STRAND: Interactions Within Ecosystems
LESSON SUBJECT: Viruses in Our Environment
LEARNING OBJECTIVE:
Students will understand:
• the basic parts of a virus
• basic factors of virus reproduction
• the virus as a non-living particle
• how viruses are spread
• factors affecting the rate of virus proliferation
• prevention and safety to decrease the incidence of virus infections
TIME REQUIRED:
60 minutes
PURPOSE:
To explore the relevance and impact of viruses within our environment.
HYPOTHESIS:
Ask the children what they think the outcome will be and why.
MATERIALS:
• Empty film canisters
• Flour
• Vinegar
• Paper for note taking
• Baking Soda
METHOD:
Teachers are to fill most of the film canisters with flour. For a class 24 students fill 3 half
way with baking soda. Fill the remaining 21 canisters with flour. On the bottom of the
baking soda canisters write the number 1. Number the bottom of the other canisters from
2-4.
1) Students are instructed to write down the name of two other students in the room.
2) The instructor will go around the classroom with a small box full of the canisters.
Each child will select a canister from the box.
3) Tell the students that some of them have just “contacted a virus”. They have not
been diagnosed, so they don’t know they’ve been infected. They are going to go
to a “party” and “share their drink” with the two people on their list. If someone
comes to them to “share” they must share and can not decline.
4) Students are to go in order to each name on their list and share their powder. They
do this by pouring all the powder from one canister into the other, shaking it
thoroughly, and then evenly pouring it back into both canisters, dividing it.
5) Students will write down the order of the student with whom they exchanged
powder.
6) Once everyone has exchanged powders, the instructor will pour vinegar into each
student’s canister. Where baking soda is present the powder will foam. This will
reveal who has been infected with the virus.
Preparation Reading
Viruses
In its simplest form, a virus is a capsule that contains genetic material — DNA or RNA. Viruses are even
tinier than bacteria. To see them, scientists must use an electron microscope, a high-powered instrument
that produces enlarged images of minute objects. To put their size into perspective, consider that, according
to the American Society for Microbiology, if you were to enlarge an average virus to the size of a baseball,
the average bacterium would be about the size of the pitcher's mound. And just one of your body's millions
of cells would be the size of the entire ballpark.
The main mission of a virus is to reproduce. However, unlike bacteria, viruses aren't self-sufficient — they
need a suitable host to reproduce. When a virus invades your body, it enters some of your cells and takes
over, instructing these host cells to manufacture what it needs for reproduction. Host cells are eventually
destroyed during this process. Polio, AIDS and the common cold are all viral illnesses.
Viruses don't have to be alive to move from cell to cell and from host to host. Within our
bodies, they travel in blood and lymph. Outside, they ride in air, water, food, or other
animals. Some bacteria have no means of moving, either, but they get around in some of
these same ways.
2c. Are Viruses Alive?
Are viruses alive?
Anyone with a cold or the flu virus feels as
if they are under attack by some organism.
But in the scientific community it's still an
open-ended question. This is why viruses
do not belong to a kingdom of living things.
Just because a virus seems alive doesn't
mean it is alive. After all, it's not even a
HIV attacks the immune system's helper T cells.
single-celled organism.
A virus is little more than a strand of DNA or RNA covered by a protein coating.
Viruses are a thousand times smaller than bacteria and come in a wide range of
shapes. Some look like weird, tall spiders whereas others look like prickly
porcupine like soccer balls.
One thing is for sure; viruses are very much a part of life on Earth and the human
experience. Viruses infect animals, plants, and even bacteria. Humans are in a
constant battle with viruses. HIV (the virus that causes AIDS), the Ebola virus,
and the West Nile virus continue to make headlines and take millions of lives.
Other maladies, such as colds, the flu, chicken pox, measles, and hepatitis, are
more common, but sometimes just as deadly. Symptoms vary depending on
which kind of cell is under attack. Cold viruses attack the nose and throat, the
rabies virus attacks the brain and nervous system, and the human
immunodeficiency virus (HIV) attacks white blood cells in the bloodstream.
Viruses can even cause some kinds of cancers and leukemia.
Live and Let Die
To determine whether a virus is alive or not, we could compare the virus's
characteristics to what many biologists consider the requirements of life. All living
things have several common characteristics. Some nonliving things may have
one or more of the characteristics but not all of them. For a virus then to be
classified as alive it must:
•
•
•
•
Reproduce
Obtain and use energy
Grow, develop, and die
Respond to the environment
Viruses do have DNA or RNA, and DNA is
the code for life. Having genetic material is
an important step towards being classified
as alive. DNA controls the evolution of the
cell and the organism. Like living things,
viruses evolve through time and thus can
adapt to their environment. But unlike cells,
viruses cannot use their genetic material by
themselves. They need a living cell in order
to function and reproduce; otherwise they
are playing dead.
Resistance Is Futile
This may look like a space capsule, but it's
actually a virus. The top part is the capsid, the
body is the sheath, and the tails at the bottom
help the virus attach to its host.
Because viruses are not cells, they can't
divide by binary fission like bacteria. Yet
they do reproduce themselves in an
extraordinary way. Their structure enables
viruses to attack a plant or animal cell called a HOST CELL. The protein shell
protecting the virus's DNA is covered with spike like protrusions. These spikes
allow the virus to latch onto the cells they infect. Once hooked on, the virus
injects its genetic material into the host cell.
The virus's DNA takes control of the cell once it's
within the cytoplasm and begins to make the cell
produce virus DNA and other parts of viruses. The
host cell is forced to expend all of its energy and
resources to help the virus replicate and make
hundreds more viruses. The poor, weak cell usually
bursts like an over inflated balloon from all the
viruses and is destroyed in the process. Then, the
replicated virus attaches itself to a new, unaffected
host cell, and the viral infection continues.
An animation of a virus infecting a
host cell.
Living things do more than just reproduce. They
also must obtain food to fuel the cell's metabolic
activity. Some organisms, such as animals, eat other living things for energy.
Other organisms, such as plants, harness the Sun's energy to make their own
food. Because viruses aren't cells and have no activity within it, it has no need for
food. However, the virus-controlled host cell needs material and energy to
reproduce the viruses. Maybe viruses can fit the requirement that life forms need
to obtain and use energy.
All other living things also grow or get bigger. A virus does nothing inside its
protein coat; therefore it does not grow. But some scientists argue that a virus's
growth occurs inside the host cell where parts of viruses are built during
reproduction.
Plants and animals react to the environment. All living things have ways of
sensing the world around them and can respond to changes in their environment.
Do viruses react? Viruses cannot move themselves, but there are some
differences in opinion that viruses do react to changes in the environment.
Remember, the virus's DNA or RNA can evolve over time, thereby increasing its
chances for survival and adapting to the environment. Like bacteria, they adapt
through genetic mutations caused by rapid reproduction. That is why it is so hard
to cure viral diseases. Viruses keep changing their DNA and protein coat to
further their "life form" and keep ahead of the game.
Definition of Viruses
Viruses are very small, infectious, obligate intracellular molecular parasites, which do not
respire, move or grow. The virus genome is composed either of DNA or RNA and directs
the viral replication by the synthesis of virion components within an appropriate host cell.
Progeny viruses are formed by de novo assembly from newly synthesized components
within the host cell.
Similar Particles
Viroids are small (200-400nt), circular RNA molecules with a rod-like secondary
structure which possess no capsid or envelope which are associated with certain plant
diseases. Their replication strategies like that of viruses - they are obligate intracellular
parasites.
Virusoids are satellite, viroid-like molecules, somewhat larger than viroids (e.g.
approximately 1000nt) which are dependent on the presence of virus replication for
multiplication (hence 'satellite'), they are packaged into virus capsids as passengers.
Prions are rather ill-defined infectious agents believed to consist of a single type of
protein molecule with no nucleic acid component. Confusion arises from the fact that the
prion protein & the gene which encodes it are also found in normal 'uninfected' cells.
These agents are associated with diseases such as Creutzfeldt-Jakob disease in humans,
scrapie in sheep & bovine spongiform encephalopathy (BSE) in cattle.
Origines of Viruses
Viral infections in the old Egypt
One of the first written records of a virus infection consists of a heiroglyph from
Memphis, the capital of ancient Egypt, drawn in approximately 1400 B.C, which depicts
Siptah. After a short rule of three years of his father Amenmesse, who seized the throne
of Egypt from the previous Pharaoh Seti II, Siptah became the seventh Egyptian king of
the 19th dynasty, ruling for about six and a half years (from 1199 to 1192 B.C). Judging
from his mummy, he died at about 20 years of age. The body’s deformed left leg suggests
that Siptah suffered from aneuromuscular disease (poliomyelitis).
At some time during the 21st dynasty, Siptah’s sarcophagus and
mummy were placed in Amenophis II’s tomb. The funeral temple
itself, situated on the edges of the area’s fertile land, was never
completed.
A photo of the unwrapped mummy of Ramses V, Egyptian
pharaoh from 1147 to1143 BC, shows pockmarks from the
smallpox virus that attacked and probably killed Egypt's ruler,
who died around 1151 B.C.