ChapterViruses, Bacteria,Protists, and Fungi

Diversity and AdaptationsWhat are some keycharacteristics of viruses,bacteria, protists, and fungi?

Chapter Preview

O VirusesDiscover Which Lock Does the Key Fit?Active Art Active and Hidden VirusesSkills Lab How Many Viruses Fit on a Pin?

O BacteriaDiscover How Quickly Can Bacteria Multiply?TO' This Bacteria for Breakfast

Analyzing Data Population ExplosionScience and History Bacteria and Foods of the World

At-HomeActivity Edible Bacteria

O ProtistsDiscover What Lives in a Drop of Pond Water?

Active Art Amoeba and Paramecium

Try This Watching Protists

Skills Activity PredictingAt-Home Activity Algae Scavenger -Hunt

O FungiDiscover Do All Molds Look Alike?

Try This Spreading SporesSkills Lab What's for Lunch?

Bacteria (blue and purple rods) and othermicroorganisms lurk in a kitchen sponge.

208 •

DJ S oueryProtists and Fungi

CHANNEL Video PreviewVideo Field Trip

ooc Video Assessment

Chapter Project

A Mushroom FarmThe fungi you're most familiar with are probablymushrooms. In some ways, mushrooms resembleplants, often growing near plants or even on them likesmall umbrellas. But mushrooms are very differentfrom plants in some important ways. In this chapterproject, you'll learn about these differences.

Your Goal To determine the conditionsneeded for mushrooms to grow

To complete this project, you must

e choose one variable anddesign a way to test how itaffects mushroom growth

e make daily observations andrecord them in a data table

e prepare a poster that describesthe results of your experiment

e follow the safety guidelines inAppendix A

Plan It! List possible hypothesesabout the way variables such as light

or moisture could affect the growth of

mushrooms. Choose one variable and

write out a plan for testing that vari-

able. After your teacher approves your

plan, start growing your mushrooms!

Chapter 7 • 209

Viruses

Reading PreviewKey Concepts• How are viruses like organisms?• What is the structure of a virus?

• How do viruses multiply?

• How can you treat a viraldisease?

Key Terms• virus • host • parasite

• bacteriophage • vaccine

Target Reading SkillSequencing As you read, maketwo flowcharts that show howactive and hidden viruses multiply.

How Active Viruses Multiply

Virus attaches to the surfaceof a living cell

Virus injects genetic materialinto cell

210

Discover Activityzone

Which Lock Does the Key Fit?1. Your teacher will give you a key.

2. Study the key closely. Think about what shape the keyholeon its lock must have. On a piece of paper, draw the shape ofthe keyhole.

3. The lock for your key is contained in the group of locks yourteacher will provide. Try to match your key to its lock withoutinserting the key into the keyhole.

Think It OverInferring How might a unique "lock" on its surface help a cellprotect itself from invading organisms?

It is a dark and quiet night. An enemy spy slips silently across theborder. Invisible to the guards, the spy creeps cautiously alongthe edge of the road, heading toward the command center.Undetected, the spy sneaks by the center's security system andreaches the door. Breaking into the control room, the spy takescommand of the central computer. The enemy is in control.

What Is a Virus?Although this spy story may read like a movie script, itdescribes events similar to those that can occur in your body.The spy acts very much like a virus invading an organism.

Characteristics of Viruses A virus is a tiny, nonlivingparticle that invades and then multiplies inside a living cell.Viruses are not cells. They do not have the characteristics oforganisms. The only way in which viruses are like organisms

is that they can multiply. Although viruses can multiply, they

multiply differently than organisms. Viruses can only multiply

when they are inside a living cell.No organisms are safe from viruses. The organism that a

virus multiplies inside is called a host. A host is a living thing

that provides a source of energy for a virus or an organism,Viruses act like parasites (PA ruh syts), organisms that live on

or in a host and cause it harm. Almost all viruses destroy their

host cells.

The Structure of Viruses Viruses are smaller than cells and

in size and shape. Some viruses are round. Others are

shaped like rods, bricks, threads, or bullets. There are even

viruses that have complex, robot-like shapes, such as the bacte-

riophage in Figure 1. A bacteriophage (bak TEER ee oh fayj) is a

that infects bacteria. In fact, its name means "bacteria eater."

Although viruses may look different from one another,

they all have a similar structure. All viruses have two basic

parts: a protein coat that protects the virus and an inner core

made of genetic material. A virus's genetic material contains

the instructions for making new viruses. Some viruses are also

surrounded by an additional outer membrane, or envelope.

The proteins on the surface of a virus play an important role

during the invasion of a host cell. Each virus contains unique

surface proteins. The shape of the surface proteins allows the

viNS to attach to certain cells in the host. Like keys, a virus's pro-

teins fit only into certain "locks," or proteins, on the surface of a

host's cells. Figure 2 shows how the lock-and-key action works.

Because the lock-and-key action of a virus is specific, a cer-

tain virus can attach only to one or a few types of cells. For

example, most cold viruses infect cells only in the nose and

throat of humans. These cells are the ones with proteins on

their surface that complement or "fit" those on the virus.

Reading What information does a virus's genetic materialCheckpoint contain?

Genetic materialVirus particle

Protein coat

Membraneenvelope

Cell's surfaceHost cell membrane proteins

(9

FIGURE 1

BacteriophageThis robot-like virus infects bacteria.

FIGURE 2

Virus Structure andInfectionAll viruses consist of geneticmaterial surrounded by a proteincoat. Some viruses, like the onesshown here, are surrounded by anouter membrane envelope. A viruscan attach to a cell only if thevirus' surface proteins can fit thoseon the cell.

Virus's outermembrane proteins

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FIGURE 3

Active and HiddenVirusesActive viruses enter cells andimmediately begin to multiply,leading to the quick death ofthe invaded cells. Hidden viruses"hide" for a while inside host cellsbefore becoming active.

O A virus attaches tothe surface ofa bacterium.

The virus injectsits genetic materialinto the bacterium.

212

How Viruses MultiplyAfter a virus attaches to a host cell, it enters the cell. Onceinside a cell, a virus's genetic material takes over many of thcell's functions. It instructs the cell to produce the virus'sproteins and genetic material. These proteins and

geneticmaterial then assemble into new viruses. Some viruses takeover cell functions immediately. Other viruses wait for a while

Active Viruses After entering a cell, an active virus immedi.ately goes into action. The virus's genetic material takes overcell functions, and the cell quickly begins to produce the virus'sproteins and genetic material. Then these parts assemble intonew viruses. Like a photocopy machine left in the "on" posi-tion, the invaded cell makes copy after copy of new viruses.When it is full of new viruses, the host cell bursts open, releaseing hundreds of new viruses as it dies.

O The bacterium burstsopen, releasing newviruses. The viruses goon to infect more cells.

Active Virus

The proteins and

genetic material

assemble into

new viruses that

fill the bacterium,

The virus's genetic material takes over the cellfunctions of the bacterium. The cell starts toproduce the virus's proteins and genetic material.

Viruses Other viruses do not immediately become

Hidde%stead, they "hide" for a while. After a hidden virus

active• host cell, The

its genetic virus does

material not

becomes appear to

part

affect of

the

the

cell's

cell's

genetic naterial.

ay stay in this inactive state for years. Each time

fjnctionsc}dditides, the virus's genetic material is copied along

the host netic material. Then, under certain conditions,

odth the host's gematerial suddenly becomes active. It takes

virus's genetic

over the the cell's

the cell

firnctions

is filll of

in

new

much

viruses

the same

and

way

bursts

that

open.

active viruses

do. Soon,that causes cold sores is an example of a hidden

The virus remain inactive for months or years inside nerve

While hidden, the virus causes no symptoms.

When it becomes active, the virus causes a swollen, painful

sore to form near the mouth. Strong sunlight and stress are

Go Onlinetwo factors that scientists believe may activate a cold sore virus.

After an active period, the virus once again "hides" in the nerveactiveeg

cells until it becomes active again.

For: Active and Hidden Viruses activityWhere in a host cell does a hidden virus "hide"

Reading it is inactive? Visit: PHSchool.comJ Checkpointwhile

Web Code: cep-1021

O A virus attachesto the surface ofa bacterium.

The new viruses crowdthe bacterium. Finally,the cell bursts open andreleases the new viruses.

Hidden Virus

The virus injectsits genetic materialinto the bacterium.

O The virus's genetic materialbecomes part of the geneticmaterial of the bacterium.

The cell begins to pro-duce the virus's proteinsand genetic material, whichassemble into new viruses.

O After some time, the virus's

genetic material removes

itself and becomes active.

Chapter 7 • 213

Viruses and Disease

FIGURE 4Viral DiseasesAlthough there is currently nocure for viral diseases, there areways to treat the symptoms andprevent their transmission.Relating Cause and Effect Whydoes the flu often pass quicklyfrom one family member toanother?

INFLUENZA (Flu)

If you've ever had a cold sore or been sick with the flu, you knthat viruses can cause disease. Some diseases, such as coldsmild—people are sick for a short time but soon recover. 0th

, are

diseases, such as acquired immunodeficiency Syndromeer

AIDS, have much more serious consequences on the body.

Viruses also cause diseases in organisms other thhumans. For example, apple trees infected by the apple mosaicvirus may produce less fruit. House pets, such as dogs and catscan get deadly viral diseases, such as rabies and distemper.

The Spread of Viral Diseases Viral diseases can bespread in various ways. For example, some viral diseases can bespread through contact with a contaminated object, while 0th.ers are spread through the bite of an infected animal. Someviruses, such as cold and flu viruses, can travel in tiny drops ofmoisture that an infected person sneezes or coughs into the air.Other viruses can spread only through contact with body flu-ids, such as blood.

Treating Viral Diseases There are currently no cures forviral diseases. However, many over-the-counter medications canhelp relieve symptoms of a viral infection. While they can makeyou feel better, these medications can also delay your recovery ifyou resume your normal routine while you are still sick. Thebest treatment for viral infections is often bed rest. Resting,drinking plenty of fluids, and eating well-balanced mealsmay be all you can do while you recover from a viral disease.

Symptoms: High fever; sore throat;headache; cough

How It Spreads: Contact with con-CHICKENPOX

Fever; rash

Treatment:

Prevention:

214 •

taminated objects;inhaling droplets

Bed rest; fluids

Vaccine (mainly forthe high-risk ill,elderly, and young)

Symptoms: red, itchy

How It Spreads: Contact with the rash;inhaling droplets

Treatment: Antiviral drug(for adults)

Prevention: Vaccine

Chickenpox virus

Viral Diseases Of course, you'd probably

ther not get sick in the first place. An important tool that

helps prevent the spr

vaccine is a substance introduced into the body to stimulate

the production of chemicals that destroy specific disease-caus-

viruses and organisms. A viral vaccine may be made from

weakened or altered viruses. Because they have been weakened

altered, the viruses in the vaccine do not cause disease.

Instead, they trigger the body's natural defenses. In effect, the

vaccine puts the body "on alert." If that disease-causing virus

ever invades the body, it is destroyed before it can cause dis-

you may have been vaccinated against diseases such as

polio, measles, and chickenpox.

Another important way to protect against viral diseases is

to keep your body healthy. You need to eat nutritious food, as

well as get enough sleep, fluids, and exercise. You can also pro-

tect yourself by washing your hands often and by not sharing

eating or drinking utensils.

Unfortunately, despite your best efforts, you'll probably get

viral infections, such as colds, from time to time. When you do

get ill, get plenty of rest, and follow your doctor's recommen-

dations. Also, it's very important to try not to infect others.

FIGURE 5

VaccinesVeterinarians can give pets vaccine

injections that protect the animalsagainst many viral diseases.

Reading Why don't vaccines cause disease themselves?Checkpoint

Section 1 Assessment

s@Target Reading Skill Sequencing Refer to your

flowcharts about how viruses multiply as you

answer Question 3.

Reviewing Key Concepts1. a. Defining What is a virus?

b Comparing and Contrasting How are viruses

similar to organisms?

c. Inferring Scientists hypothesize that virusescould not have existed on Earth beforeorganisms appeared. Use what you knowabout viruses to support this hypothesis.

2, a. Identifying basic structure do allviruses share?

b Relating Cause and Effect What role do theproteins in a virus's outer coat play in theInvasion of a host cell?

Reviewing How does an active virus

multiply?

b. Sequencing List the additional steps that

occur when a hidden virus multiplies.

c. Classifying Do you think that the cold virus

is an active virus or a hidden virus? Explain.

Reviewing What is often the best treatment

for viral diseases?

b. Explaining How are vaccines important in

preventing viral diseases?

Writing in SciencePublic Service Announcement Write apublic service announcement for a radio show

that teaches young children how to stay

healthy during cold and flu season.

Chapter 7 • 215

How Many Viruses Fiton a Pin?

ProblemHow can a model help you understand how smallviruses are?

Skills Focuscalculating, making models

Materials• straight pin • long strips of paper • pencil• meter stick • scissors • tape• calculator (optional)

Procedure1. Examine the head of a straight pin. Write a

prediction about the number of viruses thatcould fit on the pinhead. CAUTION: Avoidpushing the pin against anyone's skin.

2. Assume that the pinhead has a diameter ofabout 1 mm. If the pinhead were enlarged10,000 times, then its diameter would mea-sure 10 m. Create a model of the pinhead bycutting and taping together narrow strips ofpaper to make a strip that is 10 m long. Thestrip of paper represents the diameter of theenlarged pinhead.

3. Lay the 10-m strip of paper on the floor ofyour classroom or in the hall. Imagine creat-ing a large circle that had the strip as itsdiameter. The circle would be the pinhead atthe enlarged size. Calculate the area of theenlarged pinhead using this formula:

Area = x Radius2

Remember that you can find the radius bydividing the diameter by 2.

4. A virus particle may measure 200 nm on eachside (1 nm equals a billionth of a meter). Ifthe virus were enlarged 10,000 times, eachside would measure 0.002 m. Cut out asquare 0.002 m by 0.002 m to serve as amodel for a virus. (Hint: 0.002 m = 2 mm.)

216

5. Next, find the area in meters of one virusparticle at the enlarged size. Remember thatthe area of a square equals side x side.

6. Now divide the area of the pinhead that youcalculated in Step 3 by the area of one virusparticle to find out how many viruses couldfit on the pinhead.

7. Exchange your work with a partner, andcheck each other's calculations.

Analyze and Conclude1.

2.

3.

4.

Calculating Approximately how manyviruses can fit on the head of a pin?

Predicting How does your calculation com-pare with the prediction you made? If thetwo numbers are very different, explain whyyour prediction may have been inaccurate.

Making Models What did you learn aboutthe size of viruses by magnifying both theviruses and pinhead to 10,000 times theiractual size?

Communicating In a paragraph, explain whyscientists sometimes make and use enlargedmodels of very small things such as viruses,

More to ExploreThink of another everyday object that you could

use to model some other facts about viruses,such as their shapes or how they infect cells.Describe your model and explain why the object

would be a good choice.

These papilloma viruses, whichcause warts, are about 50 nmin diameter. V