Chapter 8: Cellular Transport and the Cell...

Cellular Transport and the Cell Cycle

What You’ll Learn■ You will discover how mole-

cules move across the plasmamembrane.

■ You will sequence the stagesof cell division.

Why It’s ImportantTransportation of substancesthrough the plasma membraneand cell reproduction are twoimportant functions that helpcells maintain homeostasis andkeep you healthy.

Look through the list ofnew vocabulary words forthe chapter. Break down thewords and try to determinetheir origins. As you readthe chapter more thorough-ly, write down definitionsfor any unfamiliar words.

To find out more about cellulartransport and the cell cycle, visitthe Glencoe Science Web site.science.glencoe.com

READING BIOLOGYREADING BIOLOGY

8ChapterChapter

Cells divide in plant root tips(above) in normal growth.Some cells are cancerous(inset) and divide indefinitely.

200

Magnification: 14 000�

BIOLOGY


http://science.glencoe.com

Section

Osmosis: Diffusion of Water

Although the plasma membrane ofa cell can act as a dam or pump forwater-soluble molecules that cannotpass freely through the membrane, itdoes not limit the diffusion of water.Recall that diffusion is the movementof particles from an area of higherconcentration to an area of lower con-centration. In a cell, water always triesto reach an equal concentration onboth sides of the membrane. The dif-fusion of water across a selectively per-meable membrane is called osmosis(ahs MOH sus). Regulating the waterflow through the plasma membrane

is an important factor in maintaininghomeostasis within the cell.

What controls osmosisIf you add sugar to water, the water

becomes sweeter as you add moresugar. As the number of sugar mole-cules increases, the number of watermolecules decreases. If a strong sugarsolution and a weak sugar solution areplaced in direct contact, water mole-cules diffuse in one direction andsugar molecules diffuse in the otherdirection until all molecules areevenly distributed throughout.

If the two solutions are separatedby a selectively permeable membranethat allows only water to diffuse across

8.1 CELLULAR TRANSPORT 201

This dam is a barrier that,when opened, allows water topass to the other side of the

floodgates. In contrast, to move waterfrom the well and out through thepump, someone must physically movethe handle that draws the water upagainst gravity. The plasma mem-brane of a cell can act as botha dam and a pump as itregulates the traffic ofions and molecules intoand out of the cell.

SECTION PREVIEW

ObjectivesExplain how theprocesses of diffusion,passive transport, andactive transport occurand why they areimportant to cells.Predict the effect of ahypotonic, hypertonic,or isotonic solution on a cell.

Vocabularyosmosisisotonic solutionhypotonic solutionhypertonic solutionpassive transportfacilitated diffusionactive transportendocytosisexocytosis

8.1 Cellular Transport

A dam and a pump regulatethe flow of water.

OriginWORDWORD

osmosisFrom the Greekword osmos, mean-ing “pushing.”Osmosis can pushout a cell’s plasmamembrane.

it, as shown in Figure 8.1, water flowsto the side of the membrane wherethe water concentration is lower. Thewater continues to diffuse until it is inequal concentration on both sides ofthe membrane. Therefore, we knowthat unequal distribution of particles,called a concentration gradient, isone factor that controls osmosis.

With your knowledge of osmosis,it is important to understand howosmosis affects cells.

Cells in an isotonic solution Most cells, whether in multicellular

or unicellular organisms, are subjectto osmosis because they are sur-rounded by water solutions. In anisotonic solution, the concentrationof dissolved substances in the solutionis the same as the concentration ofdissolved substances inside the cell.Likewise, the concentration of waterin the solution is the same as the con-centration of water inside the cell.

Cells in an isotonic solution do notexperience osmosis and they retaintheir normal shape, as shown inFigure 8.2. Most solutions, includingthe immunizations your doctor gives,are isotonic so that cells are not dam-aged by the loss or gain of water.

Cells in a hypotonic solutionIn a hypotonic solution, the con-

centration of dissolved substances islower in the solution outside the cellthan the concentration inside thecell. Therefore, there is more wateroutside the cell than inside. Cells in ahypotonic solution experience osmo-sis that causes water to move throughthe plasma membrane into the cell.With osmosis, the cell swells and itsinternal pressure increases.

As the pressure increases insideanimal cells, the plasma membrane

202 CELLULAR TRANSPORT AND THE CELL CYCLE

Water moleculeDissolved molecule

H2OH2O

Figure 8.2In an isotonic solu-tion, water moleculesmove into and out ofthe cell at the samerate, and cells retaintheir normal shape(a). Notice the con-cave disc shape of ared blood cell (b). Aplant cell has its nor-mal shape and pres-sure in an isotonicsolution (c).

Water moleculeSugar molecule

Selectivelypermeablemembrane

Before osmosis After osmosis

Figure 8.1During osmosis, water diffuses across a selectively permeablemembrane. Notice that the number of sugar molecules did notchange on each side of the membrane, but the number of watermolecules did change.

a b cMagnification: 2000�

a b c

swells, like the red blood cells shownin Figure 8.3. If the solution isextremely hypotonic, such as distilledwater, the plasma membrane may beunable to withstand this pressure andmay burst.

Because plant cells contain a rigidcell wall that supports the cell, theydo not burst when in a hypotonicsolution. As the pressure increasesinside the cell, the plasma membraneis pressed against the cell wall.Instead of bursting, the plant cellbecomes more firm. Grocers use thisreaction to keep produce lookingfresh by misting the fruits and veg-etables with water.

Cells in a hypertonic solutionIn a hypertonic solution, the

concentration of dissolved substances

outside the cell is higher than theconcentration inside the cell. Cells ina hypertonic solution experienceosmosis that causes water to flow out.

Animal cells in a hypertonic solu-tion shrivel because of decreasedpressure in the cells, as indicated inFigure 8.4. This explains why youshould not salt meat before cooking.The salt forms a hypertonic solutionon the meat’s surface. Water insidethe meat cells diffuses out, leavingthe cooked meat dry and tough.

Plant cells in a hypertonic environ-ment lose water, mainly from thecentral vacuole. The plasma mem-brane and cytoplasm shrink awayfrom the cell wall, as shown inFigure 8.4. Loss of water in a plantcell results in a drop in pressure andexplains why plants wilt.


Figure 8.3In a hypotonic solu-tion, water enters acell by osmosis, caus-ing the cell to swell(a). Animal cells, likethese red blood cells,may continue toswell until they burst(b). Plant cells swellbeyond their normalsize as pressureincreases (c).

Figure 8.4In a hypertonic solu-tion, water leaves acell by osmosis, caus-ing the cell to shrink(a). Animal cells likethese red blood cellsshrivel up as theylose water (b). Plantcells lose pressure asthe plasma mem-brane shrinks awayfrom the cell wall (c).

H2OH2O


H2OH2O


OriginWORDWORD

iso-, hypo-, hyper-From the Greekwords isos, meaning“equal,” hypo,meaning “under,”and hyper, meaning“over,” respectively.

a b c

Magnification: 1800�


Cell Membrane Simulation Ifmembranes show selective per-meability, what might happen ifa plastic bag (representing a cell’smembrane) were filled withstarch molecules on the inside andsurrounded by iodine molecules on the outside?

Procedure! Fill a plastic bag with 50 mL of

starch. Seal the bag with a twist tie.@ Fill a beaker with 50 mL of iodine solution. CAUTION:

Rinse with water if iodine gets on skin. Iodine is toxic.# Note and record the color of the starch and iodine.$ Place the bag into the beaker. CAUTION: Wash your

hands after handling lab materials.% Note and record the color of the starch and iodine 24

hours later.

Analysis1. Describe and compare the color of the iodine and starch

at the start and at the conclusion of the experiment.2. Fact: Starch mixed with iodine forms a purple color.

a. In which direction did the iodine move? What is yourevidence?

b. In which direction did the starch move? What is yourevidence?

3. Explain how this experiment illustrates selective permeability.

MiniLab 8-1MiniLab 8-1Passive Transport

Water, lipids, and lipid-solublesubstances are some of the few com-pounds that can pass through theplasma membrane by diffusion. Thecell uses no energy to move theseparticles; therefore, this movement ofparticles across membranes by diffu-sion is called passive transport.

Passive transport of other sub-stances that are not attracted to thephospholipid bilayer or are too largeto pass through can still occur byother mechanisms as long as the sub-stance is moving with the concentra-tion gradient.

You can investigate passive trans-port by performing the MiniLabshown here.

Passive transport by proteinsRecall that transport proteins help

substances move through the plasmamembrane. These proteins functionin a variety of ways to transport mole-cules and ions across the membrane.

The passive transport of materialsacross the plasma membrane with theaid of transport proteins is calledfacilitated diffusion. As illustratedin Figure 8.5, the transport proteins

204

Carrierproteins

Facilitated diffusionPassive diffusion

Channelprotein

Water molecule

Dissolved molecule

Figure 8.5Channel proteins providethe openings through whichsmall, dissolved particles,especially ions, diffuse bypassive transport.

Selective permeability

Formulating Models

View an animation of passive transport in thePresentation Builder of theInteractive CD-ROM.

CD-ROM

Carrier protein

Higher concentrationof ions

Ions

Lower concentrationof ions

Energy

provide convenient openings for particles to pass through. Facilitateddiffusion is a common method ofmoving of sugars and amino acidsacross membranes. Facilitated diffu-sion, like simple diffusion, is drivenby a concentration gradient; sub-stances on both sides of the mem-brane are trying to reach equal con-centrations.

Active TransportA cell can move particles from a

region of lower concentration to aregion of higher concentration, but itmust expend energy to counteractthe force of diffusion that is movingthe particles in the opposite direc-tion. Movement of materials througha membrane against a concentrationgradient is called active transportand requires energy from the cell.

How active transport occursIn active transport, a transport

protein called a carrier protein firstbinds with a particle of the substanceto be transported. In general, eachtype of carrier protein has a shapethat fits a specific molecule or ion.When the proper molecule bindswith the protein, chemical energyallows the cell to change the shape ofthe carrier protein so that the particleto be moved is released on the otherside of the membrane, something likethe opening of a door. Once the par-ticle is released, the protein’s originalshape is restored, as illustrated inFigure 8.6. Active transport allowsparticle movement into or out of acell against a concentration gradient.

Transport of large particlesSome cells can take in large mole-

cules, groups of molecules, or even


Figure 8.6Carrier proteins are used in active transport to pick up ions ormolecules from near the cell membrane, carry them across themembrane, and release them on the other side. Active transportrequires energy.

View an animation of activetransport in thePresentation Builderof the InteractiveCD-ROM.

CD-ROM

whole cells. Endocytosis is a processby which a cell surrounds and takes inmaterial from its environment. Thismaterial does not pass directly throughthe membrane. Instead, it is engulfedand enclosed by a portion of the cell’splasma membrane. That portion ofthe membrane then breaks away, andthe resulting vacuole with its con-tents moves to the inside of the cell.

Figure 8.7 shows the reverseprocess of endocytosis, called exocy-tosis. Exocytosis is the expulsion orsecretion of materials from a cell.


Section AssessmentSection AssessmentUnderstanding Main Ideas1. What factors affect the diffusion of water

through a membrane by osmosis?2. How do animal cells and plant cells react

differently to osmosis in a hypotonic solution?

3. Compare and contrast active transport and facilitated diffusion.

4. How do carrier proteins facilitate passive transport of molecules across a membrane?

Thinking Critically5. A paramecium expels water when the organism

is surrounded by freshwater. What can youdeduce about the concentration gradient in theorganism’s environment?

6. Observing and Inferring Osmosis is a form ofdiffusion. What effect do you think an increasein temperature has on osmosis? For more help,refer to Thinking Critically in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

Exocytosis

Nucleus

Wastes

Digestion

Endocytosis

Figure 8.7Some unicellular organisms ingest foodby endocytosis and release wastes or cellproducts from a vacuole by exocytosis.

OriginWORDWORD

endo-, exo-From the Greekwords endon, mean-ing “within,” andexo, meaning “out.”Endocytosis movesmaterials into thecell; exocytosismoves materials outof the cell.

Cells use exocytosis to expel wastes,such as indigestible particles, fromthe interior to the exterior environ-ment. They also use this method tosecrete substances, such as hormonesproduced by the cell. Because endo-cytosis and exocytosis both movemasses of material, they both requireenergy and are, therefore, both formsof active transport.

With the various mechanisms thecell uses to transport materials in andout, cells must also have mechanismsto regulate size and growth.

Section

Cell Size Limitations

Although a giant cell will neverthreaten a city, cells do come in awide variety of sizes. Some cells, suchas red blood cells, measure only 8 micrometers (µm) in diameter.Other cells, such as nerve cells in largeanimals, can reach lengths of up to 1 m but with small diameters. The cellwith the largest diameter is the yolk ofan ostrich egg measuring 8 cm! Mostliving cells, however, are between 2and 200 µm in diameter. Consideringthis wide range of cell sizes, why thencan’t most organisms be just onegiant cell?

Diffusion limits cell sizeYou know that the plasma mem-

brane allows a steady supply of nutri-ents such as glucose and oxygen toenter the cell and allows wastes toleave. Within the bounds of theplasma membrane, these nutrientsand wastes move by diffusion.

Although diffusion is a fast andefficient process over short distances,it becomes slow and inefficient as thedistances become larger. For exam-ple, a mitochondrion at the center ofa hypothetical cell with a diameter of20 cm would have to wait monthsbefore receiving molecules enteringthe cell. Because of the slow rate of

8.2 CELL GROWTH AND REPRODUCTION 207

Picture this unlikely scene. Asthe movie begins, people runscreaming madly in the

streets. In the background, a hugecell towers above the skyscrapers, itscilia-covered surface slowly wavingto propel it through the city.Flagella flail along its side, smash-ing the buildings. Proteins on theplasma membrane form a crudeface with a sneer. Although thisscene is ridiculous, how do you knowthat giant cells are not possible?What limits the size of a cell?

SECTION PREVIEW

ObjectivesSequence the events of the cell cycle.Relate the function of a cell to its organizationas a tissue, organ, andan organ system.

Vocabularychromosomechromatincell cycleinterphasemitosisprophasesister chromatidcentromerecentriolespindlemetaphaseanaphasetelophasecytokinesistissueorganorgan system

8.2 Cell Growth andReproduction

An impossiblylarge cell

10 11 121

98

76

54

321

Millimeters

4 mm

4 mm4 mm

2 mm

2 mm2 mm

1 mm

1 mm1 mm

Surface area = 6 mm2

Volume = 1 mm3


Volume = 8 mm3

diffusion, organisms can’t be just onegiant-sized cell. They would die longbefore nutrients could reach theorganelles that needed them.

DNA limits cell sizeYou have learned that the nucleus

contains blueprints for the cell’s pro-teins. Proteins are used throughoutthe cell by almost all organelles to

perform critical cell functions. Butthere is a limit as to how quickly theblueprints for these proteins can becopied in the nucleus and made intoproteins in the cytoplasm. The cellcannot survive unless there is enoughDNA to support the protein needs ofthe cell.

What happens in larger cellswhere an increased amount of cyto-plasm requires increased supplies ofenzymes? In many large cells, such asthe giant amoeba Pelomyxa shown inFigure 8.8, more than one nucleushas evolved. Large amounts of DNAin many nuclei ensure that cell activi-ties are carried out quickly and effi-ciently.

Surface area-to-volume ratioAnother size-limiting factor is the

cell’s surface area-to-volume ratio. Asa cell’s size increases, its volumeincreases much faster than its surfacearea. Picture a cube-shaped cell likethose shown in Figure 8.9. Thesmallest cell has 1 mm sides, a surfacearea of 6 mm2, and a volume of 1mm3. If the side of the cell is doubledto 2 mm, the surface area will increasefourfold to 6 � 2 � 2 = 24 mm2.Observe what happens to the volume;it increases eightfold to 8 mm3.

Figure 8.9Surface area-to-volume ratio is one of the factors that limits cellsize. Note how the surface area and the volume change as thesides of a cell double in length from 1 mm to 2 mm. Calculate thechange in surface area and volume as the cell doubles in size againto 4 mm on a side.

Figure 8.8This giant amoeba,Pelomyxa, is severalmillimeters in diame-ter. It can have up to1000 nuclei.

208


What happens to the surface area of a cell as itsvolume increases? One reason cells are small is that, as they grow, their volume increases faster than their surface area.

Analysis Look at the cubes shown below. Note the size and

magnitude of difference in surface area and volume amongthe cubes.

Thinking Critically1. How many small cubes (1 mm) do you think it would take

to fill the largest cube (4 mm)?2. Relating this example to cells, describe how a cell is

affected by its size. 3. Explain how a small change in cell size can have a huge

impact on the cell and its normal functions.

Problem-Solving Lab 8-1Problem-Solving Lab 8-1 Drawing ConclusionsWhat does this mean for cells?

How does the surface area-to-volumeratio affect cell function? If cell sizedoubled, the cell would require eighttimes more nutrients and would haveeight times more waste to excrete.The surface area, however, wouldincrease by a factor of only four.Thus, the plasma membrane wouldnot have enough surface areathrough which oxygen, nutrients, andwastes could diffuse. The cell wouldeither starve to death or be poisonedfrom the buildup of waste products.You can investigate surface area-to-volume ratios yourself in theProblem-Solving Lab shown here.

Because cell size can have dramaticand negative effects on a cell, cellsmust have some method of maintain-ing optimum size. In fact, cells dividebefore they become too large tofunction properly. Cell divisionaccomplishes other purposes, too, asyou will read next.

Cell ReproductionRecall that the cell theory states

that all cells come from preexistingcells. Cell division is the process bywhich new cells are produced fromone cell. Cell division results in twocells that are identical to the original,parent cell. Right now, as you arereading this page, many of the cellsin your body are growing, dividing,and dying. Old cells on the soles ofyour feet and on the palms of yourhands are being shed and replaced,cuts and bruises are healing, and yourintestines are producing millions ofnew cells each second. New cells areproduced as tadpoles become frogs,and as an ivy vine grows and wrapsaround a garden trellis. All organismsgrow and change; worn-out tissuesare repaired or are replaced by newlyproduced cells.

The discovery of chromosomesMost interesting to the early biolo-

gists was their observation that justbefore cell division, several short,stringy structures suddenly appearedin the nucleus. Scientists also noticedthat these structures seemed to van-ish as mysteriously as they appearedsoon after division of a cell. Thesestructures, which contain DNA andbecome darkly colored when stained,are called chromosomes (KROH muhsohmz).

Eventually, scientists learned thatchromosomes are the carriers of thegenetic material that is copied andpassed from generation to generationof cells. This genetic material is cru-cial to the identity of the cell.


4 mm4 mm

4 mm

2 mm

2 mm

2 mm1 mm

1 mm

1 mm


Volume = 1 mm3Surface area = 24 mm2

Volume = 8 mm3

OriginWORDWORD

chromosomeFrom the Greekwords chroma,meaning “colored,”and soma, meaning“body.” Chromo-somes are dark-staining structuresthat contain geneticmaterial.

Accurate transmission of chromo-somes during cell division is critical.

The structure of eukaryotic chromosomes

For most of a cell’s lifetime, chro-mosomes exist as chromatin, longstrands of DNA wrapped around pro-teins. Under an electron microscope,chromatin looks somewhat chaotic,resembling a plate of tangled-upspaghetti. This loose, seemingly

unorganized arrangement is neces-sary for the protein blueprints to becopied. However, before a cell candivide, the long strands of chromatinmust be reorganized, just as youwould coil a long strand of ropebefore storing it. As the nucleusbegins to divide, chromosomes takeon a different structure in which thechromatin becomes tightly packed.

The Cell CycleFall follows summer, night follows

day, and low tide follows high tide.Many events in nature follow a recur-ring, cyclical pattern. Living organ-isms are no exception. One cyclecommon to most living things is thecycle of the cell. The cell cycle is thesequence of growth and division of acell.

As a cell proceeds through itscycle, it goes through two generalperiods: a period of growth and aperiod of division. The majority of acell’s life is spent in the growthperiod known as interphase. Duringinterphase, a cell grows in size andcarries on metabolism. Also duringthis period, chromosomes are dupli-cated in preparation for the period ofdivision.

Following interphase, a cell entersits period of nuclear division calledmitosis (mi TOH sus). Mitosis is theprocess by which two daughter cellsare formed, each containing a com-plete set of chromosomes. Interphaseand mitosis make up the bulk of thecell cycle. One final process, divisionof the cytoplasm, takes place aftermitosis. Look at the Inside Story tofind out how many stages of growthare involved in interphase. You canuse the Problem-Solving Lab on thispage and the BioLab at the end of thischapter to investigate the rate ofmitosis.


How does the length of the cell cycle vary? The cell cyclevaries greatly in length from one kind of cell to another.Some kinds of cells divide rapidly, while others divide moreslowly.

AnalysisExamine the cell cycle diagrams of two different types of

cells. Observe the total length of each cell cycle and thelength of time each cell spends in each phase of the cell cycle.

Thinking Critically1. Which part of the cell cycle is most variable in length? 2. What can you infer about the functions of these two

types of cells? 3. Why do you think the cycle of some types of cells is faster

than in others? Explain your answer.

Problem-Solving Lab 8-2Problem-Solving Lab 8-2 Observing andInferring

7 hours 3 hours

Mitosis1 hour

11 hours

Interphase

Total = 22 hours

37 hours

7 hours

Mitosis1 hourInterphase

Total = 48 hours

3 hours


G2 The chromosomesbegin to shorten andcoil, and protein synthe-sis is in high gear. In thisstage of interphase,most of the proteinsbeing synthesized areneeded for mitosis andthe cell organizes andprepares for mitosis. Inanimals, the centriolepair replicates and pre-pares to form themitotic spindle.

S Stage During this stage of interphase,the chromosomes are replicated in thenucleus. Chromosomes divide to formidentical sister chromatids connected by acentromere.

G1 Interphase begins withthe G1 stage. At this pointthe chromosomes are notvisible under the lightmicroscope because they

are uncoiled. Proteinsynthesis is rapidly

occurring asthe cell

grows anddevelops.


The Cell Cycle

The cell cycle is divided into interphase, when most ofthe cell’s metabolic functions are carried out and the

chromosomes are replicated, and mitosis, when nuclear divi-sion occurs, leading to the formation of two daughter cells.The division of cytoplasm, called cytokinesis, follows mitosis.

Critical Thinking During which stage of the interphasedoes a cell spend most of its time? Why?

Interphase

INSIDESSTORTORYY

INSIDE

11

22

33

Mitosis When interphase is complete,the cell undergoes mitosis. Mitosis con-sists of four stages (Figure 8.12) thatresult in the formation of two daugh-ter cells with identical copies of theDNA. Following mitosis, the cytoplasmdivides, separating the two daughtercells.

44


Interphase: A Busy Time

Interphase, the busiest phase of thecell cycle, is divided into three partsas shown in Figure 8.10. During thefirst part, the cell grows and proteinproduction is high. In the next partof interphase, the cell copies its chro-mosomes. DNA synthesis does notoccur all through interphase but isconfined to this specific time. After

the chromosomes have been dupli-cated, the cell enters another shortergrowth period in which mitochondriaand other organelles are manufac-tured and cell parts needed for celldivision are assembled. Followingthis activity, interphase ends andmitosis begins.

The Phases of MitosisCells undergo mitosis as they

approach the maximum cell size atwhich the nucleus can provide blue-prints for proteins and the plasmamembrane can efficiently transportnutrients and wastes into and out ofthe cell.

Although cell division is a continu-ous process, biologists recognize fourdistinct phases of mitosis—eachphase merging into the next. Thefour phases of mitosis are prophase,metaphase, anaphase, and telophase.Refer to Figure 8.12 to help youunderstand the process as you readabout mitosis.

Prophase: the first phase of mitosis

During prophase, the first andlongest phase of mitosis, the long,stringy chromatin coils up into visiblechromosomes. At this point the chro-mosomes look hairy. As you can seein Figure 8.11, each duplicated chro-mosome is made up of two halves.The two halves of the doubled struc-ture are called sister chromatids.Sister chromatids and the DNA theycontain are exact copies of each otherand are formed when DNA is copiedduring interphase. Sister chromatidsare held together by a structurecalled a centromere, which plays arole in chromosome movement dur-ing mitosis. By their characteristiclocation, centromeres also help scien-tists identify and study chromosomes.


S phaseDNA synthesisand replication

G1 phaseRapid growth

and metabolic activity

G2 phaseCentrioles replicate;

cell preparesfor division

Interphase

Mitosis

Figure 8.10In preparation formitosis, most of thetime spent in the cellcycle is in interphase.The process of mitosis, representedhere by the yellowwedge, is shownin detail in Figure 8.12

Figure 8.11This photomicrograph shows a fully coiled chromosome. The twosister chromatids are held together by a centromere.

Sister chromatids

Centromere



Figure 8.12Mitosis begins after interphase. Follow the stages of mito-sis as you read the text. The diagrams describe mitosis inanimal cells and the photos show mitosis in plant cells.

Prophase The chromatin coilsto form visible chromosomes.

BB

Interphase precedes mitosis.Refer to the Inside Story.

AA

Metaphase The chromo-somes move to the equatorof the spindle.

CC

Anaphase The centromeressplit and the sister chromatidsare pulled apart to oppositepoles of the cell.

DD

Telophase Two distinctdaughter cells are formed.The cells separate as thecell cycle proceeds intothe next interphase.

EE






Pole

Centrioles

Nucleolus

Nucleus

Chromatin

Disappearingnuclearenvelope

Doubledchromosome

Spindlefibers

Centromere

Sisterchromatids

Twodaughtercells areformed

Nuclearenvelopereappears

As prophase continues, the nucleusbegins to disappear as the nuclearenvelope and the nucleolus disinte-grate. By late prophase, these struc-tures are completely absent. In ani-mal cells, two important pairs ofstructures, the centrioles, begin tomigrate to opposite ends of the cell.Centrioles are small, dark, cylindri-cal structures that are made of micro-tubules and are located just outsidethe nucleus, Figure 8.13. Centriolesplay a role in chromatid separation.

As the pairs of centrioles move toopposite ends of the cell, anotherimportant structure, called the spin-dle, begins to form between them.The spindle is a football-shaped,cagelike structure consisting of thinfibers made of microtubules. In plantcells, the spindle forms without cen-trioles. The spindle fibers play a vitalrole in the separation of sister chro-matids during mitosis.

Metaphase: the second stage of mitosis

During metaphase, the short sec-ond phase of mitosis, the doubledchromosomes become attached tothe spindle fibers by their cen-tromeres. The chromosomes arepulled by the spindle fibers and beginto line up on the midline, or equator,of the spindle. Each sister chromatidis attached to its own spindle fiber.One sister chromatid’s spindle fiberextends to one pole, and the otherextends to the opposite pole. Thisarrangement is important because itensures that each new cell receives anidentical and complete set of chro-mosomes.

Anaphase: the third phase of mitosis

The separation of sister chro-matids marks the beginning ofanaphase, the third phase of mitosis.


Figure 8.13Centrioles duplicate during inter-phase. In the photomicrograph,one centriole is cut crosswise andthe other longitudinally.

Microtubule

View an ani-mation of the cellcycle in the Presen-tation Builder of theInteractive CD-ROM.

CD-ROM


During anaphase, the centromeressplit apart and chromatid pairs fromeach chromosome separate from eachother. The chromatids are pulledapart by the shortening of the micro-tubules in the spindle fibers.

Telophase: the fourth phase of mitosis

The final phase of mitosis istelophase. Telophase begins as thechromatids reach the opposite polesof the cell. During telophase, manyof the changes that occurred duringprophase are reversed as the newcells prepare for their own indepen-dent existence. The chromosomes,which had been tightly coiled sincethe end of prophase, now unwind sothey can begin to direct the meta-bolic activities of the new cells. Thespindle begins to break down, thenucleolus reappears, and a newnuclear envelope forms around eachset of chromosomes. Finally, a newdouble membrane begins to formbetween the two new nuclei.

Division of the cytoplasmFollowing telophase, the cell’s

cytoplasm divides in a process calledcytokinesis (site uh kih NEE sus).Cytokinesis differs between plantsand animals. Toward the end oftelophase in animal cells, the plasmamembrane pinches in along the equa-tor as shown in Figure 8.14. As thecell cycle proceeds, the two new cellsare separated. Find out more aboutmitosis in animal cells in theMiniLab.

Plant cells have a rigid cell wall, sothe plasma membrane does not pinchin. Rather, a structure known as thecell plate is laid down across the cell’sequator. A cell membrane formsaround each cell, and new cell wallsform on each side of the cell plateuntil separation is complete.


Figure 8.14At the end oftelophase in animalcells, such as this frogegg, proteins posi-tioned just under theplasma membrane atthe equator of thecell contract and slidepast each other tocause a deep furrow.The furrow deepensuntil the cell ispinched in two.

Seeing Asters The result of theprocess of mitosis is similar in plantand animal cells. However, animal cellshave asters whereas plant cells do not.Animal cells undergoing mitosis clearlyshow these structures.

Procedure! Examine a slide marked “fish

mitosis” under low- and high-powermagnification. CAUTION: Use care when handling pre-pared slides.

@ Find cells that are undergoing mitosis. You will be able tosee dark-stained rodlike structures within certain cells.These structures are chromosomes.

# Note the appearance and location of asters. They willappear as ray or starlike structures at opposite ends ofcells that are in metaphase.

$ Asters may also be observed in cells that are in otherphases of mitosis.

Analysis1. Describe the appearance and location of asters in cells

that are in prophase.2. Explain how you know that asters are not critical to

mitosis.3. Design an experiment that tests the hypothesis that

asters are not essential for mitosis in animal cells.

MiniLab 8-2MiniLab 8-2 Comparing andContrasting

Asters



Results of mitosisMitosis is a process that guarantees

genetic continuity, resulting in theproduction of two new cells withchromosome sets that are identical tothose of the parent cell. These newdaughter cells will carry out the samecellular processes and functions as

those of the parent cell and will growand divide just as the parent cell did.

When mitosis is complete, unicel-lular organisms remain as singlecells—the organism simply multi-plied. In multicellular organisms, cellgrowth and reproduction result ingroups of cells that work together astissue to perform a specific function.Tissues organize in various combina-tions to form organs that performmore complex roles within the organ-ism. For example, cells make up mus-cle tissue, then muscle tissue workswith other tissues in the organ calledthe stomach to mix up food. Multipleorgans that work together form anorgan system. The stomach is oneorgan in the digestive system, whichfunctions to break up and digest food.

All organ systems work togetherfor the survival of the organism,whether the organism is a fly or ahuman. Figure 8.15 shows an exam-ple of cell specialization and organi-zation for a complex organism. Inaddition to its digestive system, thepanther has a number of other organsystems that have developed throughcell specialization.It is important toremember that no matter how com-plex the organ system or organismbecomes, the cell is still the mostbasic unit of that organization.


Cell (muscle cell)

Tissue(muscletissue)

Organ(stomach)

Organ system(digestivesystem)

Organism(Floridapanther)

Figure 8.15Cells of complex multi-cellular organisms areorganized into tissues,organs, and organsystems.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. Describe how a cell’s surface area-to-volume

ratio limits its size.2. Why is it necessary for a cell’s chromosomes to be

distributed to its daughter cells in such a precisemanner?

3. How is the division of the cytoplasm different inplants and in animals?

4. In multicellular organisms, describe two cellularspecializations that result from mitosis.

Thinking Critically5. At one time, interphase was referred to as the

resting phase of the cell cycle. Why do you thinkthis description is no longer used?

6. Making and Using Tables Make a table showing the phases of the cell cycle. Mentionone important event that occurs at each phase.For more help, refer to Organizing Informationin the Skill Handbook.


Section

Normal Control of the Cell Cycle

For more than a quarter of a cen-tury, scientists have worked long andhard to discover the factors that initi-ate and control cell division. A clearunderstanding of these control fac-tors can, among others, benefit med-ical research. Today, the full story isstill not known; however, scientistsdo have some clues.

Enzymes control the cell cycleMost biologists agree that a series

of enzymes monitors a cell’s progressfrom phase to phase during the cellcycle. Certain enzymes are necessary

to begin and drive the cell cycle,whereas other enzymes control thecycle through its phases. Occa-sionally, cells lose control of the cellcycle. This uncontrolled dividing ofcells can result from the failure toproduce certain enzymes, the over-production of enzymes, or the pro-duction of other enzymes at thewrong time. Cancer is one result ofuncontrolled cell division. This lossof control may be caused by environ-mental factors or by changes inenzyme production.

Enzyme production is directed bygenes located on the chromosomes.A gene is a segment of DNA thatcontrols the production of a protein.

8.3 CONTROL OF THE CELL CYCLE 217

Accurate cell division and regulationof the cell cycle is critical to thehealth of an organism. Some cells,

such as the cells lining the intestine, com-plete the cell cycle in 24 to 48 hours. Othercells, such as the cells in a frog embryo,complete the cell cycle in less than an hour.Some cells, such as nerve cells, never divideonce they mature. Despitethis diversity, the factorsthat control the cell cycle are generally similar. Amistake in the cell cycle can lead to cancer.

SECTION PREVIEW

ObjectivesDescribe the role ofenzymes in the regula-tion of the cell cycle.Distinguish betweenthe events of a normal cell cycle and the abnor-mal events that result in cancer.Identify ways to potentially reduce therisk of cancer.

Vocabularycancergene

8.3 Control of the Cell Cycle

Normal con-trol results inhealthy cells;a mistakemay result incancer.


Many studies point to the portionof interphase just before DNA repli-cation as being a key control periodin the cell cycle. Scientists have iden-tified several enzymes that triggerDNA replication.

Cancer: A Mistake in the Cell Cycle

Currently, scientists consider can-cer to be a result of changes in one ormore of the genes that produceenzymes that are involved in control-ling the cell cycle. These changes are

expressed as cancer when somethingprompts the damaged genes intoaction. Cancerous cells form massesof tissue called tumors that deprivenormal cells of nutrients. In laterstages, cancer cells enter the circula-tory system and spread throughoutthe body, a process called metastasis,forming new tumors that disrupt thefunction of organs, organ systems,and ultimately, the organism.

Cancer is the second leading causeof death in the United States,exceeded only by heart disease.Cancer can affect any tissue in thebody. In the United States, lung,colon, breast, and prostate cancersare the most prevalent types. Use theProblem-Solving Lab on this page toestimate the number of people in theUnited States who will develop thesekinds of cancers in this decade, andhow many people are expected to diefrom cancers. The Health Connectionfeature at the end of this chapter fur-ther discusses skin cancer.

The causes of cancerThe causes of cancer are difficult

to pinpoint because both genetic andenvironmental factors are involved.The environmental influences ofcancer become obvious when youconsider that people in differentcountries develop different types ofcancers at different rates. For exam-ple, the rate of breast cancer is rela-tively high in the United States, butrelatively low in Japan. Similarly,stomach cancer is common in China,but rare in the United States.

In addition, when people movefrom one country to another, cancerrates appear to follow the pattern ofthe country in which they are cur-rently living, not their country of ori-gin. Other environmental factors,such as cigarette smoke, air and waterpollution, and exposure to ultraviolet


How does the incidence of cancer vary? Cancer affectsmany different body organs. In addition, the same body organ,such as our skin, can be affected by several different types ofcancer. Some types of cancer are more treatable than others.Use the following graph to analyze the incidence of cancer.

Thinking Critically1. Which cancer type is most common? Least common?2. Which cancer type seems to be least treatable? Most

treatable?3. Offer a possible explanation for why the incidence of

basal and squamous skin cancer is so high. 4. Using breast cancer as an example, calculate the percent

of survival for this cancer type.

Problem-Solving Lab 8-3Problem-Solving Lab 8-3 Interpreting Data

Breast

Lung

Prosta

teColon

Skin:

Basal C

ell, a

nd

Squam

ousSk

in:

Mela

noma

Kind of Cancer

Num

ber o

f cas

es

840 000800 000760 000

340 000300 000260 000220 000180 000140 000100 00060 00020 000

Cancer Rates in the United States (2000)

Estimated new cases

Estimated deaths

radiation from the sun, are all knownto damage the genes that control thecell cycle. Cancer may also be causedby viral infections that damage genes.

Cancer preventionFrom recent and ongoing investi-

gations, scientists have established aclear link between a healthy lifestyleand the incidence of cancer.

Physicians and dietary expertsagree that diets low in fat and high infiber content can reduce the risk ofmany kinds of cancer. For example,diets high in fat have been linked toincreased risk for colon, breast, andprostate cancers, among others.People who consume only a minimalamount of fat reduce the potentialrisk for these and other cancers andmay also maintain a healthy bodyweight more easily. In addition,recent studies suggest that diets highin fiber are associated with reducedrisk for cancer, especially colon can-cer. Fruits, vegetables, and grainproducts are excellent dietary optionsbecause of their fiber content andbecause they are naturally low in fat.The foods displayed in Figure 8.16illustrate some of the choices that areassociated with cancer prevention.

Vitamins and minerals may alsohelp prevent cancer. Key in this cate-gory are carotenoids, vitamins A, C,


Section AssessmentSection AssessmentUnderstanding Main Ideas1. Do all cells complete the cell cycle in the same

amount of time?2. Describe how genes control the cell cycle.3. How can disruption of the cell cycle result in cancer?4. How does cancer affect normal cell functioning?

Thinking Critically5. What evidence shows that the environment influ-

ences the occurrence of cancer?

6. Observing and Inferring Although breast cancer is more prevalent than lung cancer, moredeaths are caused by lung cancer than breastcancer. Using your knowledge of how cancerspreads and factors that influence cancer, provide an explanation for this difference. For more help, refer to Thinking Critically in the Skill Handbook.


and E, and calcium. Carotenoids arefound in foods such as yellow andorange vegetables and green leafyvegetables. Citrus fruits are a greatsource of vitamin C, and many dairyproducts are rich in calcium.

In addition to diet, other healthychoices such as daily exercise and notusing tobacco also are known toreduce the risk of cancer.

Figure 8.16A healthy dietmay reduce yourrisk of cancer.


Where is mitosis most common?

M itosis and the resulting multiplication of cells are responsible forthe growth of an organism. Does mitosis occur in all areas of an

organism at the same rate, or are there certain areas within an organismwhere mitosis occurs more often? You will answer this question in thisBioLab. Your organism will be an onion, and the areas you are going toinvestigate will be different locations in its root.

INVESTIGATEINVESTIGATE

ProblemDoes mitosis occur at the same

rate in all parts of an onion root?

ObjectivesIn this BioLab, you will:■ Observe cells in two different root

areas.■ Identify the stages of mitosis in

each area.

Materialsprepared slide of onion root tipmicroscope

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

1. Copy the data table.2. Using Diagram A as a guide,

locate area X on a prepared slideof onion root tip.

3. Place the prepared slide underyour microscope and use lowpower to locate area X. CAUTION: Use care whenhandling prepared slides.

4. Switch to high power. 5. Using Diagram B as a guide:

a. Identify those cells that are inmitosis and in interphase.

b. Record in the data table thenumber of cells observed ineach phase of mitosis andinterphase for area X.

PROCEDUREPROCEDURE

Interphase

Prophase

Metaphase

Anaphase

Telophase

Phase Area X

Data Table

Area Y

Going FurtherGoing Further

Application Prepare a circle graph thatshows the total number of cells counted inarea X and the percentage of cells in eachphase of mitosis.

To find out more about mitosis, visit the Glencoe

Science Web site.science.glencoe.com

Note: It will be easier to countand keep track of cells by follow-ing rows. See Diagram C as aguide to counting.

6. Using Diagram A again, locatearea Y on the same preparedslide.

7. Place the prepared slide underyour microscope and use lowpower to locate area Y.

8. Switch to high power.

9. Using Diagram B as a guide:a. Identify those cells

that are in mitosis and in interphase.

b. Record in the data table the number of cells observed in each phase of mitosis and inter-phase for area Y.


1. Observing Which area of theonion root tip (X or Y) had thegreatest number of cells undergo-ing mitosis? The fewest? Usespecific totals from your datatable to support your answer.

2. Predicting If mitosis is associatedwith rapid growth, where do youbelieve is the location of mostrapid root growth, area X or Y?Explain your answer.

3. Applying Where might you lookfor cells in the human body thatare undergoing mitosis?

4. Calculating According to yourdata, which phase of mitosis ismost common? Least common?

5. Thinking Critically Assume thatyou were not able to observe cellsin every phase of mitosis? Explainwhy this might be.

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Y

X

High power view

Startcountinghere

Endcountinghere

Anaphase

Telophase

Metaphase

Interphase

Prophase

A

C

B

BIOLOGY


Skin cancer accounts for one-third of all malignancies diagnosed in the United States, and the incidence of skin cancer is increasing.Most cases are caused by exposure to harmful

ultraviolet rays emitted by the sun, so skin cancer most often develops on the exposedface or neck. The people most likely at risk arethose whose fair skin contains smaller amounts

of a protective pigment called melanin.

Skin is composed of two layers of tissue, theepidermis and the dermis. The epidermis is

the part that we see on the surface of our bodiesand is composed of multiple layers of closelypacked cells. As the cells reach the surface, theydie and become flattened. Eventually they flakeaway. To replace the loss, cells on the innermostlayer of the epidermis are constantly dividing.

Your body has a natural protection system toshield skin cells from potentially harmful rays ofthe sun. A pigment called melanin is produced bycells called melanocytes and absorbs the UV raysbefore they reach basal cells.

Types of skin cancersUncontrolled division of epidermal cells

leads to skin cancer. Squamous cell carcinoma isa common type of skin cancer that affects cellsthroughout the epidermis. Squamous cell cancertakes the form of red or pink tumors that cangrow rapidly and spread. Precancerous growthsproduced by sun-damaged basal cells can becomebasal cell carcinoma, another common type ofskin cancer. In basal cell carcinoma, the cancer-ous cells are from the layer of the epidermis that replenishes the shed epithelial cells. Bothsquamous cell carcinoma and basal cell carci-noma are usually discovered when they are small and can be easily removed in a doctor’soffice. Both types also respond to treatment such as surgery, chemotherapy, and radiationtherapy.

The most lethal skin cancer is malignantmelanoma. Melanomas are cancerous growths ofthe melanocytes that normally protect other cellsin the epithelium from the harmful rays of thesun. An important indication of a melanoma canbe a change in color of an area of skin to a varietyof colors including black, brown, red, dark blue,or gray. A single melanoma can have several col-ors within the tumor. Melanomas can also format the site of moles. Melanomas can be danger-ous because cancerous cells from the tumor cantravel to other areas of the body before themelanoma is detected. Early detection is essen-tial, and melanomas can be surgically removed.


ConnectionHealthHealth

Connection Skin Cancer

Scientists know that the UV rays of sunlight cancontribute to skin cancer. How can you minimizethe risk?

To find out more about skin cancer, visit the Glencoe

Science Web site.science.glencoe.com

CONNECTION TO BIOLOGYCONNECTION TO BIOLOGY

Epidermis

Melanocytes

MelaningranulesDermis

Structure of the skin

BIOLOGY


Chapter 8 AssessmentChapter 8 Assessment

SUMMARYSUMMARY

Section 8.1

Section 8.2

Section 8.3

Main Ideas■ Osmosis is the diffusion of water through a

selectively permeable membrane.■ Passive transport moves a substance with the

concentration gradient and requires no energyfrom the cell.

■ Active transport moves materials against theconcentration gradient and requires energy toovercome the opposite flow of materials withthe concentration gradient.

■ Large particles may enter a cell by endocytosisand leave by exocytosis.

Vocabularyactive transport (p. 205)endocytosis (p. 206)exocytosis (p. 206)facilitated diffusion (p. 204)hypertonic solution

(p. 203)hypotonic solution

(p. 202)isotonic solution (p. 202)osmosis (p. 201)passive transport (p. 204)

Main Ideas■ Cell size is limited largely by the diffusion rate

of materials into and out of the cell, the amountof DNA available to program the cell’s metabo-lism, and the cell’s surface area-to-volume ratio.

■ The life cycle of a cell is divided into two gen-eral periods: a period of active growth andmetabolism known as interphase, and a periodof cell division known as mitosis.

■ Mitosis is divided into four phases: prophase,metaphase, anaphase, and telophase.

■ The cells of most multicellular organisms areorganized into tissues, organs, and organ sys-tems.

Vocabularyanaphase (p. 214)cell cycle (p. 210)centriole (p. 214)centromere (p. 212)chromatin (p. 210)chromosome (p. 209)cytokinesis (p. 215)interphase (p. 210)metaphase (p. 214)mitosis (p. 210)organ (p. 216)organ system (p. 216)prophase (p. 212)sister chromatid (p. 212)spindle (p. 214)telophase (p. 215)tissue (p. 216)

Main Ideas■ The cell cycle is controlled by key enzymes that

are produced at specific points in the cell cycle. ■ Cancer is caused by genetic and environmental

factors that change the genes that control thecell cycle.

■ For some types of cancer, research has shownthat lifestyle choices like eating a healthy dietand exercising regularly can reduce the inci-dence of cancer.

Vocabularycancer (p. 217)gene (p. 217)

CHAPTER 8 ASSESSMENT 223

CellularTransport

Control of theCell Cycle

Cell GrowthandReproduction


224 CHAPTER 8 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Become an Expert on What You Fear the Most If you just can’t remember all those different parts of those important processes, don’t run away. Instead, consider it a challenge, meet the problem head on, and you’ll probably be surprised at how easy it is to conquer the toughest concepts.

1. What kind of environment is describedwhen the concentration of dissolved sub-stances is greater outside the cell than inside?a. hypotonic c. isotonic b. hypertonic d. saline

2. Osmosis is defined how?a. as an active processb. as diffusion of water through a selectively

permeable membranec. as an example of facilitated diffusiond. as requiring a transport protein

3. An amoeba ingests large food particles bywhat process?a. osmosis c. endocytosisb. diffusion d. exocytosis

4. Considering the surface area-to-volume ratio,what structure does surface area represent?a. cytoplasm c. ERb. mitochondria d. plasma membrane

5. Chromosomes are made of what?a. cytoplasm c. RNAb. centrioles d. DNA

6. Which of the following does NOT occurduring interphase?a. excretion of wastes c. protein synthesisb. cell repair d. nuclear division

7. If a cell that has eight chromosomes goesthrough mitosis, how many chromosomeswill the daughter cells have?a. 4 c. 16b. 8 d. 32

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS8. During metaphase,

the chromosomes move to the equator of what structure (shown here)?a. polesb. cell platec. centrioled. spindle

9. All but which of the following factors limitcell size?a. time required for diffusionb. elasticity of the plasma membranec. presence of only one nucleusd. surface area-to-volume ratio

10. Which of the following is NOT a knowncause of cancer?a. environmental influencesb. certain virusesc. cigarette smoked. bacterial infections

11. ________ transport requires energy.12. A red blood cell placed in a 3% salt solution

will ________.13. Sprinkling sugar on a bowl of strawberries

creates a ________ solution surrounding thestrawberries.

14. Grocers spray water on produce to increasethe ________ inside the cells.

15. Chromosomes are replicated during the________ stage of the cell cycle.

16. The ________ inside cells contain DNA andbecome darkly colored when stained.

17. Most of a cell’s life is spent carrying on theactivities of ________.

18. The ________ (shown here) is present only in an animal cell.

19. An organ consists ofseveral kinds of________.

20. A ________ is a segment of DNA that controls the production of a protein.

21. How would you expect the number of mito-chondria in a cell to be related to the amountof active transport it carries out?

22. Explain why drinking quantities of oceanwater is dangerous to humans. (Hint: Thebody excretes salt as a water solution.)

23. Suppose that all of the enzymes that controlthe normal cell cycle were identified. Suggestsome ways that this information might beused to fight cancer.

24. Making Predictions What do you think willhappen when a freshwater paramecium isplaced in salt water?

25. Observing and Inferring How does cell divi-sion in adult animals help maintain homeo-stasis?

26. Concept Mapping Complete the conceptmap using the following vocabulary terms:mitosis, cell cycle, metaphase, prophase,telophase, interphase, anaphase.

THINKING CRITICALLYTHINKING CRITICALLY

APPLYING MAIN IDEASAPPLYING MAIN IDEAS


CHAPTER 8 ASSESSMENT 225

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

Different species of organisms vary in thenumber of chromosomes found in body cells.

Interpreting Data Examine the table thenanswer the following questions.1. During late interphase, the chromo-

somes double to form chromatids thatare attached to each other. During whichphase do the chromatids separate?a. prophase c. anaphaseb. metaphase d. telophase

2. What number belongs in the spacelabeled A under Rye in the table?a. 14 c. 7b. 28 d. 21

3. If one pair of chromatids failed to separate during mitosis in rye cells, how many chromosomes would end up in the daughter cells?a. 28 and 28 c. 7 and 8b. 14 and 14 d. 15 and 13

4. Thinking Critically Using the informa-tion presented in the table, explain howthe number of chromosomes in bodycells is related to the complexity of anorganism.

Guinea Organism Human Rye Potato Pig

Number of 46 14 48 64chromosomes in body cells

Number of 92 A 96 128chromatids during metaphase of mitosis

Number of 46 14 48 64chromosomes in daughter cells

Table 8.1 Chromosome comparison of four organisms

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web site.science.glencoe.com

CD-ROM

includes

2. 3.

4. 5. 6. 7.

which includes

and

1.


Chapter 8: Cellular Transport and the Cell...

Documents

Transcript of Chapter 8: Cellular Transport and the Cell...