Chapter 3 • Cell Structure 49
Opening ActivityCell Structure Using micrographs,show students various cells from amulticellular organism, such as neu-rons, erythrocytes, and sperm cells.First have students attempt to iden-tify the cells. After the cells havebeen identified, have students sug-gest the function of each cell andhow the structure of the cell mightbe involved in that function.
GENERAL
• Vocabulary Worksheets
• Concept Mapping
Chapter Resource File
Answers
1. Molecules with an unequal dis-tribution of electrical chargesare polar molecules. Moleculeswith an equal distribution ofelectrical charges are nonpolarmolecules.
2. Carbohydrates, lipids, pro-teins, and nucleic acids areorganic compounds containingcarbon atoms covalentlybonded to hydrogen, oxygen,and other carbon atoms.However, they each differ intheir proportions of theseatoms, the manner in whichtheir molecules are puttogether, and whether othertypes of atoms are present.
3. ATP carries energy in cells.
Quick Review
Answers
Students may know that cells are the smallestliving unit of life and are likely to know thatcells contain hereditary material in thenucleus. Some may also know that cells con-tain organelles that carry out cell functions.However, students are not likely to be able toname these organelles and describe their func-tions, or distinguish between the features ofprokaryotes and eukaryotes.
Reading Activity
Looking AheadQuick ReviewAnswer the following without referring to
earlier sections of your book.
1. Distinguish between polar and nonpolar
molecules. (Chapter 2, Section 1)
2. Compare the structures of carbohydrates,
lipids, proteins, and nucleic acids. (Chapter 2,
Section 3)
3. Describe the function of ATP. (Chapter 2,
Section 3)
Did you have difficulty? For help, review the
sections indicated.
Section 1
Looking at CellsCells Under the Microscope
Types of Microscopes
Section 2
Cell FeaturesThe Cell Theory
Prokaryotes
Eukaryotic Cells
The Cell Membrane
Section 3
Cell OrganellesThe Nucleus
Ribosomes and the Endoplasmic Reticulum
Mitochondria
Structures of Plant Cells
www.scilinks.orgNational Science Teachers Association sciLINKS Internet
resources are located throughout this chapter.
Reading ActivityWrite down the title of this chapter and the titles
of its three sections on a piece of paper or in
your notebook. Leave a few blank lines after
each section title. Then write down what you
think you will learn in each section. Save your
list, and after you finish reading this chapter,
check off everything that you learned that was
on your list.
Most cells, including this one-celled organism
Paramecium, have all the equipment necessary to
perform the essential functions of life.
CellStructure
CHAPTER
3
49
Copyright © by Holt, Rinehart and Winston. All rights reserved.
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section begins byrecounting the development of themicroscope as a tool for visualizingand studying cells. After a shortdescription of the metric systemand the units used in measuringcells, this section describes thecharacteristics of microscopes andthe various types that are usedtoday.
Tell students to examine the SI units in Table 1. Then have students answer the following questions:
1.How many meters are there in a kilometer? (1,000 m)
2.How many centimeters are in a meter? (100 cm)
3.What is 20 micrometers innanometers? (20,000 nm)
ActivityMagnification Tell students thatmicroscopes magnify objects, makingthem appear larger than their actualsize. Pair students, and ask each pairto calculate the diameter of a Lincolnpenny if it were magnified 270 times.Have students report in meters, infeet (multiply meters by 3.28 ft/m),and in comparison to another object.(A Lincoln penny is 2 cm wide. Mag-nified 270 times, it would appear 5.4 m wide (17.7 ft), about as wideas a large room.) LogicalLS
GENERAL
MotivateMotivate
Bellringer
FocusFocus
Section 1
50 Chapter 3 • Cell Structure
• Directed Reading
• Active Reading GENERAL
Chapter Resource File
• Reading Organizers
• Reading Strategies
• Basic Skills WorksheetMicroscope Magnification
• Problem Solving WorksheetOperations with Small and LargeNumbers GENERAL
Planner CD-ROM
Table 1 Metric Units of Length and Equivalents
Unit Prefix Metric equivalent Real-life equivalent
Kilometer (km) Kilo- 1,000 m About two-thirds of a mile
Meter (m) 1 m (SI base unit) A little more than a yard
Centimeter (cm) Centi- 0.01 m About half the diameter of a Lincoln penny
Millimeter (mm) Milli- 0.001 m About the width of a pencil tip
Micrometer (µm) Micro- 0.000001 m About the length of an average bacterial cell
Nanometer (nm) Nano- 0.000000001 m About the length of a water molecule
Section 1 Looking at Cells
Cells Under the MicroscopeMost cells are too small to see with the naked eye; a typical human
body cell is many times smaller than a grain of sand. Scientists
became aware of cells only after microscopes were invented, in the
1600s. When the English scientist Robert Hooke used a crude
microscope to observe a thin slice of cork in 1665, he saw “a lot of
little boxes.” The boxes reminded him of the small rooms in which
monks lived, so he called them cells. Hooke later observed cells in
the stems and roots of plants. Ten years later, the Dutch scientist
Anton van Leeuwenhoek used a microscope to view water from a
pond, and he discovered many living creatures. He named them
“animalcules,” or tiny animals. Today we know that they were not
animals but single-celled organisms.
Measuring Cell StructuresMeasurements taken by scientists are expressed in metric units.
Scientists throughout the world use the metric system. The official
name of the metric system is the International System of
Measurements, abbreviated as SI. SI is a decimal system, so all rela-
tionships between SI units are based on powers of 10. For example,
scientists measure the sizes of objects viewed under a microscope
using the SI base unit for length, which is the meter. A meter, which
is about 3.28 ft (a little more than a yard), equals 100 centimeters
(cm), or 1,000 millimeters (mm). A meter also equals 0.001 kilome-
ter (km). Most SI units have a prefix that indicates the relationship
of that unit to a base unit. For example, the symbol “µ” stands for
the metric prefix micro. A micrometer (µm) is a unit of linear meas-
urement equal to one-millionth of a meter, or one-thousandth of a
millimeter. Table 1 summarizes the SI units used to measure length.
Objectives
● Describe how scientists
measure the length of
objects.
● Relate magnification and
resolution in the use of
microscopes.
● Analyze how light
microscopes function.
● Compare light
microscopes with electron
microscopes.
● Describe the scanning
tunneling microscope.
Key Terms
light microscope
electron microscope
magnification
resolution
scanning tunneling
microscope
50
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Interactive Reading AssignChapter 3 of the Holt BiologyGuided Audio CD Program to help students achieve greater success in reading the chapter.
Math Skills Using yard/metersticks, show students that the inchis the closest English equivalent tothe centimeter, and the yard is theclosest English equivalent to themeter. Ask students to measure 5 objects in centimeters and con-vert that measurement to meters,then to measure 5 objects in inchesand convert that measurement toyards. Which system is easier touse? Why? (Students likely had lesstrouble using the metric system andwill likely say that the metric systemis easier to use since it is based onequal increments and on multipliersof 10.) You may use this opportu-nity to have students research anddiscuss why the U.S. has not totallyswitched to the metric system.(Tradition is often given as a reason.)
KinestheticLS
GENERALBUILDERSKILL
SKILL
BUILDER
READINGREADING
TeachTeach
Chapter 3 • Cell Structure 51
HISTORYHISTORYCONNECTIONCONNECTION
When Hooke observed cork using a micro-scope, he observed tiny compartments. Hegave them the Latin name cellulae, meaning“small rooms.” That is the origin of the term cell.
did you know?
Standard Measures The International Bureauof Weights and Measures in France providesthe standards of the International System of Measurements. The Bureau houses thesestandard measures, such as a one-kilogrampiece of metal and a meter-long metal bar. The current SI system was established in 1960.
Transparencies
TR Bellringer
TR A10 Metric Units of Length and Equivalents
TR A4 Object Size and Magnifying Power of Microscopes
TR A5 Compound Light Microscope
Characteristics of MicroscopesSince Robert Hooke first observed cork cells, micro-
scopes have unveiled the details of cell structure. These
powerful instruments provide biologists with insight into
how cells work—and ultimately how organisms function.
Biologists use different microscopes depending on the
organisms they wish to study and the questions they want
to answer. Two common kinds of microscopes are light
microscopes and electron microscopes. In a
, light passes through one or more lenses to
produce an enlarged image of a specimen. An
forms an image of a specimen using a beam
of electrons rather than light.
An image produced by a microscope, such as the one
shown in Figure 1, is called a micrograph. Many micrographs are
labeled with the kind of microscope that produced the image—such
as a light micrograph (LM), a transmission electron micrograph
(TEM), or a scanning electron micrograph (SEM). Micrographs
often are labeled with the magnification value of the image.
is the quality of making an image appear larger than
its actual size. For example, a magnification value of 200� indicates
that the object in the image appears 200 times larger than the
object’s actual size. is a measure of the clarity of an
image. Both high magnification and good resolution are needed to
view the details of extremely small objects clearly. As shown in
Figure 2, electron microscopes have much higher magnifying and
resolving powers than light microscopes.
Resolution
Magnification
microscope
electron
microscope
light
A red blood cell is about 5 times
longer than a bacterial cell.
A Lincoln penny is about 2,000
times longer than a red blood cell.
A human is about 100 times
longer than a Lincoln penny.
20 cm2 µm 2 cm 2 m
Bacterium Blood cell Penny Hand Human
0.1 nm 1 nm 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 1 cm 10 cm 1 m 10 m
Electron microscopes
Sizes of objects
Light microscopes
Unaided eye
Bacterium
Blood cell
Penny
Hand
Human
Sizes of Objects and Magnifying Power of Microscopes
10 µm
Magnification: 270�
Figure 1 Micrograph. This
light micrograph (LM) shows
an amoeba.
Figure 2 Magnifying
power of microscopes. The
scale shows the size range of
objects that can be viewed
with electron microscopes and
light microscopes.
51
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching TipElectron Microscopy Contact a local college or university andarrange for a field trip that willintroduce your students to electronmicroscopy. Specifically requestthat the parts of the electron micro-scope be shown and explained tostudents and that the students alsobe shown how a specimen is pre-pared for viewing and how it isviewed. Also check to see if theinstitution has any other micro-scopes normally not available tohigh schools so that these too canbe shown to the students.
Visual
Using the FigureThe microscopes in your schoolmay look a bit different from theone shown in Figure 3. Give amicroscope to each pair of stu-dents. Demonstrating from thefront of the class, point out theparts of your microscopes that correspond to the microscope inthe figure. Have students find these parts on their microscopes.Encourage ELL students to make adiagram of the school microscopesthat has all of the parts labeled.
LS
GENERAL
Teach, continuedTeach, continued
52 Chapter 3 • Cell Structure
English Language Learners
StrategiesStrategiesINCLUSIONINCLUSION
Have the student use reference materials (orthe Internet) to compare and contrast thelight microscope and the electron micro-scope. The student’s work should includediagrams of each microscope with partslabeled, the types of materials that can bestudied, and different applications for eachtype of microscope. Additionally, the stu-dent could interview a professional that usesan electron microscope on the job.
• Gifted and Talented
Remind students that light waves from the specimenare bent as they pass through the ocular and objec-tive lenses of the light microscope. Refraction—thebending of light waves as they pass from one mediumto another—results in a “magnified” image of thespecimen. To assess the students’ understanding ofrefraction, ask them to identify the media throughwhich the light waves are passing when they use alight microscope. Possible answers include water, air,and glass.
Integrating Physics and Chemistry
www.scilinks.org
Topic: Microscopes
Keyword: HX4122
Types of MicroscopesDifferent types of microscopes have different qualities and uses.
Microscopes vary in magnification and resolution capabilities,
which affect the overall quality of the images they produce.
Microscopes also have different limitations. For example, electron
microscopes have high magnifying power, but they cannot be used
to view living cells. Light microscopes have lower magnifying
power, but they can be used to view living cells.
Compound Light Microscope Light microscopes that use two lenses are called compound light
microscopes. In a typical compound light microscope, such as the
one shown in Figure 3, a light bulb in the base shines light up through
the specimen, which is mounted on a glass slide. The objective lens,
closest to the specimen, collects the light, which then travels to the
ocular (AHK yoo luhr) lens, closest to the viewer’s eye. Both lenses
magnify the image. Thus, a microscope with a 403 objective lens and
a 103 ocular lens produces a total magnification of 4003.
Why not add a third lens and magnify even more? This approach
does not work because you cannot distinguish between two objects,
or “resolve” them, when they are closer together than a few hun-
dred nm. When the objects are this close, the light beams from the
two objects start to overlap!
Magnification: 1,5003
Ocular lens
Specimen
Stage
Focus
knob
Light source
Objective
lens
In a compound light microscope, a specimen is mounted on a glass slide and
is illuminated with a beam of light from below.
Figure 3 Compound light microscope
LM of sperm
52
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Activity Making a Wet Mount Have students practice preparing wetmounts. CAUTION: Slides andcover slips break easily and havesharp edges. Provide students withglass slides, cover slips, smallbeakers filled with water, and eye-droppers. Students can begin byviewing cutout letters from news-papers. Challenge students to makea bubble-free slide. Then have stu-dents prepare wet mounts usingdrops of pond water. Emphasizethat it will be much easier to findand watch organisms if studentsmake their slides bubble-free.
Kinesthetic
Writing Skills Electron micro-scopes are used in areas of researchother than biology. For example,they are important tools in Earthscience. In this field, electronmicroscopes have been used todetermine the effects of weatheringon the microstructural arrangementof the mineral components ofrocks, and the effects of chemicalson rock formation and stability.Have students prepare a report thatdescribes uses of electron micro-scopes in fields other than biology.
VerbalLS
BUILDERSKILL
LS
GENERAL
Chapter 3 • Cell Structure 53
HISTORYHISTORYCONNECTIONCONNECTION
Hans Janssen, Zacharias Janssen, and HansLippershey built the first microscope in theNetherlands between 1590 and 1608. It couldmagnify objects from 3X to 10X. Anton van Leeuwenhoek made significant improve-ments to the microscope, developing lenseswith magnifications of up to 300X. VanLeeuwenhoek produced about 400 micro-scopes and used them to study many things,including yeast, muscles, plants, and insects.
Answer
The SIAM makes molecules visible. Therefore it is useful instudying cells on the molecularlevel, such as the structure of certain biological compounds likeproteins. Other types of micro-scopes, such as the electron microscope, visualize cells andtheir organelles. These micro-scopes are useful in understandingthe overall structure of the cell.
Real Life
CulturalAwarenessCulturalAwareness
German-born Ernst Ruska and RheinholdRuedenberg, working indepedently of eachother, invented the transmission electronmicroscope 1931. In 1933, Ruska built thefirst electron microscope that was morepowerful than the light microscope and, in1986, was awarded the Nobel Prize in Physics for this achievement.
Real LifeThe most powerful compound light microscopes have a total
magnification of up to 2,0003, which is sufficient for viewing
objects as small as 0.5 µm in diameter. For you to see smaller
objects, the wavelength of the light beam must be shorter than the
wavelength of visible light. Electron beams have a much shorter
wavelength than that of visible light, so electron microscopes are
much more powerful than light microscopes.
Electron MicroscopesElectron microscopes can magnify an image up to 200,0003, and
they can be used to study very small structures inside cells or on cell
surfaces. In electron microscopes, both the electron beam and the
specimen must be placed in a vacuum chamber so that the electrons
in the beam will not bounce off gas molecules in the air. Because liv-
ing cells cannot survive in a vacuum, they cannot be viewed using
electron microscopes.
Transmission electron microscope In a transmission electron micro-
scope, shown in Figure 4, the electron beam is directed at a very thin
slice of a specimen stained with metal ions. Some structures in the
specimen become more heavily stained than others. The heavily
stained parts of the specimen absorb electrons, while those that are
lightly stained allow electrons to pass through. The electrons that
pass through the specimen strike a fluorescent screen, forming an
image on the screen. A transmission electron micrograph (TEM),
such as the one of sperm cells shown in Figure 4, can reveal a cell’s
internal structure in fine detail. TEM images are always in black
and white. However, with the help of computers, scientists often add
artificial colors to make certain structures more visible.
In a transmission electron microscope, electrons pass through a specimen,
forming an image of the specimen on a fluorescent screen.
Figure 4 Transmission electron microscope
TEM of sperm
Magnification: 7,7303
Thirty movies could be
stored on a disk the size
of a penny.
Using the scanning inter-
ferometric apertureless
microscope (SIAM)
researchers have viewed
features that are about
four atoms (1 nm) in diam-
eter. The technology could
also be used to code
information on storage
disks.
Applying Information
Would the SIAM likely
be more useful in under-
standing the overall
structure of the cell
or the structure
of biological
compounds
in the cell?
53
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Reteaching Ask students which kind of micro-scope would be most useful to highschool students studying the gen-eral structure of a leaf. (The lightmicroscope shows good detail forgeneral observations.) Ask studentswhich kind of microscope would be most useful for studying three-dimensional details of a smallorganism, such as a unicellular protist. (The SEM shows the surfacesof objects in great detail.) Ask themwhich microscope would be mostuseful in research on the internalstructures of a bacterial cell. (TheTEM shows internal detail with greatmagnification.)
Quiz1. How many centimeters are in a
meter? How do these metric sys-tem terms tell you the answer?(There are 100 centimeters in ameter. The prefix centi- means100, so a centimeter is 1/100th ofa meter.)
2.What is the difference betweenmagnification and resolution?(Magnification means to make animage larger, while resolution refersto the sharpness of the image.)
AlternativeAssessmentHave students prepare wet mountsof amoebas. Using compound lightmicroscopes, have students bringthe amoebas into focus. Using thincentimeter rulers placed on themicroscope stages within theirfields of view, have students esti-mate the sizes of the amoebas in SIunits and explain how they madetheir determinations. KinestheticLS
GENERAL
GENERAL
CloseClose
Answers to Section Review
1. A millimeter is equal to 0.001 m, or one-thousandth of a meter. A micrometer is equalto 0.000001 m, or one-millionth of a meter.
2. As the magnification increases, the resolutiondecreases; therefore the clarity of the image isreduced.
3. Light microscopes can magnify an object up to2,000X. Electron microscopes can magnify anobject up to 200,000X.
4. Specimens must be placed in a vacuum as partof the preparation for viewing with electronmicroscopes; living things cannot survive in avacuum.
5. You would use a transmission electron microscope because the electron beam passesthrough the bacterium, revealing the cell’sinternal structure in great detail.
6. A. Incorrect. A crude microscope cannot visualize electrons. B. Incorrect. A crude microscope cannot visualize electrons.C. Incorrect. Leeuwenhoek used a microscope to view single-celled organisms. D. Correct.Hooke studied cork and other plant cells with his crude microscope.
54 Chapter 3 • Cell Structure
Scanning electron microscope In a scanning electron microscope,
shown in Figure 5, the electron beam is focused on a specimen
coated with a very thin layer of metal. The electrons that bounce off
the specimen form an image on a fluorescent screen. A scanning
electron micrograph (SEM) shows three-dimensional images of cell
surfaces, such as the image of sperm cells shown in Figure 5. As
with the transmission electron microscope, images produced by the
scanning electron microscope are black and white, but often they
are artificially colored.
Scanning Tunneling MicroscopeNew video and computer techniques are increasing the resolution and
magnification of microscopes. The
uses a needle-like probe to measure differences in voltage caused by elec-
trons that leak, or tunnel, from the surface of the object being viewed. A
computer tracks the movement of the probe across the object, enabling
objects as small as individual atoms to be viewed. The computer
generates a three-dimensional image of the specimen’s surface. The
scanning tunneling microscope can be used to study living organisms.
scanning tunneling microscope
In a scanning electron micro-
scope, electrons bounce off a
specimen, forming a three-
dimensional image of the
specimen on a fluorescent
screen.
Figure 5 Scanning
electron microscope
SEM of sperm
Describe the relationship between a meter, amillimeter, and a micrometer.
Describe how magnification and resolution affect the appearance of objects viewed under a microscope.
Compare the magnifying power of a light micro-scope with the magnifying power of an electronmicroscope.
Critical Thinking Recognizing Differences
Explain why electron microscopes cannot beused to view the structure of living cells.
Critical Thinking Comparing Functions
Assume that for the purposes of your investiga-tion, you need detailed images of the internalstructure of a bacterium. What type of micro-scope would you select for that that task? Explain your answer.
The English scientistRobert Hooke used a crude microscope to examine
A electrons C individual atoms
B cork cells D single-celled organisms
Standardized Test PrepStandardized Test Prep
Section 1 Review
54
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 2
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section introducesstudents to the cell theory. It con-tinues by discussing the similaritiesand differences between prokary-otic cells and eukaryotic cells, andcloses by describing the cytoskele-ton and cell membrane.
Have the following list written onthe chalkboard when students enterthe room: rocks, grass, soil, water,telephone poles, and grasshoppers.Have students work with a partnerto make two new lists: those itemson the list that are comprised ofcells and those items not comprisedof cells. Have them write a rationalefor each answer. (Grass, grasshoppers,and telephone poles are comprised ofcells. They are either living or wereonce living. Rocks, soil, and waterare not comprised of cells. They arenonliving.) Logical
ActivityBacteria in Yogurt Smear someyogurt with live cultures on amicroscope slide. Mix a drop ofwater into the smeared yogurt andadd a cover slip. Allow students toexamine the slide under high powerusing a compound light micro-scope. They should see bacteria ofthe genus Lactobacillus. Ask themto compare the size of these cellswith the sizes of cells on preparedslides of human and plant tissues.
KinestheticLS
GENERAL
MotivateMotivate
LS
Bellringer
FocusFocus
Chapter 3 • Cell Structure 55
• Directed Reading
• Active Reading
• Data Sheet for Math Lab GENERAL
GENERAL
Chapter Resource File
• Reading Organizers
• Reading Strategies
• Basic Skills Worksheets Length, Area, and Volume Measure-ment and Scale Drawings
• Problem Solving WorksheetRatios and Proportions GENERAL
GENERAL
Planner CD-ROM
Transparencies
TR Bellringer
TR B2 Relationship Between SurfaceArea and Volume
TR B4 Animal Cells
TR B8 Lipid Bilayers
TR B10 Membrane Proteins
The Cell TheoryIt took scientists more than 150 years to fully appreciate the discov-
eries of Hooke and Leeuwenhoek. In 1838, the German botanist
Mattias Schleiden concluded that cells make up not only the stems
and roots but every part of a plant. A year later, the German zoolo-
gist Theodor Schwann claimed that animals are also made of cells.
In 1858, Rudolph Virchow, a German physician, determined that
cells come only from other cells. The observations of Schleiden,
Schwann, and Virchow form the , which has three parts:
1. All living things are made of one or more cells.
2. Cells are the basic units of structure and function in organisms.
3. All cells arise from existing cells.
Cell SizeSmall cells function more efficiently than large cells. There are
about 100 trillion cells in the human body, most ranging from 5 µm
to 20 µm in diameter. What is the advantage of having so many tiny
cells instead of fewer large ones? All substances that enter or leave
a cell must cross that cell’s surface. If the cell’s surface area–to-
volume ratio is too low, substances cannot enter and leave the cell in
numbers large enough to meet the cell’s needs. Small cells can
exchange substances more readily than large cells because small
objects have a higher surface area–to-volume ratio than larger
objects, as shown in Table 2. As a result, substances do not need to
travel as far to reach the center of a smaller cell.
cell theory
Cell Features Section 2
Objectives
● List the three parts of the
cell theory.
● Determine why cells must
be relatively small.
● Compare the structure of
prokaryotic cells with that
of eukaryotic cells.
● Describe the structure of
cell membranes.
Key Terms
cell theory
cell membrane
cytoplasm
cytoskeleton
ribosome
prokaryote
cell wall
flagellum
eukaryote
nucleus
organelle
cilium
phospholipid
lipid bilayer
Side length Surface area VolumeSurface area/volume ratio
1 mm 6 mm2 1 mm3 6:1
2 mm 24 mm2 8 mm3 3:1
4 mm 96 mm2 64 mm3 3:2
1 mm
2 mm
4 mm
Table 2 Relationship Between Surface Area and Volume
55
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Demonstration Cut three cubes of varying sizesfrom a potato. Pour food coloringinto three beakers, and place a cubein each beaker. After about 5 min.,remove each cube and cut it in half.Have students observe the results.Ask them to determine how thesurface area-to-volume ratio ofeach cube affected the penetrationof the food coloring into the cube.(The food coloring traveled the samedistance in each cube. However, thesmallest cube will be more completelycolored than others because it has thegreatest surface area-to-volume ratio.)
VisualLS
GENERAL
TeachTeach
56 Chapter 3 • Cell Structure
CalculatingSurface Area and Volume
Skills AcquiredCalculating, analyzing,applying
Teacher’s NotesBring in cube-shaped game diceof three different sizes. Havestudents measure the sides ofthe dice. Then have them calcu-late the surface area-to-volumeratios of the dice and comparetheir results.
Answers to Analysis1. SA 5 24 mm2, V 5 8 mm3,
ratio is 3:1
2. SA 5 6 mm2, V 5 1 mm3,ratio is 6:1
3. By being flat, a Parameciumspreads its volume over a largearea. The surface area-to-volume ratio is increasedbecause there is more surfacearea per unit volume.
x + 6x - 7 - 0
76
0
52
MISCONCEPTION
ALERT
Shape vs. Size Large cells do not neces-sarily have small surface area-to-volumeratios. Many large cells have shapes thatallow them to maintain a large surface area-to-volume ratio. A cell could growlarge in one or two dimensions but remainsmall in others. For example, parts of neurons are very long cylinders with smalldiameters, whereas epithelial cells are broadand flat. In both cases, the surface area-to-volume ratio is quite large.
Besides requiring a relatively high surface area-to-volume ratio in order to live, cells also have a totalcellular density that permits them to function efficientlyin their surrounding environments. Given that cellsmust have water to survive and are primarily com-posed of water, ask students if they would expectthem to have a density less than, about equal to, ormore than that of water. Ask students to defend theirresponses. If a cell’s density is different from that of its nearby habitat, what might account for this densitydifference?
Integrating Physics and Chemistry
www.scilinks.org
Topic: Cell Features
Keyword: HX4034
Common Features of CellsCells share common structural features, including an outer bound-
ary called the . The cell membrane encloses the cell
and separates the cell interior, called the (SITE oh plaz
uhm), from its surroundings. The cell membrane also regulates
what enters and leaves a cell—including gases, nutrients, and
wastes. Within the cytoplasm are many structures, often suspended
in a system of microscopic fibers called the . Most
cells have ribosomes. (RIE buh sohmz) are the cellular
structures on which proteins are made. All cells also have DNA,
which provides instructions for making proteins, regulates cellular
activities, and enables cells to reproduce. Some specialized cells
such as red blood cells, however, later lose their DNA.
Ribosomes
cytoskeleton
cytoplasm
cell membrane
Calculating Surface Area and Volume Background
You can improve your understanding of the relationship
between a cell’s surface area and its volume by practicing
with the large cube in Table 2.
<
x + 6x - 7 - 0
2
8
4930
52
Paramecium (SEM)
Magnification: 2303
1. Find the total surface area of the cube.
• side length sld 5 4 mm
• surface area of one side 5 l 3 l 5 l2
• surface area of one side sl2d 5 4 mm 3 4 mm 5 16 mm2
• total surface area 5 6 3 l25 6 3 16 mm
25 96 mm
2
2. Calculate the volume of the cube.
• height (h) 5 l 5 4 mm
• volume 5 l23 h 5 16 mm
23 4 mm 5 64 mm
3
3. Determine the surface area–to-volume ratio. A ratio compares two num-
bers by dividing one number by the other. A ratio can be expressed in three ways:
in words as a fraction with a colon
x to y x_y x:y
For the surface area–to-volume ratio, divide total surface area by volume.
5
Divide both numbers by their greatest common factor:
53
2
s96 4 32d
s64 4 32d
96
64
total surface area
volume
Analysis
1. Calculate the surface area–
to-volume ratio of the cube
with a side length of 2 mm
in Table 2.
2. Calculate the surface area–
to-volume ratio of the cube
with a side length of 1 mm
in Table 2.
3. Critical Thinking
Relating Concepts How
does the flatness of the
single-celled Paramecium
shown above affect the cell’s
surface area–to-volume ratio?
56
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching Tip Cell Walls Tell students that thecell wall varies among differenttypes of organisms. In plants, thecell wall is composed of cellulosefibers embedded in a polysaccharideand protein matrix. In eubacteria,the cell wall is composed of pepti-doglycan, a polymer of sugarscross-linked by a short polypeptide.In fungi, the cell wall is composedof chitin, a polysaccharide.
Interpreting Visuals Draw stu-dents’ attention to Figure 6, whichshows colorized electron micro-graphs of bacterial cells. Electronmicrographs are always black andwhite. Tell students that any colorshown in electron micrographs is usually digitally applied; that is,the colors are “painted on” bycomputers. These colors are artifi-cial; the living cell is not colored asis shown in the micrograph. Askstudents why colorized electronmicrographs might be useful. (To highlight structures and “pointthem out.”) Have students deter-mine which structures are beingpointed out in Figure 6. (Uppermicrograph from outside to inside:capsule, cell wall, cell membrane,cytoplasm with ribosomes, DNA.Lower micrograph: the flagella areyellow with a red “halo” and the“body” of the bacterium is green.)
GENERALBUILDERSKILL
Chapter 3 • Cell Structure 57
did you know?
Prokaryotes Modern prokaryotesinclude archaebacteria and eubacte-ria. They can be found in nearlyany environment on Earth, includ-ing volcanic vents at the bottom ofthe ocean and ice in Arctic andAntarctic regions.
Trends in MicrobiologyBacteria Classification This textbook usesthe six-kingdom system of classification.However, the research of Carl Woese, Professorof Microbiology at University of IllinoisUrbana-Champaign, and his colleagues, sug-gests that archaebacteria and bacteria areuniquely distinct. In 1980, Woese suggested a three-domain classification. Bacteria andArchaea consist of prokaryotes, while Eukaryaconsists of all eukaryotes. The numerous king-doms within each domain correspond to phylain the six-kingdom system. Today, the three-domain system of classification is accepted andused widely in the field of microbiology.
Prokaryotes The smallest and simplest cells are prokaryotes. A (proh
KAIR ee oht) is a single-celled organism that lacks a nucleus and other
internal compartments. Without separate compartments to isolate
materials, prokaryotic cells cannot carry out many specialized func-
tions. Early prokaryotes lived at least 3.5 billion years ago. For nearly
2 billion years, prokaryotes were the only organisms on Earth. They
were very simple and small (1–2 µm in diameter). Like their ancestors,
modern prokaryotes are also very small (1–15 µm). The familiar
prokaryotes that cause infection and cause food to spoil belong to
a subset of all prokaryotes that is commonly called bacteria.
Characteristics of ProkaryotesProkaryotes can exist in a broad range of environmental conditions.
Many prokaryotes, including some bacteria that cause infection in
humans, grow and divide very rapidly. Some prokaryotes do not need
oxygen to survive. Other prokaryotes cannot survive in the presence
of oxygen. Some prokaryotes can even make their own food.
The cytoplasm of a prokaryotic cell includes everything inside the
cell membrane. As Figure 6 shows, a prokaryote’s enzymes and ribo-
somes are free to move around in the cytoplasm because there are
no internal structures that divide the cell into compartments. In
prokaryotes, the genetic material is a single,
circular molecule of DNA. This loop of pro-
karyotic DNA is often located near the center
of the cell, suspended within the cytoplasm.
Prokaryotic cells have a sur-
rounding the cell membrane that provides
structure and support. The cells of fungi and
plants also have cell walls; only animal cells
and some protists lack cell walls. Prokaryotes
lack an internal supporting skeleton, so they
depend on a strong cell wall to give the cell
shape. A prokaryotic cell wall is made of
strands of polysaccharides connected by
short chains of amino acids. Some prokary-
otic cell walls are surrounded by a structure
called a capsule, which is also composed
of polysaccharides. The capsule enables
prokaryotes to cling to almost anything,
including teeth, skin, and food.
Many prokaryotes have (fluh JEL
uh), which are long, threadlike structures
that protrude from the cell’s surface and
enable movement. Prokaryotic flagella
rotate, propelling the organism through its
environment at speeds of up to 20 cell
lengths per second. Figure 6 shows a
prokaryote with several flagella.
flagella
cell wall
prokaryote
Magnification: 61,8503
Figure 6 Prokaryotes.
Prokaryotic cells have little
internal structure. Many also
have a capsule and flagella.
Reading Effectively
For many words ending in
-um, the plural is formed by
changing the -um to -a. For
example, the plural of bac-
terium is bacteria, and the
plural of flagellum is flagella.
57
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Using the Figure Draw students’ attention to Figure 7.This figure shows most of theorganelles that are commonlyfound in animal cells. Explain thatfor the sake of clarity only a few of the microtubules and micro-filaments have been drawn. In reality, these structures form adense network (the cytoskeleton)inside the cell. Point out that thenuclear envelope actually consistsof two lipid bilayers. Visual
Reading Organizer As studentsread about prokaryotes andeukaryotes, have them design achart that identifies and describesall of the differences betweenprokaryotic and eukaryotic cells.Encourage ELL students toexchange their organizer withnative English speakers to check for accuracy.
Logical
Teaching TipEukaryotic Cells Because all multicellular plants and animals arecomposed of eukaryotic cells, stressthat the eukaryotic cell can be anentity in itself, not just a compo-nent of a larger organism. Havestudents research one-celledeukaryotic organisms, like a yeastor a one-celled protist, and comparethem with eukaryotic cells that arepart of a multicellular plant or animal. Students should includedrawings, and record their findingson a one-page fact sheet.
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Teach, continuedTeach, continued
The Largest Cell Students may be surprisedto learn that the largest eukaryotic cell in theworld is about the size of a baseball! This cellis the yolk of an ostrich egg.
58 Chapter 3 • Cell Structure
CareerCareer
Cytotechnologist Cytotechnologists stain,mount, and study cells to detect malignanciesor other abnormal conditions. They then reportall findings to a pathologist. A cytotechnologistmust be able to obtain precise results and workunder stress during emergency situations. Anundergraduate degree in cytotechnology ormedical technology is usually needed for entry-level positions. Invite a cytotechnologist from alocal hospital to talk to your class. Ask them todiscuss recommended high school courses,working conditions, employment opportunities,and salary ranges during their talk.
English Language Learners
English Language Learners
Mitochondrion
Microfilaments
Lysosome
Ribosomes
Golgi
apparatus
Smooth ER
Rough ER
Cell membrane
Microtubules
Nuclear pore
Nuclear envelope
Nucleus
Nucleolus
Figure 7 Animal cell. Like
all eukaryotic cells, animal cells
contain a cell membrane, a
nucleus, and other organelles.
Eukaryotic CellsThe first cells with internal compartments were primitive eukaryotic
cells, which evolved about 2.5 billion years ago. A (yoo
KAIR ee oht) is an organism whose cells have a nucleus. The
(NOO klee uhs) is an internal compartment that houses the
cell’s DNA. Other internal compartments, or organelles, enable
eukaryotic cells to function in ways different from prokaryotes. An
is a structure that carries out specific activities in the cell.
The major organelles in an animal cell are shown in Figure 7. The
cytoplasm includes everything inside the cell membrane but outside
the nucleus. A complex system of internal membranes connects
some organelles within the cytoplasm. These membranes provide
channels that guide the distribution of substances within the cell.
The membranes also form envelopes called vesicles that move pro-
teins and other molecules from one organelle to another.
Many single-celled eukaryotes use flagella for movement. Short
hairlike structures called (SIL ee uh) protrude from the surface
of some eukaryotic cells. Flagella or cilia propel some cells through
their environment. In other cells, cilia and flagella move substances
across the cell’s surface. For example, cilia on cells of the human res-
piratory system, shown in Figure 8, sweep mucus and other debris
out of the lungs.
A web of protein fibers, shown in Figure 9, makes up the
cytoskeleton. The cytoskeleton holds the cell together and keeps the
cell’s membranes from collapsing. The fluid surrounding the cyto-
plasm’s organelles, internal membranes, and cytoskeleton fibers is
called the cytosol.
cilia
organelle
nucleus
eukaryote
Figure 8 Cilia. Cilia on
cells lining the respiratory
system remove debris from
air passages.
58
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching Tip Prokaryotic Cells vs. EukaryoticCells Have students make aGraphic Organizer similar to theone on the bottom of this page thatcompares prokaryotic cells witheukaryotic cells.
ActivityAmoeboid Movement Have students make wet mounts of liveamoeba. These protists move andfeed by means of pseudopods, or“false feet.” Pseudopods are cellextensions formed by actin fiberscontinuously contracting andexpanding, pulling the cell mem-brane in one place and pushing itout in another, as described on thispage. In fact, amoeboid movementis a dramatic example of actin-based cell movement. Although students will not be able to see theactin fibers, they will be able toobserve the granular cytoplasmstreaming into the projection as itbegins to form. Explain to studentsthat their own white blood cellsexhibit such movement to catchand ingest foreign invaders such as bacteria. Visual
Paired Reading Assign studentsto cooperative pairs, and have eachstudent read this page silently. Asthey read, have students indicatepassages they understand with acheck mark and passages they donot understand with a questionmark. Then have the partners discuss what they did or did notunderstand. Ask each pair to writea short paragraph summarizing the structure and function of the cytoskeleton. You may wish to pair ELL students with nativeEnglish speakers.
InterpersonalLS
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Chapter 3 • Cell Structure 59
English Language Learners
The CytoskeletonThe cytoskeleton provides the inte-
rior framework of an animal cell,
much as your skeleton provides the
interior framework of your body. The
cytoskeleton is composed of an intri-
cate network of protein fibers
anchored to the inside of the plasma
membrane. By linking one region to
another, they support the shape of
the cell, much as steel beams anchor
the sides of a building to one another.
Other fibers attach the nucleus and
other organelles to fixed locations in
the cell. Because protein fibers are
too small for a light microscope to
reveal, biologists visualize the
cytoskeleton by attaching fluorescent dyes to antibodies. An anti-
body is an immune system protein specialized to bind to one
particular kind of molecule—in this case—cytoskeleton proteins.
When the cell is examined under fluorescent light, the fibers glow
because of the fluorescent antibody attached to them.
There are three different kinds of cytoskeleton fibers: (1) long,
slender microfilaments made of the protein actin, (2) hollow tubes
called microtubules made of the protein tubulin, and (3) thick ropes
of protein called intermediate fibers.
Actin Fibers The actin fibers of the cytoskeleton form a network
just beneath the cell surface that is anchored to membrane proteins
embedded within the cell membrane. By contracting or expanding,
the actin fibers play a major role in determining the shape of ani-
mal cells by pulling the plasma membrane in some places and
pushing it out in others. If you examine the surface of a protist such
as the one shown in Figure 10, you will find it alive with motion.
Tiny projections extend out from the surface like fingers. Each is a
temporary projection of the plasma membrane that shoots out and
then retracts.
Microtubules Microtubules within the cytoskeleton act as a highway
system for the transportation of information from the nucleus to
different parts of the cell. RNA molecules are transported along
microtubular “rails” that extend through the interior of the cell like
train tracks. The RNA molecules, in complexes with proteins, are
attached to so-called motor proteins that chug along microtubules
like locomotives on tracks. The motor proteins drag the RNA-protein
complexes along with them like freight cars.
Intermediate Fibers The intermediate fibers of the cytoskeleton
provide a frame on which ribosomes and enzymes can be confined
to particular regions of the cell. The cell can organize complex
metabolic activities efficiently by anchoring particular enzymes
near one another.
Microtubules
Nucleus
Endoplasmicreticulum
Mitochondrion
Ribosomes
Figure 9 The cytoskeleton.
The cytoskeleton’s network of
protein fibers anchors cells
organelles and other compo-
nents of the cytoplasm.
Figure 10 Cytoskeletal
projections. The multiple
spikes on the surface of this
marine amoeba are projections
of the cytoskeleton stretching
the cell membrane outward.
59
Graphic Organizer
Use this graphic organizer with
Teaching Tip on this page.
can be
bacteria
prokaryotic
organelles
animals
plants
fungi
protists
which are found in
which containwhich lackwhich are known as
eukaryotic
Cells
Copyright © by Holt, Rinehart and Winston. All rights reserved.
60 Chapter 3 • Cell Structure
AnswerThe cells are frozen very quickly,which prevents the formation oflarge ice crystals that woulddamage the cells.
Real Life
Group Activity Cell Membrane Model Organizethe class into groups. Tell eachgroup to make a model of the cellmembrane to help visualize itsstructure. Suggest that students cutoff half of one leg of several woodenclothespins. Different colors can beused to represent the hydrophobic(nonpolar) and hydrophilic (polar)ends. Proteins can be representedby buttons, bottle caps, and card-board tubes. Place completed models around the classroom.
Kinesthetic
Using the FigureDraw students’ attention to Figure 11, and then have studentsreview the terms polar and non-polar. Be certain students under-stand that the nonpolar interior ofthe lipid bilayer repels ions andpolar substances. Remind themthat even though water moleculesare polar, they are small enough tomove through the lipid bilayer.Make sure students understandthat membranes are found in manyplaces in cells, such as around theentire cell, mitochondria, the Golgiapparatus, lysosomes, and thenucleus. Ask students to list cellstructures that lack membranes.(ribosomes, microfilaments, micro-tubules, and cell walls) VisualLS
GENERAL
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GENERAL
did you know?
Phospholipids Phospholipids in a lipidbilayer can move about 2 µm in one second.Proteins also move, but because of their greatersize, their movement is slower. The membraneremains fluid unless the temperature decreasesto the point at which the membrane solidifies.If the phospholipids are rich in unsaturatedfatty acids, the membrane will remain fluid atlower temperatures. If the phospholipids arerich in saturated fatty acids, the membrane willbe more viscous at any given temperature.
Remind students that the cell membrane’s selectivepermeability is the result of how water, ions, and othersubstances interact with the polar and non-polar por-tions of the phospholipid bilayer. These differences inpolarity also determine how various proteins areembedded in the lipid bilayer.
Integrating Physics and Chemistry
Teach, continuedTeach, continued
The Cell MembraneThe cytoplasm of a cell is contained by its membrane. Cell mem-
branes are not rigid like an eggshell. Rather, they are fluid like a
soap bubble. The fluidity of cell membranes is caused by lipids,
which form the foundation of membranes. The lipids form a barrier
that separates the inside of the cell from the outside of the cell. This
barrier allows only certain substances in the cell’s environment to
pass through. This selective permeability of the cell membrane
determines which substances enter and leave the cell.
The Cell Membrane as a BarrierThe selective permeability of the cell membrane is caused mainly by
the way phospholipids interact with water. A is a lipid
made of a phosphate group and two fatty acids. As shown in
Figure 11, a phospholipid has both a polar “head” and two nonpolar
“tails.” You may recall that the polar ends of water molecules will
form weak bonds with other polar substances. The head of a phos-
pholipid, which contains a phosphate group, is polar and is
attracted to water. In contrast, the two fatty acids, or tails, are non-
polar and therefore are repelled by water.
In a cell membrane, the phospholipids are arranged in a double
layer called a , as shown in Figure 11. The nonpolar tails
of the phospholipids make up the interior of the lipid bilayer.
Because water both inside and outside the cell repels the nonpolar
tails, they are forced to the inside of the lipid bilayer. Ions and most
polar molecules, including sugars and some proteins, are repelled
by the nonpolar interior of the lipid bilayer. The lipid bilayer allows
lipids and substances that dissolve in lipids to pass through.
lipid bilayer
phospholipid
Real Life
Donated blood is frozen
in a special process
called cryopreservation.
Similar methods are used
to preserve human eggs,
embryos, and blood from
the umbilical cord, a rich
source of immune-system
cells.
Finding Information
Research how cryo-
preservation
methods enable
cells to with-
stand freezing.
Polar
Nonpolar
Polar
Lipid bilayer
Polar
head
Non-
polar
tails
The lipid bilayer is the foundation
of the cell membrane.
The arrangement of phospholipids
in the lipid bilayer makes the cell
membrane selectively permeable.
A phospholipid’s “head” is polar, and
its two fatty acid “tails” are nonpolar.
Cell membranes are made of a double layer of phospholipids, called a lipid bilayer.
Figure 11 Lipid bilayer
60
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Answers to Section Review
1. If the surface area-to-volume ratio of a cell istoo small, substances cannot penetrate the cellquickly enough to meet the needs of the cell.
2. Prokaryotic cells lack organelles; eukaryoticcells have organelles, which enable them tocarry out unique, specialized functions inorganized ways.
3. Answers will vary, but may include markerproteins, which help cells recognize cells oftheir own type; receptor proteins, which bindto signal molecules; transport proteins, whichmove substances into and out of the cell; andenzymes, which aid in biochemical reactions.
4. Schleiden, Schwann, and Virchow observedthat plants as well as animals are composed of cells, which are the basic units of structureand function in living things and that cells ariseonly from other cells.
5. A. Incorrect. Flagella are not needed for celldivision. B. Correct. Flagella are structures ofmotility. C. Incorrect. Flagella play no role inmaintaining cell shape. D. Incorrect. Flagellaare not used to make cell proteins.
Reteaching Assign students to two cooperativegroups. Have group A represent aprokaryotic cell, and have group Brepresent a eukaryotic cell. Haveeach group take turns stating acharacteristic that its cell has orsomething that its cell is able to do.Write these characteristics on the board. Give the other group an opportunity to challenge theanswers. Award one point for eachcorrect answer, and deduct onepoint for each incorrect answer.
Quiz1. True or false: a spherical large
cell has a larger surface area-to-volume ratio than a sphericalsmall cell. (False. The sphericalsmall cell has the larger surface-area-to-volume ratio.)
2.Where is the DNA located in aeukaryotic cell? (in the nucleus)
3. What does the term “selectivelypermeable” mean in regards to acell membrane? (Some moleculescan pass through the membraneand some cannot.)
AlternativeAssessmentWorking in pairs, have studentsconstruct 3 “cells” out of thickpaper, using the measurementsgiven in Table 2. Tell students toseal the sides of the cells with cello-phane tape, and to leave the top of each cell open. Give the studentsenough sand to fill each of thecubes, and tell them to use thesematerials to show visually the sur-face area-to-volume ratio of thethree cells. Ask each pair to explainto you orally how the surface area-to-volume ratio differs among thecells. (Answers may vary dependingon the size and shape of the constructed cells.)
GENERAL
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CloseClose
Chapter 3 • Cell Structure 61
Carbohydrate
portion1. Cell-surface marker:
Identifies cell type
Phospholipid heads
Protein
portion
Phospholipid tails
2. Receptor protein:
Recognizes and
binds to substances
outside the cell
3. Enzyme:
Assists chemical
reactions inside
the cell
4. Transport protein:
Helps substances
move across
cell membraneLipid
bilayer
Outside of cell
Inside of cell
Membrane Proteins Various proteins are located in the lipid bilayer of a cell membrane.
What keeps these proteins within the lipid bilayer? You may recall
that proteins are made of amino acids and that some amino acids
are polar, while others are nonpolar. The nonpolar part of a mem-
brane protein is attracted to the interior of the lipid bilayer but is
repelled by the water on either side of the lipid bilayer. In contrast,
the polar parts of the protein are attracted to the water on either
side of the lipid bilayer. This attraction helps to hold the protein in
the lipid bilayer. The motion and fluidity of phospholipids enable
some membrane proteins to move around within the lipid bilayer.
As shown in Figure 12, cell membranes contain different types of
proteins. Marker proteins attached to a carbohydrate on the cell’s sur-
face advertise cell type—such as a liver cell or a heart cell. Receptor
proteins bind specific substances, such as signal molecules, outside
the cell. Enzymes embedded in the cell membrane are involved in
important biochemical reactions in the cell. Transport proteins aid the
movement of substances into and out of the cell.
The cell membrane contains various proteins with specialized functions.
Figure 12 Membrane proteins
Section 2 Review
Describe the importance of the surface area–to-volume ratio of a cell.
Compare the structure of a eukaryotic cell withthat of a prokaryotic cell.
Critical Thinking Comparing Functions
Describe the functions of two types of cell-membrane proteins.
Analyze the three parts of the cell theory anddescribe two observations of early scientists thatsupport it.
A bacterium that lost itsflagella would be unable to
A move C make proteins
B divide D maintain its shape
Standardized Test PrepStandardized Test Prep
61
Copyright © by Holt, Rinehart and Winston. All rights reserved.
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section focuses on the organelles of eukaryotic cells,beginning with the nucleus. Next,this section explores how proteinsare packaged and distributed, andthe role of mitochondria in the production of ATP. Lastly, the sec-tion describes structures found inplant cells that are not found inanimal cells.
Provide students with microscopeslides of eukaryotic cells. Have the students find the nucleus usingcompound light microscopes. Havethe students give rationales for whythey identified the structure theydid as the nucleus. Visual
ActivityCell Structures Using a lightmicroscope, show students a prepared slide of a cheek cell. Then show students electron micro-graphs of various cell parts andorganelles. Have students comparethese micrographs with the illustra-tions in this book. Ask them toattempt to find these structures inthe cheek cell. Only the cytoplasm,nucleus, and cell membrane will beobserved easily. Remind studentsthat the other structures either aretoo small to be seen with the lightmicroscope or may need to bestained in a different way to be seen.
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MotivateMotivate
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Bellringer
FocusFocus
Section 3
• Directed Reading
• Active Reading
• Data Sheet for Quick Lab GENERAL
GENERAL
Chapter Resource File
• Reading Organizers
• Reading Strategies
• Supplemental ReadingThe Lives of a Cell
Planner CD-ROM
62 Chapter 3 • Cell Structure
StrategiesStrategiesINCLUSIONINCLUSION
Ask students to develop a chart listing thedifferent organelles of a cell. The chartshould include the names of each organelle,the functions of each organelle, and threestructures found in plant cells that are notfound in animal cells. From the chart, thestudent can design a poster showing all ofthe cell’s organelles.
GENERAL
• Learning Disability• Attention Deficit Disorder
Nuclear
pores
Nuclear envelope
Nucleolus
Section 3 Cell Organelles
The Nucleus Most functions of a eukaryotic cell are controlled by the cell’s
nucleus. As shown in Figure 13, the nucleus is surrounded by a
double membrane called the nuclear envelope, also called the
nuclear membrane. The nuclear envelope is made of two lipid
bilayers that separate the nucleus from the cytoplasm.
Scattered over the surface of the nuclear envelope are many
small channels through the envelope called nuclear pores.
Substances that are made in the nucleus, including RNA-ribosomal
protein complexes, move into the cytoplasm by passing through
the nuclear pores. Ribosomes are partially assembled in a region
of the nucleus called the nucleolus, which is also shown in Figure
13. Recall from Section 2 that ribosomes are the structures on
which proteins are made.
The hereditary information of a eukaryotic cell is coded in the
cell’s DNA, most of which is stored in the nucleus. Eukaryotic
DNA is wound tightly around proteins. Most of the time, DNA
exists as elongated and thin strands, which appear as a dark mass
under magnification. When a cell is about to divide, however, the
DNA strands, called chromosomes, wind up into a more compact
form and appear as dense, rod-shaped structures. The number of
chromosomes in a eukaryotic cell differs between species.
Human body cells have 46 chromosomes, while the cells of gar-
den peas have 14 chromosomes. You will learn more about DNA
and chromosomes later in this book.
Objectives
● Describe the role of
the nucleus in cell
activities.
● Analyze the role of internal
membranes in protein
production.
● Summarize the importance
of mitochondria in eukaryotic
cells.
● Identify three structures in
plant cells that are absent
from animal cells.
Key Terms
endoplasmic reticulum
vesicle
Golgi apparatus
lysosome
mitochondrion
chloroplast
central vacuole
The nucleus is surrounded by a double membrane called the nuclear envelope.
Figure 13 Nucleus
62
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Group Activity Selling Cells Have students workin groups of two or three to prepareadvertisements for cell organelles.Have each group choose anorganelle they want to “sell,” andhave them prepare print, audio, or video ads. Interpersonal
Using the FigureDraw students’ attention to Figure 14. Tell students that the figure shows an increasing level ofdetail from left to right. On the left,the entire cell is depicted, with theER circled. To the right of the cell,the ER in the circle is magnified toshow a greater level of detail. Andto the right of the circle is an elec-tron micrograph of ER. Labels pointout the same structures in the diagram as in the ER. However, the diagram shows the ER three-dimensionally, emphasizing itssheet-like nature. The electronmicrograph is a thin slice of a cell,so it has a two-dimensional qualityshowing a cross-sectional view.
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Chapter 3 • Cell Structure 63
Enzymes found in the abundant smooth ERof the liver help detoxify drugs and environ-mental pollutants. Detoxification usuallyinvolves a series of chemical reactions withinthe smooth ER of the liver that make the drugmore water soluble, allowing it to be excretedin the urine. The ingestion of many drugs,including barbiturates and alcohol, trigger anincrease in the amount of smooth ER andaccompanying enzymes in liver cells.
MEDICINEMEDICINECONNECTIONCONNECTION
Transparencies
TR Bellringer
TR B13 Processing of Proteins
TR B12 Mitochondrion
TR B9 Organelles
Ribosomes and the Endoplasmic Reticulum
Unlike prokaryotic cells, eukaryotic cells have a system of internal
membranes that play an essential role in the processing of proteins.
Cells make proteins on ribosomes. Each ribosome is made of dozens
of different proteins as well as RNA. Some of the ribosomes in a
eukaryotic cell are suspended in the cytosol, as they are in prokary-
otic cells. These “free” ribosomes make proteins that remain inside
the cell, such as proteins used to build new organelles.
Production of Proteins
Proteins that are exported from the cell, such as some signal
molecules, are made on the ribosomes that lie on the surface
of the endoplasmic reticulum, shown in Figure 14. The
(ehn doh PLAZ mihk rih TIHK yuh luhm), or
ER, is an extensive system of internal membranes that move pro-
teins and other substances through the cell. Like the cell mem-
brane, the membranes of the ER are made of a lipid bilayer with
embedded proteins.
The part of the ER with attached ribosomes is called rough ER
because it has a rough appearance when viewed in the electron
microscope. The rough ER helps transport the proteins that are
made by its attached ribosomes. As each protein is made, it crosses
the ER membrane and enters the ER. The portion of the ER that
contains the completed protein then pinches off to form a vesicle. A
is a small, membrane-bound sac that transports substances
in cells. Because certain proteins are enclosed inside vesicles, these
proteins are kept separate from proteins that are produced by free
ribosomes in the cytoplasm.
The rest of the ER is called smooth ER because it lacks ribosomes
and thus appears smooth when viewed in the electron microscope.
The smooth ER performs various functions, such as making lipids
and breaking down toxic substances.
vesicle
endoplasmic reticulum
www.scilinks.org
Topic: Proteins
Keyword: HX4151
Smooth ER
Ribosomes
Rough ER
The ER moves proteins and other substances within eukaryotic cells.
Figure 14 Endoplasmic reticulum
63
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Reading Hint As students read thesection, ask them to list questionsthey have from the reading. Whenstudents have compiled their lists,ask students to share their ques-tions orally with the class. Make alist of questions on the board, andthen assign the questions to pairs ofstudents. Ask students to answerthe questions by pointing out pas-sages in the book that explain theanswers. Have students researchanswers to the questions unan-swered by this book.
Teaching TipWhat Am I? Have each studentchoose one cell part or organelleand write a “What Am I?” essay inwhich the student pretends to bethat structure. The essay should be written in the first person andinclude the function and structureof that cell part. Encourage stu-dents to be creative in their writingstyles. Have each student read hisor her essay aloud in class. Otherstudents should try to guess thestructure or organelle presented in the essay. Verbal
Co-op Learning
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64 Chapter 3 • Cell Structure
HISTORYHISTORYCONNECTIONCONNECTION
In 1945, Belgian-American cytologist AlbertClaude began electron microscope studies of the cell and discovered the endoplasmicreticulum and the detailed structure of mito-chondria. Along with Christian de Duve andGeorge E. Palade, Claude was awarded theNobel Prize in Physiology or Medicine in1974 for discoveries of the structural andfunctional organization of the cell.
Several diseases have been attributed toimproperly functioning lysosomes. Tay-Sachsdisease is caused by the deficiency of a lysoso-mal enzyme that digests lipids. As a result,cells in the brain become filled with lipids,causing impairment. Pompe’s disease resultswhen a lysosomal enzyme that breaks downglycogen is absent, causing liver damage.
REAL WORLDREAL WORLDCONNECTIONCONNECTION
Packaging and Distribution of ProteinsVesicles that contain newly made proteins move through the cytoplasm
from the ER to an organelle called the Golgi apparatus. The
(GOHL jee) is a set of flattened, membrane-bound sacs that
serves as the packaging and distribution center of the cell. Enzymes
inside the Golgi apparatus modify the proteins that are received in
vesicles from the ER. The modified proteins are then enclosed in new
vesicles that bud from the surface of the Golgi apparatus. Other vesi-
cles include (LIE seh sohms), which are small, spherical
organelles that contain the cell’s digestive enzymes. The ER, the Golgi
apparatus, and lysosomes work together in the production, packaging,
and distribution of proteins, as summarized in Figure 15.
Step Ribosomes make proteins on the rough ER. The proteins
are packaged into vesicles.
Step The vesicles transport the newly made proteins from the
rough ER to the Golgi apparatus.
Step In the Golgi apparatus, proteins are processed and then
packaged into new vesicles.
Step Many of these vesicles move to the cell membrane and
release their contents outside the cell.
Step Other vesicles, including lysosomes, remain within the
cytoplasm. Lysosomes digest and recycle the cell’s used
components by breaking down proteins, nucleic acids,
lipids, and carbohydrates.
lysosomes
apparatus
Golgi
BIOgraphic
Proteins are made by
ribosomes on the
rough ER.
Processing of Proteins
1
Vesicles carry proteins
from the rough ER to
the Golgi apparatus.
2Proteins are modified in
the Golgi apparatus and
enter new vesicles.
3
Some vesicles release
their proteins outside
the cell.
4
Other vesicles remain in
the cell and become
lysosomes.
5
Nucleus
Proteins are processed by an internal system of membranes.
Figure 15
Interpreting Graphics
As you read, use Steps 1–5
in the text, shown in red, to
help you follow the same
numbered steps shown in
Figure 15.
64
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3 • Cell Structure 65
MISCONCEPTION
ALERT
Mitochondria in Plant CellsMake sure students understandthat plant cells, as well as ani-mal cells and almost all othereukaryotic cells, contain mito-chondria. Many students thinkthat because plants performphotosynthesis, which makestheir own food as well as ATP,that they do not contain mito-chondria. However, it is impor-tant for students to understandthat plants use the products of photosynthesis to fuel themanufacture of ATP in themitochondria. MitochondrialATP synthesis takes place inparts of plants that do notundergo photosynthesis, such as the roots, and when it is dark in parts of plants that doundergo photosynthesis, such as the leaves.
Using the FigurePoint out the infolding of the innermembrane of the mitochondrion.Ask students to suggest a purposefor this infolding of the membrane.(Enzymes for the reactions that takeplace here are located on these mem-branes, and the infolding increasesthe surface area.) Ask students tospeculate on how effective a mito-chondrion without the folds wouldbe. (With less surface area to carryout its chemical reactions, it mightnot be able to carry out its series ofreactions, or might produce muchless ATP.) Next, have students predict what might happen to anorganism if the mitochondria in itscells suddenly became only half asefficient. (Life processes that requireenergy might not be able to takeplace, might slow down, or might not be able to sustain themselves for as long a time.)
did you know?
Endosymbiosis The theory of endosymbiosisis a widely accepted explanation of the originof various cell organelles. The theory holds thatprokaryotes lived in association with othercells but lost their ability to reproduce inde-pendently, becoming organelles of today’seukaryotes. Scientists think that chloroplastsevolved from endosymbiotic photosynthetic bac-teria and mitochondria evolved from endosym-biotic aerobic bacteria. This theory is supportedby the fact that both chloroplasts and mito-chondria have their own DNA and can be inac-tivated with antibiotics that affect prokaryotesbut not eukaryotes.
MitochondriaNearly all eukaryotic cells contain many (miet uh
KAHN dree uh), like the one shown in Figure 16. A mitochondrion is
an organelle that harvests energy from organic compounds to make
ATP, the main energy currency of cells. Although some ATP is made
in the cytosol, most of a cell’s ATP is made inside mitochondria.
Cells that have a high energy requirement, such as a muscle cell,
may contain hundreds or thousands of mitochondria. Figure 16
shows that a mitochondrion has two membranes. The outer mem-
brane is smooth. The inner membrane is greatly folded, however,
and its surface area is large. The two membranes form two com-
partments, one inside and one outside the mitochondrion’s inner
membrane. It is here that the chemical reactions that produce ATP
during cell metabolism take place.
Mitochondrial DNAThe nucleus is not the only organelle in the cell that contains nucleic
acids. Mitochondria also have DNA and ribosomes, and mitochon-
dria make some of their own proteins. However, most mitochondrial
proteins are made by free ribosomes in the cytosol. Mitochondrial
DNA is independent of nuclear DNA and similar to the circular DNA
of prokaryotic cells. This fact supports the widely accepted theory
that primitive prokaryotes are the ancestors of mitochondria. You
will learn more about the origin of mitochondrial DNA later in
this book.
mitochondria
Inner
membrane
Outer
membrane
In a eukaryotic cell, mitochondria make most of the ATP.
Figure 16 Mitochondrion
The word mitochondrion is
from the Greek words
mitos, meaning “a thread”
and chrondros, meaning
“grain.” Knowing this makes
it easier to remember that a
mitonchondrion is a small,
elongated cell organelle.
65
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Reteaching Pass out copies of electron micro-graphs of cells to students. Askeach student to color in 3 cellorganelles of their choosing, eachwith a different color. Then ask students to name the 3 organelles,identifying them by their color, and to describe the job of those 3 organelles within the cell.
Quiz1. The mitochondrion has the nick-
name “the powerhouse of thecell.” Explain why this is a goodnickname. (The mitochondrion isthe organelle [house] in which ATPis synthesized. ATP is the energycurrency that powers the cell.)
2.Name two organelles withinplant cells that are not presentwithin animal cells. (chloroplastsand central vacuoles)
AlternativeAssessmentHave students use food to make amodel of a eukaryotic cell. Gelatin(cytoplasm) could be poured into a large, clear cellophane bag (cellmembrane). Organelles could be represented by kidney beans(mitochondria), poppy seeds (ribosomes), sections of lasagnanoodles (ER and Golgi apparatus),peppercorns (lysosomes), spaghettinoodles (cytoskeleton), and anorange (nucleus). KinestheticLS
GENERAL
GENERAL
CloseClose
Answers to Section Review
1. The nucleus contains DNA, directs cell activities,and assembles ribosomal proteins and RNA.
2. The proteins, made at the ribosomes attachedto the ER, pass through the ER. The proteinsare packaged into vesicles and transported tothe Golgi apparatus, where they are modifiedand repackaged. Some of these vesicles releasetheir contents from the cell.
3. Mitochondria produce most of the ATP usedfor chemical reactions in eukaryotic cells.
4. The cell wall contains cellulose and is thick andsomewhat rigid. When the central vacuole is
full, it pushes the other cell contents against thecell wall, providing added rigidity.
5. The digestive enzymes of the cell are storedwithin membranous vesicles so that they donot digest other cell structures.
6. A. Incorrect. The nucleus directs the activitiesof the cell. B. Incorrect. The lysosome is a stor-age vacuole for digestive enzymes. C. Incorrect.The mitochondrion generates ATP. D. Correct.The Golgi apparatus is the packaging and distri-bution center of a eukaryotic cell.
66 Chapter 3 • Cell Structure
Structures of Plant Cells The organelles described in this section are found in both animal
cells and plant cells. However, plant cells have three additional
structures that are not found in animal cells, shown in Figure 17.
Unique Features of Plant CellsCell wall The cell membrane of a plant cell is surrounded by a thick
cell wall, composed of proteins and carbohydrates, including the
polysaccharide cellulose. The cell wall helps support and maintain the
shape of the cell, protects the cell from damage, and connects it with
adjacent cells.
Chloroplasts Plant cells contain one or
more . Chloroplasts are
organelles that use light energy to make
carbohydrates from carbon dioxide and
water. Chloroplasts are found not only in
plants but also in a wide variety of eukary-
otic algae, such as seaweed. Chloroplasts,
along with mitochondria, supply much of
the energy needed to power the activities
of plant cells. Like mitochondria, chloro-
plasts are surrounded by two membranes,
contain their own DNA, and are thought
to be the descendents of ancient prokary-
otic cells.
Central vacuole As shown in Figure 17,
much of a plant cell’s volume is taken up
by a large, membrane-bound space called
the (VAK yoo ohl). The
central vacuole stores water and may
contain many substances, including ions,
nutrients, and wastes. When the central
vacuole is full, it makes the cell rigid. This
rigidity enables a plant to stand upright.
central vacuole
chloroplasts
Describe the role of the nucleus in cellactivities.
Sequence the course of newly made proteinsfrom the rough ER to the outside of the cell.
Describe the role of mitochondria in the metab-olism of eukaryotic cells.
Explain how a plant cell’s central vacuole andcell wall help make the cell rigid.
Critical Thinking Inferring Relationships
What is the importance of a cell enclosing itsdigestive enzymes inside lysosomes?
Which organelle serves as the packaging and distribution center of aeukaryotic cell?
A nucleus C mitochondrion
B lysosome D Golgi apparatus
Standardized Test PrepStandardized Test Prep
Section 3 Review
Chloroplast
Central vacuole
Cell wall
Figure 17 Plant cell. Plant cells have a cell
wall, chloroplasts, and a large central vacuole
(shown in blue).
66
Copyright © by Holt, Rinehart and Winston. All rights reserved.
AlternativeAssessmentAssign students to cooperativepairs. Have each pair devise a testthat includes the material coveredin this chapter. Each pair must also provide an answer key. Set theparameters for the test. For exam-ple, designate the number and typeof questions allowed. After the testsare collected, exchange them withthe other pairs, and have the pairstake the tests. Let the pairs checktheir own answers when they havecompleted the test. Co-op Learning
GENERAL
Answer to Concept Map
The following is one possible answer toPerformance Zone item 15.
Chapter 3 • Cell Structure 67
include
which containwhich contain
Eukaryotic cells
cell wall
animal cells
cell membrane
plant cells
mitochondriachloroplasts
central vacuole
Key Concepts
Study CHAPTER HIGHLIGHTS
ZONE
Key Terms
Section 1
light microscope (51)
electron microscope (51)
magnification (51)
resolution (51)
scanning tunneling
microscope (54)
Section 2
cell theory (55)
cell membrane (56)
cytoplasm (56)
cytoskeleton (56)
ribosome (56)
prokaryote (57)
cell wall (57)
flagellum (57)
eukaryote (58)
nucleus (58)
organelle (58)
cilium (58)
phospholipid (60)
lipid bilayer (60)
Section 3
endoplasmic reticulum (63)
vesicle (63)
Golgi apparatus (64)
lysosome (64)
mitochondrion (65)
chloroplast (66)
central vacuole (66)
BIOLOGYBIOLOGY
Unit 1—Use this unit to review the key
concepts and terms in this chapter.
Looking at Cells
● Microscopes enable biologists to examine the details of cell
structure and to understand how organisms function.
● Scientists use the metric system to measure the size of objects.
● Light microscopes have a low magnification and can be used
to examine living cells.
● Electron microscopes have a high magnification but cannot
be used to examine living cells.
● The scanning tunneling microscope uses a computer to
generate a three-dimensional image of an object.
Cell Features
● The cell theory has three parts.
● Small cells function more efficiently than large cells because
small cells have a higher surface-area-to-volume ratio than
large cells.
● All cells have a cell membrane, cytoplasm, ribosomes, and DNA.
● Prokaryotic cells lack internal compartments.
● Eukaryotic cells have a nucleus and other organelles, as well
as a cytoskeleton of microscopic protein fibers.
● The lipid bilayer of a cell membrane is made of a double
layer of phospholipid molecules.
● Proteins in cell membranes include enzymes, receptor
proteins, transport proteins, and cell-surface markers.
Cell Organelles
● The nucleus of a eukaryotic cell directs the cell’s activities
and stores DNA.
● In eukaryotic cells, an internal membrane system produces,
packages, and distributes proteins.
● Mitochondria harvest energy from organic compounds to ATP.
● Lysosomes digest and recycle a cell’s used components.
● Plant cells have three structures that animal cells lack: a cell
wall, chloroplasts, and a central vacuole.
3
2
1
67
Copyright © by Holt, Rinehart and Winston. All rights reserved.
ANSWERS
Understanding Key Ideas
1. c
2. a
3. d
4. d
5. c
6. a
7. The cell membrane regulateswhat substances enter and leavethe cell, thus maintaining theintegrity of the cell.
8. A scanning electron microscopeproduced the image.
9. Because of the presence of hydro-gen ions in lysosomes, one caninfer that the inside of the lyso-some is acidic. Digestive enzymesin a lysosome therefore work bestin an acidic environment.
10. One possible answer to the con-cept map is found at the bottomof the Study Zone page.
Critical Thinking
11. The arrangement of phospholipidsin the lipid bilayer influences thepermeability of this bilayerbecause the nonpolar lipidtails repel water (and otherpolar/water-soluble molecules).
12. Muscles cells use ATP when they contract. Having manymitochondria would help providethe large amount of ATP neededfor contraction.
13. Antibiotics can kill bacterial cells,while not harming human cells.Drugs that kill eukaryotic para-sites may also harm eukaryotichuman cells.
Alternative Assessment
14. Answers will vary. Have students access theInternet and other resources for this informa-tion. Students may focus on the role of vari-ous types of transport proteins in maintainingthe organs.
Section Questions
1 1, 2, 8
2 3, 4, 7, 11, 14
3 5, 6, 9, 10, 12, 13
Assignment Guide
68 Chapter 3 • Cell Structure
CHAPTER 3
Understanding Key Ideas
1. The main advantage of the transmissionelectron microscope is that it allows theviewer to seea. three-dimensional images of cell surfaces.b. the organelles of living cells.c. a cell’s internal structure in fine detail.d. the actual colors of a cell’s components.
2. The maximum size of a cell is determinedby the ratio between the cell’sa. surface area and volume.b. volume and organelles.c. organelles and cytoplasm.d. cytoplasm and nucleus.
3. Eukaryotic cells differ from prokaryoticcells in that eukaryotic cells a. lack organelles.b. have DNA but not ribosomes.c. are smaller than prokaryotic cells.d. have a nucleus.
4. In the cell membrane, the fatty acids ofphospholipid molecules a. face the cytoplasm.b. face the outside of the cell.c. are on both sides of the membrane.d. are in the interior of the membrane.
5. One function of the Golgi apparatus is to a. store DNA.b. make carbohydrates.c. modify proteins.d. digest and recycle the cell’s wastes.
6. Structures present in plant cells but notpresent in animal cells include a. chloroplasts and the central vacuole.b. mitochondria and the cell wall.c. ribosomes and ER.d. lysosomes and the Golgi apparatus.
7. Explain how the cell membrane con-tributes to a cell’s ability to maintainhomeostasis.
8. What kind of microscope produced theimage of cilia shown below?
9. Transport proteins in the membrane of alysosome move hydrogen ions into thelysosome. Use this information to predictwhether digestive enzymes in a lysosomework best in a neutral, a basic, or an acidic environment. (Hint: See Chapter 2,Section 2.)
10. Concept Mapping Make a conceptmap that compares plant cells with animalcells. Include the following terms in yourconcept map: cell membrane, cell wall,central vacuole, chloroplasts, andmitochondria.
Critical Thinking
11. Recognizing Relationships How does thearrangement of phospholipids influencethe permeability of the lipid bilayer?
12. Inferring Relationships Muscle cells havemore mitochondria than some other kindsof eukaryotic cells. In what way wouldhaving many mitochondria be beneficial tomuscle cells?
13. Applying Information Drugs that rid thebody of eukaryotic parasites often havemore side effects and are harder on thebody than drugs that act on bacterial para-sites. Suggest a reason for this difference.
Alternative Assessment
14. Interactive Tutor Unit 1 Cell Transport and
Homeostasis Write a report summarizing therole of the cell membrane in the preservationof body organs donated for transplant.
PerformanceZONE
CHAPTER REVIEW
68
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3 • Cell Structure 69
C
D
E
F
B
A
Standardized Test Prep
Understanding ConceptsDirections (1–4): For each question, write ona separate sheet of paper the letter of thecorrect answer.
1 What structure houses a eukaryotic cell’sDNA? A. cell wallB. cytoskeletonC. ERD. nucleus
2 Which of the following is not a proteinthat might be found in cell membranes?F. enzymeG. lipidH. markerI. transporter
3 What structures are found in both eukaryotic cells and prokaryotic cells?A. mitochondrion and ERB. nucleus and cell membraneC. mitochondrion and ribosomeD. cell membrane and ribosome
4 What property of phospholipids makesthem ideal for making up the selectivelypermeable cell membrane? F. They repel small ions.G. They react readily with water molecules.
H. They form triple layers that insulate the cell.
I. They have a nonpolar region and apolar region.
Directions (5): For the following question,write a short response.
5 Analyze why smaller pieces of food cookfaster than larger pieces of food, based onthe relationship between surface area andvolume.
Reading SkillsDirections (6): Read the passage below.Then answer the question.
Microbiologists study the growth, structure, development, and many othercharacteristics of bacteria and other microorganisms. Some microbiologists alsostudy the action of microorganisms on livingand dead tissue. This career requires at leasta two-year technical training degree from acommunity college or technical institution.Many microbiologists have a four-year bachelor’s degree plus a master’s or doctoraldegree.
6 What tools would be most useful for amicrobiologist? A. centrifuges and syringesB. nets and specimen cagesC. electron and light microscopesD. balances and graduated cylinders
Interpreting GraphicsDirections (7): Base your answer to question7 on the diagram below.
Animal Cell
7 What is the function of the structurelabeled A?F. making ATPG. making carbohydratesH. making proteins I. moving proteins through the cell
Test
When possible, use the text in the test to answer
other questions. For example, use a multiple-choice
answer to “jump start” your thinking about another
question.
69
Question 4 Answer I is the correctchoice. The nonpolar tails repelwater, while the polar headsattract water. This allows phos-pholipids to form double layersthat keep many molecules fromentering or exiting the cell. AnswerF is incorrect because the polarheads of phospholipids attractsmall ions. Answer G is incorrectbecause the polar heads interact,not react, with water molecules.Answer H is incorrect because theyform a double layer, not a triplelayer.
Question 5 Smaller pieces of foodhave significantly less volume thanlarger pieces, yet their surface areais only slightly smaller; thus, theyhave a larger surface-area-to-vol-ume ratio, resulting in more sur-face area exposed to heat whilecooking.
Question 6 Answer C is the cor-rect choice. Answer A is incorrectbecause these tools allow scientiststo examine tissues and blood sam-ples, not as useful to microbiolo-gists. Answer B is incorrectbecause these tools are used tocapture and contain larger organ-isms. Answer D is incorrectbecause these tools allow scientiststo measure larger samples, whichis less useful to microbiologists.
Question 7 Answer F is the cor-rect choice. The mitochondriamake ATP, which is important forenergy transfer in living things.Answer G is incorrect because thisstructure is not a chloroplast,which makes carbohydrates.Answer H is incorrect because thisstructure is not a ribosome or therough endoplasmic reticulum,which make proteins. Answer I isincorrect because this structure isnot the rough endoplasmic reticu-lum, the Golgi apparatus, or avesicle, which move proteinsthrough the cell.
Answers
1. D
2. G
3. D
4. I
5. Smaller pieces of food have a larger surface-area-to-volume ratio than larger pieces.
6. C
7. F
Standardized Test Prep
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