VIRUSES, BACTERIA AND PROTISTS
I. VIRUSES
A. Viruses are not included in the classification scheme for living organisms because they are
noncellular and cannot be classified with cellular organisms. Other reasons why viruses are
not considered to be living include the following:
1. They do not metabolize compounds to generate their supply of energy.
2. They do not respond to stimuli.
3. They can only reproduce inside of a living cell.
B. Louis Pasteur-1884-suggested that something smaller than bacteria was responsible for
causing rabies.
1. Dimitri Ivanowsky-a Russian biologist, proved that viruses were capable of causing
certain illnesses. His work was conducted in 1890’s. Viruses are pathogens.
2. Bacteriophages-viruses that infect bacteria.
C. Viral Structure
1. Viruses are extremely small and occur in a variety of shapes.
2. All viruses contain at least two major parts:
a. An outer covering referred to as a Capsid. This protective structure is
composed of proteins.
b. A nucleic acid-either RNA or DNA. However, a virus never contains both
RNA and DNA.
3. Most viruses do contain enzymes that are involved in producing their nucleic acid.
D. Viruses are classified based on:
1. Their type of nucleic acid (either RNA or DNA).
2. Their size and shape
3. The presence or absence of an outer coat.
E. Viral Reproduction
1. Viruses are referred to as obligate intracellular parasites which means that they can
only reproduce inside of another cell.
2. Viruses can be distinguished based on the type of reproductive cycle that they exhibit.
Viral reproductive cycles are as follows:
a. The Lytic Cycle-steps/events here:
1) The virus attaches to a host cell.
2) Next, the virus injects its nucleic acid into the host cell.
3) The viral nucleic acid takes control of the host cell and begins
synthesizing new viruses in the host cell.
4) When the new viruses are mature, they cause lysis of the host cell.
5) The newly produced viruses are then able to go out and infect other
healthy cells.
b. The Lysogenic Cycle-steps/events
1) In this cycle, viral nucleic acid becomes incorporated into the host cell
DNA.
2) The viral nucleic acid at some point will turn on the production of new
viruses but this may not happen immediately.
3) At some point, the viral nucleic acid will force the host cell to go
through the same events as in the Lytic Cycle of Viral Reproduction.
4) Can you name a virus that functions in this fashion?
F. Several Types of Viruses
1. Human immunodeficiency virus (HIV)
2. Herpes zoster virus
3. Epstein-Barr Virus
G. Other illnesses caused by Viruses:
1. The common cold
2. The Flu
3. Cold sores
4. Rabies
5. Measles
6. Polio
7. Mumps
8. Warts
H. Antibiotics do not kill viruses. A few drugs have been developed that have shown some
promise in fighting viruses. Much more research is needed in this area; however.
I. Viroids-infectious, noncoding RNA that causes some plant illnesses. These can damage
commercial crops.
II. BACTERIA
A. These are classified as living organisms because they exhibit all of the characteristics of living
things.
B. Bacterial Cell Structure
1. Recall that bacteria are prokaryotic, so they have very simple cells.
2. The major parts of a bacterial cell include the following:
a. Cell wall composed of
b. A nucleoid-
c. Ribosomesd. Some bacteria contain plasmids and flagella.
C. Bacteria can be classified based on a variety of factors, including their cell shape. Cell shapes
in bacteria include:
1. Spirillum
2. Bacilli
3. Cocci
D. Bacteria reproduce through several means, including binary fission and conjugation.
E. Remember that prokaryotic cells are classified into 2 domains: the archaea and the eubacteria.
1. The archaea are extremely simple and they usually occupy unique habitats. Whereas,
the eubacteria are often thought of as being more advanced.
F. Types of Archaea
1. Methanogens-found in anaerobic environments in swamps and marshes. They produce
methane as an end product of their metabolism.
2. Halophiles-require high salt concentrations for survival. Where would halophiles thrive?
3. Thermoacidophiles-thrive in extremely hot and acidic environments. Where might these
be found?
G. All other types of bacteria are classified as being in the Domain Eubacteria.
1. Cyanobacteria are classified in the Domain as well. This group of organisms includes:
a. Oscillatoria
b. Nostoc
2. Members of this Domain can be both helpful and harmful to human beings.
3. How are bacteria in this Domain helpful to humans?
a. They produce oxygen via photosynthesis.
b. They convert atmospheric nitrogen in useful forms of nitrogen
(Nitrogen Fixation)
4. Many of the bacteria in this group can cause illnesses in humans.
5. Some of the illnesses caused by bacteria in this Domain include:
a. Strep throat
b. Staph infection
c. Lyme disease
d. Botulism
e. Tetanus
f. The Plague
g. Syphilis, Gonorrhea, Chlamydia
h. Whooping cough
i. Acne
j. Anthrax
H. How are bacterial illnesses treated?
KINGDOM PROTISTA
I. GENERAL CHARACTERISTICS OF PROTISTS
A. They are all eukaryotic. This is the first Kingdom that exhibits eukaryotic cells.
B. Most Protists are unicellular but they can be filamentous and multicellular.
C. Most can move by means of cilia, flagella or pseudopodia.
D. They typically reproduce by asexual means but many Protists can reproduce sexually as well.
1. They can also form cysts which can lie dormant for years before developing into a new
protists.
E. They range from being plant-like to animal-like.
II. PROTISTS ARE CLASSIFIED INTO THREE MAJOR GROUPS:
A. Autotrophic Protists-includes the following groups:
1. Green algae (Phylum Chlorophyta)
2. Red algae (Phylum Rhodophyta)
3. Brown algae (Phylum Phaeophyta)
4. Diatoms (Phylum Bacillariophyta)
5. Dinoflagellates (Pyrrophyta)
6. Euglenoids (Phylum Euglenophyta)
B. Heterotrophs by Ingestion of Food Materials
1. Zooflagellates (Phylum Zoomastigophora)
2. Amoeba (Phylum Rhizopoda)
3. Foraminiferans (Phylum Foraminifera)
4. Radiolarians (Phylum Actinopoda)
5. Ciliates (Phylum Ciliophora)
6. Sporozoans (Phylum Apicomplexa)
7. Slime molds (Phylum Myxomycota and Phylum Acrasiomycota)
C. Heterotrophs by Absorption
1. Water molds (Phylum Oomycota)
III. PHYLUM CHLOROPHYTA-The Green Algae
A. Most members of this division are aquatic and all members of this group contain chloroplasts
and chlorophyll; therefore they are photosynthetic.
B. Types of Green Algae:
1. Chlamydomonas-aquatic, unicellular.
a. Move by means of flagella.
b. Contain a Pyrenoidc. They typically reproduce by asexual means but they can reproduce sexually
under certain conditions.
2. Volvox-aquatic, colonial organism. The cells that make up the colony are all
Chlamydomonas-like cells.
a. Reproduces asexually by daughter colony formation.
b. It can reproduce sexually under certain conditions.
3. Spirogyra-a filamentous green alga.
a. Contains a spiral-shaped chloroplast.
b. Reproduces asexually but it can reproduce sexually by means of a process
known as Conjugation. Steps in Conjugation:
4. Ulva-a multicellular, marine green algal specimen.
a. Reproduces sexually through a process known as Alternation of Generations.
1) This process is how complex land plants reproduce. This indicates that
Ulva is probably closely related to land plants.
5. Chara-a multicellular, freshwater green algal specimen.
a. It also reproduces via Alternation of Generations.
IV. PHYLUM RHODOPHYTA-The Red Algae
A. These are mostly multicellular and they tend to live in warm marine waters. There are a
few freshwater species.
B. Their color comes from an abundant supply of what major red pigment?
C. Interesting Points on Red Algae
1. Some forms of Red Algae have cell walls that are composed of calcium carbonate. These
algae can contribute to the formation of coral reefs.
2. Some Red Algae produce Agar, the compound used in many labs to grow bacteria.
3. Other Red Algae produce Carrageen, a compounds that used in processing chocolate
and certain cosmetics.
4. Porphyra-is grown as a food source in Japan. The reddish-brown wrappings around sushi
rolls is actually a layer of dried Porphyra.
V. PHYLUM PHAEOPHYTA-The Brown Algae
A. Brown algae are mostly multicellular and the majority of brown algae live in cool marine
habitats.
B. Brown algae are often referred to as seaweeds.
C. What pigment gives them their major typical brown color pattern?
D. Most brown algae exhibit an alternation of generations life cycle.
E. Examples of Brown algae:
1. Fucus
2. Macrocystis
3. Sargassum
VI. PHYLUM BACILLARIOPHYTA-The Diatoms
A. The diatoms are unicellular and they are found in both marine and freshwater environments.
B. The cell walls of diatoms are composed of silica, a compound that is also found in glass.
1. Silica can be used in cleansers as an abrasive.
C. Diatoms typically reproduce sexually; however, they can reproduce by sexual means under
certain conditions.
D. They contain the golden brown pigment fucoxanthin.
VII. PHYLUM PYRROPHYTA-The Dinoflagellates
A. These organisms are unicellular, enclosed by a cellulose cell wall and most members of this
Phylum contain 2 flagella.
B. These organisms can produce what are known as “blooms.” What are blooms?
C. Two species of Dinoflagellates can produce large red blooms in some ocean habitats. These
blooms are known as “Red Tides.”
1. The Dinoflagellates in Red Tides can produce a neurotoxin that kills fish. Humans who
eat shellfish that have been contaminated by these dinoflagellates can develop
Paralytic Shellfish Poisoning.
VIII. DIVISION EUGLENOPHYTA
A. Members of this Phylum are all unicellular, freshwater organisms.
B. Organisms in this Phylum are difficult to classify because some of them have a chloroplast and
some do not. Are they plants or animals?
C. All Euglenoids move by means of a flagellum.
D. They have a distinct eyespot. What is the function of this structure?
E. They reproduce asexually by simple cell division.
IX. PHYLUM ZOOMASTIGOPHORA-The Zooflagellates
A. These organisms are all colorless and most are parasitic. They move by means of flagella.
B. Organisms in this Phylum include:
1. Trypanosomes-these are transmitted to humans by the Tsetse Fly. What illness do these
organisms cause?
2. Giardia-is a major cause of diarrhea in humans. Humans contract this from drinking
freshwater that is infected with Giardia cysts.
X. PHYLUM RHIZOPODA-The Amoeboids
A. These live in a variety of different habitats.
B. All members of this Phylum move by means of pseudopodia. What are these structures?
C. These organisms phagocytize their food. What does this mean?
D. Entamoeba histolytica-causes amoebic dysentery.
XI. PHYLUM FORAMINIFERA
A. These are mostly marine organisms that are covered by a calcium carbonate shell known
as a test.
XII. PHYLUM CILIOPHORA-The Ciliates
A. These are mostly freshwater organisms and all members of this Phylum contain cilia. What are
the cilia used for?
B. Paramecium
1. Digests food through a gullet.
2. Reproduce asexually and sexually via conjugation.
XIII. PHYLUM APICOMPLEXA-The Sporozoans
A. Members of this Phylum are nonmotile parasites. These organisms form spores at some point
in their lives.
B. Organisms in this Phylum:
1. Pneumocystis carinii-causes a type of pneumonia that is most common in AIDS patients.
2. Plasmodium vivax-is the cause of one type of malaria. This organism is passed on to
humans by Anopheles mosquitoes.
3. Toxoplasma gondii-causes toxoplasmosis.
XIV. PHYLUM MYXOMYCOTA-The Plasmodial Slime Molds
A. These appear as a creeping glob of slime.
B. In their sexual reproduction, these slime molds produce fruiting bodies which release
reproductive spores.
XV. PHYLUM ACRASIOMYCOTA-The Cellular Slime Molds
A. These exists as collections of individual amoeboid-like cells.
B. These are most commonly found in soil where they feed on bacteria and yeasts.
XVI. PHYLUM OOMYCOTA-The Water Molds
A. These typically parasitize fish and decompose remains in freshwater habitats.
B. Phytopthora infestans-a well known water mold. What did this organism cause?