Video: Understanding Viruses
Answer the following questions as you are watching the video.
1. In the video, viruses are called the simplest form of life on Earth”
a)What makes viruses seem like living organisms?
Viruses can reproduce themselves only if they enter and control a host cell. Viruses
contain either DNA or RNA.
b)What characteristics distinguish them from living organisms?
Viruses do not have their own reproductive machinery. They need to control a host cell to
reproduce themselves. They do not contain organelles, or cytoplasm. They have no
ability to make or store energy.
2. Why weren’t viruses “discovered” until the 1930’s?
Viruses were too small to be seen by traditional light microscopes. The electron
microscope was developed during the 1930’s, which improved the magnification of the
image.
3. The 1918 influenza epidemic killed at least 20 million people worldwide. What are the
factors that led to it being such a large epidemic?
At the end of the First World War, troops returning from the battlefield in France carried
the virus around the world. The way that viruses were transferred between people was
unknown, so measures people took to protect themselves (face masks) were ineffective.
20 million people died of the epidemic, but 1 in 5 people contracted the disease. Most
deaths occurred within days of contracting the disease.
4. Edward Jenner developed the first vaccine, a vaccine for small pox. Describe how he
developed the vaccine and what was a bit controversial (and ethically questionable) about
his research?
Cowpox and small pox are very similar viruses. Cowpox virus is a much milder version
of the deadly disfiguring small pox virus. Jenner noticed that milk maids did not usually
contract small pox and associated the irregularity with the fact that milk maids must
become immune to small pox after they contract cow pox virus while working closely with
cows. Jenner injected his infant son with cow pox virus as a vaccine against small pox.
His son got sick but then recovered. Later he injected his son with live small pox virus.
No small pox developed in his son.
5. When your immune system responds to a foreign substance such as a virus, many
types of cells are involved. What do the following 3 types of cells do during the immune
response?
a) antibodies:
Antibodies are proteins. They identify and neutralize foreign invaders like
bacteria and viruses. Each antibody targets an antigen present on the invading organism. This
antigen is like a key that helps the antibody identify the organism. The antibody acts by
tagging or neutralizing its target.
b) white blood cells: Many types of cells destroy virus-infected cells.
c) memory cells: Immediately recognize future invaders quickly mobilizing an immune
response
6. Why are flu strains used to develop the flu vaccine often grown in chicken embryos?
When viruses are developed inside an unnatural host, they are too weak to cause disease,
but strong enough to cause immunity. Chicken embryos are in ready supply and can be
used to quickly produce large amounts of vaccine.
7. What is the difficulty with developing vaccines for RNA viruses? Give an example of
a common RNA virus.
RNA viruses change ftequently. New vaccines need to be developed. Swine flu, Asian flu,
Influenza and AIDS are all RNA viruses.
8. What was unique about the polio vaccine, developed by Jonas Salk in the late 1940’s?
Salk killed the virus with formaldehyde and injected it into people. The dead virus
altered their immune system without infection.
9. In 1967, the World Health Organization decided to eliminate small pox from the
world. How did they manage to accomplish this by 1978?
Health care workers immunized everyone everywhere, breaking the chain of infection.
Small Pox has no other hosts other than humans.
10. At a research centre in Moscow and the Centre for Disease Control (CDC) in Atlanta
samples of small pox (as well as many other viruses) are kept in freezers. There are
contrasting viewpoints o maintaining such a collection of viruses.
“We didn’t want to totally eliminate the virus small pox because we didn’t really
understand the virus and what made it tick. It’s part of the whole basic fundamental
argument about diversity-biological diversity. Can we afford to lose these organisms
that have established themselves in a particular ecological niche?”
“But the greater danger is the possibility of smallpox escaping from a freezer somewhere
where there might be a forgotten stock stored for years form now when people have
forgotten about it.”
What is your opinion and why?
(Depends on individual’s viewpoint)
11. What are some characteristics of the AIDS virus that make it so difficult to develop a
vaccine for?
They mutate very quickly.