Reading Essentials for Biology Glencoe (794133), страница 22
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Inside the cell, nutrients andwastes move by diffusion. Because a cell’s size can slow the rateof diffusion, cells have to have a way of limiting their growth.Fortunately, cells divide before they become too big and unable tofunction well. Cell division also has other purposes.Cell ReproductionWhen cells divide, new cells are produced from one cell. Thetwo cells that are produced are identical to the original cell. Justbefore cells divide, several short, stringy structures appear in thenucleus.
These structures are called chromosomes.What do chromosomes do?Chromosomes (KROH muh sohmz) contain DNA and arethe carriers of the genetic material that is copied and passed fromgeneration to generation. For most of a cell’s lifetime, chromosomes exist as something called chromatin (KROH muh tihn).Chromatin is long, stringy strands of DNA.
Without the properamount of DNA, the cell cannot survive. Therefore the chromosomes must be accurately passed on to new cells.Identify theMain Idea As you read thissection, stop after everyparagraph and put what youread into your own words.Highlight the main idea ineach paragraph.1. What structures appear inthe nucleus shortly beforecell division?________________________________________________________________________The Cell CycleThe cell cycle is the time of growth and division of a cell. Acell’s life cycle is divided into two periods. There is a period ofREADING ESSENTIALSChapter 883NameDateClassSection8.2Cell Growth and Reproduction, continuedgrowth called interphase. There is also a period of nuclear division called mitosis.What is interphase?Analyze theDiagram As you read aboutmitosis, highlight each stagein the diagram below.During interphase a cell grows in size, carries on metabolism,duplicates chromosomes, and prepares for division.
Interphase isthe busiest phase of the cell cycle.What is mitosis?Mitosis (mi TOH sus) follows interphase. It is the process ofnuclear division in which two daughter cells form. Each of thesedaughter cells contains a complete setStages of Mitosisof chromosomes that are identical tothose of the parent cell.A ProphaseThe chromatincoils to formchromosomes.Disappearingnuclear envelopeDoubledchromosomeCentromereB MetaphaseThe chromosomesmove to the centerof the cell.Sister chromatidsC AnaphaseCentromeres splitand sister chromatidsare pulled to theopposite sides ofthe cell.D TelophaseTwo new nucleiare formed and adouble membranebegins to formbetween them.NuclearenvelopereappearsTwo daughtercells are formed84Chapter 8What are the phases ofmitosis?There are four phases of mitosis.Each phase merges into the next phase.The four phases are prophase, metaphase, anaphase, and telophase asshown in the illustration to the left.Prophase is the first and longestphase.
During prophase the chromatincoils up to form chromosomes. Eachduplicated chromosome is made upof two identical halves, called sisterchromatids. Centromeres(SEN truh meers) hold the sisterchromatids together.During metaphase, the second phaseof mitosis, the doubled chromosomesare pulled to the center of the cell.Anaphase is the third phase of mitosis.During this phase, the centromeres ofthe sister chromatids split apart.
Thisseparates the sister chromatids fromeach other. In telophase, the last phaseof mitosis, the chromatids move toopposite sides of the cell. Two nuclei areformed—one on each side of the cell.Finally, a new double membrane beginsto form between the two new nuclei.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Spindle fibersNameDateClassSection8.2Cell Growth and Reproduction, continuedCytokinesisFollowing telophase, the cell’s cytoplasm divides and separates into two new identical cells. This is called cytokinesis(si toh kih NEE sus).Results of MitosisCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.When mitosis is complete, one-celled organisms remain assingle cells.
The organism simply multiplied into two organisms.These daughter cells eventually will repeat the same cell cycleas the parent cell and will grow and divide. In larger organisms,cell growth and reproduction result in groups of cells that worktogether as tissue to perform a certain function. Tissues organizein combinations to form organs. Organs perform specific complextasks within the organism. Multiple organs that work togetherform an organ system, such as the digestive system. The stomachis one organ in the digestive system. It functions to digest food.
Itis important to remember that no matter how complex the organsystem or organism becomes, the cell is still the most basic unit ofthat organization.2. What do tissues organizeto form?________________________________________________________________________◗ After You ReadMini Glossaryanaphase: the third phase of mitosis in which thecentromeres split and the sister chromatidsof each chromosome are pulled apartinterphase: cell growth period where a cellincreases in size, carries on metabolism, andduplicates chromosomes prior to divisioncell cycle: continuous sequence of growth (interphase) and division (mitosis) in a cellmetaphase: short second phase of mitosis wheredoubled chromosomes move to the centerof the cellcentromere (SEN truh meer): cell structure thatjoins two sister chromatids of a chromosomechromatin (KROH muh tihn): long strands ofDNA found in the eukaryotic cell nucleus;coils up to form chromosomeschromosomes (KROH muh sohmz): cell structures that contain DNA and carry thegenetic material that is copied and passedfrom generation to generation of cellscytokinesis (si toh kih NEE sus): cell process following mitosis in which the cell’s cytoplasmdivides and separates into new identical cellsREADING ESSENTIALSmitosis (mi TOH sus): period of nuclear cell division in which two daughter cells areformed, each containing a complete setof chromosomesorgan: group of two or more tissues organizedto perform complex activities within anorganismorgan system: multiple organs that worktogether to perform a specific life functionprophase: first and longest phase of mitosis wherechromatin coils into visible chromosomesChapter 885NameDateClassSection8.2Cell Growth and Reproduction, continuedsister chromatid: identical half of duplicatedparent chromosome formed during theprophase stage of mitosis; the halves areheld together by a centromeretelophase: final phase of mitosis during whichnew cells prepare for their own independent existencetissue: groups of cells that work together to perform a specific function1.
Circle the terms from the Mini Glossary that identify the phases of mitosis. Then, in thespace provided, list them in the order they occur.1.3.2.4.2. Use the diagram below to help you review the cell cycle by providing two facts for eachperiod.InterphaseMitosis1. _____________________________1. _____________________________1. _____________________________1. _____________________________1.
_____________________________1. _____________________________2. _____________________________2. _____________________________2. _____________________________2. _____________________________2. _____________________________2. _____________________________3. Fill in the blanks with the following terms: tissues, sister chromatids, cell cycle, mitosis,and chromosomes.a. Two identical halves of a duplicated parent chromosome are calledb. The process of cell division is calledc...are the carriers of genetic material that is copied and passed fromgeneration to generation.d. Thee.is the period of growth and division of a cell.are groups of cells that work together to perform specific functions.Visit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about cell growth and reproduction.86Chapter 8READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.The CellCycleNameDateClassSection8.3 Control of the Cell Cycle◗ Before You ReadSC.F.1.4.5 The student knows that complex interactions among the different kinds of molecules in the cell cause distinct cycles of activity governed by proteins.
SC.F.1.4.8 The student knows that cell behavior can be affected by molecules from other parts of theorganism or even from other organisms. Also covers SC.F.2.4.2This section is about cancer and what happens when cells grow out of control. Experts agree thata healthful diet can reduce the risk of cancer. On the lines below list foods that you think belong in ahealthful diet.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Normal Control of the Cell CycleThe cell cycle is controlled by conditions both inside the celland in the cell’s environment. When something goes wrong withnormal cell conditions, cells lose control of the cell cycle.Cancer is a growth that occurs when uncontrolled cell divisiontakes place.
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