bacteria

controlling bacteria

Bacteria in food or water usually can be killed by heating it to a high temperature. Generally, this temperature is at least 71 C (160 F). Bacteria on surfaces such as countertops and floors can be killed with disinfectants, such as chlorine bleach. Bacterial infections in people can be treated with antibiotic drugs. These drugs kill bacteria and may quickly cure the disease. If youve ever had strep throat, you were probably prescribed an antibiotic to treat it. Some bacteria have developed antibiotic resistance. They have evolved traits that make them resistant to one or more antibiotic drugs. You can see how this happens in Figure 8.14. Its an example of natural selection. Some bacteria are now resistant to most common antibiotic drugs. These infections are very hard to treat.

benefits of bacteria

Bacteria help usand all other living thingsby decomposing wastes. In this way, they recycle carbon and nitrogen in ecosystems. In addition, photosynthetic cyanobacteria are important producers. On ancient Earth, they added oxygen to the atmosphere and changed the course of evolution forever. There are billions of bacteria inside the human digestive tract. They help us digest food. They also make vitamins and play other important roles. We use bacteria in many other ways as well. For example, we use them to: create medical products such as vaccines. transfer genes in gene therapy. make fuels such as ethanol. clean up oil spills. kill plant pests. ferment foods. Do you eat any of the fermented foods pictured in Figure 8.12? If so, you are eating bacteria and their wastes. Yum!

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bacteria and disease

You have ten times as many bacterial cells as human cells in your body. Luckily for you, most of these bacteria are harmless. However, some of them can cause disease. Any organism that causes disease is called a pathogen. Diseases caused by bacterial pathogens include food poisoning, strep throat, and Lyme disease. Bacteria that cause disease may spread directly from person to person. For example, they may spread when people shake hands with, or sneeze on, other people. Bacteria may also spread through food, water, or objects that have become contaminated with them. Some bacteria are spread by vectors. A vector is an organism that spreads bacteria or other pathogens. Most vectors are animals, commonly insects. For example, deer ticks like the one in Figure 8.13 spread Lyme disease. Ticks carry Lyme disease bacteria from deer to people when they bite them.

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grampositive and gramnegative bacteria

Different types of bacteria stain a different color when Gram stain is applied to them. This makes them easy to identify. Some stain purple and some stain red, as you can see in Figure 8.11. The two types differ in their outer layers. This explains why they stain differently. Bacteria that stain purple are called gram-positive bacteria. They have a thick cell wall without an outer membrane. Bacteria that stain red are called gram-negative bacteria. They have a thin cell wall with an outer membrane.

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bacteria and people

Bacteria and people have many important relationships. Bacteria make our lives easier in a variety of ways. In fact, we could not survive without them. On the other hand, many bacteria can make us sick. Some of them are even deadly. For a dramatic overview of the many roles of bacteria, watch this stunning video: MEDIA Click image to the left or use the URL below. URL:

classifying bacteria

Bacteria are the most diverse organisms on Earth. Thousands of species of bacteria have been discovered. Many more are thought to exist. The known species are classified on the basis of various traits. For example, they may be classified by the shape of their cells. They may also be classified by how they react to a dye called Gram stain.

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classifying bacteria by shape

Bacteria come in several different shapes. The different shapes can be seen by examining bacteria under a light microscope. Therefore, its relatively easy to classify them by shape. There are three types of bacteria based on shape: bacilli (bacillus, singular), or rod shaped. cocci (coccus, singular), or sphere shaped. spirilli (spirillus, singular), or spiral shaped. You can see a common example of each type of bacteria in Figure 8.10.

counting bacteria

Bacteria are the most abundant living things on Earth. They live in almost all environments. They are found in the air, ocean, soil, and intestines of animals. They are even found in rocks deep below Earths surface. Any surface that has not been sterilized is likely to be covered with bacteria. The total number of bacteria in the world is amazing. Its estimated to be about 5 million trillion trillion. If you write that number in digits, it has 30 zeroes!

instructional diagrams

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questions

Which statement about the diversity of bacteria is false?

a. Bacteria are the most diverse organisms on Earth

b. Thousands of species of bacteria have been discovered

-->  c. Few if any bacterial species remain to be discovered

d. Bacteria increase diversity by genetic transfer

Salmonella bacteria are

a. prokaryotes.

b. bacillus bacteria.

c. a common cause of food poisoning.

-->  d. all of the above

Bacteria

-->  a. are the most abundant organisms on Earth.

b. have fewer species than any other domain.

c. can be observed only with an electron microscope.

d. all of the above

Bacteria that are classified as gram-negative

a. stain purple with gram stain

-->  b. have an outer membrane

c. lack a cell wall

d. two of the above

Bacteria can help people by

a. making fuels

b. cleaning up oil spills

c. making vaccines

-->  d. all of the above

Gram-positive bacteria have a(n)

-->  a. thick cell wall.

b. outer membrane.

c. cell nucleus.

d. two of the above

Lyme disease is caused by bacteria that are spread by

a. mosquitoes.

b. black flies.

-->  c. deer ticks.

d. bed bugs.

All bacteria

a. die at temperatures higher than 37 C

-->  b. can be killed with chlorine bleach

c. are resistant to antibiotics

d. are poisoned by oxygen

Bacteria live in Earths

a. crust.

b. ocean.

c. atmosphere.

-->  d. all of the above

How many bacterial cells normally live in and on the human body?

a. a few hundred

b. about a thousand

c. several million

-->  d. trillions

The development of antibiotic resistance is an example of

a. gene therapy.

b. biotechnology.

c. gene cloning.

-->  d. natural selection.

The best way to kill bacteria in drinking water is to

-->  a. raise its temperature to the boiling point (100 C).

b. add a large amount of chlorine bleach to it.

c. dissolve antibiotic drugs in it.

d. pass it through a sieve.

A spiral-shaped bacterium is classified as a spirillus.

-->  a. true

b. false

Bacteria that form biofilms are multicellular prokaryotes.

a. true

-->  b. false

Bacteria cover Earths surface but are not found far below it.

a. true

-->  b. false

There are more bacteria than any other organisms on Earth.

-->  a. true

b. false

Yogurt is made with the help of bacteria.

-->  a. true

b. false

__A book lying on your desk is likely to be covered with bacteria.

-->  a. true

b. false

__Bacteria are the most diverse organisms on Earth.

-->  a. true

b. false

__Bacteria stain differently with gram stain depending on whether they have a cell nucleus.

a. true

-->  b. false

__All bacteria cause human illnesses.

a. true

-->  b. false

__Some bacteria can be used as pesticides.

-->  a. true

b. false

__Pickles and cheese on a cheeseburger are both made with the help of bacteria.

-->  a. true

b. false

__Strep throat is a bacterial infection.

-->  a. true

b. false

____sphere-shaped bacterium

a. gram

b. spirillus

c. vector

d. bacillus

e. pathogen

-->  f. coccus

g. antibiotic

____organism that spreads pathogens from host to host

a. gram

b. spirillus

-->  c. vector

d. bacillus

e. pathogen

f. coccus

g. antibiotic

____name of the dye used to color bacteria

-->  a. gram

b. spirillus

c. vector

d. bacillus

e. pathogen

f. coccus

g. antibiotic

____rod-shaped bacterium

a. gram

b. spirillus

c. vector

-->  d. bacillus

e. pathogen

f. coccus

g. antibiotic

____type of drug used to treat bacterial infections

a. gram

b. spirillus

c. vector

d. bacillus

e. pathogen

f. coccus

-->  g. antibiotic

____organism that causes disease

a. gram

b. spirillus

c. vector

d. bacillus

-->  e. pathogen

f. coccus

g. antibiotic

____spiral-shaped bacterium

a. gram

-->  b. spirillus

c. vector

d. bacillus

e. pathogen

f. coccus

g. antibiotic

diagram questions

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