Table Of ContentU
N
NIT Dear Colleague,
From Microorganisms U I
It’s only natural. Because we’re animals our- T
selves, we tend to be more interested in the lives of
to Plants 6
other animals. We tend to think of evolution largely
Chapters in terms of the origins of major groups of animals,
20 Viruses and and we often consider the well-being of ecosystems
Prokaryotes
in terms of the animals that may or may not be
21 Protists and Fungi
present and part of the food chain. But, if we force
22 Introduction to Plants
ourselves to think in purely biological terms, we
23 Plant Structure
and Function animals make up only a tiny part of the range and
24 Plant Reproduction diversity of life on Earth. The real players, the ones
and Response
that have changed this planet in fundamental ways,
introduce the
are microorganisms and plants. Students don’t
always appreciate this, and it’s a special challenge
• Unity and Diversity of Life to open their eyes to these remarkable forms of life.
• Structure and Function
Every time I take a walk through the woods
• Growth, Development,
and Reproduction near my house, I’m struck by the obvious ways in
• Cellular Basis of Life which plants dominate the landscape, and by the
• Interdependence in Nature
not-so-obvious ways in which decomposers such as
“In sports, a most bacteria, fungi, and slime molds shape the living
valuable player, or MVP, is world. Even more amazing are the protists, whose
the person most responsible for a
various members exemplify nearly every conceiv-
team’s success. Which organisms are
the MVPs of life? Certainly not us—we able way of making a living on this little planet.
could disappear from this planet, and
Indeed, the cellular and biochemical diversity of
other forms of life would go on just fine.
The real stars of life on Earth, its these organisms is so great that, compared to them,
MVPs, are its microorganisms, all animals are pretty much the same. If that’s a
fungi, and plants. We almost
shock to your students, point out to them that biolo-
never notice these super-
stars, unless we look very gists now suspect that huge numbers of bacteria
closely, but without
live deep beneath the surface, thriving in darkness,
them our lives would
be impossible.” often under some of the most extreme conditions
imaginable. In fact, the abundance of underground
bacteria is so great that their mass might dwarf all
571
life found on Earth’s surface.
Students may know that microorganisms and
plants are essential to our lives, but many have a
0001_Biology_UnitOpener_Options.indd 571 7/16/09 1:35:03 PM
difficult time believing that these organisms are just
as alive as you or I. Nonetheless, as teachers, one
of the greatest gifts we can give our students is to
extend their vision beyond the obvious—and I can
think of no better way to do exactly that than to
spend some time investigating these extraordinary
organisms.
From Microorganisms to Plants 571
CHAPTER
Viruses and Prokaryotes
PLANNER
Chapter Contents Time Core Resources
Chapter Preview Student Edition, pp. 572–573 Biology.com Untamed Science Video •
Chapter Mystery, p. 573 Vocabulary Flash Cards
20.1 Viruses SC.912.N.1.1, 1 period Student Edition, pp. 574–579 Study Workbook B 20.1 Worksheets
The Discovery of Viruses • SC.912.L.14.6 1/2 block Inquiry 20.1 Quick Lab, p. 575 l2 Spanish Study Workbook 20.1 Worksheets
Viral Infections Study Workbook A 20.1 Worksheets l2 Biology.com 20.1 Lesson Overview •
Biology.com Visual Analogy: How a Lytic Virus Is Like 20.1 Lesson Notes • 20.1 Self-Test •
an Outlaw • InterActive Art: Two Types of 20.1 Lesson Assessment
Virus Reproduction
Assessment Resources Book Visual Quiz l2
20.2 Prokaryotes SC.912.E.7.1, 1 period Student Edition, pp. 580–585 Study Workbook B 20.2 Worksheets
SC.912.L.14.3,
Classifying Prokaryotes • SC.912.L.15.5, 1/2 block Study Workbook A 20.2 Worksheets l2 Spanish Study Workbook 20.2 Worksheets
Structure and Function • SC.912.L.15.6, Biology.com Art Review: Prokaryote Structure and Biology.com 20.2 Lesson Overview •
The Importance of Prokaryotes SC.912.L.15.15, Classification 20.2 Lesson Notes • 20.2 Self-Test •
SC.912.L.16.17,
Assessment Resources Book Visual Quiz l2 20.2 Lesson Assessment
SC.912.L.17.9
20.3 Diseases Caused by SC.912.N.1.1, 1/2 period Student Edition, pp. 586–593 Study Workbook B 20.3 Worksheets
SC.912.N.1.6,
Bacteria and Viruses SC.912.L.14.6, 1/4 block Inquiry 20.3 Analyzing Data, p. 591 l2 Spanish Study Workbook 20.3 Worksheets
Bacterial Diseases • Viral Diseases • SC.912.L.14.52, Study Workbook A 20.3 Worksheets l2 Biology.com 20.3 Lesson Overview •
Emerging Diseases • Biology & HE.912.C.1.8, Biology.com Data Analysis: MRSA on the Rise • 20.3 Lesson Notes
MA.912.S.3.2
Society: Should More Vaccinations Art in Motion: Prion Infection Mechanism •
Be Required? 20.3 Self-Test • 20.3 Lesson Assessment
Chapter Pre-Lab SC.912.N.1.1, 1 period Student Edition, p. 594 l2 Lab Manual B Controlling Bacterial Growth
SHCE..991122..CL..114.8.6, 1/2 block Lab Manual A Controlling Bacterial Growth l2 • Data Analysis: MRSA on the Rise • Hands-On
Activity: How Do Viruses Differ?
Differentiated Instruction Tools
Study Workbook B includes worksheets with lesson-level differentiated instruc-
Differentiated Instruction Key
tion support and explanations of differentiated instruction teaching strategies.
Lab Manual B includes skills labs, simplified chapter labs, and hands-on activities. l1 Special Needs or Struggling Students
Ell English Language Learners
ELL Handbook explains ways to make Biology more accessible to ELL students.
lPR Less Proficient Readers
Spanish Study Workbook is a Spanish translation of Study Workbook A. l2 On-Level Students
Multilingual Glossary is the glossary translated into ten languages. l3 Advanced Students
572a Chapter 20
Additional Resources Chapter Review
Chapter Preview Student Edition, pp. 572–573 Biology.com Untamed Science Video •
Student Edition Study Guide, p. 595 l2
Chapter Mystery, p. 573 Vocabulary Flash Cards
Study Workbook A Chapter 20 Vocabulary Review l2 •
Chapter 20 Chapter Mystery/21st Century Skills Activity l2 l3
20.1 Viruses 1 period Student Edition, pp. 574–579 Study Workbook B 20.1 Worksheets l1 Ell lPR
Transparencies, pp. 240–248 l1 Ell lPR l2
The Discovery of Viruses • 1/2 block Inquiry 20.1 Quick Lab, p. 575 Spanish Study Workbook 20.1 Worksheets Ell Biology.com Untamed Science Video • Editable Worksheets of
Viral Infections Study Workbook A 20.1 Worksheets Biology.com 20.1 Lesson Overview •
Study Workbooks A and B and Lab Manuals A and B •
Biology.com Visual Analogy: How a Lytic Virus Is Like 20.1 Lesson Notes • 20.1 Self-Test •
Chapter 20 Flash Cards and Crossword Puzzle
an Outlaw • InterActive Art: Two Types of 20.1 Lesson Assessment
Virus Reproduction
Untamed Science DVD • Classroom Resources CD
Assessment Resources Book Visual Quiz
(includes lesson presentations and editable worksheets)
20.2 Prokaryotes 1 period Student Edition, pp. 580–585 Study Workbook B 20.2 Worksheets l1 Ell lPR
Classifying Prokaryotes • 1/2 block Study Workbook A 20.2 Worksheets Spanish Study Workbook 20.2 Worksheets Ell Chapter Assessment
Structure and Function • Biology.com Art Review: Prokaryote Structure and Biology.com 20.2 Lesson Overview •
The Importance of Prokaryotes Classification 20.2 Lesson Notes • 20.2 Self-Test •
Student Edition Assessment, pp. 596–599 l2
Assessment Resources Book Visual Quiz 20.2 Lesson Assessment
Study Workbook B Chapter 20 Chapter Review l1 Ell lPR •
20.3 Diseases Caused by 1/2 period Student Edition, pp. 586–593 Study Workbook B 20.3 Worksheets l1 Ell lPR Chapter 20 Taking a Standardized Test l1 Ell lPR
Bacteria and Viruses 1/4 block Inquiry 20.3 Analyzing Data, p. 591 Spanish Study Workbook 20.3 Worksheets Ell Assessment Resources Book Chapter 20 Test A l2 •
Bacterial Diseases • Viral Diseases • Study Workbook A 20.3 Worksheets Biology.com 20.3 Lesson Overview • Chapter 20 Test B l1 Ell lPR
Biology.com Chapter 20 Assessment • Editable Worksheets
Emerging Diseases • Biology & Biology.com Data Analysis: MRSA on the Rise • 20.3 Lesson Notes
of Chapter 20 Visual Quizzes and Chapter 20 Tests A and B
Society: Should More Vaccinations Art in Motion: Prion Infection Mechanism •
Be Required? 20.3 Self-Test • 20.3 Lesson Assessment
ExamView Assessment Suite • Classroom Resources CD
Chapter Pre-Lab 1 period Student Edition, p. 594 Lab Manual B Controlling Bacterial Growth (includes lesson presentations and editable worksheets)
1/ block Lab Manual A Controlling Bacterial Growth • Data Analysis: MRSA on the Rise • Hands-On
2 Time: 1 period, 1/2 block
Activity: How Do Viruses Differ? l1 Ell lPR
Pressed for Time?
Preview the Chapter Introduce the vocabulary for Lesson section of The Discovery of Viruses, and Viral Infections.
20.1. Preview the images on pp. 1040–1043 in the Discuss Figure 20–3. Assign students to read all of Lesson
Diversity of Life guide and discuss the variations that exist 20.2 and discuss Figures 20–7 and 20–13.
among different bacteria.
Assess Assign questions 1 and 2 in the 20.1 Assessment,
Cover the Chapter Quickly In 20.1, have students read the 20.2 Assessment, and questions 1–23 and 37–42 of
the definition of a virus, the Structure and Composition the Chapter 20 Assessment.
Viruses and Prokaryotes 572b
0
FLoRIda NeXT GeNeRaTIoN
2 sUNshINe sTaTe sTaNdaRds
Viruses and
Connect to the Big Idea
Nature of science SC. 912.N.1.1, SC.912.N.1.6;
R earth and space science SC.912.E.7.1; organization
Use the photograph of colonies of bacteria Prokaryotes and development of Living organisms SC.912.L.14.3,
E The mad cows
to introduce the topic of microbes. Point SC.912.L.14.6, SC.912.L.14.52; diversity and evolution
T out that bacteria are not the only type of of Living organisms SC.912.L.15.6, SC.912.L.15.15; In 1986, something
heredity and Reproduction SC.912.L.16.17; strange began to
pmicrobe. Ask students if they can identify other Interdependence SC.912.L.17.9; health Literacy: concepts
happen to cattle
microbes. (Sample answer: viruses) Ask students to Cellular Basis of Life HE.912.C.1.8; Reading/Language arts LA.910.4.2.2;
A in Great Britain.
identify some diseases microbes cause in people. Q: A re all microbes that make us sick made of living cells? mathematics MA.912.S.3.2. See lessons for details. Without warning, the
(Sample answer: Microbes cause colds and the flu.)
H animals began acting
Also, explain that not all bacteria cause illness. Ask
strangely, losing control
Cstudents to anticipate the answer to the question,
of their movements, staggering
Are all microbes that make us sick made
and stumbling, and eventually dying.
of living cells?
Farmers watched helplessly as the
Have students read over the Chap- disease they called “mad cow” spread
ter Mystery. Have a class discussion through their cattle. The disease affected
about possible causes of BSE. After more than 30,000 cattle in 1991.
students have completed Chapter 20, have them Studies of the brains of cattle killed
speculate how the solution to the Chapter Mystery by mad cow disease showed that large
might be used to help answer the chapter Essential areas of the animals’ brains had been
Question. destroyed. Under the microscope,
the holes in the tissue made the brain
resemble a sponge. Because of this,
Have students preview the chapter the disease was given the name bovine
vocabulary terms using the Flash Cards. spongiform encephalopathy, or BSE. But
the cause of the disease was a mystery.
As you read this chapter, look for clues
that explain the culprit behind this
disease. Then, solve the mystery.
Never stop exploring Your world.
Finding what caused this disease is only
the beginning. Take a video field trip
with the ecogeeks of Untamed Science to
explore the other side of the story—you’ll
see that not all microbes are “bad.”
Colonies of E. coli bacteria
“Understanding by Design” is registered as a trademark with the Patent
and Trademark Office by the Association for Supervision of Curriculum
Development (ASCD). ASCD has not authorized, approved, or sponsored
this work and is in no way affiliated with Pearson or its products.
Chapter 20 • Flash Cards • Untamed Science Video • Chapter Mystery
NEXT GENERATION SUNSHINE STATE STANDARDS
572 Viruses and Prokaryotes 573
For the full text of all benchmarks, see the Course
Overview in the front matter of this book.
Key standards: Chapter 20 covers benchmarks from
0572_Bio10_se_Ch20_CO_0572 572 2/22/11 3:30 PM 0572_Bio10_se_Ch20_CO_0573 573 2/22/11 3:30 PM
Standard 14, Organization and Development of Understanding by Design
Living Organisms, including SC.912.L.14.6 Explain
Chapter 20 describes prokaryotes, viruses, and the diseases they cause. The graphic
the significance of genetic factors, environmental
organizer at the right shows how these topics are connected to the chapter’s Big Idea,
factors, and pathogenic agents to health from the
Essential Question, and Guiding Questions. Together, these ideas and questions help
perspectives of both individual and public health.
students build toward the Unit 6 Enduring Understanding that from micro organisms
to plants, organisms vary widely in the way they carry out basic life processes.
pERFORMANCE GOALS
In Chapter 20, there are many chances to assess your students’ understanding of
viruses and prokaryotes. For example, students will write a comic-strip illustrating a
lytic or lysogenic infection, analyze data on trends in bacterial infection, and prepare
an informational flier to help curb the unnecessary use of antibiotics.
572 Chapter 20
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C
FLoRIda NEXT GENERaTIoN
sUNshINE sTaTE sTaNdaRds H
Viruses and
What’s Online
Nature of science SC. 912.N.1.1, SC.912.N.1.6;
A
Earth and space science SC.912.E.7.1; organization
Prokaryotes and development of Living organisms SC.912.L.14.3,
ThE mad Cows P
SC.912.L.14.6, SC.912.L.14.52; diversity and Evolution
of Living organisms SC.912.L.15.6, SC.912.L.15.15; In 1986, something Extend your reach by using T
heredity and Reproduction SC.912.L.16.17; strange began to these and other digital assets offered at
E
Interdependence SC.912.L.17.9; health Literacy: Concepts happen to cattle Biology.com.
Cellular Basis of Life HE.912.C.1.8; Reading/Language arts LA.910.4.2.2;
in Great Britain. R
Q: A re all microbes that make us sick made of living cells? mathematics MA.912.S.3.2. See lessons for details. Without warning, the CHAPTER MYSTERY
What was the cause of the cows’ symptoms? Stu-
animals began acting 2
dents use clues to gather information about the
strangely, losing control
cause of “mad cow” disease, or bovine spongiform 0
of their movements, staggering
encephalopathy.
and stumbling, and eventually dying.
Farmers watched helplessly as the
UNTAMED SCIENCE VIDEO
disease they called “mad cow” spread
Have students take a video field trip to learn more
through their cattle. The disease affected
about beneficial bacteria.
more than 30,000 cattle in 1991.
Studies of the brains of cattle killed
by mad cow disease showed that large
areas of the animals’ brains had been
destroyed. Under the microscope,
the holes in the tissue made the brain
resemble a sponge. Because of this,
the disease was given the name bovine
spongiform encephalopathy, or BSE. But
the cause of the disease was a mystery.
As you read this chapter, look for clues
that explain the culprit behind this
disease. Then, solve the mystery.
Never stop Exploring Your world.
Finding what caused this disease is only VISUAl ANAlOGY
the beginning. Take a video field trip How is a virus like an outlaw? Students can go online
with the ecogeeks of Untamed Science to to find out.
explore the other side of the story—you’ll
see that not all microbes are “bad.” INTERACTIVE ART
Colonies of E. coli bacteria
By working with a dynamic diagram, students will
understand more about virus reproduction.
ART REVIEW
Activities help students compare archaea and bac-
teria, learn the structure of a typical prokaryotic
Chapter 20 • Flash Cards • Untamed Science Video • Chapter Mystery
cell, and match pictures of bacteria to the names of
their shapes.
572 Viruses and P rokaryotes 573
DATA ANAlYSIS
Students analyze data about MRSA to identify fac-
tors contributing to its increasing prevalence.
Chapter 20
Big Idea: Cellular
ART IN MOTION
Basis of Life Encourage students to see what prions are like and
20.1 GQ: What is a virus? how these tiny particles set off a chain reaction in
the brain.
Chapter 20 EQ:
20.2 GQ: What are prokaryotes, and why are
Are all microbes that
they important?
make us sick made
of living cells?
20.3 GQ: How can we prevent bacterial and
viral diseases from spreading?
Viruses and Prokaryotes 573
1
. Structure and Composition Viruses differ widely T4Bacteriophage
0Getting Started in terms of size and structure, as you can see in
Figure 20–1. Most viruses are so small they can
Head DNA
2 Viruses be seen only with the aid of a powerful electron
microscope. The protein coat surrounding a virus Tail
Objectives is called a capsid. In addition, some viruses, such as Tail fiber
N
SC.912.L.14.6 Explain the significance of genetic factors, environmental factors, the influenza virus, have an additional membrane sheath
20.1.1 Explain how viruses reproduce. and pathogenic agents to health from the perspectives of both individual and public that surrounds the capsid. The simplest viruses
O health. Also covered: SC.912.N.1.1 contain only a few genes, whereas the most complex
20.1.2 Explain how viruses cause infection.
may have hundreds of genes. TEM 60,000×
S Key Questions THINK ABOUT IT Imagine that you have been To enter a host cell, most viruses have proteins
How do viruses reproduce? presented with a great puzzle. Farmers have on their surface membrane or capsid that bind to Tobacco Mosaic Virus
SStudent Resources begun to lose their valuable tobacco crop to a receptor proteins on the cell. In either case, the pro-
What happens after a virus
plant disease that first appears as a yellowing teins “trick” the cell to take in the virus, or in some
E infects a cell?
Study Workbooks A and B, 20.1 Worksheets of the leaves. Eventually the leaves wither cases just its genetic material. Once inside the cell, RNA
LSpanish Study Workbook, 20.1 Worksheets Vocabulary and fall, killing the plant. To determine the viral genes are eventually expressed and may
virus what is causing the disease, you take leaves destroy the cell. Capsid
Lab Manual A, 20.1 Quick Lab Worksheet capsid from a diseased plant and crush them Because viruses must bind precisely to proteins proteins
bacteriophage to produce a liquid extract. You place a on the host cell surface and then use the host’s
Lab Manual B, 20.1 Hands-On Activity Worksheet
lytic infection few drops of that liquid on the leaves of genetic system, most viruses infect only a very
lysogenic infection healthy plants. A few days later, the leaves specific kind of cell. Plant viruses infect plant cells;
Lesson Overview • Lesson Notes prophage turn yellow where you put the drops. most animal viruses infect only certain related spe- TEM 400,000×
• Activities: Visual Analogy, InterActive Art retrovirus You use a light microscope to look for a germ that might cause the cies of animals; bacterial viruses infect only certain
• Assessment: Self-Test, Lesson Assessment Taking Notes disease, but none can be seen. In fact, when even the tiniest of cells are types of bacteria. Viruses that infect bacteria are Influenza Virus
filtered out of the liquid, the liquid still causes the disease. You hypoth- called bacteriophages, which literally means “bac-
Venn Diagram Make a Venn
diagram in which to record esize that the liquid must contain disease-causing agents so small that teria eaters.” Capsid RNA
For corresponding lesson in the they are not visible under the microscope and can pass right through
the similarities and differences
Foundation Edition, see pages 480–484. between viruses and cells. Fill the filter. Although you cannot see the tiny disease-causing particles, Figure 20–1 Diversity of Viral
it in as you read the lesson. you’re sure they are there. What would you do next? How would you Forms Viruses come in a wide
deal with the invisible? variety of sizes and shapes. Three
types of viruses are shown here.
Interpret Diagrams What kind
Activate Prior Knowledge The Discovery of Viruses of nucleic acid does each virus Surface Membrane
type have? proteins envelope
Have students raise their hands if they have ever How do viruses reproduce? TEM 21,000×
missed out on some important event, such as a foot- If you think you could have carried out the investigation described
ball game, because they had a cold. Explain that a above, congratulations! You’re walking in the footsteps of a 28-year-
cold is an example of an illness caused by a virus. old Russian biologist, Dmitri Ivanovski. In 1892, Ivanovski demon- SC.912.N.1.1
strated that the cause of this particular plant disease—called tobacco
Tell students Lesson 20.1 describes the structure of British scientists
carefully investigated mosaic disease—was found in the liquid extracted from infected
viruses and what happens when a virus infects a cell.
the veterinary histories plants. But he could not pin down the culprit. How Do Viruses Differ in Structure? Analyze and Conclude
oAfl l1 16699 c haattdle b weeitnh gBiSvEe.n Discovery of Viruses In 1897, Dutch scientist Martinus Beijerinck 1 M2a ke m3 od4el s o5f two6 of t7he v8iruse9s shown in Figure 20–1. 1. Use Models Which parts of
your models are found in all
Students should infer that a substance in faenedd beonnriec hmeeda wl pitrho mteiena t snuagmgeesdt ethde tshea pt atirntiyc lpeasr vtiirculesse si,n a tfhteer jtuhicee L caatuins ewdo trhde fdoirs “epasoei,s oannd.” hTeh en, 1 2 La3b el t4h e p5arts 6of ea7ch o8f yo9ur virus models. viruses?
the meat and bone meal protein added fHroomw csolauuldg httheirse d cattle. itno b1a9c3c5o, mthoe sAaimc evriricuasn. Lbiivoicnhge omrgisatn Wisemnsd delol Sntoatn cleryy sitsaolllaiztee,d s ocr Sytsatanllse yo f 1 2 c3e n Mti4me aestue5rrse. aCn6odn rve7ecrot rtd8h eth lee9n legnthg tohf oefa ceha cmh oodf eylo iunrt ov inrauns ommoedteelrss ibny 2of. oDnrea owr Cbootnhc loufs iyoonus r Wmhoidcehl sp aarrets
to the cattle’s feed caused the spread of par daicsteicaes es?pread inferred that viruses were not truly alive. This is a conclusion that biol- using the following formula: 1 cm = 10 million nm. found in only some viruses?
BSE. Students can go online to Biology.com to ogists still recognize as being valid today. A virus is a nonliving particle 1 2 3 4 M5easu6re th7e len8gth 9of each virus you modeled. Divide the 3. Calculate How many times
gather their evidence. made of proteins, nucleic acids, and sometimes lipids. Viruses length of each model by the length of the actual virus to determine larger are your models than the
can reproduce only by infecting living cells. how much larger each model is than the virus it represents. viruses they represent?
NEXT GENERATION SUNSHINE STATE STANDARDS
574 Lesson 20.1 • Lesson Overview • Lesson Notes Viruses and Prokaryotes 575
For the full text of all benchmarks, see the Course
Overview in the front matter of this book.
Other key benchmarks: SC.912.N.1.1 Define a 0574_Bio10_se_Ch20_S1_0574 574 2/22/11 3:31 PM 0574_Bio10_se_Ch20_S1_0575 575 2/22/11 3:32 PM
Teach for Understanding
problem based on a specific body of knowledge, for
example: biology, chemistry, physics, and earth/space
ENDURING UNDERSTANDING From microorganisms to plants, organisms vary widely
science.
in the way they carry out basic life processes.
GUIDING QUESTION What is a virus?
EVIDENCE OF UNDERSTANDING After completing the lesson, give students the
following assessment to show their understanding of the characteristics of viruses.
Have students work in pairs to make comic strips depicting either a lytic or a
lysogenic infection. Explain that a comic strip uses a series of illustrations and text to
depict action. Provide several appropriate comic strips as models. Tell students that
their comic strips should be creative and scientifically accurate.
574 Chapter 20 • Lesson 1
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L
Structure and Composition Viruses differ widely T4Bacteriophage E
in terms of size and structure, as you can see in
Teach
Figure 20–1. Most viruses are so small they can Head DNA S
Viruses be seen only with the aid of a powerful electron
microscope. The protein coat surrounding a virus Tail S
is called a capsid. In addition, some viruses, such as Tail fiber Build Science Skills
O
SC.912.L.14.6 Explain the significance of genetic factors, environmental factors, the influenza virus, have an additional membrane sheath
and pathogenic agents to health from the perspectives of both individual and public that surrounds the capsid. The simplest viruses Have students examine the structure and composi-
health. Also covered: SC.912.N.1.1 N
contain only a few genes, whereas the most complex tion of the three viruses shown in Figure 20–1.
may have hundreds of genes. TEM 60,000×
Then, have students use the information in the figure
Key Questions THINK ABOUT IT Imagine that you have been To enter a host cell, most viruses have proteins
How do viruses reproduce? presented with a great puzzle. Farmers have on their surface membrane or capsid that bind to Tobacco Mosaic Virus and the text on this page to write a paragraph com- 2
begun to lose their valuable tobacco crop to a receptor proteins on the cell. In either case, the pro- paring and contrasting the viruses. Remind students
What happens after a virus 0
plant disease that first appears as a yellowing teins “trick” the cell to take in the virus, or in some that comparing and contrasting involves identifying
infects a cell?
of the leaves. Eventually the leaves wither cases just its genetic material. Once inside the cell, RNA both similarities and differences. Ask volunteers to .
Vocabulary and fall, killing the plant. To determine the viral genes are eventually expressed and may share their paragraphs with the class. 1
virus what is causing the disease, you take leaves destroy the cell. Capsid
capsid from a diseased plant and crush them Because viruses must bind precisely to proteins proteins
bacteriophage to produce a liquid extract. You place a on the host cell surface and then use the host’s DIFFERENTIATED INSTRUCTION
lytic infection few drops of that liquid on the leaves of genetic system, most viruses infect only a very
lysogenic infection healthy plants. A few days later, the leaves specific kind of cell. Plant viruses infect plant cells; LpR Less Proficient Readers Students who might
prophage turn yellow where you put the drops. most animal viruses infect only certain related spe- TEM 400,000× have difficulty reading the text on this page can base
retrovirus You use a light microscope to look for a germ that might cause the cies of animals; bacterial viruses infect only certain their compare/contrast paragraph exclusively on the
Taking Notes disease, but none can be seen. In fact, when even the tiniest of cells are types of bacteria. Viruses that infect bacteria are Influenza Virus information in Figure 20–1. Explain that their para-
filtered out of the liquid, the liquid still causes the disease. You hypoth- called bacteriophages, which literally means “bac-
Venn Diagram Make a Venn graphs should include ways the viruses are similar
esize that the liquid must contain disease-causing agents so small that teria eaters.” RNA
diagram in which to record Capsid and ways they are different.
they are not visible under the microscope and can pass right through
the similarities and differences
between viruses and cells. Fill the filter. Although you cannot see the tiny disease-causing particles, Figure 20–1 Diversity of Viral
it in as you read the lesson. you’re sure they are there. What would you do next? How would you Forms Viruses come in a wide
deal with the invisible? variety of sizes and shapes. Three ELL Focus on ELL:
types of viruses are shown here.
Interpret Diagrams What kind Access Content
The Discovery of Viruses of nucleic acid does each virus Surface Membrane
How do viruses reproduce? type have? proteins envelope TEM 21,000× ALL SpEAKERS Have students use the
Lesson Preview strategy to enhance their
If you think you could have carried out the investigation described
comprehension of the content of Lesson 20.1.
above, congratulations! You’re walking in the footsteps of a 28-year-
old Russian biologist, Dmitri Ivanovski. In 1892, Ivanovski demon- SC.912.N.1.1 Have students locate and read the boldface
British scientists strated that the cause of this particular plant disease—called tobacco heads in the lesson and preview each of the
carefully investigated mosaic disease—was found in the liquid extracted from infected figures and captions. Then, have students form
the veterinary histories plants. But he could not pin down the culprit. How Do Viruses Differ in Structure? Analyze and Conclude
small groups. Within the groups, have them
oAfl l1 16699 c haattdle b weeitnh gBiSvEe.n Discovery of Viruses In 1897, Dutch scientist Martinus Beijerinck 1 M2a ke m3 od4e ls o5f two6 of t7he v8iruse9s shown in Figure 20–1. 1. Use Models Which parts of discuss the lesson topics and figures. Ask each
your models are found in all
faenedd beonnriec hmeeda wl pitrho mteiena t snuagmgeesdt ethde tshea pt atirntiyc lpeasr vtiirculesse si,n a tfhteer jtuhicee L caatuins ewdo trhde fdoirs “epasoei,s oannd.” hTeh en, 1 2 La3b el 4th e p5arts6 of ea7ch o8f yo9ur virus models. viruses? group to produce a written summary of its
from slaughtered cattle. in 1935, the American biochemist Wendell Stanley isolated crystals of 1 2 3 M4e asu5re a6nd re7cord8 the9 length of each of your virus models in 2. Draw Conclusions Which parts discussion. Beginning and intermediate speakers
How could this tobacco mosaic virus. Living organisms do not crystallize, so Stanley centimeters. Convert the length of each model into nanometers by of one or both of your models are should be paired with advanced and advanced
par daicsteicaes es?pread inferred that viruses were not truly alive. This is a conclusion that biol- using the following formula: 1 cm = 10 million nm. found in only some viruses? high speakers to complete the written summary.
ogists still recognize as being valid today. A virus is a nonliving particle 1 2 3 4 M5easu6re th7e len8gth 9of each virus you modeled. Divide the 3. Calculate How many times Student Wkbks A/B, Appendix S8, Lesson
made of proteins, nucleic acids, and sometimes lipids. Viruses length of each model by the length of the actual virus to determine larger are your models than the
can reproduce only by infecting living cells. how much larger each model is than the virus it represents. viruses they represent? Preview.
574 Lesson 20.1 • Lesson Overview • Lesson Notes Viruses and Prokaryotes 575
virus, have them measure the vertical
rod at the center of the field of view.)
• Divide this length by the magnifica-
pURpOSE Students will make models of tion. The resulting number is the
two different viruses and conclude that length of the actual virus.
viruses differ in structure.
ANALYZE AND CONCLUDE
MATERIALS metric ruler, scissors, tape,
1. a capsid and either DNA or RNA
craft materials
2. Sample answers: tail fiber, tail sheath,
pLANNING Write the following steps
head, membrane envelope
on the board to help students find the
length of the actual virus. They will need 3. Answers will vary. Call on volunteers Answers
these results to answer Question 3. to share their answers and explain
FIGURE 20–1 The T4 bacteriophage has DNA; the
their calculations.
• Measure the image of the viruses in tobacco mosaic virus and influenza virus have RNA.
Figure 20–1. (For the tobacco mosaic
Viruses and Prokaryotes 575
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1
Viral Infections Lysogenic Infection Some bacterial viruses, including the bacterio- BUILD Vocabulary
.
0Teach phage lambda, cause a lysogenic infection, in which a host cell is not WOrD OrIgINS The adjective
continued What happens after a virus infects a cell? immediately taken over. Instead, the viral nucleic acid is inserted into lytic, the verb lyse, and the prefix
2 After a virus has entered a host cell, what happens? Inside living the host cell’s DNA, where it is copied along with the host DNA with- lyso - all come from the Greek
word lyein, meaning “to loosen
cells, viruses use their genetic information to make multiple copies out damaging the host. Viral DNA multiplies as the host cells multiply.
Lead a Discussion of themselves. Some viruses replicate immediately, while others In this way, each generation of daughter cells derived from the original or break up.”
N
initially persist in an inactive state within the host. These two host cell is infected.
Discuss viral infections with students. patterns of infection are called lytic infection and lysogenic infection. Bacteriophage DNA that becomes embedded in the bacterial host’s
O DNA is called a prophage. The prophage may remain part of the DNA of
Ask In a lytic infection, how does the virus make Lytic Infections In a lytic infection, a virus enters a bacterial cell, the host cell for many generations. Influences from the environment—
Smore copies of itself? (by inserting its genetic infor- makes copies of itself, and causes the cell to burst, or lyse (lys). Bac- including radiation, heat, and certain chemicals—trigger the prophage
mation into a cell, which directs the cell to make and teriophage T4 is an example of a bacteriophage that causes such an to become active. It then removes itself from the host cell DNA and
S infection. Bacteriophage T4 has a DNA core inside a protein capsid directs the synthesis of new virus particles. The lysogenic infection
assemble new viral parts)
that binds to the surface of a host cell. The virus injects its DNA into now becomes an active lytic infection, as shown in Figure 20–3.
E
Ask Why can a lytic virus remain in a particular host the cell, and the cell then begins to make messenger RNA (mRNA) The details of viral infection in eukaryotic cells differ in many ways
Lcell only for a limited time? (It eventually destroys the from the viral genes. The viral mRNA is translated into viral proteins from viral infection of bacteria by bacteriophages. But for the most
host cell by causing it to burst.) that act like a molecular wrecking crew, chopping up the cell’s DNA. part, the basic patterns of infection in animals and other eukaryotes
Figure 20–2 How a Lytic Virus Is Under the control of viral genes, the host cell’s metabolic system are similar to the lytic and lysogenic infections of bacteria.
Like an Outlaw A lytic virus is similar now makes thousands of copies of viral nucleic acid and capsid
DIFFERENTIATED INSTRUCTION to the Wild West of the American proteins. The viral DNA is assembled into new virus particles. Before in Your Notebook Describe how a lysogenic infection can change
frontier in the demands the virus long, the infected cell lyses, releasing hundreds of virus particles that into a lytic infection.
L1 Struggling Students Use these basic questions makes on its host. Use Analogies After may go on to infect other cells. In its own way, a lytic virus is similar
you learn about lysogenic infections
to help students understand the sequence of events on the next page, modify this story to to an outlaw in the Wild West of the American frontier, as illustrated
in a lytic infection. make it analogous to a lysogenic cycle. in Figure 20–2. Figure 20–3 Comparing
Two Types of Bacteriophage Prophage
Infection Viruses that infect
Ask What is the first step in a lytic infection? (The
bacteria, called bacteriophages,
virus enters a cell.) may infect cells in one of LYSOGENIC INFECTION
two ways: lytic infection
Ask What happens after the virus gets into the cell? or lysogenic infection. The viral DNA inserts
(The cell makes copies of the virus.) itself into the bacterial The prophage may
chromosome, where it replicate with the
Ask What happens after many copies of the virus is called a prophage. bacterium for many
have been made? (The cell lyses, and hundreds of generations.
The virus injects DNA
virus particles are released.) into a bacterium. LYTIC INFECTION
Have students use Figure 20–2 to compare a lytic Viral genes are The prophage can
virus to an outlaw. transcribed exit the bacterial
by the host cell. chromosome and
enter a lytic cycle.
Ask In this analogy, what represents the host cell?
Viral enzymes lyse
(the town)
the bacterium’s cell
Ask Think about how viruses enter host cells. Extend wall. The new viruses
escape and infect The bacterium makes
the analogy to describe the outlaw’s entrance other bacterial cells. new viral proteins and
First, the outlaw eliminates the Next, the outlaw demands to be Finally, the outlaw forms a gang
into town. (Answers should describe the outlaw town’s existing authority. outfitted with new equipment from that leaves the town to attack new nucleic acids.
being sneaky or using trickery to gain entrance to Lytic Infection The host cell’s DNA the local townspeople. communities. The proteins
is chopped up. Lytic Infection Viruses use the host Lytic Infection The host cell bursts, and nucleic acids
the town.) cell to make viral DNA and viral releasing hundreds of virus assemble into new viruses.
proteins. particles.
Ask Think about how viruses exit host cells. Extend
the analogy to describe the condition of the town
after the outlaw leaves. (Answers will vary, but 576 Lesson 20.1 • Visual Analogy Lesson 20.1 • InterActive Art 577
should describe the outlaw destroying the town or
leaving it in disarray as he leaves.)
Quick Facts
Have students go online for further
exploration of the Visual Analogy: How a CLASSIFYING VIRUSES
Lytic Virus Is Like an Outlaw.
Viruses are nonliving particles; therefore, they are not classified into the domains,
kingdoms, and other groupings used by scientists to classify living organisms. Instead,
viruses are classified by their chemical and physical properties. The major division
Answers focuses on the type of genetic material a virus contains; thus there are DNA viruses
and RNA viruses. Viruses are then further classified by their sizes and the shapes of
FIGURE 20–2 A correct response will include an
their protein coats. Another method of classifying viruses is by the type of host a virus
analogy for the prophage being a part of the
infects; using this strategy, viruses are classified as animal viruses, plant viruses, and
bacterium for an extended period of time. Sample
bacterial viruses, or bacteriophages.
answer: The outlaw pretends to be looking for work,
takes a job at a nearby ranch, and hides out there for
a time.
576 Chapter 20 • Lesson 1
L
Viral Infections Lysogenic Infection Some bacterial viruses, including the bacterio- BUILDVocabulary E
phage lambda, cause a lysogenic infection, in which a host cell is not Word orIgIns The adjective Use Visuals
What happens after a virus infects a cell? immediately taken over. Instead, the viral nucleic acid is inserted into lytic, the verb lyse, and the prefix S
After a virus has entered a host cell, what happens? Inside living the host cell’s DNA, where it is copied along with the host DNA with- lwysoord - alylle cino,m me efaronmin gth e“t oG lroeoeske n Have students use Figure 20–3 to compare lyso S
cells, viruses use their genetic information to make multiple copies out damaging the host. Viral DNA multiplies as the host cells multiply.
or break up.” genic and lytic infections. Distribute a blank T-Chart
of themselves. Some viruses replicate immediately, while others In this way, each generation of daughter cells derived from the original
O
initially persist in an inactive state within the host. These two host cell is infected. to each student. Have students label the left side
patterns of infection are called lytic infection and lysogenic infection. Bacteriophage DNA that becomes embedded in the bacterial host’s Similarities and the right side Differences. Have them
N
DNA is called a prophage. The prophage may remain part of the DNA of complete their TCharts by entering ways in which
Lytic Infections In a lytic infection, a virus enters a bacterial cell, the host cell for many generations. Influences from the environment—
makes copies of itself, and causes the cell to burst, or lyse (lys). Bac including radiation, heat, and certain chemicals—trigger the prophage lytic and lysogenic infections are similar in the left
teriophage T4 is an example of a bacteriophage that causes such an to become active. It then removes itself from the host cell DNA and column and ways they are different in the right col 2
infection. Bacteriophage T4 has a DNA core inside a protein capsid directs the synthesis of new virus particles. The lysogenic infection umn. Then, have students form small groups, review
0
that binds to the surface of a host cell. The virus injects its DNA into now becomes an active lytic infection, as shown in Figure 20–3. their TCharts, and make any necessary revisions.
the cell, and the cell then begins to make messenger RNA (mRNA) The details of viral infection in eukaryotic cells differ in many ways .
from the viral genes. The viral mRNA is translated into viral proteins from viral infection of bacteria by bacteriophages. But for the most Study Wkbks A/B, Appendix S30, TChart. 1
that act like a molecular wrecking crew, chopping up the cell’s DNA. part, the basic patterns of infection in animals and other eukaryotes Transparencies, GO15.
Figure 20–2 How a Lytic Virus Is Under the control of viral genes, the host cell’s metabolic system are similar to the lytic and lysogenic infections of bacteria.
Like an Outlaw A lytic virus is similar now makes thousands of copies of viral nucleic acid and capsid
to the Wild West of the American proteins. The viral DNA is assembled into new virus particles. Before In Your Notebook Describe how a lysogenic infection can change DIFFERENTIATED INSTRUCTION
frontier in the demands the virus long, the infected cell lyses, releasing hundreds of virus particles that into a lytic infection.
makes on its host. Use Analogies After may go on to infect other cells. In its own way, a lytic virus is similar L1 Special Needs Have students work with a part
you learn about lysogenic infections
on the next page, modify this story to to an outlaw in the Wild West of the American frontier, as illustrated ner in order to complete the T-Chart. When students
make it analogous to a lysogenic cycle. in Figure 20–2. FIgure 20–3 Comparing have completed their work, draw a TChart on the
Two Types of Bacteriophage Prophage board, and label the columns Similarities and Differ
Infection Viruses that infect
bacteria, called bacteriophages, ences. Ask students to volunteer information from
may infect cells in one of LYSOGENIC INFECTION their charts, and record their responses on the board.
two ways: lytic infection
or lysogenic infection. The viral DNA inserts After the chart on the board is complete, discuss
itself into the bacterial The prophage may each point to clarify similarities of and differences
chromosome, where it replicate with the
between lytic and lysogenic infections.
is called a prophage. bacterium for many
generations.
The virus injects DNA L3 Advanced Students Have students learn more
into a bacterium. LYTIC INFECTION
about applications of bacteriophages in genetic engi
neering and medicine. Ask each student to write a
onepage paper summarizing his or her findings.
Viral genes are The prophage can
transcribed exit the bacterial Students can learn more about virus
by the host cell. chromosome and
reproduction from the InterActive Art: Two
enter a lytic cycle.
Types of Virus Reproduction.
Viral enzymes lyse
the bacterium’s cell
wall. The new viruses
escape and infect The bacterium makes
other bacterial cells. new viral proteins and
First, the outlaw eliminates the Next, the outlaw demands to be Finally, the outlaw forms a gang
nucleic acids.
town’s existing authority. outfitted with new equipment from that leaves the town to attack new
Lytic Infection The host cell’s DNA the local townspeople. communities. The proteins
is chopped up. Lytic Infection Viruses use the host Lytic Infection The host cell bursts, and nucleic acids
cell to make viral DNA and viral releasing hundreds of virus assemble into new viruses.
proteins. particles.
576 Lesson 20.1 • Visual Analogy Lesson 20.1 • InterActive Art 577
0574_Bio10_se_Ch20_S1_0576 576 3/26/11 1:57 AM 0574_Bio10_se_Ch20_S1_0577 577 3/26/11 1:57 AM
Check for Understanding
ONE-MINUTE RESPONSE
Write the following prompt on the board, and give students about a minute to write
a quick response summarizing their understanding.
• What happens when a cell is infected by a lytic virus? (Responses should describe
the virus injecting its genetic material into a cell, making copies of itself, and caus-
ing the cell to burst, releasing many copies of the virus.)
ADJUST INSTRUCTION Answers
If responses are incorrect or incomplete, have students review Figure 20–3. Ask them
IN YOUR NOTEBOOK Students should describe a
to locate the part of the figure describing a lytic infection. (Hint: Follow the steps
prophage exiting the bacterial chromosome and
described along the path of blue arrows.) Have a volunteer read aloud the description
entering a lytic cycle.
of the sequence of events in a lytic infection.
Viruses and Prokaryotes 577
0572_mlbio10_Ch20_0577 577 12/14/11 9:45 AM
1
TThhee v viriuruss m maakkeess m maannyy TThhee c cooppieiess a arere t rtarannsslalatetedd b byy Viruses and Cells
.
ccooppieiess o of fi tists R RNNAA.. ththee h hoosst ti nintoto n neeww v viriaral lp paartrsts..
0Teach continued TnTnheheewew p v paviarirurtrussts sea esass ssa seanemndmdb bb lbeuleu ri srnistnt toft rof or omm Characteristic Virus Cell
2 ththee h hoosst tc ceelll.l. Structure DNA or RNA in capsid, Cell membrane, cytoplasm; eukaryotes also contain
some with envelope nucleus and many organelles
Expand Vocabulary
N Reproduction Only within a host cell Independent cell division, either asexually or sexually
After students have read the information about the Genetic Code DNA or RNA DNA
CCyytotopplalassmm
O
viruses that cause the common cold and AIDS, tell Growth and No Yes; in multicellular organisms, cells increase in number
them the word part retro- means “backward.” Development and differentiate
S
A Closer Look at Two RNA Viruses About 70 percent of viruses Obtain and Use Energy No Yes
Ask Why is the word retrovirus used to describe
S contain RNA rather than DNA. In humans, RNA viruses cause a wide Response to Environment No Yes
HIV? (The genetic information of a retrovirus like
range of infections, from relatively mild colds to severe cases of AIDS.
EHIV is copied from RNA to DNA instead of from DNA Certain kinds of cancer also begin with an infection by viral RNA. Change Over Time Yes Yes
to RNA.)
L The Common Cold What happens when you get a cold? Cold
Figure 20–4 Common Cold
Ask If the virus that causes the common cold is also Infection Mechanism Once viruses attack with a very simple, fast-acting infection. A capsid settles Viruses and Cells Viruses must infect living cells in order Figure 20–6 Comparing Viruses and
an RNA virus, why is it not called a retrovirus? (In the cold virus has penetrated on a cell, typically in the host’s nose, and is brought inside, where a to grow and reproduce, taking advantage of the nutrients Cells The differences between viruses and cells
a cell infected with the common cold virus, RNA thhoes th’so cste’sll uclealrls m, iat cuhsiense trhye t o vhiorsatl cperlol’tse rinib mosaokmese sm manisyt ankeew t hceo pviieras lo Rf NthAe fvoirra tlh Re NhAos. tM’s oeawnnw mhiRleN, tAh e and cellular machinery of their hosts. This means that all aonre t hliisst eidnf oinr mthaist iochna, rwt.o uFoldr myo aun c lOaspsiinfyio vnir uBsaesse d
is not copied to make DNA. Instead, the viral RNA replicate itself. and translate it into capsids and other viral proteins. The new capsids viruses are parasites. Parasites depend entirely upon other as living or nonliving? Explain.
is translated by the cell’s ribosomes to produce assemble around the viral RNA copies, and within 8 hours, the host living organisms for their existence, harming these organ-
isms in the process.
viral proteins.) cell releases hundreds of new virus particles to infect other cells.
Despite the fact that they are not alive, viruses have many
HIV The deadly disease called acquired immune deficiency syndrome of the characteristics of living things. After infecting living
DIFFERENTIATED INSTRUCTION (AIDS) is caused by an RNA virus called human immunodeficiency cells, viruses can reproduce, regulate gene expression, and
virus (HIV). HIV belongs to a group of RNA viruses that are called even evolve. Some of the main differences between cells and When scientists
ELL English Language Learners Write the word Figure 20–5 HIV Infection retroviruses. The genetic information of a retrovirus is copied from viruses are summarized in Figure 20–6. injected extracts
retrovirus on the board. Separate the word into its Mechanism In contrast to the RNA to DNA instead of from DNA to RNA. Although viruses are smaller and simpler than the from BSE-infected
parts, and explain that the word part retro- means cHoIVld mviarukes,s aa rDetNroAv icruosp syu ochf iatsse lf When a retrovirus infects a cell, it makes a DNA copy of its RNA, smallest cells, it is unlikely that they were the first organ- cinotwo mbricaein, tthises umei ce
“backward.” Introduce other words containing the that inserts into the host’s DNA. which inserts into the DNA of the host cell. Retroviral infections are isms. Because viruses are dependent upon living organisms, developed BSE. The
word part retro-, such as retroactive, retrofit, and ret- Tmhaenrey, ciet lml cayyc lreesm.ain inactive for sbiamctielarria tlo h loyssto, gtehnei cv iirnafle DctNioAn sm oafy b raecmteariina. iMnauccthiv eli kfoe ra m praonpyh caeglle c iync lae s iItn s feaecmt, st hmeo firres tli kveirluy stehsa mt vaiyr uhsaevse d eevvoellvoepde dfr oafmte rt hliev ignegn ecteilcls . ewxhteranc tths einyd cuocnetda iBnSeEd envoe n
rospective. Then, ask students to describe in an oral
before making new virus particles and damaging the cells of the host’s material of living cells. Viruses have continued to evolve, nucleic acids (RNA or
or written sentence why the word retrovirus is used immune system. Once activated, it begins to destroy the very system along with the cells they infect, for billions of years. DNA). Could a virus be
the cause of BSE?
to describe some viruses. AA D DNNAA c cooppyy o of ft hthee of the body that would normally fight infection.
vviriaral lR RNNAA i sis m maaddee..
LPR Less Proficient Readers Have students who
12.11.11
struggle with reading work in pairs to master the LS GLE 21
information on this page. Have one student in each TThhee c cooppyy i sis i ninsseertretedd
pair read the information and examine the figure inintoto t hthee h hoosst’ts’s g geennoommee.. Review Key Concepts
describing the common cold virus. Ask the other stu- 1. a. Review What do viruses depend on for their Structure and Function
reproduction? 3. Compare the structure of a virus to the
dent in each pair to read the information and exam- CCyytotopplalassmm
ItI ti sis l alateter rt rtarannssccrirbibeedd b. Compare and Contrast How is viral reproduction structure of both a prokaryotic cell and a
ine the figure describing HIV. Then, have each pair of aanndd t rtarannsslalatetedd i nintoto different from that of cell-based organisms? eukaryotic cell. Use a graphic organizer of
students work together to develop an explanation of nneeww v viriaral lp paartrsts.. 2. a. Review Describe each of the two paths viruses your choice to organize the information.
why HIV is classified as a retrovirus, but the virus that may follow once they have entered a cell. You may wish to refer to Chapter 7, which
discusses the structures of cells in detail.
causes the common cold is not. Call on students to b. Compare and Contrast How are lytic and lyso-
genic infections similar? How are they different?
share their explanations with the class. TThhee p paartrsts a asssseemmbblele i nintoto
NNuuccleleuuss
nneeww v viriurusseess a anndd b buursrst t
frforomm t hthee h hoosst tc ceelll.l. Lesson 20.1 • Self-Test • Lesson Assessment
578 Chapter 20 • Lesson 1 Viruses and Prokaryotes 579
0574_Bio10_se_Ch20_S1_0578 578 3/26/11 1:58 AM 0574_Bio10_se_Ch20_S1_0579 579 3/26/11 1:58 AM
Check for Understanding
QUESTION BOARD
Establish a section of a bulletin board or white board in the classroom to be used by
students to post questions about concepts or processes they do not understand. Have
students post any questions they might have about viruses on the board. Assure stu-
dents they do not need to leave their names with their questions.
ADJUST INSTRUCTION
Read over students’ questions to identify common questions or areas of confusion.
Use each as a topic of discussion to address students’ questions or correct their
misconceptions.
578 Chapter 20 • Lesson 1
0572_mlbio10_Ch20_0578 578 12/14/11 9:45 AM
