Name___________________ Viruses
Read, annotate, and answer all the questions
completely.
A virus is a tiny, nonliving particle that enters and
then reproduces inside a living cell. Biologists
consider viruses to be nonliving because viruses
are not cells. Viruses do not use energy to grow or
to respond to their surroundings. They cannot
reproduce on their own.
Viruses can only multiply when they are inside a living cell. They can attack
all organisms. The organism that a virus enters and multiplies inside is called a
host. A host is an organism that provides a source of energy for a virus or
another organism. Organisms that live on or in a host and cause harm to the host
are called parasites. Most viruses are like parasites because they destroy the
cells in which they multiply.
1. Why do biologists consider viruses to be nonliving? (Give a complete answer.)
__Viruses are not cells , they do use energy, grow, respond to their environment, or
reproduce on their own___________
2. True or false? Viruses multiply the same way as other organisms.
3. Circle the name of a living thing that provides energy for a virus or an organism.
a. parasite
b. host
c. bacteriophage
d. particle
4. Viruses act like __parasites____because they destroy the cells in which they multiply.
Viruses vary in shape and size. Viruses can be
round, or rod-shaped, or shaped like bricks,
threads, or bullets. (See picture on top of
page.)The shape of the virus determines what
cells it can attack because the virus needs to
fit on the cell just right. Some viruses,
including the bacteriophage, have complex, robot like shapes. (A bacteriophage is
a virus that infects bacteria.) But viruses can attack any living organism, such as
plants, animals, bacteria, and computers. No, wait, computers aren’t living! 
Viruses are much smaller than cells. They are smaller than bacteria. They
are measured in nanometers, which is one billionth of a meter. Scientists may
name a virus after the disease it causes, the organisms they infect, the
scientists who first identified it, or the place where it was first found,
i.e. the West Nile virus.
5. What shapes do viruses come in? _various-rods, cylinders, spheres, spacecraft_____
6. What organisms can viruses infect? ___all-plant, animal, even bacteria________
7. A virus that infects bacteria is called a(n) ___bacteriophage____________
8. True or false? Viruses are larger than bacteria.
9. How are viruses named? _______after the disease it causes, or the organism it affects,
or who first identified it, or place it was found______________________
All viruses have two basic parts: a protein coat
called a capsid that protects the virus and an inner core
made of genetic material. Some viruses are
surrounded by an additional membrane envelope. Each
virus contains unique proteins on its outer surface.
The capsid protects the virus and allows it to attach to, or lock onto,
only certain host cells.
13. What is the purpose of the capsids? __to protect the genetic material inside_____
14. True or false? Ant virus can attach itself to any living cell.
15. Label the two basic parts of a virus in this
diagram
After a virus attaches to a host cell, it
sends its genetic materials into it. An active
virus immediately takes over the cell's
functions. It instructs the cell to copy its DNA
and produce the virus's proteins and genetic
material. These proteins and genetic material
then assemble into new viruses in what is
called the lytic cycle. The lytic cycle
consists of the following steps: a. Attachment-the virus attaches to the cell;
b. Injection-it injects its genetic material; c. Production-the cell then
reproduces the virus’ material; d. Assembly-the parts assemble to make new
viruses, and lastly, when the cell is full of new viruses, e. Release-the host cell
bursts (lyses) open and releases the new viruses.
Infected cell with virus genetic material
When a hidden virus enters a host cell,
the virus's genetic material actually
becomes part of the cell's genetic
material. Each time the cell reproduces
itself, the virus parts are reproduced also.
The virus's genetic material may stay inactive for a long
time in the lysogenic cycle. Then for some unknown reason
it can start to assemble, just like in the lytic cycle, make new viruses until
the host cell bursts open and releases them. You see this with cold sores,
caused by a hidden herpes virus, that reoccur.
Match the kind of virus with the way it multiplies in a cell. Viruses may be used
more than once
_b___16. the lytic cycle
a. hidden virus
_a___17. the lysogenic cycle
b. active virus
_a__ 18. The virus stays inactive for a long time.
_b___19. The virus immediately begins to multiply after entering the cell.
_b___20. The virus's genetic material becomes part of the cell's genetic material
21. List the 5 steps of the lytic cycle.
a. __attachment__________b. __injection_________ c.___production_______
d.___assembly________ e. ____release (lyses)_____
Rabies is an example of a virus that affects animals. Trees
can be affected by them. Some of the diseases in humans
caused by viruses are ebola virus, AIDS, chickenpox, polio, and
smallpox. Vaccines are a way to limit the effects of some of the
diseases caused by viruses since they cannot be destroyed with
antibiotics. Vaccines contain some of the virus in a weakened
form so that the body can develop antibodies to fight the
disease should the person ever come in to full contact with it. Scientists have
developed antiviral drugs as well. However, unlike antibiotics, they do not kill
viruses; instead they inhibit their development by making it hard for them to
attach to a cell or by preventing them from injecting their genetic material.
Scientists are learning how to take
advantage of viruses’ ability to inject cells. If
the DNA in a cell has been damaged, it is
injected with a virus with good DNA and then
sent to the sick cell. Scientist are hoping that experimenting with gene
therapy will cure many diseases including cancer.
22. List some diseases humans caused by viruses? __flu, measles, mumps, aids, ebola, chickenpox,
polio_____
23. Name a virus that affects animals. ___rabies____
24. What is a vaccine? ___a form of the virus in a weakened or dead state that is injected
into the body to get the immune system to respond to it and develop antibodies_________
25. What is the purpose of getting a vaccine? _the immune system remember the disease so
that if it tries to attack the body it will not be successful_____________________
26. True or False? Antiviral drugs kill viruses that make us sick.
27. Scientists are using the virus’s ability to enter into a cell in __gene therapy__ to inject
good DNA to replace damaged DNA.