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Viruses and Bacteria
What is a Virus?
• A virus is a tiny, nonliving particle that enters
and reproduces inside a living cell.
• A virus is considered nonliving because they
do not have all the characteristics necessary
for life.
• What are the characteristics necessary for life?
What is a Virus?
• Viruses are not cells and do not have cells.
• Viruses also do not use their own energy to
grow or respond to their surroundings.
• Viruses cannot make or eat food and do not
produce waste.
What is a Virus?
• The only thing that makes a virus similar to an
organism is that it can multiply.
• Viruses multiply in a different way than
organisms do. They can only multiply when
they are inside a living cell.
What is a Virus?
• The organism that a virus enters and
multiplies inside of is called a host.
– The virus acts as a parasite, which is something
that lives in or on a host and causes it harm.
– Almost all viruses destroy the cells where they
multiply.
Virus Shape and Size
• Viruses can come in all different types of
shapes.
• Viruses also come in different sizes, but all
viruses are much, much smaller than even the
smallest cells.
– This makes viruses even smaller than bacteria.
Virus Structure
• Although viruses look different from each
other, they all have a similar structure.
• All viruses have two basic parts:
– A protein that protects the virus
– An inner core of genetic material
Virus Structure
• Each virus contains unique surface proteins
which allow the virus to attach to a host cell.
Active Viruses
• After entering a cell, an active virus’s genetic
material takes over cell functions.
• The cell quickly begins to produce the virus’s
proteins and genetic material.
• These parts then assemble into new viruses.
• When the cell is full, it bursts open, releasing
hundreds of new viruses as it dies.
Hidden Viruses
• After a hidden virus enters a host cell, its
genetic material becomes part of the cell’s
genetic material.
• Hidden viruses do not appear to affect the
cell’s functions and may stay inactive for many
years.
Hidden Viruses
• Each time the host cell with a hidden virus
divides, the virus’s genetic material is copied
along with the host’s genetic material.
• Under certain conditions, the virus then
becomes active.
Viruses and Disease
• Many diseases are caused by viral infections.
• Some of these diseases, like colds, are gone
after a short period of time, while others
never go away.
Gene Therapy
• In gene therapy, scientists inject genetic
material they want reproduced into a virus,
and then as the virus enters a host cell, the
cell reproduces that genetic material instead
of the virus.
Bacteria
• Bacteria were discovered by a Dutch merchant
named Anton van Leeuwenhoek.
• He made this discovery in the late 1600s when
he saw wormlike organisms in a sample he
was looking at under a microscope.
Bacteria Cells
• Bacteria are single-celled organisms.
• They are prokaryotes, which means that their
genetic material is not held in a nucleus.
Bacteria Cells
• Bacteria cells have cell walls that protect
them.
• Beneath the cell walls is a cell membrane that
controls what can go in or out of the cell.
Bacteria Cells
• Like plant and animal cells, bacteria have a
gel-like cytoplasm filling the inside of the cell.
• In the cytoplasm are ribosomes which
produce proteins.
• The genetic material can also be found in the
cytoplasm.
Bacteria Cells
• Bacteria cells do not have any of the other
organelles that plant and animal cells have.
• Some bacteria also have flagellum coming off
of the cell that help the cell move.
• See page 49.
Bacteria Cells
• Bacteria cells come in three different shapes:
– Spherical
– Rodlike
– Spiral
Bacteria Cells
• Bacteria can vary greatly in size, the largest
being about the size of a period printed in a
book. Most are much, much smaller and
cannot be seen without the help of a
microscope.
Bacteria Food
• Some bacteria are autotrophs, which means
they make their own food.
– Some use energy from the sun like plants.
– Others use energy from chemical substances in
their environment.
Bacteria Food
• Other bacteria are heterotrophs, which means
they need to eat.
– These organisms consume a variety of different
food sources.
Bacteria Reproduction
• When bacteria have plenty of food, the right
temperature, and other suitable conditions,
they thrive and reproduce frequently.
– However, these three things are often not all
present.
Bacteria Reproduction
• Bacteria reproduce through binary fission.
• Binary fission is when one cell divides to form
two identical cells.
Bacteria Reproduction
• Binary fission is considered asexual
reproduction because it only involves one
parent.
– Because only one parent is involved, the offspring
is completely identical to the parent.
Bacteria Reproduction
• Some bacteria can undergo sexual
reproduction, which involves two instead of
one parent.
– This happens through a process called
conjugation, where one bacterium gives its
genetic material to another.
Bacteria Reproduction
• Conjugation does not produce new bacteria, it
just changes the genetic makeup of bacteria.
Bacteria Reproduction
• If the environment that a bacteria is living in is
not suitable for reproduction, some bacteria
can form endospores.
– An endospore is a small, round, thick-walled cell
that exists inside of the bacteria cell and contains
some cytoplasm and genetic material.
Bacteria Reproduction
• Endospores can survive many years in harsh
conditions.
• Once the conditions are suitable for
reproduction, endospores open up and the
bacteria begins to grow and multiply.
Bacteria in Nature
• Most bacteria are actually harmless or helpful
to people.
– In fact, people depend on bacteria.
Bacteria in Nature
• Bacteria are involved in:
– Oxygen production
– Food production
– Environmental recycling
– Environmental cleanup
– Health
– Medicine
Bacteria in Nature
• Oxygen Production
– Autotrophic bacteria which use the sun’s energy
to make their own food produce oxygen, just like
plants.
– Since bacteria existed long before plants, and the
atmosphere used to lack oxygen, scientists believe
oxygen was first added to Earth’s atmosphere by
these autotrophic bacteria.
Bacteria in Nature
• Food Production
– Many foods would not exist if it weren’t for
bacteria.
• For example:
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–
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Cheese
Pickles
Vinegar
Alcohol
Yogurt
Sour cream
Many more
Bacteria in Nature
• Food Production
– Some bacteria break down food chemicals,
causing them to go bad.
– This can be slowed or stopped by refrigeration,
heating, or pasteurization.
• Pasteurization is the heating of liquids so high that
harmful bacteria is killed without changing the taste.
Bacteria in Nature
• Environmental Recycling
– Some heterotrophic bacteria are decomposers,
which means that they break down large
chemicals in dead organisms into smaller
chemicals.
– By breaking down these chemicals, the chemicals
can then be reused by living organisms.
Bacteria in Nature
• Environmental Cleanup
– Some bacteria is used to help cleanup after oil
spills, since they take in this oil as food.
Bacteria in Nature
• Health
– Bacteria living in your body helps in all kinds of
ways.
• Some help you digest food.
• Some make vitamins.
• Some fight off disease-causing organisms.
Bacteria in Nature
• Medicine
– Some bacteria either produce medicine or are
used as medicine.
• Penicillin
• Insulin