Chapter Introduction

Lesson 1 What areBacteria?

Lesson 2 Bacteria in Nature

Lesson 3 What are Viruses?

Chapter Wrap-Up

What are bacteria and viruses and why are they important?

What do you think?

Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.

1. A bacterium does not have a nucleus.

2. Bacteria cannot move.

3. All bacteria cause diseases.

Do you agree or disagree?

4. Bacteria are important for making many types of food.

5. Viruses are the smallest living organisms.

6. Viruses can replicate only inside an organism.

Do you agree or disagree?

• What are bacteria?

• How do bacteria obtain food?

What are Bacteria?

• bacterium

• flagellum

• fission

• conjugation

• endospore

What are Bacteria?

Bacteria are microscopic prokaryotes that live in almost every habitat on Earth and in or on almost every organism, both living and dead.

Characteristics of Bacteria

bacteria

from Greek bakterion, means “small staff”

Characteristics of Bacteria (cont.)

What are bacteria?

Other prokaryotes, called archaea, are similar to bacteria and share many characteristics with them, including the lack of membrane-bound organelles.

Characteristics of Bacteria (cont.)

• A typical bacterium consists of cytoplasm and DNA surrounded by a cell membrane and a cell wall.

• Most bacteria have DNA that is one coiled, circular chromosome.

• Many bacteria also have one or more small circular pieces of DNA called plasmids that are separate from their other DNA.

Characteristics of Bacteria (cont.)

Characteristics of Bacteria (cont.)

Some bacteria have specialized structures that help them survive.

• Bacteria are much smaller than plant or animal cells.

• They have one of three basic shapes:

• round or sphere-shaped

• rod-shaped

• spiral-shaped.

Characteristics of Bacteria (cont.)

• Bacteria live in many different places and obtain food in various ways.

• Some bacteria make their own food by using light energy, like plants.

• Others take in their nutrients from living hosts.

• Other bacteria use energy from chemical reactions to make their food.

Characteristics of Bacteria (cont.)

• Some bacteria break down food to obtain energy.

• These bacteria often live on dead organic matter.

Characteristics of Bacteria (cont.)

Characteristics of Bacteria (cont.)

How do bacteria obtain food?

• Bacteria that can live where there is no oxygen are called anaerobic.

• Bacteria that need oxygen are called aerobic.

Characteristics of Bacteria (cont.)

Some bacteria are able to find their resources by moving around with special whiplike structures called flagella.

Characteristics of Bacteria (cont.)

Some bacteria twist or spiral as they move, and others use their pili like grappling hooks or create threadlike structures that enable them to push away from a surface.

Characteristics of Bacteria (cont.)

• Bacteria reproduce asexually by fission—cell division that forms two genetically identical cells.

• Genetic variation can be increased by a process called conjugation, in which two bacteria of the same species attach to each other and combine their genetic material.

Characteristics of Bacteria (cont.)

Conjugation creates genetic diversity by transferring DNA between two bacteria cells.

• An endospore forms when a bacterium builds a thick internal wall around its chromosome and part of the cytoplasm.

• An endospore can protect a bacterium from intense heat, cold, or drought.

Endospores

Endospore Formation

• Prokaryotes called archaea are similar to bacteria, but the ribosomes of archaea more closely resemble the ribosomes of eukaryotes than those of bacteria.

• Archaea contain molecules in their plasma membranes that are not found in any other known organisms and often live in extreme environments.

Archaea

• Bacteria are unicellular prokaryotes.

• Many bacteria feed on dead organic matter.

• Bacteria can increase genetic diversity by sharing DNA through conjugation.

A. DNA

B. cytoplasm

C. bacterium

D. flagella

What are the long whiplike structures bacteria use to move?

A. conjugation C.reproduction

B. fission D.inflammation

During which process do two bacteria of the same species attach to each other and combine their genetic material?

A. bacterial

B. light

C. anaerobic

D. aerobic

Like green plants, some bacteria make their own food by using what type of energy?

1. A bacterium does not have a nucleus.

2. Bacteria cannot move.

Do you agree or disagree?

• How can bacteria affect the environment?

• How can bacteria affect health?

Bacteria in Nature

• decomposition

• nitrogen fixation

• bioremediation

• pathogen

Bacteria in Nature

• antibiotic

• pasteurization

• Most bacteria are beneficial and only a fraction cause diseases.

• Many organisms, including humans, depend on bacteria to survive.

• Some bacteria help with digestion and other body processes.

Beneficial Bacteria

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• Bacteria aid in the processes of decomposition and nitrogen fixation.

• Decomposition is the breaking down of dead organisms and organic waste.

• Nitrogen fixation is the conversion of nitrogen into a form that plants can use.

• Organisms use nitrogen to make proteins.

Beneficial Bacteria (cont.)

The roots of some plants, including beans and peas, have nodules that contain nitrogen-fixing bacteria.

• The use of organisms, such as bacteria, to clean up environmental pollution is called bioremediation.

• These organisms often break down harmful substances into less harmful material that can be used as landfill or fertilizers.

• Bacteria are used to make foods such as yogurt, cheese, buttermilk, vinegar, and soy sauce.

Beneficial Bacteria (cont.)

Beneficial Bacteria (cont.)

What are some ways that bacteria are beneficial to the environment?

Of the 5,000 known species of bacteria, relatively few are considered pathogens—agents that cause disease.

Harmful Bacteria

pathogen

from Greek pathos, means “to suffer”; and gen, means “to produce”

Harmful Bacteria (cont.)

• Some pathogens normally live in your body, but cause illness only when your immune system is weakened.

• Other bacterial pathogens can enter your body through a cut, the air you breathe, or the food you eat.

• Once inside your body, they can reproduce and cause disease.

Harmful Bacteria (cont.)

• Bacteria can harm your body and cause disease in one of two ways.

• Some bacteria make you sick by damaging tissue.

• Other bacteria cause illness by releasing toxins.

Harmful Bacteria (cont.)

Describe one way that bacteria can be harmful to health.

• Antibiotics are chemicals that stop the growth and reproduction of bacteria.

• Many types of bacteria have become resistant to antibiotics over time.

Harmful Bacteria (cont.)

Harmful Bacteria (cont.)

resistance

Science Use the capacity of an organism to defend itself against a disease

Common Use the act of opposing something

Harmful Bacteria (cont.)

• Random mutations occur to a bacterium’s DNA that enable it to survive or “resist” a specific antibiotic.

• Over time, resistant bacteria will reproduce to become more common.

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• Over time bacteria on food reproduce and begin breaking down the food, causing it to spoil.

• Pasteurization is a process of heating food to a temperature that kills most harmful bacteria.

Harmful Bacteria (cont.)

How does pasteurization affect human health?

Harmful Bacteria (cont.)

• Bacteria can help some organisms, including humans and cows, digest food.

• Bacteria can be used to break down harmful substances such as uranium.

• Some bacteria are pathogens and cause diseases in humans and other organisms.

A. dangerous

B. beneficial

C. fatal

D. useless

Which term best describes bacteria’s relationship to organisms?

A. nitrogen fixation

B. decomposition

C. bioremediation

D. digestion

What term describes the conversion of nitrogen into a form that plants can use?

A. pathogens

B. bacteria

C. antibiotics

D. antibodies

What is the name for chemicals that stop the growth and reproduction of bacteria?

3. All bacteria cause diseases.

4. Bacteria are important for making many types of food.

Do you agree or disagree?

• What are viruses?

• How do viruses affect human health?

What are Viruses?

• virus

• antibody

• vaccine

What are Viruses?

• A virus is a strand of DNA or RNA surrounded by a layer of protein that can infect and replicate in a host cell.

• A virus does not have a cell wall, a nucleus, or any other organelles present in cells.

• Viruses can have different shapes, such as crystal, cylinder, sphere, and bacteriophage shapes.

Characteristics of Viruses

Viruses can have different shapes.

• A virus is not a living thing because it does not have all the characteristics of a living organism.

• A virus can make copies of itself in a process called replication, but it must rely on a living organism to do so.

Characteristics of Viruses (cont.)

Characteristics of Viruses (cont.)

Are viruses alive? Explain why or why not.

• Viruses must use organisms to carry on the processes that we usually associate with a living cell.

• Viruses have no organelles so they are not able to take in nutrients or use energy.

• Viruses must be inside a cell, called a host cell, to replicate.

Characteristics of Viruses (cont.)

• When a virus enters a cell, it can either be active or latent.

• Latent viruses go through an inactive stage and their genetic material becomes part of the host cell’s genetic material.

• Once it becomes active, a virus takes control of the host cell and replicates.

Characteristics of Viruses (cont.)

Active Virus

• A virus can only attach to a host cell with specific molecules on its cell wall or cell membrane.

• After a virus attaches to a host cell, its DNA or RNA enters the host cell.

• Once inside, the virus either starts to replicate or becomes latent.

Characteristics of Viruses (cont.)

Latent Virus

Characteristics of Viruses (cont.)

• After a virus becomes active and replicates in a host cell, it destroys the host cell.

• Copies of the virus are then released into the host organism, where they can infect other cells.

• As viruses replicate, their DNA or RNA frequently mutates, enabling them to adjust to changes in their host cell.

• Most viruses attack and destroy specific cells, which causes the symptoms of disease.

• Some viruses, like influenza, begin to replicate immediately and cause symptoms soon after infection.

Viral Diseases

• Other viruses, like HIV (human immunodeficiency virus), might not cause symptoms right away because the infected cells might continue to function normally for a period of time after infection.

• People infected with latent viruses might not know for many years that they have been infected.

Viral Diseases (cont.)

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• Since viruses are constantly changing, viral diseases can be difficult to treat.

• One of the best ways to prevent a viral infection is to limit contact with an infected human or animal.

Treating and Preventing Viral Diseases

• An antibody is a protein that prevents an infection in your body.

• When a virus infects a person, their body begins to make antibodies.

• Antibodies bind to viruses and other pathogens and prevent them from attaching to a host cell.

Treating and Preventing Viral Diseases(cont.)

immunity

from Latin immunis, means “exempt, free”

Treating and Preventing Viral Diseases(cont.)

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• Antibodies target viruses and signal the body to destroy them, making it easier for the body to fight infection if the same pathogen enters the body again.

• Natural immunity develops when a mother passes antibodies on to her unborn baby.

Treating and Preventing Viral Diseases(cont.)

• A vaccine is a mixture containing material from one or more deactivated pathogens, such as viruses.

• When an organism is given a vaccine for a viral disease, the vaccine triggers the production of antibodies.

• After being vaccinated against a particular pathogen, the organism will not get as sick if exposed to the same pathogen again.

Treating and Preventing Viral Diseases(cont.)

• Scientists are researching new ways to treat and prevent viral diseases in humans, animals, and plants.

• Viruses have been used by some scientists to treat genetic disorders and cancer using gene transfer.

Research with Viruses

How do viruses affect human health?

Research with Viruses (cont.)

• A virus is a strand of DNA or RNA surrounded by a layer of protein.

• Viruses cause human diseases such as chicken pox and influenza.

• A person’s body produces proteins called antibodies that prevent an infection by viruses.

A. DNA

B. antibodies

C. organisms

D. pathogens

What do viruses use to carry on the processes that we usually associate with a living cell?

A. molecules

B. mutations

C. diseases

D. pathogens

What enables a virus to adjust to changes in their host cells?

A. pathogens

B. antibodies

C. diseases

D. viruses

A vaccine contains what kind of deactivated substance?

5. Viruses are the smallest living organisms.

6. Viruses can replicate only inside an organism.

Do you agree or disagree?

Key Concept Summary

Interactive Concept Map

Chapter Review

Standardized Test Practice

Bacteria are unicellular prokaryotes, and viruses are small pieces of DNA or RNA surrounded by protein. Both bacteria and viruses may infect the human body; they can cause harmful diseases or can be useful.

• Bacteria and archeans are unicellular organisms without nuclei. They have structures for movement, obtaining food, and reproduction.

• Bacteria exchange genetic information in a process called conjugation. They reproduce asexually by fission.

Lesson 1: What are Bacteria?

Lesson 2: Bacteria in Nature

• Bacteria decompose materials, play a role in the nitrogen cycle, clean the environment, and are used in food.

• Some bacteria cause disease, while others are used to treat it.

• A virus is made up of DNA or RNA surrounded by a protein coat.

• Viruses can cause disease, can be made into vaccines, and are used in research.

Lesson 3: What are Viruses?

A. eukaryotes

B. organelles

C. prokaryotes

D. ribosomes

Which type of cells are bacteria?

A. cytoplasm

B. flagella

C. cells

D. genetic material

When two bacteria of the same species attach to each other during conjugation, what are they combining?

A. antibiotics

B. pathogens

C. proteins

D. ribosomes

What are disease-causing bacteria called?

A. DNA

B. host cells

C. organelles

D. proteins

What do viruses lack that would enable them to carry on life functions?

A. active

B. disease

C. latent

D. deactivated

Which term describes a virus that might not cause symptoms right away?

A. eukaryotes

B. organelles

C. archaea

D. bacteria

What is the name of the microscopic prokaryotes that live in or on almost every organism?

A. spiral-shaped

B. spongy

C. diamond-shaped

D. bean-shaped

In addition to being sphere-shaped or rod-shaped, what other shape might bacteria take?

A. bacterial resistance

B. bioremediation

C. decomposition

D. pasteurization

What is the name for the process of heating food to a temperature that kills most harmful bacteria?

A. bacterium

B. bacteriophage

C. virus

D. mutation

What is the name of a strand of DNA or RNA surrounded by a layer of protein that can infect and replicate in a host cell?

A. virus

B. pathogen

C. antibody

D. disease

Which of these is a protein that prevents an infection in your body?