Download Mission Debriefing for a science class and bacteria

MISSION DEBRIEFING: Teacher Guide
Activity 2: Gummy Germs
In this activity, the students will compare and contrast
viruses and bacteria as to size, structure, and method of
reproduction.
Background
Most people are familiar with the term virus and the term bacterium. For one thing, these agents
cause most of the infectious diseases that people get. Few people, however, know how these two
types of infectious agent differ. Viruses and bacteria are unlike in many ways including:
Size
Bacteria range in size from 0.1 to 10 micrometers (µm). A micrometer is only one millionth of a
meter. Viruses are much smaller than bacteria. Most are between 0.02 and 0.3 µm in size.
Structure
As a prokaryotic cell, a bacterium lacks many of the internal structures found in the cells of
higher organisms. Typically, a bacterium has a rigid, outer cell wall. Just beneath the cell wall is
the cell membrane, which surrounds the fluid or cytoplasm of the cell. Embedded in the
cytoplasm are protein synthesizing bodies known as ribosomes, a chromosome of genetic
material (DNA) with instructions to duplicate the cell, and plasmid DNA that has genes that
confer on the bacterium special properties.
Unlike a bacterium, a virus is not a cell. A typical virus is composed of genetic material (DNA
or RNA) surrounded by a protein coat called a capsid. Some viruses have a structure outside of
capsid called an envelope that is formed from the membrane of the cell the virus infects.
Method of Reproduction
Bacteria and viruses differ in their method of reproduction in one very important way. Bacteria
can reproduce by themselves and viruses cannot. Bacteria reproduce by a method called binary
fission, a process in which one bacterial cell divides into two identical daughter cells. Viruses,
on the other hand, must invade a living cell (host) and use the cell’s machinery to duplicate its
genetic material, synthesize proteins and package the newly made viruses for release into the
surrounding environment.
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MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING: Teacher Guide
Gummy Germs
Learning Objectives
The student will:
1. distinguish between a virus and a bacterium on the basis of size, structure and method of
reproduction.
2. create an edible model of a virus and a bacterium.
Materials
1. Gummy Germs Student Activity Sheets:
A. Gummy Germs: Bacterium Structure
B. Gummy Germs: Virus Structure
C. Gummy Germs: Discussion Questions
2. package of gelatin (must make a gelatin that is clear enough to see through)
3. clean plastic freezer bags (not too stiff so you can shape bag).
4. candies and other foods to represent cell structures. Suggested candies are:
A. three different colors of Fruit Roll-ups ® (cell wall, cell membrane, virus capsid)
B. licorice (flagellum)
C. gummy worms(chromosome)
D. gummy ring candies (plasmid DNA)
E. round candies such as SKITTLES® (ribosomes)
F. gum drops or candy corns (virus spikes)
5. small and large containers
6. Knives or other straight edges
7. computers with Internet access or reference books on bacteria and viruses.
Procedure
Note: this activity is designed to produce bacterium and virus models in a size ratio of 5:1. The
difference in size between the largest bacterium and the smallest virus is greater than this ratio.
1.
2.
3.
4.
Review with the class the differences between a bacterium and a virus.
Split the class into groups of four or more, and then have the students wash their hands.
Give each group one package of gelatin and the other modeling materials.
Instruct the students to add enough gelatin to a freezer bag to make a small virus
(approximately one inch in diameter). They should make up the gelatin according to the
manufacturer’s instructions, and then place the bag in the small container.
5. To a second bag, have the students add enough gelatin to make a bacterium with a
diameter five times the size of the virus (approximately five inches,) and make it up
according to the manufacturer’s instructions. Next, they should place the bag in the large
container.
6. Have the students add the internal parts of each germ to the bags.
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MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING: Teacher Guide
7. For the bacterium add:
• Chromosome (gummy worm) – place it in the center of the bag.
• Plasmid DNA (gummy ring candy) – spread 2 or more spread throughout the bag.
• Ribosomes (round candies) - 10 or more spread through out the bag.
For the virus add:
• Genetic material (small pieces of gummy worm) – place it in center of the bag.
8. Seal each bag with a twist tie, and allow the molds to solidify in a refrigerator.
9. After they have become solid, remove the molds from the bags.
10. Have the student choose the colors of Fruit Roll-ups ® they would like to designate as
cell membrane, cell wall, and capsid.
11. Tell the students to wrap the bacterium model with the food for the cell membrane and
then the one for cell wall. Have them insert the licorice (flagellum) into one end of the
model.
12. Next, the student should wrap the virus model with the capsid Fruit Roll-ups ®. Note:
If you wish the student can add an envelope to the virus by wrapping the model with
the Fruit Roll-ups ® designated for the cell membrane of the bacterium.
13. Layer the outer surface of the virus with the spikes (gum drops or candy corn). Students
can then cut each model in half with a knife or other straight edge to see it in cross
section.
14. Direct the students to complete the Gummy Germs: Discussion Questions Student
Activity Sheet using bacterium and virus reference books or Internet resources. Have
student discuss their findings in class.
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MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING: Teacher Guide
Gummy Germs
Extension Activities
•
•
•
Science: Compare and contrast the structures of a prokaryotic and eukaryotic cell. Make
an edible model of each cell type.
History: Research the origin of mitochondria in relation to prokaryotic cells.
Health: Research how anti-viral and anti-bacterial drugs work.
Standards
National Science Education Standards, Grades 5-8
• Science Content Standard A: All students should develop abilities necessary to do
scientific inquiry.
• Science Content Standard C: All students should develop understanding of structure and
function in living systems.
• Science Content Standard C: All students should develop understanding of diversity and
adaptations of organisms.
Books
•
•
Ward, B. 2000. Eyewitness Book: Epidemics. New York: Doring Kindersley.
Snedden, R. 2000. A World of Microorganisms. Chicago: Heinemann Library.
Web Site
•
•
•
Stalking the Mysterious Microbe
http://www.microbe.org/
CELLS Alive!
http://www.cellsalive.com/
The Bad Bug Book
http://vm.cfsan.fda.gov/~mow/intro.html
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MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING:
Student Activity Sheet
Gummy Germs
Bacterium Structure
plasmid DNA:
This genetic material is a small
piece of circular DNA. It is
instrumental in the passing on of
special properties, such as
antibiotic resistance.
cell wall:
The cell wall gives the
bacterium its shape,
protects the inside of the
cell from the environment,
and helps to anchor the
flagellum. It also keeps the
cell from bursting in certain
environments.
chromosomal DNA:
This genetic material is large,
circular DNA and contains the
information required to make a
new bacterium.
ribosome:
Ribosomes are protein
synthesizing bodies.
Unlike the ones found in
“true” cells, bacterial
ribosomes are
freestanding structures
found throughout the
cytoplasm.
cell membrane:
This thin layer closest to the
cytoplasm regulates the flow
of material in and out of the
cell.
cytoplasm:
This gel-like matrix
is where functions
such as growth,
metabolism and
replication take
place.
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flagellum:
Some bacteria have flagella
(flagellum singular), which
are hair-like structures used
for locomotion.
MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING:
Student Activity Sheet
Gummy Germs
Virus Structure
genetic material:
Information required to make a new virus is contained in either DNA or RNA.
There can be as few as four to seven genes or as many as 200 genes in viral
genetic material. Some of these genes code for proteins that restrict the host cell
from making anything but viral proteins.
Animal
Virus
capsid (in yellow):
It is the protein coat of a virus. It
protects the virus and helps it attach
to a host cell.
envelope (in blue):
Many viruses have an envelope after they
have infected a host cell. As the virus
leaves, it takes with it the host cell
membrane, which becomes the envelope.
A virus without an envelope is called a
“naked virus.”
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spikes (in red):
An interesting feature of a virus is its
spikes. There are different types of spikes,
and they have different functions. Some
enable the virus to attach to the host cell.
Others are involved in injecting genetic
material, and some are used to help the
virus exit the host cell.
MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING:
Student Activity Sheet
Gummy Germs
In this activity, you will compare and contrast a virus and a
bacterium based on size, structure and method of reproduction.
Then you will create models of a virus and a bacterium that you
can eat.
Materials
1.
2.
3.
4.
Gummy Germs Student Activity Sheets
package of gelatin
clean plastic freezer bags
candies and other foods to represent cell structures. Candies are:
A. three different colors of Fruit Roll-ups ® (cell wall, cell membrane, virus capsid)
B. licorice (flagellum)
C. gummy worms(chromosome)
D. gummy ring candies (plasmid DNA)
E. round candies such as SKITTLES® (ribosomes)
F. gum drops or candy corns (virus spikes)
5. a small and a large container
6. knife or other straight edge
7. computer with Internet access or reference books on bacteria and viruses
Procedure
WASH YOUR HANDS BEFORE STARTING.
1.
2.
3.
5.
6.
Add enough gelatin to one freezer bag to make a small virus (approximately 1 inch in
diameter).
Add enough gelatin to a second bag to make a bacterium with a diameter five times the
size of the virus.
Make up the gelatin according to manufacturer’s directions.
4.
Place the virus bag in the small container and place the bacterium
bag in the large container.
Add the internal parts of each germ:
For the bacterium:
• Chromosome (gummy worm) – place it in the center of the bag.
• Plasmid DNA (gummy ring candies) – spread two or more spread throughout the
bag.
• Ribosomes (round candies) - 10 or more spread through out the bag
For the virus:
• Genetic Material (small pieces of gummy worm) – place it in center of the bag.
Seal each bag with a twist tie and allow the molds to solidify in a refrigerator.
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MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING:
7.
8.
9.
10.
11.
12.
Student Activity Sheet
After they have become solid, remove the molds from the bags.
Choose the colors of the Fruit Roll-ups ® you would like to be the cell membrane and
cell wall of the bacterium and the capsid of the virus.
Wrap the bacterium model with the Fruit Roll-ups ® for the cell membrane and then the
one for cell wall. If you want your bacterium to have a have flagellum, insert the licorice
into one end of the model.
Wrap the virus model with the capsid Fruit Roll-ups ®. Note: If you wish the virus to
have an envelope, wrap some of the Fruit Roll-ups ®that you used for the bacterium’s
cell membrane around the capsid layer.
Layer the outer surface of the virus with the spikes (gum drops or candy corn). Cut each
model in half with a knife or other straight edge to see it in cross section.
Complete the Gummy Germs: Discussion Questions Student Activity Sheet using
bacterium and virus reference books or Internet resources. Discuss your findings with the
class.
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MISSION THREE: NEMESIS IN NEUROPOLIS
MISSION DEBRIEFING:
Student Activity Sheet
______
Name______________________ Class_________ Date
Gummy Germs
Discussion
1. A virus is much smaller than a bacterium. What advantages do you think size gives a
virus over a bacterium?
2. A bacterium has many structures that a virus does not. What are the advantages of having
so many different parts?
3. Find information about the structures of viruses not covered in the Gummy Germs
activity. List these structures and their functions.
4. Find information about the structures of bacteria not covered in the Gummy Germs
activity. List these structures and their functions
5. What advantage does having a flagellum give a bacterium?
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MISSION THREE: NEMESIS IN NEUROPOLIS