be either free-living or parasitic, requiring
  multiple hosts.

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Critical Thinking
(1) Some protozoan parasites are very difficult
to grow in test tubes because they lose the
ability to produce certain key enzymes or growth
factors when outside their host. How could this
host-parasite relationship be similar to that
described in the Endosymbiosis Hypothesis? How
could it be different?
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(2) Food Vacuoles

• Membrane-bound chambers containing digestive
  enzymes that break down small food molecules
  ingested by heterotrophic protozoans.

(3) Zooplankton

• Population of organisms that is made up by
  numerous protozoan species a critical trophic
  level in aquatic ecosystems.

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(A) Reproduction

• All protozoa are capable of binary fission
  (asexual), where one divides into two identical
  offspring however some are capable of sexual
  reproduction as well.

(1) Multiple Fission (asexual)

• A form of asexual reproduction where a number
  (gt2) of identical offspring are yielded.

(2) Conjugation (sexual)

• Individuals from opposite mating-strains pair
  up and exchange genetic material (slightly more
  complex than conjugation in bacteria).

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Critical Thinking
(2) The process of conjugation is complex,
requiring an expenditure of energy and resources.
How can you relate the high biological cost of
conjugation to the adaptive advantage of
exchanging genetic material?
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(B) Classification

• Protozoa belong to Kingdom Protista and are
  further classified into four phyla, distinguished
  by form of locomotion

(1) Phylum Sarcodina
(2) Phylum Ciliophora
(3) Phylum Zoomastigina
(4) Phylum Sporozoa
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(C) Adaptations

• Many species of protozoa have physiological
  mechanisms for monitoring conditions/noxious
  chemicals in their environment.

(1) Eyespot

• Localized region of pigment that can detect
  changes in the amount of sunlight (dark or light).

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(2) Cyst

• A dormant form characterized by a hardened
  external covering in which metabolic activity
  ceases.

NOTE Stressors include drought, nutrient
deficiency, decreased oxygen levels, or
pH/temperature changes. Emergence occurs when
conditions become favorable once again.
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Critical Thinking
(3) Many parasitic protozoa, such as Entamoeba
histolytica, are able to form cysts whenever they
pass out of a host. Why would cyst formation
represent an advantage to a parasitic protozoan?
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(D) Evolution (1.5 b.y.a.)

• Descended from the earliest eukaryotic cells,
  followed prokaryotes (bacteria) possibly due to
  endosymbiosis.

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26-2 Protozoan Diversity
I. Phylum Sarcodina (40,000 species of sarcodines)

• Include amoebas, which inhabit fresh water,
  saltwater, and soil, and are characterized by
  cytoplasmic extensions called pseudopodia and
  flexible cell membranes.

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(1) Pseudopodia

• Large, rounded cytoplasmic extensions that
  function in movement.

(2) Endoplasm

• Inner portion of the cytoplasm that pushes
  against the ectoplasm.

(3) Ectoplasm

• Outer layer of cytoplasm that is pushed outward
  to create a blunt, armlike extension.

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Critical Thinking
(4) Many species of protozoa feed by means of
pseudopodia. What do you believe could be the
stimulus that might cause these cytoplasmic
extensions to form?
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(4) Ameboid Movement

• The simultaneous extension and contraction of
  the pseudopodia to initiate movement (powered by
  cytoplasmic streaming).

(5) Cytoplasmic Streaming

• Internal flowing of a cells cytoplasm includes
  ameboid movement

(6) Contractile Vacuole

• Organelle that expels fluid from the cell in
  order to maintain homeostasis (i.e., freshwater
  protists are usually hypertonic relative to their
  habitat).

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(A) Ecological Role

• Calcium-rich layer of sediment deposited at the
  bottoms of oceans from the tests of dead
  foraminifera.

(1) Test

• A protective but porous CaCO3 shell (slender
  pseudopodia extend through these openings) that
  covers the delicate cell membrane of some
  sarcodines, including foraminifera.

(2) Foraminifera

• Ancient group of shelled sarcodines found
  primarily in oceans with chambered tests.

(3) Radiolarians

• Oldest of foraminifera, inhabit shallow waters
  and usually have a radial arrangement of spines
  that extend through their test.

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(B) Human Diseases

• Although the majority of amoebas are
  free-living, some parasitize the large intestines
  of humans or other animals.

(1) Amebic Dysentery (Entamoeba histolytica)

• Amoeba enter through the consumption of
  contaminated food or water and as the amoeba
  grow, enzymes are secreted that agitate the
  intestinal lining resulting in painful ulcers.

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II. Phylum Ciliophora (8,000 species of ciliates)

• Swim by cilia and are abundant in ponds and
  slow-moving streams containing bacteria, algae,
  and decaying organic matter. (e.g., Paramecium
  Caudatum)

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(A) Internal Structure

• Ciliates have the most elaborate organelles of
  any protozoa and are multinucleate.

(1) Pellicle Oral Groove

• A clear, elastic layer of protein surrounding
  the cell membrane (pellicle) the pellicle
  contains a funnel-like tube lined with cilia
  (oral groove)

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(2) Mouth Pore Gullet

• Beating cilia sweep in food particles into the
  mouth pore, of which opens into the gullet where
  food vacuoles are formed and circulated.

(3) Anal Pore

• Vacuoles of indigestible materials are moved to
  the anal pore where they are expelled into the
  surroundings.

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(4) Macronucleus (larger)

• Contains multiple copies of DNA and is
  responsible for metabolic, developmental, and
  asexual reproductive functions.

(5) Micronucleus (smaller)

• Participates in the exchange of genetic material
  between individual ciliates during conjugation.

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(B) Reproduction (asexual and sexual)

• Asexually via binary fission and sexually via
  conjugation.

NOTE Following conjugation, each paramecium
divides, producing a total of four genetically
identical paramecia. Because genetic material is
exchanged between the two original paramecia, the
four offspring paramecia are genetically
different from either original paramecium.
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Critical Thinking
(5) Many biologists suggest that paramecia are
more complex than amoebas. What adaptations in
paramecia would justify this claim?
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III. Phylum Zoomastigina (2,500 species of
zooflagellates)

• Characterized by the presence of one or more
  flagella, constructed by microtubules and used
  for locomotion (e.g., Giardia lamblia)

(A) Human Disease

• Although most are free-living, feeding on
  smaller organisms, many of the zooflagellates
  belonging to the genus Trypanosoma are parasites
  (using bloodsucking insects as carriers from host
  to host)

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(1) Trypanosomiasis (African Sleeping Sickness)

• Transmitted by a bite of the tsetse fly,
  resulting in fever, neurological degradation, and
  ultimately coma.

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(2) Chagas Disease (South America)

• Transmitted by a bite of the kissing bug,
  resulting in fever and severe cardiac damage.

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(3) Giardiasis (U.S.A.)

• Contaminated water with Giardia lamblia that
  produces severe diarrhea and intestinal cramps.

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IV. Phylum Sporozoa (6,000 species of sporozoans)

• Characterized by adult forms with no locomotion
  most are parasitic with complex life cycles in
  which a spore (infective form with a resistant
  coat) is developed.

(1) Toxoplasmosis (Toxoplasma gondii)

• A disease resulting from a sporozoan found in
  birds, rodents, and domestic cats that can be
  dangerous to a developing fetus or newborn.

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(A) Plasmodium (four species infect humans, all
involving a mosquito)

• Genus of sporozoans that is responsible for
  causing malaria and more human deaths than any
  other genus in recorded history.

(1) Malaria

• Infected victims die of anemia, kidney failure,
  or brain damage afflicts 500 million (killing as
  many as 2.7 million) annually.

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(2) Sporozites (liver-stage parasite)

• When an infected mosquito bites a person,
  Plasmodium sporozites enter the bloodstream and
  travel to the liver cells where they divide
  repeatedly forming new spores called merozoites.

(3) Merozoites (erythrocyte-stage parasite)

• Emerge and infect red blood cells in order to
  reproduce asexually the destruction of RBCs and
  the release of toxins produce the symptoms.

(4) Gametocytes (specialized cells developed from
merozoites)

• Ingested when a female mosquito (Anopheles)
  bites an infected person, combining zygotes which
  hatch into new sporozites that migrate to the
  salivary glands of the mosquito.

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Critical Thinking
(5) Observing the micrograph below depicting the
sporozoan Plasmodium, what evolutionary advantage
does Plasmodium gain by forming gametocytes?
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Critical Thinking
(6) Biologists are working to develop a vaccine
against malaria, but since malaria has several
life stages, biologists must decide which life
stage to develop a vaccine against. Some
biologists are trying to develop a vaccine
against gametocytes as a way of controlling
malaria. If they are successful in developing
this vaccine, how will it help people living in
areas where malaria regularly grows?
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Revisiting Cell Structure and Function

• Unicellular organisms contain structures that
  perform specialized functions, including feeding
  and locomotion.

Assessing Prior Knowledge

• Describe at least five cellular organelles and
  their functions.

• Predict what will happen if a protozoan such as
  an amoeba is placed in a distilled water solution.

• Define host and parasite.