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_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 1 _ 8 8 9 4 0 organisms division called the cells inanorganism gothrough ofgrowth, acycle development, and edn setas rmaCl oa raim From aCell to anOrganism Reading Essentials Phases oftheCell Cycle The Cell Cycle The Cell Cycle andCell Division From aCell toanOrganism its lifeininterphase. is theperiodofacell’s growth anddevelopment are interphaseandthemitotic(miTAH tihk)phase. number ofhourssunlightchangeinaregularcycle. fall. Asseasonschange,temperature,precipitation,andthe Some areashavefourseasons—winter, spring,summer, and that theweatherchangesinaregularpatterneachyear. 6 this lesson,reread thestatements andseeifyou have changedyour mind. if you agree withthestatement oraDifyou disagree. After you’ve read whether you agree ordisagree withthem.Place anAintheBefore column What doyou think? . i n eoeSaeetAfter Statement Before d d There aretwomainphasesinthecellcycle.These Cells alsogothroughcycles,justliketheseasons. No matterwhereyoulive,haveprobablynoticed • • •

1 to producenewcells. to replacecellsthatareoldordamaged,and to growanddevelop, 3. 2. 1. At theendofcell cycle, theoriginal cell no for growth. Cell divisionisimportant longer exists. Cell divisionproduces two identicalcells.

cell cycle Readthethree statements below anddecide . Thecellcyclemakesitpossiblefor . A cell spends most of . Acellspendsmostof Interphase Most

cycle? main phasesofthecell quizzes. discuss theanswers to the another student. Together, Exchange quizzes with idea undereachheading. question aboutthemain Create aQuiz • • Key Concepts 1. Name cycle important? cycle Why istheresult ofthecell cell cycle? What are thephasesof 3TUDY#OACH Key Concept Check What are thetwo

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e ic t s a o A cell reproduces during the A cell reproduces Most cells go through three stages during during stages three go through cells Most e nterphas I rapid growth and replication, or copying, of the copying, of the or and replication, rapid growth called organelles, structures membrane-bound in a cell, genetic information of DNA, the copying and cell division. preparation for • • • The time it takes a cell to complete the cell cycle depends mitotic phase. The mitotic phase has two stages, as shown in mitotic phase has two stages, mitotic phase. The the the first stage, the contents of During the figure below. fluid, or cell’s During the second stage, the nucleus divide. phase creates two new cytoplasm, divides. The mitotic no longer exists. identical cells. The original cell During the Mitotic Phase During Interphase During cell cycle by a shorter phase of the Interphase is followed phase. called the mitotic interphase: on the type of cell that is dividing. Recall that a eukaryotic cell has membrane-bound organelles, including a nucleus. The cell cycle for some eukaryotic cells might only take eight minutes. The cell cycle for other eukaryotic cells might take Most of the cells in the human body can up to one year. complete the cell cycle in about 24 hours. The cells of some the fertilized egg For example, organisms divide very quickly. of the zebra fish divides into 256 cells in 2.5 hours. Length of a Cell Cycle Cell of a Length Phase Mitotic 2

Which stage of

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_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 1 _ 8 8 9 4 0 called a chromosome. Thesisterchromatids are heldtogetherby astructure brain remaininG stop thecellcycleatG food. Mostcellscontinuethecellcycle.However, somecells line yourstomachmakeenzymesthathelpyoudigest edn setas rmaCl oa raim From aCell to anOrganism Reading Essentials chromosomes called Each pairiscalledaduplicatedchromosome. and formchromosomes.Acell’s DNAisarranged aspairs. a copyofthegeneticinformation.Thenewstrandscoilup becauseeachnewcellgets strands ofDNA.Thisisnecessary of chromatinarecopied,sotherenowtwo identical During theSstage,acellgrowsandcopiesitsDNA.Strands The SStage The G Phases ofInterphase Interphase This isaperiodofrapidgrowth.G normal cellfunctions.Forexample,duringG the cellcycle.DuringG shown inthetablebelow. strands ofchromatintangledtogether. like aplateofspaghetti.Thisisbecausethenucleuscontains scientists adddyetoacellininterphase,thenucleuslooks Chromatin islong,thinstrandsofDNAinthenucleus.If called chromatin(KROHmuhtun)duringinterphase. copies itsDNAandpreparesforcelldivision.Acell’s DNAis as makingproteins,follow. Eachcellthatisactivelydividing growth, in which thecellgetsbigger. Cellularactivities,such 6 . hs tg Description Phase Mitotic Stage Interphase Phase i n d d Interphase canbedividedintothreedifferentstages,as A newcellbeginsinterphasewithaperiodofrapid

3 1

Stage centromere. ThesecondstageofinterphaseistheSstage. ThefirststageofinterphaseistheG Phases oftheCell Cycle yoiei divisionof cytoplasm cytokinesis

1 sister chromatids

anddonotdivideagain. ioi divisionofnucleus mitosis G G growth andchromosome replication; S 2 1 1 , acellgrowsandcarriesoutits 1 stage. Mature nerve cellsinyour stage.Maturenerve ognle replication organelle growth andcellular functions; organelle replication replication organelle growth andcellular functions; 1

make upaduplicated isthelongeststageof 1 Two identical the cellsthat 1 stage. stages ofinterphase? the cell? location ofthechromatin in during theSstage? 4 Name 4. Interpreting Tables Identify 3. 5. Explain Reading Check Reading Check What are the What happens What isthe 22/22/10 2:10:46PM / 41 2 2 / 1 0

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0 1 / 2 2 / Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 22/22/10 2:10:50 PM mitosis, In stage. stage. 2 the cytoplasm and cytokinesis, are the two new cells that result that result the two new cells are In . . read the descriptions in this section. Daughter cells , the cell stores energy that will be used that will be used stores energy , the cell 2 . The last stage of interphase is the G is the of interphase last stage The Stage 2 Mitosis, like interphase, is a process that can be divided The mitotic phase of the cell cycle follows interphase. The mitotic phase of the cell cycle the nucleus divide, During mitosis, the contents of During cytokinesis, the cytoplasm divides and two new During cell division, the organelles are distributed the organelles are distributed During cell division, daughter cell will have ten different chromatids. Chromatids daughter cell will have ten different are now called chromosomes. daughter cells form. The organelles that were made during interphase are divided between the daughter cells. into different phases. Follow along with the diagrams on the next page as you (mi TOH sus) and cytokinesis (si toh kuh NEE sus). (mi TOH sus) and cytokinesis divide the nucleus and its contents sister chromatids of the forming two identical nuclei. The This from each other. duplicated chromosomes separate genetic information. For gives each daughter cell the same chromosomes example, a cell that has ten duplicated the cell divides, each actually has 20 chromatids. When processing mitochondria and chloroplasts, have their own and chloroplasts, have processing mitochondria on can make copies of themselves DNA. These organelles materials produces other organelles from their own. A cell materials and lipids. A cell makes these such as proteins inside the nucleus. using the information in the DNA stages of interphase. Organelles are copied during all phase: mitosis There are two stages of the mitotic between the two new cells. Before a cell divides, it makes a new cells. Before a cell divides, between the two the two new cells can This way, copy of each organelle. organelles, such as the energy- Some function properly. This is another period of growth and the final preparation final preparation the and of growth period is another This S DNA during the energy to copy A cell uses for mitosis. G stage. During Phases of Mitosis The Mitotic Phase The The G The Replication Organelle during the mitotic phase of the cell cycle. of the cell cycle. mitotic phase during the its contents divide its contents mitosis and cytokinesisfrom

2 How many many How What 4

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n i . 6 0 4 9 8 8 _ 1 Reading Check Reading L _ E an Organism to a Cell From Essentials Reading R _ 8 important for a cell to make important to a cell for of each organelle a copy division? before stage? 42 8. Calculate 7. Discuss 6. Describe 6. Describe happens during the G happens during the chromatids are in twenty are chromatids chromosomes? duplicated 0 0 _ 1 0 0 _ 4 0 2 CC204_001_008_RE_L1_889406.indd 4 CC204_001_008_RE_L1_889406.indd 5 2 0 4 _ 0 0 1 _ 0 0 8 _ R E

_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 1 _ 8 8 9 4 0 identical chromosomesreachoppositeendsofthecell. begins togetlonger. Anaphase endswhenthetwosetsof chromosomes movetooppositesidesofthecell,cell single-stranded chromosomes.Asthe they areseparated,thechromatidsnowtwoidentical from eachotherandarepulledinoppositedirections.Once form in the cytoplasm. the form in membrane breaksdown.Structurescalledspindlefibers microscope.Thenucleolusdisappearsandthenuclear form duplicated chromosomesthatcanbeseenwitha the copiedchromatincoilstogethertightly. Thecoils edn setas rmaCl oa raim From aCell to anOrganism Reading Essentials nuclei form. of chromosomesateitherendthecell.Two newidentical begin touncoil.Anuclearmembranegrowsaroundeachset divide chromosomesbegintodisappear. Thechromosomes Telophase Anaphase Metaphase Prophase because itmakesthenewcellssame. is the shortestphaseinmitosis.Itisanimportant cell willreceiveonecopyofeachchromosome.Metaphase along themiddleofcell.Thismakessurethateachnew Notice inthefigureabovethatchromosomeslineup chromosomes tothemiddleofcellduringmetaphase. 6 . M of file at themiddle l C i ine upinsin n h d thecell etaphase d romosomes

5 . Duringthefirstphaseofmitosis,calledprophase, gl Inanaphase,thetwosisterchromatidsseparate Duringtelophase,thespindlefibersthathelped Thespindlefiberspullandpushtheduplicated e P Spindle fibersbe n Th C rop opie uc e nuc l h ear mem d ase DNAcon l eo l us

b d rane isappears, an d g enses into c in to form b rea k s d . own. d h t romosomes h e . T elophas T S C t A n h w pindle fibersbe h e c romosomes o u i cle h d r entic o a m r mem e a a tin l n . b

u b e clei f r g a g in to break down. ne in to unwin center ofacell? chromosomes lineupinthe phase ofmitosis dothe 9 Identify 9. 10. State phases ofmitosis? o fo rm rms . Visual Check Ana Reading Check T t t s S S oward o he cell h a h pindle ister chromatids separate. r orten, pu orten, e ce ou d p . has n ll d .

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0 1 / 2 2 / Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 22/22/10 2:10:55 PM multicellular organisms. The cell multicellular organisms. The cell The cell cycle results in two new cells. These daughter The cell cycle results in two new for some Cell division is a form of reproduction Cell division allows multicellular organisms, such as After the last phase of mitosis, the cytoplasm of a cell of a cytoplasm the of mitosis, phase the last After wall cells is different. A new cell Cytokinesis in plant happens because cells divide and increase in number as you grow and develop. cells, or two new paramecia. Cell division is also important cells, or two new paramecia. Cell in other methods of reproduction in which the offspring are identical to the parent organism. humans, to grow and develop from one cell (a fertilized egg). In humans, cell division begins about 24 hours after fertilization. Cell division continues quickly for the first few years of life. During the next few years, you will probably go through a period of rapid growth and development. This 46 chromosomes. When that cell divides, it produces two chromosomes. 46 The cell cycle is new cells, each with 46 chromosomes. some organisms. It is important for reproduction in important for growth in or damaged cells and repair cycle also helps replace worn-out damaged tissues. an organism called a unicellular organisms. For example, into two new daughter paramecium reproduces by dividing forms in the middle of a plant cell. Organelles called vesicles of a plant cell. Organelles forms in the middle called a cell form a membrane-bound disk join together to the cell wall then grows outward toward plate. The cell plate until two new cells form. They also are the same as cells are genetically the same. that no longer exists. A human cell has original cell the divides in a process called cytokinesis. The specific steps of The specific steps cytokinesis. in a process called divides In an that is dividing. the type of cell depend on cytokinesis or squeezes contracts, cell, the cell membrane animal the cell. Fibers around middle of the around the together, forms a crease, called a This pull together. center of the cell furrow gets deeper and in the middle of the cell. This furrow, and divides cell membrane comes together deeper until the the cell. Growth Reproduction Results of Cell Division Results of Cell Dividing the Cell’s Components the Cell’s Dividing 25% = cytokinesis For what For If the 100 6

d × d n i . 6 0 4 9 0.25 8 8 _ =

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an Organism to a Cell From Essentials Reading R _ Math Skills Math 8 44

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12. Compare and animal cells. in plant cells 11. Calculate Percentage be expressed as 6.0 hours/ be expressed the calculate To hours. 24 and then divide, percentage, a 100. Add multiply by sign. percent A percentage is a ratio that is a ratio A percentage 100. number to a compares cell entire the length of the If 24 hours cycle is 24 hours, Ifequals 100%. part of the it can cycle takes 6.0 hours, group of organisms is cell cell is of organisms group of division a form reproduction? interphase? interphase period in certaininterphase mammals takes 12 hours, cycleand the cell is 20 hours, is what percentage 0 0 _ 1 0 0 _ 4 0 2 CC204_001_008_RE_L1_889406.indd 6 CC204_001_008_RE_L1_889406.indd 7 2 0 4 _ 0 0 1 _ 0 0 8 _ R E

_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 1 _ 8 8 9 4 0 edn setas rmaCl oa raim From aCell to anOrganism Reading Essentials Repair Replacement damage. cellsoftencausepermanent in interphase.Injuriestonerve cellsstopthecellcycle cells continuetodivide.Somenerve together. These newcellspatchthebrokenpiecesofboneback When a bone breaks,celldivisionproducesnewcells. new cells eachdaytoreplacetheonesthatruboff. surface isconstantlydividing.Thisproducesmillionsof rubbing or flakingoff.Alayerofcellsbelowtheskin’s damaged. Theoutermostlayerofyourskinisalways grown. Celldivisionreplacescellsthatwearoutorare 6 . i n d d Not alldamagecanberepaired.Thisisbecausenot Cell divisionisalsoimportantforrepairingdamage. Cell divisioncontinuesevenafteranorganismisfully

7 important? result ofthecell cycle 1. Discuss 14.

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END OF LESSON chromosomes chromosomes spindle uncoil, fibers disappear, nuclear membrane grows each set around of chromosomes, new and two nuclei form the phase in which the nucleus and its its which the nucleus and the phase in two identical chromosomes that make up make that chromosomes identical two ED the period of a cell’s growth and development development and growth a cell’s the period of onnect C a duplicated chromosome a duplicated contents divide contents Log on to ConnectED.mcgraw-hill.com ConnectED.mcgraw-hill.com on to Log find this to textbook your and access resources. lesson’s interphase: interphase: sus): TOH (mi mitosis chromatids: sister duplicated chromo- duplicated somes line up in the middle of the cell the stage in which the the stage in which the . cell cycle 8 the two new cells that result from mitosis mitosis from result that new cells the two

d the structure that holds together two sister sister two holds together the structure that d n i . 6 a cycle of growth, development, and division that division that and development, a cycle of growth, 0 4 9 8 8 _ 1 L cytoplasm and its contents divide cytoplasmits contents and and cytokinesis most cells in an organism go through in an organism most cells chromatids _ E Choose one of your quiz questions and write it on the first line below. Then write your below. Choose one of your quiz questions and write it on the first line answer to that question on the line that follows. Complete the table below to explain what happens in each phase of mitosis. Complete the table below to explain Review the terms and their definitions in the Mini Glossary. Write a sentence that Write Mini Glossary. and their definitions in the Review the terms describes the agree with the statement or a D if you disagree. disagree. or a D if you the statement with agree mind? change your Did you Reread the statements at the beginning of the at the beginning the statements Reread with an A if you column in the After lesson. Fill an Organism to a Cell From Essentials Reading R What do you think What happens What within the cell? Phases of Mitosis Prophase Metaphase Anaphase Telophase _ 8

46 3. 2. 1. cytokinesis kuh NEE sus): toh (si cells: daughter Mini Glossary cell cycle: centromere: 0 0 _ 1 0 0 _ 4 0 2 CC204_001_008_RE_L1_889406.indd 8