biology - chapter 7
DESCRIPTION
Science of biology and transport cellular, structure and funtion.TRANSCRIPT
Section {Cell Discovery and TheoryT:i:{::;|:K@ The invention ofthe micros'cope led to thediscovery of iglls.
Section 2 'The Plasma Membrane'{i:í;'i::KM The p|asmamembrane helps to maintain acell's homeostasis.
Section 3 ' : .
Structures and Organellesi¡.iilliii!,i({fÁ Eukaryotic cells' icontain organelles that allow thespecialization and the separationof functions within the cell.
Sectio¡r 4Cellular Transportil.il,tlXff!| cel lu lar transportmoves substances within the celland moves substances into andout of the cell.
About ten tril l ion cells make upthe human body.
The largest human cells are aboutthe diameter of a human hair.
The 200 different types of cellsin the human body come fromjust one cell.
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What is a cell?All things are made of atoms and molecules, but onlyin living things are the atoms and molecules orga-nized into cells. In this lab, you will use a compoundmicroscope to view slides of living things andnonliving things.
Procedure @ tr f¡eEL Read and complete the lab safety form-
2. Construct a data table for recording yourobservations.
3. Obtain slides of the various specimens.
4. View the slides through a m¡croscope at thepower designated by your teacher"
5. As you view the slides, fill out the data tableyou constructed.
Analysisl. Describe some of the ways to distinguish
between the l¡v¡ng things and the nonlivingth¡ngs.
2. Write a definition of a cell based on vourobservations.
study the ent¡re chaptef onl¡ne
exDlore the Interact¡ve Time L¡ne,Concepts ¡n Motion, the Interad¡veTable, M¡croscopy L¡nkt V¡rtual Labtand links to virtual dissections
access Web links for more informat¡on,projectt and act¡v¡ties
review content onl¡ne with the Inter-act¡ve Tutor, and take Self-Check Qu¡zzes
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4[dNB Use this Foldable withSection 7.4. As you study the section,consider the role of energy in each of thecellular transoort methods discussed.
Cellular Transport Makethis Foldable to help youcharacterize the variousmethods of cellular transport.
STEP I Place two sheets of notebookpaper 1.5 cm apart as illustrated.
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Chapter 7 . Cellular Structure and Funct¡on
Objectives
) Relate advances in microscopetechnology to discoveries about cells.
) Compare compound l¡ghtmicroscopes with electronm¡croscopes.
) Summarize the pr¡nciples of thecell theory.
) Differentiate betr¡veen aprokaryotic cell and a eukaryotic ce,,.
Review Vocabularyorganization: the orderly structureof cells in an organism
New Vocabularycellcell theoryptasma memorane0rgane eeukaryotic cellnucleusprokaryotic cell
Cell Discovery and Theory
ffi$ffi@ The invention of the microscope led to the discoveryof cells.
Real-world Reading Link The different parts ofyour body m¡ght seem tohave nothing in common. Your heart, for example, pumps blood throughout yourbody, while your sk¡n protects and helps cool you. Howeve¡ all your body partshave one thing in common-they are composed of cells.
History of the Cell TheoryFor centuries, scientists had no idea that the human body consists oftril-lions ofcells. Cells are so small that their existence was unknown beforethe invention ofthe microscope. In 1665, as indicated in Figure 7.1, anEnglish scientist r.ramed Robert Hooke made a simple microscope andlooked at a piece of cork, the dead cells ofoak bark. Hooke observedsmall, box-shaped structures, such as those shown in Figure 7.2. Hecalled them cellulae (the Latin word meaning small roorrs) because theboxlike cells of cork reminded him of the cells in which monks live at amonasterf It is from Hooke's work that we have the term c¿ll. A cell isthe basic structural and functional unit ofall living organisms.
During the late 1600s, Dutch scientist Anton van Leeuwenhoek(LAY vun hook)-inspired by a book written by Hooke-designed hisown microscope. To his surprise, he saw living organisms in pondwater. milk, and various other substances. The work ofthese scientistsand others led to new branches ofscience and many new and exciting
,, discoveries.F¡9ure 7.1
Microscopes in FocusThe ¡nvention of microscopes, improvementsto the instruments, and new microscope tech-niques have led to the devefopment of the /celltheorv and ¿ better understandinoof cells.
1565 Robert Hookeobserves cork and namesthe t¡ny chambers that hesees cells. He publishesdrawings of cells, fleasand other m¡nute bodiesin his book Mioographia.
1830-f855 scientistsdiscover the cell nucleus(1833) and propose thatboth Dlants and animalsare comoosed of cells ,f l839).
1590 Dutch lens grinders Hans and zacha-rias Janssen invent the first compoundm¡croscope by plac¡ng two lenses in a tube.
f683 Dutch biologisrAnton van Leeuwenhoekdiscovers single-celled,animal{ike organisms,now called orotozoans.
182 Chapter 7 . Cellular structure and tunction
The cell theory Naturalists and scientists continued observing theliving microscopic world using glass lenses. In 1838, German scientistMatthias Schleiden carefully studied plant tissues and concluded thatall plants are composed ofcells. A year late¡ another German scientist,Theodor Schwann, reported that animal tissues also consisted ofindi-vidual cells. Prussian physician Rudolph Virchow proposed in 1855 thatall cells are produced from the division of existing cells. The observa-tions and conclusions ofthese scientists and others are summarized asthe cell theory. The cell theory is one ofthe fundamental ideas ofmod-ern biology and includes the following three principles:
1. All living organisms are composed of one or more cells.
2. Cells are the basic unit of structure and organization of all livingorgamsms.
3. Cells arise only from previously existing cells, with cells passingcopies of their genetic material on to their daughter cells.
Réading check Can cells appear spontaneously without geneticmaterial from Drevious cells?
¡o Figure 7.2 Robert Hooke used a basicl¡ght m¡croscope to see what looked likeempty chambers in a cork sample,lnfet What do you think Hooke wouldhave seen ¡f these were living cells?
[A!'Nm |db 'Review Based on what you've readabout cells, how would you nowanswer the analysis questions?
Microscope TechnologyThe discovery of cells and the development of the cell theory would nothave been possible without microscopes. Improvements made to micro-scopes have enabled scienJísts to study cells in detail, as described inFiguré 7.1,
Turn back to the opening pages ofthis chapter and compare the mag-nifications ofthe skin shown there. Note that the detail increases as themagnification and resolution-the ability of the microscope to makeindividual components visible-increase. Hooke and van Leewenhoekwould not have been able to see the individual structures within humanskin cells with their microscopes. Developrnents in microscope technol-ogy have given scientists the ability to study cells in greater detail thanearly scientists ever thought possible.
f939 Ernest EverettJust writes the textbookBíology of the CellSrfface after y€ars ofstudying the strudureand function of cells.
t981 The scann¡ng tunnelingmicroscope (STM) allowsscient¡sts to see individualaloms,
f880-f890 l-ouisPasteur and RobertKoch, using compoundmicroscopes, pioneeredthe studv of bacteria.
Lynna m¡(robiolog¡st, pro.poses the idea thatsome organellesfound in eukaryoteswere once free-livingpfokafyotes.
ú¡¡ncePús In tl¡r¡¡* Interact¡ve Time LineTo Iearn more about these discoveries andother5, v¡sit b¡oloqvqmh.com. g¡ologrf9. . f
Section 1-. Cel¡ Discoverv and Theorv 183
€ompound light microscopes The modern compound lightmicroscope consists ofa series ofglass lenses and uses visible light to pro-duce a magnified image. Each lens in the series magnifies the image of theprevious lens. For example, when two lenses each individually magnify 10times, the total magnification would be 100 times (10 X 10). Scientrstsoften stain cells with dyes to see them better when using a light microscopebecause cells are so tiny, thin, and translucent. Over the years, scientistshave developed vadous techniques and modifications for light micro-scopes, but the properties ofvisible light will always limit resolution withthese microscopes. Objects cause light to scatter, which blurs images. Themaximum magnification without blurring is around 1000X.
Electron m¡croscopes As they began to study cells, scientists neededgreater magnification to see the details oftiny parts ofthe cel1. During thesecond World Wa¡ in the 1940s, they developed the electron microscope.Instead oflenses, the electron microscope uses magnets to aim a beam ofelectrons at thin slices ofcells. This type ofelectron microscope is called atransmission electron microscope (TEM) because electrons are passed, ortransmitted, through a specimen to a fluorescent screen. Thick parts ofthe specimen absorb more electrons than thin parts, forming a black-and-white shaded image of the specimen. Transmission electron microscopescan magnify up to 500,000X, but the specimen must be dead, sliced verythin, and stained with heavy metals.
Over the past 65 years, many modifications have been made to theoriginal electron microscopes. For example, thelcanning electron micro-scope (SEM) is one modification that directs electrons over the surface ofthe specimen, producing a three-dimensional image. One disadvantageofusing a TEM and an SEM is that only nonliving cells and tissues canbe observed. To see photomicrographs made with electron microscopes,visit biofogygmh,com and click on Microscopy Links.
Disrover CellsHow can you describe a new discovety? lmagine you are a scientist looking through the eyepiece ofsome new-fangled instrument called a microscope and you see a field of similarly shaped objects. Youmight recognize that the shapes you see are not merely coincidence and random objects. Your wholeidea ol the nature of matter is changing as you vie\rf these objects.
P¡ocedure @glfuE: L Read and complete the lab safety form.2. Prepare a data table in which you will record observations and drawings for three slides.3. View the slide images your teacher projects for the class.4. Describe and draw what you see. Be sure to ¡nclude enough deta¡l iri your drawings to conveythe
information to other scientists who have not observed cells.
Analycls1. Descr ibe What analogies or terms could explain the images in your drawings?2. Explain How could you show Hooke, with twenty-first-century technology, that his find¡ngs
were va lid?
catr¡iiltts IN t¡Io[o$Y
Technology RepresentativeCompanies that manufacturescientific equ¡pment employ represen-tatives to demonstrate and explainthe¡r products to the scientificcommunity. A technology representa-tive is an expert in these newtechnology products and brings thisexpertise to scientists who might usethe products in the laboratory Formore information on biology careers.visit b¡oloqvqmh.com.
t84 Chapter 7 . Cellular Structure and Function
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Another type of microscope, the scanning tunneling electron mrcro-scope (STM), invoives bringing the charged tip ofa probe extremelyclose to the specimen so that the electrons "tunnel" through the smallgap between the specimen and the tip. This instrument has enabled sci-entists to create three-dimensional computer images ofobjects as smallas atoms. Unlike TEM and SEM, STM can be used with live specimens.F¡gure 7,3 shows DNA, the cellt genetic material, magnified with ascanning tunneling electron microscope.
The atomic force microscope (AFM) measures various forcesbetween the tip ofa probe and the cell surface. To learn more aboutAFM, read the Cutting Edge Biology fea[)re af rhe end ofthis chapter.
Basic Cell TypesYou have learned, according to the ceil theor¡ that cells are the basrcunits ofall living organisms. By observing your own body and the livingthings around you, you might infer that ceils must exist in various shapesand sizes. You also might infer that cells differ based on the function theyperform for the organism. Ifso, you are correct! However, all cells have atleast one physical trait in common: they all have a structure called aplasma membrane. A plasma membrane, labeled in Figure 7.4, is a spe-cial boundary that helps control what enters and leaves the cell. Each ofyour skin cells has a plasma membrane, as do the cells ofa rattlesnake.This critical structure is described in detail in the next section.
Cells generally have a number of functions in common. For exam-ple, most cells have genétic material in some form that providesinstructions for making substances that the cell needs. Cells also breakdown molecules to generate energy for metaboiism. Scientists havegrouped cells into two broad categories. These categories are prokary-otic (pro kar ee AW tik) cells and eukaryotic (yew kar ee AW tik) cells.F¡gure 7.4 shows TEM photomicrographs ofthese two cell types. Theimages ofthe prokayotic cell and eukaryotic cell have been enlarged soyou can compare the cell structures. Eukaryotic cells generally are oneto one hundred times lareer than prokaryotic cells.
Reading Check compare the sizes of prokaryotic cells andeukaryotic cells.
DNA
s F¡gure 7,3 The scann¡ng tunnel¡ngmicroscope (sTM) provides images, such as th¡sDNA molecule ¡n wh¡ch cracks and depressionsappear darker and raised areas appear lighter.Name an application for which an SfMmight be used.
ñ Figuré 7.4 The prokaryotic cell on the leftis smaller and appears less complex than theeukaryot¡c cell on the r¡ght.
Eukaryot¡c cell
Séct¡on I . Cell Discovery and Theory 185
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Eukaryote :Prokaryote :ea- prelu; from Creek. meaning trrre ;pro- prefix: from Creek. meaning :beJore :-kary f rom Creek. meaning nucleus . . .1.
Ssstisr¡ Z¿jltSedion Summary) lVicroscopes have been used as a
tool for scientific study since thelate 1 500s.
) Scientists use different types ofmicroscopes to study cells.
) The celltheory summarizes threeprinciples.
) There are h¡vo broad groups ofcell types-prokaryotic cells andeukaryotic cells.
) Eukaryotic cells conta¡n a nucleusand organelles.
Look again at Figure 7.4 and compare the types ofcells. You can seewhy scientists place them into two broad categories that are based oninternal structures. Both have a plasma membrane, but one cell containsmany distinct internal structures called organelles-specialized struc-tures that carry out specific cell functions.
Eukaryotic cells contain a nucleus and other organelles thatare bound by membranes, also referred to as membrane-boundorganelles. The nucleus is a distinct central organelle that cont¿insthe cel1's genetic material in the form of DNA. Organelles enablecell functions to take place in different parts of the cell at the sametime. Most organisms are made up of eukaryotic cells and are calledeukaryotes. However, some unicellular organisms, such as somealgae and yeast, are also eukaryotes.
Prokaryotic cells are defined as cells without a nucleus or othermembrane-bound organelles. Most unicellular organisms, such as bacte-ria, are prokaryotic cells. Thus they are called prokaryotes. Many scientiststhink that prokaryotes are similar to the first organisms on Earth.
Origin of cell d¡vers¡ty Ifyou have ever wondered why a companymakes two products that are similar, you can imagine that scientistshave asked why there are two basic types ofcells. The answer might bethat eukaryotic cells evolved from prokaryotic cells millions ofyearsago. Accor<iing to the endosymbiont theor¡ a symbiotic mutual rela-tionship involved one prokaryotic cell living inside of another. Theendosymbiont theory is discussed in greater detail in Chapter 14.
Imagine how organisms would be different ifthe eukaryotic formhad not evolved. Because eukaryotic cells are larger and have distrnctorganelles, these cells have developed specific functions. Having specificfunctions has led to cell diversit¡ and thus more diverse organisms thatcan adapt better to their environments. Life-forms more complex thanbacteria might not have evolved without eukaryotic cells.
Understand Main Ideas1. ffiffi@ Explain how the
develooment and imDrovement ofmicroscopes changed the study ofliving organisms.
2. Compare and contrast a com'pound light microscope and anelectron mrcroscope.
3. Summarize the cell theory¿. Differentiate the olasma
membrane and the orqanelles.
5. De¡onba how you would deter-mine ifthe cells of a newly discov-ered organism were prokaryotic oreukaryotic.
6. GmBiology lf the over-all magnification of a series of h¡rolenses is 30X, and one lens magnr-fied 5x, what is the magnification ofthe other lens? Calculate the totalmagnification if the 5X lens isreplaced by a 7x iens.
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Chapter 7 . Cellular Structure and Function"t.,osrgf
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Objectives
) Describe how a cell's plasmamembrane functions.
) ldentify.the roles of proteinlcarbohydrates, and cholesterol inthe p¡asma membrane.
Review Vocabularyion: an atom or group of atoms witha positive or negat¡ve electric charge
New Vocabularyselective permeabilityphospholipid bilayertransport proternfluid mosaic model
3" Figure 7,5Left:The fish net selectively captures fish whileallowing water and other debris to passthrough.Right: similarly, the plasma membrane selectssubstances entering and leaving the cell.
The Plasma Membrane
W@ The plasma membrane helps to ma¡ntain a cell'shomeostasis,
Real-World Reading l-ink When you approach your school, you might passthrough a gate in a fence that sunounds the school grounds. This fence preventspeople who should not be there from entering and the gate allows studenttstaff, and parents to enter. Prokaryotic cells and eukaryotic cells have a structurethat mainta¡ns control of their internal env¡ronments.
Function of the Plasma MembraneRecall from Chapter 1 that the process of maintaining balance in anorganism's internal environment is called homeostasis. Homeostasis isessential to the survival of a cell. One ofthe structures that is primarilyresponsible for homeostasis is the plasma membrane. The plasmamembrane is a thin, flexible boundary between a cell and its environ-ment that allows nutrients into the cell and allows waste and otherproducts to leave the cell. All prokaryotic cells and eukaryotic cellshave a plasma membrane to separate them from the watery environ-ments in which they exist.
A key property of the plasma membrane is selective permeability(pur mee uh BIH luh tee), by which a membrane allows some sub-stances to pass through while keeping others out. Consider a fish net asan analogy ofselective permeability. The net shown in Figure 7.5 hasholes that allow water and other substances in the water to passthrough but not the fish. Depending on the size ofthe holes in the net,some kinds of fish might pass through, while others are caught. Thediagram in Figure 7.5 illustrates selective permeability ofthe plasma
membrane. The arrows show that substances enter and leave the cellthrough the plasma membrane. Control of how, when, and how muchofthese substances enter and leave a cell relies on the structure oftheplasma membrane.
{f neading check Define the term selective permeability.
outsidethe cell
Section 2 . The Plasma lvlembrane
Outs¡de the cell
Cholesterol
Phosphol¡pidbilayer
Polar heads Nonpolar tails
lnside the cell
Transportprotein
¡. Figure 7,6 lhe phospholipid bilayer lookslike a sandwich, with the polar heads facing theouts¡de and the nonpolar tails facing the inside.lnÍef How do hydrophobic substancescfoss a plasma membrane?
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PolarScience usage: having an unequaldistribution of charge.The positive end of a polnr moleculeah:racts the negatiye end of a polarmolecule.
Common usage: telating to a geo-graphic pole or region.The polar íce cap in Greenland ís, ona v e r a g e , L o k m t h i c k . . . , . , . . . . , . . . . . .
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Structure of the Plasma Membrane(
Other components of the plasma membran€ Movingwith and among the phospholipids in the plasma membrane are
cholesterol, proteins, and carbohydrates' When found on the outer
surface of the plasma membrane, proteins called receptors transmit
sienals to the inside of the cell' Proteins at the inner surface anchor
tlie plasma membrane to the cell's internal support structure, giving
the cell its shape. Other proteins span the entire membrane and cre-
ate tunnels through which certain substances enter and leave the cell'
These transport proteins move needed substances or waste materials
through the plasma membrane, and therefore contribute to the selec-
tive permeability of the plasma membrane.
(f neading check Describe the benefit of a bilayer structure for theplasma memDrane
Locate the cholesterol molecules in Figure 7.6' Nonpolar cholesterol
is repelled by water and is positioned among the phospholipids. Choles-
terol helps to prevent the fatty-acid tails ofthe phospholipid bilayer from
sticking together, which contributes to the fluidity of the plasma mem-
brane. Although avoiding a high-cholesterol diet is recommended,
cholesterol plays a critical role in plasma membrane structure and it is
an important substance for maintaining homeostasis in a cell.
Other substances in the membrane, such as carbohydrates attatched
to proteins, stick out from the plasma membrane to define the cell's
characteristics and help cells identify chemical signals. For example,
carbohydrates in the membrane might he$ disease-fighting cells rec-
ognize and attack a potentialiy harmful cell.
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Question Session work witha Dartner and ask each other questionsabout the plasma membrane. Discusseach other's answers. Ask as manyquestions as you think of while takingturns.
Deúa and Obs€ntaffonsHow are protein channels lnvolved in the deathof nerve cells after a stroke? A stroke occurswhen a blood clot blocks the flow of oxygen-containing blood in a portion of the brain. Nervecells in the brain that release glutamate are sen-sitive to the lack of oxygen and release a flood ofglutamate when oxygen is low. During the gluta-mate flood, the calcium pump is destroyed. Thisaffects the movement of calcium ions into andout of nerve cells. When cells contain excess cal-cium, homeostasis is disrupted.
Th¡nk Cr¡t¡cálly1. Interpret How does the glutamate flood
destroy the calcium pump?2. Predict what would happen if Ca'z. levels were
lowered in the nerve cell during a stroke.
*Data obt¿ined from:Choi, D.W 2005. Neurodegener¡tion:cellulardefen(es destroyed.^/¿ture 433:696 598.
¡n the cell
Section 2. The Plasma lvlembrane 189
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Nonpolar tailgroups
Togethe¡ the phospholipids in the bilayer create a "sea" in whichother molecules can float, like apples floating in a barrel ofwater. This"sea" concept is the basis for the fluid mosaic model of the plasmamembrane. The phospholipids can move sideways within the mem-brane just as apples move around in water. At the same time, othercomponents in the membrane, such as proteins, also move among thephospholipids. Because there are different substances in the plasmamembrane, a pattern, or mosaic, is created on the surface. You can seethis pattern in Figure 7.7. The components of the plasma membraneare in constant motion, sliding past one another.
Understand Main ldeas1. WW@ Describe how the
plasma membrane helps mainta¡nhomeostasis in a cell.
2. Explain how the inside of acell remains separate from itsenvironment.
3. Diagram the plasma membrane;label each component.
4. ldentify the molecules in theplasma membrane that providebasic membrane structure, cellidentity, and membrane fluidity.
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; 1:1.r. Figure 7.7 The f¡uid mosaic model refers. :.:to a plasma membrane with substances thati.¡ i can move around wilhin the membrane.' " '6gncePts ln t¡¡¡¡*
Interadive F¡gure To see an animation of thefluid mosaic model, visit biologvgmh.com.
Sectiq& t¿**Section Summary) Selective permeability is a properly of
the plasma membrane that allows ¡t to(ontrol what enters and leaves the ceu.
) The plasma membrane is made up oftwo layers of phospholipid molecules.
) Cholesterol and transport proteinsa¡d in the function of the plasmamembrane.
I The fluid mosaic model describes theplasrna membrane.
Exo{'a,irt whal elfect more choles-teról in the plasma membrane willhave on the membrane.
tMElIEIEbniobsyUsing what you know about theterm /ros¿lr, write a paragraphdescribing another biological mosaic,
l9l¡ Chapter 7 . Cellular Structure and Funct¡on
Objectives
t ldent¡fy the structure and'funct¡on of the parts of a typicaleukaryotic cell.
) Compare and contraststructures of plant and animal cells.
Review Vocabularyenzyme: a protein that speeds up therate of a chemicál reaction
New Vocabularycytoplasmcytos keletonftbos0menucte0tusendoplasmic reticulumGolgi apparatusvacuolelysosomecentr¡olemitochondrionchloroplastce l lwal lc i l iumflagellum
" Figure 7,8 Microlubulesand microfilaments make upthe cytoskeleton.
Structures and Organelles
Wffi@ Eukaryotic cells contain organelles that allow thespecialization and the separat¡on of functions within the cell.
Real-tlllorld Reading Link Suppose you start a company to manufacture hikingboots. Each pair o{ boots could be made individually by one person, but it would bemore effic¡ent to use an assembly line" Similarly, eukaryotic cells have specializedstructures that perform specific tasks, much like a factory
Cytoplasm and CytoskeletonYou just have investigated the part ofa cell that functions as the boundarybetween the inside and outside environments. The environment inside theplasma membrane is a semifluid material called cytoplasm. In a prokary-
otic cell, all ofthe chemical processes ofthe cell, such as breaking downsugar to generate the energy used for other functions, take place directly inthe cltoplasm. Eukaryotic cells perform these processes within organellesin their cytoplasm. At one time, scientists thought that cell organellesfloated in a sea of cytoplasm.
More recentl¡ cell biologists have discovered that organelles do not floatfreely in a cell, but are supported by a structure within the c¡oplasm simi-lar to the structure shown in Figure 7,8. The cytoskeleton is a supportingnetwork oflong, thin protein fibers that form a framework for the cell andprovide an anchor for the organelles inside the cells. The cytoskeleton alsohas a function in cell movement and other cellular activities.
The cytoskeleton is made ofsubstructures called microtubules andmicrofilaments. Microtubules are long, hollow protein cylinders that forma rigid skeleton for the cell and assist in moving substances within the cell.Microfilaments are thin protein threads that help give the cell shape andenable the entire cell or parts of the cell to move. Microtubules and micro-filaments rapidly assemble and disassemble and slide past one another.This allows cells and orsanelles to move.
Plasmamembrane
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Section 3 . Structures and Organelles l9l
Cytoplasm
/ Mitochondrion
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@ Prokaryotic Cell(not to scale)
Cytoplasm
Nucleolus
Microtubule
Roughendoplasm¡creticulum
Smoothendoplasmicret¡culum
Ribosomes
Ribosomes
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Nuclearpore
Figure 7.9Compare the illustrations of a plant cel , animal cell, and prokaryotic celi. Some organelles are only founcl in plant cells-others, only inanimal cells. Prokaryotic cells do not have membrane bound orqanelles.
l\4 icrotub u leNucleus
Centr¡ole-
Roughendoplasmicrel|cutum
LysosomeSmoothendoplasm¡cret¡culum
PlasmamemDrane
Golg¡appararus
Plasmamembrane
O Plant cell
Nulleus Nucleolus
Cytoplasm
Golgiapparatus
g¡yrcefts h UQti6¡ Interactive Fiqure To see an an¡mat¡onof plant and animal cells, visit bioloqyqmh.com.
t92 Chapter 7 . Céllular Structure and Funct¡on
Cell StructuresIn a factor¡ there are seParate areas set up for performing different
tasks. Eukaryotic cells also have separate areas for tasks. Membrane-
bound organelles make it possible for different chemical processes to
take place at the same time in different parts ofthe cytoplasm'
Organelles carry out essential cell processes, such as protein synthe-
sis,-energy transformation, digestion of food, excretion ofwastes, and
cell division. Each organelle has a unique structure and functjon' You
can compare organelles to a factory's offices' assembly lines, and
other important areas that keep the factory running. As you read
about the different organelles, refer to the diagrams ofplant and ani-
mal cells in F¡gure 7.9 to see the organelles of each type.
The nucleus ]ust as a factory needs a manager, a cell needs an organ-
elle to direct the cell processes. The nucleus, shown in Figure 7'10, is
the cellt managing structure. It contains most of the cell's DNA, which
stores information used to make proteins for cell growth, function, and
reoroduction.The nucleus is surrounded by a double membrane called the nuclear
envelope. The nuclear envelope is similar to the plasma membrane,
exceptlhe nuclear membrane has nuclear pores that allow larger-sized
subsiances to move in and out ofthe nucleus. Chromatin, which is a
complex DNA attached to protein, is spread throughout the nucleus'
(f neading check Describe the role of the nucleus.
Ribosomes One of the functions of a cell is to produce proteins' The
organelles that help manufacture proteins are called ribosomes. Ribo-
somes are made of two components-RNA and protein-and are not
bound by a membrane like other organelles. Within the nucleus js the
site of ribosome production called the nucleolus' shown in F¡gure 7'1o'
Cells havé many ribosomes that produce a variety ofproteins that
are used by the cell or are moved out and used by other cells' Some ribo-
somes float freely in the cytoplasm, while others are bound to another
organelle called the endoplasmic reticulum. Free-floating ribosomes
produce proteins for use within the cytoplasm ofthe cel1. Bound ribo-
,omes p-du." proteins that will be bound within membranes or used
by other cells.
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CytoplasmCytoskeletonryfe- prefix; from Greek, meaning
c e \ | . . . . . . . . . . . . . '
'q Figure 7.f 0 The nucleus of a cell is athree-dimensional shape. The photomicro-graph shows a cross-section of a nucleus
lnlet Explain why all the cross-sedions ofa nucleus arc not ident¡cal.
Nucleaf pore
Nuclearenvelope
ColorEnhancedTE[¡ Magnification: 560x
section 3 . Structures and organelles 193
' -r Figure 7.lf Ribosomes are simplestructures made of RNA and protein that maybe attached to the surface of the roughendoplasm¡c reticulum. They look l ike bumpson the endoplasm¡c reticulum.
Rough endoplasmic reticulum Color-Enhanced TEll
Ribosome
Smooth endoplasmic reticulum
Endoplasmic ret¡culum The endoplasmic reticulum(en duh PLAZ mihk . rih TIHK yuh lum), also called ER, is a mem-brane system offolded sacs and interconnected channels that serves asthe site for protein and lipid synthesis. The pleats and folds ofthe ERprovide a large amount of surface area where cellular functions cantake place. The area of ER where ribosomes are attached is called roushendoplasmic reticulum. Notice in Figure 7,tt that the rough ERappears to have bumps on it. These bumps are the attached ribosomesthat will produce proteins for export to other cells.
F¡gure 7.11 also shows that there are areas ofthe ER that do not haveribosomes attached. The area of ER where no ribosomes are attached iscalled smooth endoplasmic reticulum. Although the smooth ER has noribosomes, it does perform important functions for the cell. For exam-ple, the smooth ER provides a membrane surface where a variety ofcomplex carbohydrates and lipids. including phospholipids, are synthe-sized. Smooth ER in the liver detoxifies harmful substances.
tld[tdl ̂ üNAf,fSlS ffiS W.mReal Lab Data*
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How is vesicle traffic from the ER to the Golgiapparatus regulated? some proteins are synthe-sized by ribosomes on the endoplasmic reticulum(ER)- The proteins are processed in the ER, andvesicles containing these proteins pinch off andm¡grate to the Golgi apparatus. sc¡entists currentlyare study¡ng the molecules that are involved infusing these vesicles to the Golgi apparatus.Th¡nk Cr¡t¡Gallyl. Interpret a Diagram Name two complexes
on the Golg¡ apparatus that might be involved.in vesicle fusion.
2, Hypothesize an explanation for vesicle trans-port based on what you have read about cvto-plasm and the cytoskeleton.
Data and Observations
"Data obtalned from:Brittle, E. E., and Watert [4. G.2000.ER"to-golgi traffic-this bud's for yo!. Sc/ence 289:403-404.
t94 Chapter 7 . Cellular Structure and Function
ColorEnhanced TEIVI [,lagn]f icationr 5505xVes¡cle leaving the Golgi apparatus
Golg¡ apparatus
Golgi apparatus After the hiking boots are made in the factor¡
they must be organized into pairs, boxed, and shipped. Similarl¡ afterproteins are made in the endoplasmic reticulum, some might be trans-
ferred to the Golgi (GAWL jee) apparatus, illustrated in Figure 7.12.
The Golgi apparatus is a flattened stack of membranes that modifies,
sorts, and packages proteins into sacs called vesicles. Vesicles then can
fuse with the cell's plasma membrane to release proteins to the envi-
ronment outside the cell. Observe the vesicle in Figure 7'12.
Vacuoles A factory needs a place to store materials and waste prod-
ucts. Similarly, ce1ls have membrane-bound vesicles called vacuoles for
temporary storage of materials within the cytoplasm. A vacuole, such
as the plant vacuole shown in F¡gure 7'13, is a sac used to store food,
enzymes, and other materials needed by a cell. Some vacuoles store
waste products. Interestingly, animal cells usually do not contain Yacu-
oles. If animal cells do have vacuoles, thev are much smaller than those
in nlant cells.
¡"r F¡gure 7.f2 Flattened stacks ofmembranes make up the Golgi apparatus.
$ F¡gure 7.'13 Plant cells have largemembrane-bound storage compartmentscalled vacuoles.
vacuole
CoorEnha¡.€dTEM ¡,4agn fc¿ton: 1000 <
Section 3 . Structures and organelles
\o F¡gure 7,14 Lysosomes contain digestiveenzymes that can break down the wastescontained in vacuoles.
CoorEnh¿nced L[4 [ ¡ ¡q¡ fc¿ton I1,000 <
Lysosome
Lysosomes Factories and cells also need clean-up crews. In the cell,lysosomes, shown in F¡gure 7.14, are vesicles that contain substancesthat digest excess or worn-out organelles and food particles. Lysosomesalso digest bacteria and viruses that have entered the cell. The mem-brane surrounding a lysosome prevents the digestive enzymes insidefrom destroying the cell. Lysosomes can fuse with vacuoles and dis-pense their enzymes into the vacuole, digesting the wastes inside.
Centrioles Previously in this section you read about microtubulesand the cytoskeleton. Groups of microtubules form another strucrurecalled a centriole (SEN tree ol). Centrioles, shown in F¡gure 2.15, areorganelles made of microtubules that function durinq cell division.Centrioles are located in the cytoplasm of animal celi-s and most pro-tists and usually are near the nucleus. You will learn about cell divisionand the role ofcentrioles in Chaoter 9.
,' Figure 7.15 Centrioles are made ofmicrotubules and play a role in cell division
Co or-Enhanced Tt[4 ¡,4agnilicat¡oni 40,000x
t96 Chapter 7 . Cellular Strucfure and Funct¡on
Co orEnh¡nced TElt4 ¡,4agnif icationr 14,000x
Mitochondrion
lnnermembrane
0utermemDrane
Mitochondria Imagine now that the boot factory has its own gen-
erator that produces the electricity it needs. Cells also have energy
generzLtors called mitochondria (mi tuh KAHN dree uh; singular,
mitochondrion) that convert fuel particles (mainly sugars)' into usable
energy. Figure 7.16 shows that a mitochondrion has an outer mem-
brane and a highly folded inner membrane that provides a large surface
area for breaking the bonds in sugar molecules. The energy produced
from that breakage is stored in the bonds ofother molecules and later
used by the cell. For this reason, mitochondria often are referred to as
the "powerhouses" of cells.
ChloroP¡asts Factory machines need electricity that is generated by
burning fossil fuels or by collecting energy from alternative sources,
such as the Sun. Plant cells have their own way ofusing solar energy.
In addition to mitochondria, plants and some other eukaryotic cells
contain chloroplasts' which are organelles that capture light energy
and convert it to chemical energy through a process called photosyn-
thesis. Examine Figure 7'17 and notice that inside the inner mem-
brane are many smal1, disk-shaped compartments cailed thylakoids. It
is here that the energy from sunlight is trapped by a pigment called
chlorophyll. Chlorophyll gives leaves and stems their green color'
Chloroplasts belong to a group ofplant organelles called plastids, some
of which are used for storage. Some plastids store starches or lipids. Others,
such as chromoplasts, contain red, orange, or yellow pigments that trap
light cnergy and give color to plant structures such as flowers or leaves.
¡,' Figure 7.16 Mitochondria make energyavailable to the cell.Descr¡be t te membÍane structure of amitochondrion.
'! Figure 7.17 In plantt chloroplastscapture and convert lighf energy to chem¡calenergy.
Color EnhancedlE¡,4 l,4ag¡ification: 37,000x
Ihylakoid Chloroplast
Section 3 . Structures and organelles 197
Planl cell 1
s Figure 7.f8 The ¡llustration shows plantcells and their cellwalls. Compare this to thetransmission electron m¡crograph showing lhecell walls of adjacent plant cells.
Cell wall Another structure associated with plant cells is the cellwall, shown in Figure 7.18, The cell wall is a thick, rigid, mesh offibers.that surrounds the gutside ofthe plasma membiane, protectingthe cell and giving it support. Rigid cell walls allow plants tó stand atvarious heights-from blades ofgrass to California iedwoods. plantcell walls are made ofa carbohydrate called cellulose, which sives thewal l i ts inf lexible character isr ics. Table 7.1 l ists cel lwal ls anávariousother cell structures.
Cilia and flagella Some eukaryotic cell surfaces have structurescalled cilia and flagella that project outside the plasma membrane. Asshown in Figure 7.19, cilia (singular, cilium) aie short, numerous pro_jections that look like hairs. The motion of cilia is similar to the motionofoars in a rowboat. Flagella (singular, flagellum) are longer dnd lessnumerous than 4lia. These projections move with a whiplike motion.Cilia and flagella are composed of microtubules arransed in a 9 + 2configuration, in which nine pairs of microtubules suriound two sinelemicrotubules. Typicall¡ a cell has one or two flasella.- Prokaryotic cilia and flagella contain cytoplásm and are enclosedby_the plasma membrane. They consist ofproiein building blocks.While both structures are used for cell movement, cilia arie also foundon stationary cel1s.
t9a
e F¡gure 7.19 The hairlike structures in rhephotomicrograph are cilia, and the taiflikestructures are flagella. Both structures functionin cell movement.lnler Where in the body of an animatwould you predict cilia might be found?
Cifia on the surface of a para mecium Bacter¡a with flagella
Chapter 7 . Cellular Structure and Function
Cell wall
Centrioles
Chloroplast
Ci l ia
Cytoskeleton
Endoplasmlcreticulum
Flagella
Golgi apparatus
Lysosome
M¡tochondrion
Nucleus
Plasma membrane
Ribosome
Summary of Cel! Structures
aonc.pt* ñ lrt¡ti¡nInt€ractive Table To explore moreabout cell structures, visitbiologyqmh.com.
Plant cells, fungi cells,and some prokaryotes
Animal cells and. most protist cells
Plant cells only
Some animal cells,protist cellt andprokaryotes
All eukaryotic cells
All eukaryotic cells
Some animal cells.prokaryotes, andsome plant cells
All eukaryotic cells
. Animal cells only
All eukaryotic cells
All eukaryotic cells
All eukaryotic cells
All cells
Plant cells-one large;animal cells-a fewsmall
An inflexible banier that provides support and protects theplant cell
Organelles that occur in pairs and are important for celldivision
A double-membrane organelle with thylakoids containingchlorophyll where photosynthesis takes place
Proiections from cell surfaces that aid in locomotion andfeeding; also used to sweep substances along surfaces
A framework for the cell within the cytoplasm
A highly folded membrane that is the s¡te of proteinsynthesis
Projections that aid in locomotion and feeding
A flattened stack of tubular membranes that modifiesproteins and packages them for distribution outside the cell
A vesicle that contains digestive enzymes for the breakdownof excess or worn-out cellular substances
A membrane-bound organelle that makes energy availableto the rest of the cell
control center of the cell that contains coded directions forthe production of proteins and cell division
A flexible boundary that controls the movement ofsubstances into and out of the cell
0rqanelle that is the site of protein synthesis
A membrane-bound vesicle for the temporary storage ofmaterials
Section 3. Structures and organelles l9!)
{raltfinR$ IN ¡HOt d¡üV
Science Commun¡cationsSpecialist Many publishers ofsc¡entific material hire commun¡cationsspec¡al¡sts to write about research andits importance to the general public.this often is accomplished throughpress releasel ad1 pamphleb, andtargeted mailings. For more informa-tion on biology careert visitbiologygmh.com.
l&x*srsxl*nüUnderstand Main
Comparing CellsTable 7.'l summarizes the structures ofeukaryotic plant cells and ani-mal cells. Notice that plant cells contain chlorophyll-they can captureand transform energy from the Sun into a usable form of chemicalenergy. This is one ofthe main characteristics that distinguishes plantsfrom animals. In addition, remember that animal cells usually do notcontain vacuoles. Ifthey do, vacuoles in animal cells are much smallerthan vacuoles in plant cells. Also, animal cells do not have cell walls.Cell walls give plant cells protection and support.
Organelles at WorkWith a basic understanding of the structures found within a cell, itbecomes easier to envision how those structures work together to per-form cell functions. Take, for example, the synthesis ofproteins.
Protein synthesis begins in the nucleus with the information containedin the DNA. Genetic information is copied and transferred to anothergenetic molecule called RNA. Then RNA and ribosomes, which have beenmanufactured in the nucleolus, leave the nucleus through the pores ofthenuclear membrane. Together, RNA and ribosomes man-ufacfrre proteins.Each protein made on the rough ER has a particular function; it mighrbecome a protein that forms a part of the plasma membrane, a protein thatis released from the cell or a protein transported to other organilles. Otherribosomes will float freely in the cytoplasm and make proteins as well.
Most ofthe proteins made on the surface ofthe ER are sent to theGolgi apparatus. The Golgi apparatus packages the proteins in vesiclesand transports them to other organelles or out ofthe cell. Other organ-elles use the proteins to carry out cell processes. For example, lysosomesuse proteins, enzymes in particula¡ to digest food and waste. Mitochon_dria use enzymes to produce a usable form ofenergy for the cell.
After reading about the organelles in a cell, it becomes clearer whypeople equate the cell to a factor¡ Each organelle has its job to do, andthe health ofthe cell depends on all ofthe components working together.
$&nA¡*Section Summary) Eukaryot¡c cells contain membrane.
bound organelles in the cytoplasmthat perform cell funct¡ons.
) Ribosomes are the sites of proteinsynthes¡s.
) Mitochondria are the powerhousesof cells.
) Plant and animal cells contain manyof the same organelles, while otherorganelles are unique to either plantcells or animal cells.
1 .Ideas
W@ ldentify the role ofthe nucleus in a eukaryotic cell.
Summarize the role of the endo-plasmic reticulum.
Analogy Make a flowchartcomparing the parts of a cell to anautomobile production line.
Infer why some scientists do notconsider ribosomes to be cell0rganel¡es.
5. l*ypothosizo how lysosomeswould be involved in changing acaterpillar into a butterfly.
6. @ElEilE@$iotogyCategorize the structures and organ-elles in Table 7.1 ¡nto lists based oncell type, then draw a concept mapillustrating your organization.
Chapter 7 . Cellular Structure and Functton