Chapter 2
Viruses and Bacteria
Section 1 Viruses
What is a Virus A virus is a tiny, nonliving particle that enters and
reproduces inside a living cell.
Characteristics of Viruses They are considered nonliving. They
cannot make food, take in food, or produce waste. The only way in
which viruses are like organisms is that they are able to multiply.
Although viruses can multiply, they do so differently than
organisms. Viruses can multiply only when they are inside a living
cell.
A host is an organism that provides a source of energy for a virus or
another organism. A virus acts like a parasite, or an organism that
lives on or in a host and causes it harm. Almost all viruses destroy the
cells in which they multiply.
Virus Shapes Viruses vary widely in shape. A bacteriophage is a virus
that infects bacteria. Its name means “bacteria eater”.
Virus Sizes Viruses are measured in nanometers (nm). One nanometer
is one billionth of a meter. The smallest measure about 20 nm, while
the largest measure more than 200 nm.
Naming Viruses Some are named after the disease they cause or the
for the organism that they infect. Some are named after people—
Epstein-Barr virus was named after the two scientists who first
identified it.
The Structure of Viruses All viruses have two basic parts: a protein
coat that protects the virus and an inner core made of genetic
material. Some are surrounded by an additional outer membrane, or
envelope. Each virus contains unique surface proteins that allow it to
attach to proteins on a host cell. These proteins fit together like a
lock and key.
How Viruses Multiply After a virus enters a cell, its genetic material
takes over many of the cells functions. It instructs the cell to produce
the virus’s proteins and genetic material. These proteins and genetic
material then assemble into new viruses.
Active Viruses go into action and once copied cause the host cell to
burst thus releasing new viruses.
Hidden Viruses do not become active immediately. Instead they may
“hide” for months or even years. Sunlight or stress may cause them to
become active.
Viruses and the Living World
Viruses and Disease Viruses affect humans, house pets, and even
plants.
Usefulness of Viruses Viruses can be used for gene therapy. Genetic
material can be inserted into a virus and knowing it will invade cells, it
can be used to control those cells for the better.
Section 2 -- Bacteria
The Bacterial Cell In the late 1600s, a Dutch merchant by the name
of Anton van Leeuwenhoek found them accidently when he was looking
at scrapings from his teeth.
Cell Structurers Bacteria are prokaryotes. The genetic material in
their cells is not contained in a nucleus. Their cells also lack many
other structures that are found in eukaryotes. Most bacterial cells
are surrounded by a rigid cell wall that protects the cell. Just inside
the cell wall is the cell membrane, which controls what materials pass
into and out of the cell. The gel-like material inside the cell membrane
is called cytoplasm. Ribosomes are in the cytoplasm. They produce
proteins. Some bacteria have flagellum, a long whiplike structure that
helps the cell move.
Cell Shapes The chemical makeup of the cell wall determines the
shape of the bacterial cell. Bacteria are rodlike, spherical, or spiral
shaped.
Cell Sizes The largest known bacterium is about the size of a period
at the end of a sentence. The average size of bacteria is about 0.5 to
1 micrometer in diameter. A micrometer is one millionth of a meter.
Obtaining Food and Energy Bacteria must have a source of food and
a way of breaking down the food to release it’s energy.
Obtaining Food Some bacteria are autotrophs. They may capture the
suns energy as plants do. Others may use chemical substances in their
environment to make their food. Heterotrophic bacteria may consume
a variety of foods—from milk and meat, to decaying leaves.
Respiration
The process of breaking down food to release its energy
is called respiration.
Reproduction When bacteria have plenty of food, the right
temperature, and other suitable conditions, they thrive and reproduce
frequently.
Asexual Reproduction
Bacteria reproduce by a process called binary
fission, in which one cell divides to form two identical cells. This is a
form of asexual reproduction. Asexual reproduction is a reproductive
process that involves only one parent and produces offspring that are
identical to the parent.
Sexual Reproduction
involves two parents who combine their genetic
material to produce a new organism, which differs from both parents.
During a process called conjugation, one bacterium transfers some of
its genetic material to another through a thin, threadlike bridge that
joins the two cells. When the bacteria divide by binary fission, the
new genetic material passes to the new cells.
Endospore Formation Some bacteria can survive harsh conditions by
forming endospores. An endospore is a small, rounded, thick-walled,
resting cell that forms inside a bacterial cell. It contains the cell’s
genetic material and some of its cytoplasm.
The Role of Bacteria in Nature Bacteria are involved in oxygen and
food production, environmental recycling and cleanup, and in health
maintenance and medicine production.
Oxygen Production Autotrophic bacteria use the sun’s energy to
produce oxygen.
Food Production Some bacteria are used to produce food—cheese,
sauerkraut, and pickles. Pasteurization, named after Louis Pasteur, is
a process where food is heated enough to kill bacteria in food.
Look at pages 54 & 55
Environmental Recycling Some bacteria are decomposers. They break
down large chemicals in dead organisms into small chemicals.
Environmental Cleanup Some types of bacteria consume hydrocarbons.
Health and Medicine Some types of bacteria live in your intestines
and help you digest food. Some make vitamins and others compete for
space with disease causing bacteria. Some are used to make insulin.
Section 3--Viruses, Bacteria, and Your Health
How Infectious Diseases Spread Infectious diseases are illnesses
that pass from one organism to another. They can spread through
contact with an infected person, a contaminated object, an infected
animal, or an environmental source.
 Contact with an infected person
 Contact with a contaminated object
 Contact with an infected animal
 Contact with environmental sources
Some bacteria produce a toxin or poison that can cause death.
Treating Infectious Diseases
Bacterial Diseases Fortunately, many bacterial diseases can be cured
with medications known as antibiotics. An antibiotic is a chemical that
can kill bacteria without harming a person’s cells. Antibiotic resistance
results when some bacteria are able to survive in the presence of an
antibiotic.
Viral Diseases Unlike with bacterial diseases, there are currently no
medications that can cure viral diseases. The best treatment for viral
infections is often a good diet and bed rest.
Preventing Infectious Diseases Vaccines are important tools that help
prevent the spread of infectious diseases. A Vaccine is a substance
introduced into the body to stimulate the production of chemicals that
destroy specific viruses or bacteria. A vaccine may be made from dead
or altered viruses or bacteria. Keeping your body healthy also helps
protect you from infectious diseases.