Download Microorganisms: Viruses

Microorganisms: Viruses
Key Concepts and Words
KEY CONCEPTS
VOCABULARY
virus
1. Viruses are microscopic, non-living particles that are composed of nucleic acid (either
DNA or RNA, but never both), proteins, and in some cases, lipids, which take one of three
basic shapes: polyhedral, helical, or complex, and can be classified as enveloped or naked
(non-enveloped).
virion
nucleic acid
deoxyribonucleic
acid (DNA)
ribonucleic acid
(RNA)
2. Viruses invade and reproduce inside living, or host cells and then destroy the host cells
in which they replicate.
protein
lipid
capsid
helical virus
polyhedral virus
3. Viruses cause such diseases and conditions as common colds, smallpox, influenza,
Ebola, warts, and acquired immune deficiency syndrome (AIDS).
enveloped virus
complex virus
viral genome
gene expression
bacteriophage
4. Microbiologists and epidemiologists continually study the causes, spread, and control of
viruses in an attempt to reduce the effects of viral spread among individuals, families, and
communities.
macrophage
immune system
vaccine
interferon
5. There are differences between viruses and bacteria, including their requirements for
growth and replication, the body’s primary immune system defenses against viral and
bacterial infections, and the effective treatments (i.e., viral drugs, vaccines, antibiotics) of
these infections.
RECOMMENDATIONS FOR CLASSROOM USE
While we encourage you to use as many or all of the articles and activities in this key, if your time is limited, refer to the
chart below to help you determine what is most important for you to cover with your students.
Recommended Article
Recommended
Science Activity
Key Concepts
Addressed
1. Definition, structure, and
function of viruses
Swine Flu: Worry Winds Down
1
1, 2, 3
2. Viral life cycle: attachment,
growth, and reproduction
Ewww! Don’t Touch That!
2
1, 2, 3
3. Mechanisms of virus spread
and infection outcomes
Ewww! Don’t Touch That!
3
1, 2, 3, 4
Topic
endemic
pandemic
epidemic
4. Epidemiology research
Don’t Want the Flu? Just Add
Water
4
1, 2, 3, 4
5. Viruses vs. pathogenic
bacteria; host defense
mechanisms and treatments
Tracking a Deadly Sickness
5
2, 3, 4, 5
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Ewww! Don’t Touch That!
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SCIENCE ACTIVITIES
Activity 1—(Key concepts 1, 2, 3): Achoo! Do your students know that the common cold is caused by a virus? Review or
introduce the fundamentals of viruses, including the fact that they are composed of nucleic acid (either DNA or RNA, but
never both), proteins, and in some cases, lipids. The DNA or RNA includes just enough instructions (genes) to direct its
host cell to make more viruses. Explain also that microbiologists describe viruses either by the types of organisms they
infect, whether they contain DNA or RNA, or according to their structure (shape and size). Viruses have three basic
shapes: polyhedral, helical, or complex. Their structure can be enveloped or naked (non-enveloped) and can remain
dormant for long periods before being reactivated by favorable conditions (e.g., reduced host defense or toxins), thereby
going from latent to productive infections. Finally, review the fact that viruses can attack animals (including humans),
plants, and even bacteria; the latter are called bacteriophages.
After reviewing basic concepts, divide students into pairs to select one or more viruses to learn their taxonomy, host,
genome, and morphology. Students can observe microscopic images of viruses online at The Big Picture Book of Viruses.
Additional virus photos can be found at Science Stock Photography.
VIDEO: Students can view Microbiology: Viruses and Virus Infected Cells (see Related Videos below).
Activity 2—(Key concepts 1, 2, 3): After completing Activity 1, instruct students to create a flow chart, 3D model, or poster
depicting the steps of the viral life cycle from the time a virus attaches to a host cell until it destroys its host and moves on
to infect new cells. Students should include the following main steps and additional, interim events (not outlined in detail
here):
a)
b)
c)
d)
e)
f)
Attachment: the virus attaches to specific receptors on the host cell
Entry: the virus secretes chemicals to weaken the host cell wall and injects either DNA or RNA. (Entry looks
different for enveloped and naked viruses.)
Replication: the virus begins to replicate itself inside the host cell
Assembly (or Maturation): the host cell aids the virus in “assembling” and filling the cell with the virus
Release: the virus releases enzymes that digest the host cell wall (a different process for enveloped and naked
viruses)
Reinfection: after “digesting” the host cell wall, the new virus particles continue to infect new cells and the entire
cycle repeats
VIDEO: Students can view Microbiology: Viruses, Virus Infected Cells, How Flu Viruses Attack, and Understanding Virus
Mutations (see Related Videos below).
Activity 3—(Key concepts 1, 2, 3, 4): To help students understand how a cold virus can spread so rapidly, conduct the
following simulation with the whole class.
[NOTE: This activity is adapted from a popular HIV-education simulation done in health and science classes nationwide to
teach about the spread of sexually-transmitted diseases. Although this activity is focused solely on the spread of a cold
virus, teachers of older students may wish to extend the discussion into lessons specific to HIV and other sexually
transmitted viruses.]
Teacher Prep prior to starting the simulation:
a) Fill paper or plastic drinking cups—one for each student, minus one—about 1/4 full of distilled water. Have
available one eye dropper per student.
b) In a glass, mix 1/2 teaspoon of sodium carbonate (washing soda, available in grocery stores’ laundry aisles)
with 1/2 cup of water. Stir until dissolved and the liquid is clear. Pour 1/4 cup of the mixture into one of the
drinking cups you will distribute to students. [NOTE: Remember which student received this doctored cup, but
do not tell this student that he/she has something other than water.]
c) Have on hand about 5mL solution of phenolphthalein (a pH indicator), readily available at school science supply
outlets.
Conduct the simulation with students:
a) Distribute one cup (with pre-filled water) and one dropper to each student. Give your secretly selected student
the cup containing the sodium carbonate solution.
b) Instruct students to move around the room for about 4 minutes, mingling with one another and using their
droppers to exchange fluid with at least 3 people, one at a time. They do this by putting about 1/2 a dropper-full
of liquid into their classmates cup and vice-versa. SAFETY NOTE: Advise students they are never to ingest any
of the liquid at any time.
c) When done, collect droppers and then have students return to their seats with cups in hand.
d) Explain to students that they just simulated the spread of the common cold—a virus spreads when an infected
person coughs or sneezes, causing small droplets of infected saliva to be suspended in the air and inhaled by
others. Viruses can also be spread through sharing the same utensils or glasses if the airborne droplets have
landed on those as well.
e) Tell students that one person had the simulated cold virus to begin with and you’re the only one who knows who
it was. Explain that you gave one student a cup with sodium carbonate in water that made the solution
sufficiently alkaline so that phenolphthalein (an indicator of solutions with pH of 8 or higher) turns pink when it
touches an alkaline solution.
f)
One by one, have each student come to you, as you drop the pH indictor into their cups. If the fluid turns a pink
color, it indicates they were infected by the virus. If it stays clear, they did not come in contact with the virus.
g) Extend the activity by having students take on the role of epidemiologists, trying to find “ground zero” or the
person who had the initial virus. Students will need to backtrack, if they can, remembering who exchanged
fluids with whom and in what order.
h) Culminate the activity by discussing ways to avoid exposure and prevent cold (and flu) virus transmission.
VIDEO: Students can watch Virus Infected Cells, How Flu Viruses Attack, and Virus Crisis (see Related Videos below).
Activity 4—(Key concepts 2, 3, 4, 5): The spread of viruses can negatively affect local, national, and international
communities in multiple ways. Scientists work diligently to learn about virus mutations, spread, and potential eradication.
Scientists have long known that the flu virus spreads more rapidly in dry air. But they’ve just recently determined that
when humidity levels are low, the flu virus spreads more easily. Air temperature doesn’t matter when it comes to flu
survival or spread. Have students compare relative and absolute humidity and learn how humidity is expressed. Then
have students measure and record the humidity in the air by making a hygrometer. Keep a weekly record of
measurements, compare and contrast relative and absolute humidity, and graph the data. Students may also wish to
compare humidity readings inside and outside the classroom. Is there a notable difference? Why or why not? Would a
virus have a better chance of attaching and replicating in a host cell inside or outside their classroom? Why? Students
may wish to use Scientific Method to organize and analyze their data.
VIDEO: Students can watch Microbiology: Viruses, Virus Infected Cells, and Virus Crisis (see Related Videos below).
Activity 5—(Key concepts 2, 3, 4, 5): People commonly confuse viruses and pathogenic bacteria, not knowing which is
making us sick. Have students compare and contrast strains of viruses and pathogenic bacteria. Students should
investigate such things as size, survival methods (e.g., viruses need a host while bacteria do not), reproduction, and
methods of eradication (e.g., antibiotics can kill bacteria only; vaccines and antiviral drugs can fight some viruses). (See
Microbiology: Bacteria Key—in Teacher Resources—for lessons about bacteria.)
Next, have students learn how the human body keeps invading pathogens at bay. Investigate the ways that our skin,
mouths, stomachs, and breathing passages act as barriers, and how the body’s immune system triggers inflammatory
responses. Students should investigate ways that large white blood cells, called macrophages, respond by wrapping
around invading viruses to digest, or eradicate them, or secrete chemical messengers into the bloodstream to signal
helper T cells to fight the virus. Further, students can investigate the flu vaccine and nasal spray that helps protect people
from the flu by working together with the immune system to help create antibodies (cells that fight viruses). Culminate the
activity by having students write a comprehensive flu prevention and treatment plan to share with peers.
VIDEO: Students can watch Microbiology: Viruses and How Your Immune System Works (See Related Videos below).
CROSS-CURRICULAR EXTENSIONS
Social Studies/Geography: Have students investigate the historic 1918 influenza pandemic, as well as other historic
virus outbreaks (e.g., Ebola, HIV, hantavirus, swine flu). Create a class timeline to show when and where the outbreaks
occurred and how long each lasted. Have students identify the spread of each on a world map, and summarize the
medical, social, economic, and political ways in which each affected the individuals and communities that were infected.
Geography/Math: Students can track the spread of the recent H1NI (swine flu) outbreak and then graph the data from the
maps. Compare and contrast the flu’s spread in the U.S. and in other countries. Create standard bar, line, or pie graphs to
display, analyze, and discuss data. What is the latest trend in the flu spread? Is it slowing or increasing?
Vocabulary: Learn the etymologies (origin or derivation of words) and meanings of the terms endemic, epidemic, and
pandemic. Identify each virus discussed during all class activities as epidemic, pandemic, or endemic, and give examples
of each (e.g., malaria and measles are endemic diseases, while AIDS in Africa has reached epidemic proportions). Have
students learn common Latin and Greek root words that appear throughout studies in microbiology. Look at the article for
examples. Create a class chart showing root words, their meanings, and examples of modern English words derived from
them. Keep this as an ongoing, year-long chart that students update regularly.
Careers: Invite students to learn about the careers of people who study viruses, including epidemiologists,
microbiologists, virologists, and immunologists. What special protective measures do such professionals have to take
when working with viruses, bacteria, and other potentially dangerous microbes in the lab or in the field? What are the
educational and training requirements for such careers?
WRITING ASSESSMENT
Assess students’ understanding of the core science concepts addressed by having them write a detailed response to the
following:
Explain which of the following may one day become a cure for the common cold and tell why: a new antibiotic, a
vaccine made from a cold virus, a humid location, and a new type of cough syrup.
Also explain which ones would not be able to cure a cold.
For the Teacher: Students’ answer will vary, but should include some discussion that only a vaccine could potentially
eradicate a virus. Humidity would slow the spread, although it wouldn’t cure a virus that has already infected someone.
Antibiotics only kill bacteria and cough syrup only treats symptoms so they would be useless in the effort to rid the body of
a virus.
RELATED WEB SITES
Virology
The Microbial World
Microbe World
American Museum of Natural History: Epidemic! The World of Infectious Disease
Microbiology On-Line: Virology
Centers for Disease Control: Seasonal Flu
Centers for Disease Control: H1N1 Flu
Centers for Disease Control: West Nile Virus
Pandemic Flu
World Health Organization: Pandemic Preparedness
The Great Pandemic: The U.S. in 1918-1919
RELATED VIDEOS
Virus Infected Cells
Microbiology: Viruses
How Flu Viruses Attack
Virus Crisis
Understanding Virus Mutations
How Your Immune System Works
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