Name
CHAPTER 10
Class
Date
Bacteria and Viruses
SECTION
2 Bacteria’s Role in the World
National Science
Education Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
LS 1f
• How are some bacteria helpful?
• How are some bacteria harmful?
Are All Bacteria Harmful?
Bacteria are everywhere. They live in our water, our
food, and our bodies. Some bacteria cause disease.
However, most of the types of bacteria are helpful to
organisms and the environment. Some bacteria move
nitrogen throughout the environment. Other bacteria help
recycle dead animals and plants. Still other bacteria are
used to help scientists make medicines. Bacteria help us
every day.
How Are Bacteria Helpful to Plants?
Plants need nitrogen to live. Although nitrogen makes
up about 78% of the air, plants cannot use this nitrogen
directly. They need to take in a different form of nitrogen.
Bacteria in the soil take nitrogen from the air and change
it into a form that plants can use. This process is called
nitrogen fixation.
STUDY TIP
Outline As you read, make
an outline of this section. Use
the header questions to help
you make your outline.
Say It
Discuss Does it surprise you
to learn that not all bacteria
are harmful? What were some
things you used to believe
about bacteria? With a partner,
talk about how your view of
bacteria has changed.
Bacteria’s Role in the Nitrogen Cycle
Most animals get the nitrogen they
need by eating plants.
Nitrogen in the air
enters the soil.
Bacteria are found in the
soil and in nodules on the
roots of plants. The bacteria
change nitrogen into a form
that plants can use.
TAKE A LOOK
1. Explain How do most
animals get the nitrogen that
they need?
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Bacteria and Viruses
Name
SECTION 2
Class
Date
Bacteria’s Role in the World continued
How Are Bacteria Helpful to the Environment?
Math Focus
2. Calculate An ounce
(1 oz) is equal to about 28 g.
If 1 g of soil contains 25
billion bacteria, how many
bacteria are in 1 oz of soil?
Bacteria are useful for recycling nutrients and cleaning
up pollution. In nature, bacteria break down dead plants
and animals. Breaking down dead matter helps recycle
the nutrients so they can be used by other organisms.
Some bacteria are used to fight pollution.This process
is called bioremediation. Bioremediation means using
microorganisms, such as bacteria, to clean up harmful
chemicals. Bioremediation is used to clean up oil spills
and waste from cities, farms, and industries.
How Are Bacteria Helpful to People?
MAKING FOOD
Many of the foods you eat are made with the help of
bacteria. Bacteria are commonly used in dairy products.
Every time you eat cheese, yogurt, buttermilk, or sour
cream, you are also eating bacteria. These products are
made using milk and bacteria. Bacteria change the sugar
in milk, called lactose, into lactic acid. Lactic acid adds
flavor to the food and preserves it.
Bacteria are used to make
many kinds of food.
MAKING MEDICINES
What’s the best way to fight bacteria that cause disease? Would you believe that the answer is to use other
bacteria? An antibiotic is a medicine that can kill bacteria and other microorganisms. Many antibiotics are made
by bacteria.
READING CHECK
3. Explain What does
genetic engineering let
scientists do?
GENETIC ENGINEERING
When scientists change an organism’s DNA, it is called
genetic engineering. For example, scientists have put
genes from different organisms into bacteria. The added
DNA gives the bacterium instructions for making different proteins. Genetic engineering lets scientists make
products that are hard to find in nature.
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Bacteria and Viruses
Name
SECTION 2
Class
Date
Bacteria’s Role in the World continued
Genes from the Xenopus
frog were used to produce the first genetically
engineered bacteria.
Scientists have used genetic engineering to produce
insulin. The human body needs insulin to break down
and use sugar. People who have a disease called diabetes cannot make enough insulin. In the 1970s, scientists
found a way to put genes into bacteria so that the bacteria would produce human insulin.
Critical Thinking
4. Infer Why do you think it
is helpful to engineer bacteria to produce insulin?
How Can Bacteria Be Harmful?
Some bacteria can be harmful to people and other
organisms. Bacteria that cause disease are called
pathogenic bacteria. Pathogenic bacteria get inside a
host organism and take nutrients from the organism’s
cells. Pathogenic bacteria can harm the organism. Today,
people protect themselves from some bacterial diseases
by vaccination. Many bacterial infections can be treated
with antibiotics.
Bacteria can cause disease in other organisms as well
as people. Bacteria can rot or discolor a plant and its fruit.
To stop this, plants are sometimes treated with antibiotics.
Scientists also try to grow plants that have been genetically
engineered to resist bacteria that cause disease.
READING CHECK
5. Identify What can be used
to treat bacterial infections?
Vaccines can protect you
from bacterial diseases such
as tetanus and diphtheria.
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Bacteria and Viruses
Name
Class
Section 2 Review
Date
NSES
LS 1f
SECTION VOCABULARY
antibiotic medicine used to kill bacteria and
other organisms
bioremediation the biological treatment of
hazardous waste by living organisms
pathogenic bacteria bacteria that cause disease
1. Define What is nitrogen fixation?
2. Complete Fill in the process chart for the nitrogen cycle. Be sure to describe
what is happening during each step.
Nitrogen from the
air passes into the
soil.
3. Explain What are two ways that bacteria are helpful to other living things?
4. Explain What is genetic engineering?
5. Explain How do pathogenic bacteria harm an organism?
6. Identify Relationships Legumes, which include peanuts and beans, are good
nitrogen-fixers. Legumes are also a good source of amino acids. What chemical
element would you expect to find in amino acids?
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Bacteria and Viruses
Life Science Answer Key continued
6. They break down materials in the environ-
3. Some scientists think that bacteria similar to
ment and absorb them.
7. 23
8. ability to move
9. Answers may vary. Venus’ flytrap is in kingdom Plantae.
cyanobacteria started living in larger cells.
The bacteria made food for themselves and
the larger cells. The larger cells gave the
bacteria protection. This relationship may
have led to the first plant cells.
4. heat lovers, salt lovers, methane makers
5. Yes; although some archaea can live in harsh
environments where bacteria cannot survive, some archaea live in more moderate
places, such as the ocean. Bacteria live in
most places, other than the most extreme
environments, so they are likely to be found
in the same environments as some archaea.
Review
1. Domain Eukarya is made up of only
eukaryotes. Domains Bacteria and Archaea
are made up of only prokaryotes.
2. As scientists discover more organisms that
do not fit into existing groups, they add new
groups.
3. Linnaeus probably did not know that many
of these organisms existed. Because they are
so small, and because many archaea live in
extreme environments, Linnaeus would not
have been able to study the characteristics
of these organisms.
4. kingdom Protista
SECTION 2 BACTERIA’S ROLE IN THE
WORLD
1. by eating plants
2. 700 billion
3. It lets them make products that are hard to
find in nature.
4. The insulin can be taken out of the bacteria
and given to people with diabetes.
5. antibiotics
Chapter 10 Bacteria and
Viruses
Review
1. Nitrogen fixation is a process in which cer-
SECTION 1 BACTERIA AND ARCHAEA
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
They are single-celled and have no nucleus.
a single loop inside the cell
by binary fission
They are the same.
bacilli, cocci, spirilla
Cocci don’t dry out as quickly.
Bacilli have a large surface area to help
them take in nutrients.
as producers, consumers, or decomposers
Not all archaea have cell walls. When they
do, the walls are made of different materials
than those in bacterial cell walls.
methane makers
Archaea—they can survive in harsher environments than most bacteria.
2.
3.
4.
5.
Review
1. Bacteria, Archaea, Eukarya
2. Bacteria: Some can form endospores to
6.
tain bacteria take in nitrogen from the air
and change it to a form that plants can use.
Nitrogen from the air passes into the soil.
Bacteria in the soil and on plant roots change
nitrogen to another form. Plants use this form.
Animals eat the plants to get nitrogen.
Possible answers: Bacteria in soil turn nitrogen into a form that plants can use. Some
bacteria break down dead plant and animal
matter. This makes nutrients available to
other living things.
In genetic engineering, scientists change the
genes of bacteria or any living thing. Scientists
can put genes from one organism into another.
They get into a host organism and take
nutrients from the host’s cells.
nitrogen
SECTION 3 VIRUSES
survive harsh conditions; they are the most
plentiful organisms on Earth.
Archaea: Some can live in extreme environments; not all have cell walls.
Center: prokaryotes, no nucleus, singlecelled, reproduction by binary fission
1. Viruses change quickly.
2. They cannot reproduce without a host; they
cannot eat or grow.
3. DNA and RNA
4. spacecraft shape
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Life Science